Renames app to 'schist'

56 files changed, 1686 insertions, 0 deletions

diff --git a/rust/schist_core/src/lib.rs b/rust/schist_core/src/lib.rs
new file mode 100644
index 0000000..fd56999
--- /dev/null
+++ b/rust/schist_core/src/lib.rs
@@ -0,0 +1,10 @@
+use diesel_migrations::{embed_migrations, EmbeddedMigrations};
+
+pub mod models;
+pub mod queries;
+pub mod schema;
+pub mod traits;
+
+mod utils;
+
+pub const MIGRATIONS: EmbeddedMigrations = embed_migrations!("migrations");
diff --git a/rust/schist_core/src/models/account.rs b/rust/schist_core/src/models/account.rs
new file mode 100644
index 0000000..2df43e1
--- /dev/null
+++ b/rust/schist_core/src/models/account.rs
@@ -0,0 +1,15 @@
+use diesel::prelude::*;
+use serde::{Deserialize, Serialize};
+
+use crate::models::datetime_utc::DatetimeUtc;
+
+#[derive(
+    Insertable, Queryable, Identifiable, Selectable, Debug, PartialEq, Clone, Serialize, Deserialize,
+)]
+#[diesel(table_name = crate::schema::accounts)]
+pub struct Account {
+    pub id: i32,
+    pub name: String,
+    pub opening_balance: i32,
+    pub opening_date: DatetimeUtc,
+}
diff --git a/rust/schist_core/src/models/budget.rs b/rust/schist_core/src/models/budget.rs
new file mode 100644
index 0000000..e6fb4c9
--- /dev/null
+++ b/rust/schist_core/src/models/budget.rs
@@ -0,0 +1,42 @@
+use serde::Serialize;
+
+use super::budget_update::BudgetUpdate;
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq, Serialize)]
+pub struct Budget {
+    pub quantity: i32,
+    pub period: i32,
+}
+
+impl From<&BudgetUpdate> for Budget {
+    fn from(budget_update: &BudgetUpdate) -> Self {
+        Self {
+            quantity: budget_update.new_budget,
+            period: budget_update.new_period,
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::{models::date_utc::DateUtc, traits::nowlike::Nowlike};
+
+    use super::*;
+
+    #[test]
+    fn when_from_budget_update_then_returns_budget() {
+        let quantity = 2;
+        let period = 3;
+        let budget_update = BudgetUpdate {
+            id: 0,
+            category_id: 1,
+            date: DateUtc::now(),
+            new_budget: quantity,
+            new_period: period,
+        };
+
+        let budget = Budget::from(&budget_update);
+
+        assert_eq!(budget, Budget { quantity, period });
+    }
+}
diff --git a/rust/schist_core/src/models/budget_update.rs b/rust/schist_core/src/models/budget_update.rs
new file mode 100644
index 0000000..c7221b1
--- /dev/null
+++ b/rust/schist_core/src/models/budget_update.rs
@@ -0,0 +1,16 @@
+use derive_builder::Builder;
+use diesel::prelude::*;
+use serde::Serialize;
+
+use crate::models::{category::Category, date_utc::DateUtc};
+
+#[derive(Builder, Clone, Serialize, Queryable, Identifiable, Selectable, Associations, Debug, PartialEq, Eq, Insertable)]
+#[diesel(table_name = crate::schema::budget_updates)]
+#[diesel(belongs_to(Category))]
+pub struct BudgetUpdate {
+    pub id: i32,
+    pub category_id: i32,
+    pub date: DateUtc,
+    pub new_budget: i32,
+    pub new_period: i32,
+}
diff --git a/rust/schist_core/src/models/category.rs b/rust/schist_core/src/models/category.rs
new file mode 100644
index 0000000..55c7b97
--- /dev/null
+++ b/rust/schist_core/src/models/category.rs
@@ -0,0 +1,10 @@
+use derive_builder::Builder;
+use diesel::prelude::*;
+use serde::{Deserialize, Serialize};
+
+#[derive(Builder, Queryable, Identifiable, Selectable, Debug, PartialEq, Serialize, Deserialize, Insertable)]
+#[diesel(table_name = crate::schema::categories)]
+pub struct Category {
+    pub id: i32,
+    pub name: String,
+}
diff --git a/rust/schist_core/src/models/category_balance.rs b/rust/schist_core/src/models/category_balance.rs
new file mode 100644
index 0000000..796b40b
--- /dev/null
+++ b/rust/schist_core/src/models/category_balance.rs
@@ -0,0 +1,7 @@
+use serde::Serialize;
+
+#[derive(Serialize)]
+pub struct CategoryBalance {
+    pub category_id: i32,
+    pub balance: i32,
+}
diff --git a/rust/schist_core/src/models/category_budget.rs b/rust/schist_core/src/models/category_budget.rs
new file mode 100644
index 0000000..9796261
--- /dev/null
+++ b/rust/schist_core/src/models/category_budget.rs
@@ -0,0 +1,9 @@
+use serde::Serialize;
+
+use super::budget::Budget;
+
+#[derive(Serialize)]
+pub struct CategoryBudget {
+    pub category_id: i32,
+    pub budget: Option<Budget>,
+}
diff --git a/rust/schist_core/src/models/category_transfer.rs b/rust/schist_core/src/models/category_transfer.rs
new file mode 100644
index 0000000..7b36054
--- /dev/null
+++ b/rust/schist_core/src/models/category_transfer.rs
@@ -0,0 +1,12 @@
+use derive_builder::Builder;
+use diesel::prelude::*;
+
+#[derive(Builder, Queryable, Identifiable, Selectable, Debug, PartialEq, Insertable)]
+#[diesel(table_name = crate::schema::category_transfers)]
+pub struct CategoryTransfer {
+    pub id: i32,
+    pub description: String,
+    pub quantity: i32,
+    pub from_category_id: i32,
+    pub to_category_id: i32,
+}
diff --git a/rust/schist_core/src/models/date_utc.rs b/rust/schist_core/src/models/date_utc.rs
new file mode 100644
index 0000000..55d9e3f
--- /dev/null
+++ b/rust/schist_core/src/models/date_utc.rs
@@ -0,0 +1,309 @@
+use std::{borrow::Borrow, fmt, str::FromStr};
+
+use anyhow::{Context, Error, Result};
+use chrono::{DateTime, Datelike, NaiveDate, NaiveTime, Utc};
+use diesel::{
+    backend::Backend,
+    deserialize::{self, FromSql, FromSqlRow},
+    expression::AsExpression,
+    serialize::{self, ToSql},
+    sql_types::Text,
+    sqlite::Sqlite,
+};
+use serde::{Deserialize, Serialize};
+
+use crate::traits::{dateable::Dateable, nowlike::Nowlike};
+
+use super::datetime_utc::DatetimeUtc;
+
+#[derive(
+    Eq,
+    PartialEq,
+    Ord,
+    PartialOrd,
+    Serialize,
+    Deserialize,
+    Clone,
+    Debug,
+    AsExpression,
+    FromSqlRow,
+)]
+#[diesel(sql_type=Text)]
+pub struct DateUtc {
+    chrono_datetime_utc: DateTime<Utc>,
+}
+
+impl DateUtc {
+    pub fn from_ymd(year: i32, month: u32, day: u32) -> Result<Self> {
+        Ok(Self {
+            chrono_datetime_utc: NaiveDate::from_ymd_opt(year, month, day)
+                .with_context(|| format!("failed to construct date from ymd {:04}-{:02}-{:02}", year, month, day))?
+                .and_hms_opt(0, 0, 0).unwrap()
+                .and_utc()
+        })
+    }
+
+    pub fn with_hms(&mut self, hour: u32, min: u32, sec: u32) -> Result<DatetimeUtc> {
+        DatetimeUtc::from_ymd_and_hms(
+            self.year(), self.month(), self.day(), hour, min, sec,
+        )
+    }
+
+    pub fn day_diff(&self, other: &DateUtc) -> u32 {
+        self.chrono_datetime_utc
+            .num_days_from_ce()
+            .abs_diff(other.chrono_datetime_utc.num_days_from_ce())
+    }
+
+    fn is_day_str(str: &str) -> bool {
+        if str.len() != 10 {
+            return false;
+        }
+        for (ix, ch) in str.chars().enumerate() {
+            if ix == 4 || ix == 7 {
+                if ch != '-' {
+                    return false;
+                }
+            } else {
+                if ch < '0' || ch > '9' {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+}
+
+impl Nowlike for DateUtc {
+    fn now() -> Self {
+        let now = Utc::now();
+        Self::from_ymd(
+            now.year(),
+            now.month(),
+            now.day(),
+        ).unwrap()
+    }
+}
+
+impl Dateable for DateUtc {
+    fn year(&self) -> i32 {
+        self.chrono_datetime_utc.year()
+    }
+
+    fn month(&self) -> u32 {
+        self.chrono_datetime_utc.month()
+    }
+
+    fn day(&self) -> u32 {
+        self.chrono_datetime_utc.day()
+    }
+}
+
+impl From<DatetimeUtc> for DateUtc {
+    fn from(datetime_utc: DatetimeUtc) -> Self {
+        Self {
+            chrono_datetime_utc: datetime_utc
+                .borrow()
+                .to_string()
+                .parse::<DateTime<Utc>>().unwrap()
+                .with_time(NaiveTime::from_hms_opt(0, 0, 0).unwrap()).unwrap(),
+        }
+    }
+}
+
+impl<T> From<T> for DateUtc where T: Borrow<DateTime<Utc>> {
+    fn from(chrono_datetime_utc: T) -> Self {
+        Self {
+            chrono_datetime_utc: chrono_datetime_utc
+                .borrow()
+                .with_time(NaiveTime::from_hms_opt(0, 0, 0).unwrap()).unwrap(),
+        }
+    }
+}
+
+impl fmt::Display for DateUtc {
+    /// Converts to a day string, YYYY-MM-DD, in UTC
+    /// Example: 10.30am 24 Oct 2024 UTC -> "2024-10-24"
+    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        let date_str = self.chrono_datetime_utc.to_rfc3339();
+        let day_str = date_str
+            .split_at_checked(10)
+            .unwrap()
+            .0;
+        write!(f, "{}", day_str)
+    }
+}
+
+impl FromStr for DateUtc {
+    type Err = anyhow::Error;
+
+    /// Constructs DatetimeUtc from a day string, YYYY-MM-DD, in UTC
+    /// Example: "2024-10-24" -> Midnight 24 Oct 2024 UTC
+    fn from_str(date_str: &str) -> Result<Self> {
+        if !Self::is_day_str(&date_str) {
+            Err(Error::msg(format!("{} is not a day string in YYYY-MM-DD format", date_str)))
+        } else {
+            let mut datetime_str = String::from(date_str);
+            datetime_str.push_str("T00:00:00.000Z");
+            Ok(Self {
+                chrono_datetime_utc: datetime_str.parse()?,
+            })
+        }
+    }
+}
+
+impl ToSql<Text, Sqlite> for DateUtc {
+    fn to_sql<'b>(
+        &'b self,
+        out: &mut diesel::serialize::Output<'b, '_, Sqlite>,
+    ) -> serialize::Result {
+        out.set_value(self.to_string());
+        Ok(serialize::IsNull::No)
+    }
+}
+
+impl FromSql<Text, Sqlite> for DateUtc {
+    fn from_sql(bytes: <Sqlite as Backend>::RawValue<'_>) -> deserialize::Result<DateUtc> {
+        let str = <String as FromSql<Text, Sqlite>>::from_sql(bytes)?;
+        Ok(str.parse()?)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::traits::timeable::Timeable;
+
+    use super::*;
+
+    #[test]
+    fn when_from_ymd_then_ymd_are_as_expected() {
+        let date_utc = DateUtc::from_ymd(1970, 11, 23);
+
+        assert!(date_utc.is_ok());
+        let date_utc = date_utc.unwrap();
+        assert_eq!(date_utc.year(), 1970);
+        assert_eq!(date_utc.month(), 11);
+        assert_eq!(date_utc.day(), 23);
+    }
+
+    #[test]
+    fn when_from_ymd_then_to_string_as_expected() {
+        let date_utc = DateUtc::from_ymd(1970, 11, 23);
+
+        assert!(date_utc.is_ok());
+        assert_eq!(date_utc.unwrap().to_string(), "1970-11-23");
+    }
+
+    #[test]
+    fn when_from_invalid_ymd_then_err() {
+        let date_utc_1 = DateUtc::from_ymd(1970, 0, 23);
+        let date_utc_2 = DateUtc::from_ymd(1970, 13, 23);
+        let date_utc_3 = DateUtc::from_ymd(1970, 11, 0);
+        let date_utc_4 = DateUtc::from_ymd(1970, 11, 31);
+        let date_utc_5 = DateUtc::from_ymd(1971, 2, 29);
+
+        assert!(date_utc_1.is_err());
+        assert_eq!(date_utc_1.unwrap_err().to_string(), "failed to construct date from ymd 1970-00-23");
+        assert!(date_utc_2.is_err());
+        assert_eq!(date_utc_2.unwrap_err().to_string(), "failed to construct date from ymd 1970-13-23");
+        assert!(date_utc_3.is_err());
+        assert_eq!(date_utc_3.unwrap_err().to_string(), "failed to construct date from ymd 1970-11-00");
+        assert!(date_utc_4.is_err());
+        assert_eq!(date_utc_4.unwrap_err().to_string(), "failed to construct date from ymd 1970-11-31");
+        assert!(date_utc_5.is_err());
+        assert_eq!(date_utc_5.unwrap_err().to_string(), "failed to construct date from ymd 1971-02-29");
+    }
+
+    #[test]
+    fn when_from_string_then_ymd_are_as_expected() {
+        let date_utc: Result<DateUtc> = "1970-11-23".parse();
+
+        assert!(date_utc.is_ok());
+        let date_utc = date_utc.unwrap();
+        assert_eq!(date_utc.year(), 1970);
+        assert_eq!(date_utc.month(), 11);
+        assert_eq!(date_utc.day(), 23);
+    }
+
+    #[test]
+    fn when_from_string_then_to_string_as_expected() {
+        let date_utc: Result<DateUtc> = "1970-11-23".parse();
+
+        assert!(date_utc.is_ok());
+        assert_eq!(date_utc.unwrap().to_string(), "1970-11-23");
+    }
+
+    #[test]
+    fn when_from_invalid_string_then_err() {
+        let date_utc_1: Result<DateUtc> = "1970-00-23".parse();
+        let date_utc_2: Result<DateUtc> = "1970-13-23".parse();
+        let date_utc_3: Result<DateUtc> = "1970-11-0".parse();
+        let date_utc_4: Result<DateUtc> = "1970-11-31".parse();
+        let date_utc_5: Result<DateUtc> = "1971-02-29".parse();
+
+        assert!(date_utc_1.is_err());
+        assert!(date_utc_2.is_err());
+        assert!(date_utc_3.is_err());
+        assert!(date_utc_4.is_err());
+        assert!(date_utc_5.is_err());
+    }
+
+    #[test]
+    fn with_with_hms_then_ymd_hms_are_as_expected() {
+        let datetime_utc = DateUtc::from_ymd(1970, 11, 23).unwrap().with_hms(12, 55, 16);
+
+        assert!(datetime_utc.is_ok());
+        let datetime_utc = datetime_utc.unwrap();
+        assert_eq!(datetime_utc.year(), 1970);
+        assert_eq!(datetime_utc.month(), 11);
+        assert_eq!(datetime_utc.day(), 23);
+        assert_eq!(datetime_utc.hour(), 12);
+        assert_eq!(datetime_utc.minute(), 55);
+        assert_eq!(datetime_utc.second(), 16);
+    }
+
+    #[test]
+    fn when_with_invalid_hms_then_err() {
+        let datetime_utc_1 = DateUtc::from_ymd(1970, 11, 23).unwrap().with_hms(25, 0, 0);
+        let datetime_utc_2 = DateUtc::from_ymd(1970, 11, 23).unwrap().with_hms(0, 61, 0);
+        let datetime_utc_3 = DateUtc::from_ymd(1970, 11, 23).unwrap().with_hms(0, 0, 61);
+
+        assert!(datetime_utc_1.is_err());
+        assert!(datetime_utc_2.is_err());
+        assert!(datetime_utc_3.is_err());
+    }
+
+    #[test]
+    fn when_from_datetime_utc_at_different_times_on_same_day_then_eq() {
+        let datetime_utc1 = DateUtc::from_ymd(1970, 11, 23).unwrap().with_hms(0, 0, 0).unwrap();
+        let datetime_utc2 = DateUtc::from_ymd(1970, 11, 23).unwrap().with_hms(23, 59, 59).unwrap();
+        let date_utc1 = DateUtc::from(datetime_utc1);
+        let date_utc2 = DateUtc::from(datetime_utc2);
+
+        assert_eq!(date_utc1, date_utc2);
+    }
+
+    #[test]
+    fn given_today_when_day_diff_today_then_return_0() {
+        let start = DateUtc::from_ymd(2000, 1, 1).unwrap();
+        let end = DateUtc::from_ymd(2000, 1, 1).unwrap();
+
+        let day_diff = start.day_diff(&end);
+        let neg_day_diff = end.day_diff(&start);
+
+        assert_eq!(day_diff, 0);
+        assert_eq!(day_diff, neg_day_diff);
+    }
+
+    #[test]
+    fn given_today_when_day_diff_tomorrow_then_return_1() {
+        let start = DateUtc::from_ymd(2000, 1, 1).unwrap();
+        let end = DateUtc::from_ymd(2000, 1, 2).unwrap();
+
+        let day_diff = start.day_diff(&end);
+        let neg_day_diff = end.day_diff(&start);
+
+        assert_eq!(day_diff, 1);
+        assert_eq!(day_diff, neg_day_diff);
+    }
+}
diff --git a/rust/schist_core/src/models/datetime_utc.rs b/rust/schist_core/src/models/datetime_utc.rs
new file mode 100644
index 0000000..98d1d6c
--- /dev/null
+++ b/rust/schist_core/src/models/datetime_utc.rs
@@ -0,0 +1,223 @@
+use std::{fmt::Display, str::FromStr};
+
+use anyhow::{Context, Result};
+use chrono::{DateTime, Datelike as ChronoDatelike, NaiveDate, Timelike as ChronoTimelike, Utc};
+use diesel::{
+    backend::Backend,
+    deserialize::{self, FromSql, FromSqlRow},
+    expression::AsExpression,
+    serialize::{self, ToSql},
+    sql_types::Text,
+    sqlite::Sqlite,
+};
+use serde::{Deserialize, Serialize};
+
+use crate::traits::{dateable::Dateable, nowlike::Nowlike, timeable::Timeable};
+
+#[derive(
+    PartialEq,
+    Eq,
+    PartialOrd,
+    Ord,
+    Serialize,
+    Deserialize,
+    Clone,
+    Debug,
+    AsExpression,
+    FromSqlRow,
+)]
+#[diesel(sql_type=Text)]
+pub struct DatetimeUtc {
+    chrono_datetime_utc: DateTime<Utc>,
+}
+
+impl DatetimeUtc {
+    pub fn from_ymd_and_hms(year: i32, month: u32, day: u32, hour: u32, min: u32, sec: u32) -> Result<Self> {
+        Ok(Self { chrono_datetime_utc: NaiveDate
+            ::from_ymd_opt(year, month, day)
+            .with_context(|| format!("failed to construct datetime from ymd {:04}-{:02}-{:02}", year, month, day))?
+            .and_hms_opt(hour, min, sec)
+            .with_context(|| format!("failed to construct datetime from hms {:02}:{:02}:{:02}", hour, min, sec))?
+            .and_utc()
+        })
+    }
+}
+
+impl FromStr for DatetimeUtc {
+    type Err = anyhow::Error;
+
+    /// Constructs DatetimeUtc from a date string in ISO format, in UTC
+    /// Example: "2024-10-24T10:30:00.000" -> 10.30am 24 Oct 2024 UTC
+    fn from_str(datetime_str: &str) -> Result<Self> {
+        let chrono_datetime_utc = datetime_str.parse::<DateTime<Utc>>()?;
+        Ok(Self {
+            chrono_datetime_utc,
+        })
+    }
+}
+
+impl Display for DatetimeUtc {
+    /// Converts to a date string in ISO format, in UTC
+    /// Example: 10.30am 24 Oct 2024 UTC -> "2024-10-24T10:30:00.000Z"
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(f, "{}", self.chrono_datetime_utc.to_rfc3339_opts(chrono::SecondsFormat::Millis, true))
+    }
+}
+
+impl Nowlike for DatetimeUtc {
+    fn now() -> Self {
+        let now = Utc::now();
+        Self::from_ymd_and_hms(
+            now.year(),
+            now.month(),
+            now.day(),
+            now.hour(),
+            now.minute(),
+            now.second(),
+        ).unwrap()
+    }
+}
+
+impl Dateable for DatetimeUtc {
+    fn year(&self) -> i32 {
+        self.chrono_datetime_utc.year()
+    }
+
+    fn month(&self) -> u32 {
+        self.chrono_datetime_utc.month()
+    }
+
+    fn day(&self) -> u32 {
+        self.chrono_datetime_utc.day()
+    }
+}
+
+impl Timeable for DatetimeUtc {
+    fn hour(&self) -> u32 {
+        self.chrono_datetime_utc.hour()
+    }
+
+    fn minute(&self) -> u32 {
+        self.chrono_datetime_utc.minute()
+    }
+
+    fn second(&self) -> u32 {
+        self.chrono_datetime_utc.second()
+    }
+}
+
+impl ToSql<Text, Sqlite> for DatetimeUtc {
+    fn to_sql<'b>(
+        &'b self,
+        out: &mut diesel::serialize::Output<'b, '_, Sqlite>,
+    ) -> serialize::Result {
+        out.set_value::<String>(self.to_string());
+        Ok(serialize::IsNull::No)
+    }
+}
+
+impl FromSql<Text, Sqlite> for DatetimeUtc {
+    fn from_sql(bytes: <Sqlite as Backend>::RawValue<'_>) -> deserialize::Result<DatetimeUtc> {
+        let str = <String as FromSql<Text, Sqlite>>::from_sql(bytes)?;
+        Ok(str.parse()?)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn when_from_ymd_and_hms_then_ymd_and_hms_are_as_expected() {
+        let datetime_utc = DatetimeUtc::from_ymd_and_hms(1970, 11, 23, 12, 55, 16);
+
+        assert!(datetime_utc.is_ok());
+        let date_utc = datetime_utc.unwrap();
+        assert_eq!(date_utc.year(), 1970);
+        assert_eq!(date_utc.month(), 11);
+        assert_eq!(date_utc.day(), 23);
+        assert_eq!(date_utc.hour(), 12);
+        assert_eq!(date_utc.minute(), 55);
+        assert_eq!(date_utc.second(), 16);
+    }
+
+    #[test]
+    fn when_from_ymd_and_hms_then_to_string_as_expected() {
+        let date_utc = DatetimeUtc::from_ymd_and_hms(1970, 11, 23, 12, 55, 16);
+
+        assert!(date_utc.is_ok());
+        assert_eq!(date_utc.unwrap().to_string(), "1970-11-23T12:55:16.000Z")
+    }
+
+    #[test]
+    fn when_with_invalid_ymd_and_hms_then_err() {
+        let datetime_utc_1 = DatetimeUtc::from_ymd_and_hms(1970, 0, 23, 12, 55, 16);
+        let datetime_utc_2 = DatetimeUtc::from_ymd_and_hms(1970, 13, 23, 12, 55, 16);
+        let datetime_utc_3 = DatetimeUtc::from_ymd_and_hms(1970, 11, 0, 12, 55, 16);
+        let datetime_utc_4 = DatetimeUtc::from_ymd_and_hms(1970, 11, 31, 12, 55, 16);
+        let datetime_utc_5 = DatetimeUtc::from_ymd_and_hms(1971, 2, 29, 12, 55, 16);
+        let datetime_utc_6 = DatetimeUtc::from_ymd_and_hms(1970, 11, 23, 25, 0, 0);
+        let datetime_utc_7 = DatetimeUtc::from_ymd_and_hms(1970, 11, 23, 0, 61, 0);
+        let datetime_utc_8 = DatetimeUtc::from_ymd_and_hms(1970, 11, 23, 0, 0, 61);
+
+        assert!(datetime_utc_1.is_err());
+        assert_eq!(datetime_utc_1.unwrap_err().to_string(), "failed to construct datetime from ymd 1970-00-23");
+        assert!(datetime_utc_2.is_err());
+        assert_eq!(datetime_utc_2.unwrap_err().to_string(), "failed to construct datetime from ymd 1970-13-23");
+        assert!(datetime_utc_3.is_err());
+        assert_eq!(datetime_utc_3.unwrap_err().to_string(), "failed to construct datetime from ymd 1970-11-00");
+        assert!(datetime_utc_4.is_err());
+        assert_eq!(datetime_utc_4.unwrap_err().to_string(), "failed to construct datetime from ymd 1970-11-31");
+        assert!(datetime_utc_5.is_err());
+        assert_eq!(datetime_utc_5.unwrap_err().to_string(), "failed to construct datetime from ymd 1971-02-29");
+        assert!(datetime_utc_6.is_err());
+        assert_eq!(datetime_utc_6.unwrap_err().to_string(), "failed to construct datetime from hms 25:00:00");
+        assert!(datetime_utc_7.is_err());
+        assert_eq!(datetime_utc_7.unwrap_err().to_string(), "failed to construct datetime from hms 00:61:00");
+        assert!(datetime_utc_8.is_err());
+        assert_eq!(datetime_utc_8.unwrap_err().to_string(), "failed to construct datetime from hms 00:00:61");
+    }
+
+    #[test]
+    fn when_from_string_then_ymd_and_hms_are_as_expected() {
+        let date_utc: Result<DatetimeUtc> = "1970-11-23T12:55:16.000Z".parse();
+
+        assert!(date_utc.is_ok());
+        let datetime_utc = date_utc.unwrap();
+        assert_eq!(datetime_utc.year(), 1970);
+        assert_eq!(datetime_utc.month(), 11);
+        assert_eq!(datetime_utc.day(), 23);
+        assert_eq!(datetime_utc.hour(), 12);
+        assert_eq!(datetime_utc.minute(), 55);
+        assert_eq!(datetime_utc.second(), 16);
+    }
+
+    #[test]
+    fn when_from_string_then_to_string_as_expected() {
+        let datetime_utc: Result<DatetimeUtc> = "1970-11-23T12:55:16.000Z".parse();
+
+        assert!(datetime_utc.is_ok());
+        assert_eq!(datetime_utc.unwrap().to_string(), "1970-11-23T12:55:16.000Z")
+    }
+
+    #[test]
+    fn when_from_invalid_string_then_err() {
+        let datetime_utc_1: Result<DatetimeUtc> = "1970-00-23T00:00:00.000Z".parse();
+        let datetime_utc_2: Result<DatetimeUtc> = "1970-13-23T00:00:00.000Z".parse();
+        let datetime_utc_3: Result<DatetimeUtc> = "1970-11-0T00:00:00.000Z".parse();
+        let datetime_utc_4: Result<DatetimeUtc> = "1970-11-31T00:00:00.000Z".parse();
+        let datetime_utc_5: Result<DatetimeUtc> = "1971-02-29T00:00:00.000Z".parse();
+        let datetime_utc_6: Result<DatetimeUtc> = "1970-11-23T25:00:00.000Z".parse();
+        let datetime_utc_7: Result<DatetimeUtc> = "1970-11-23T00:61:00.000Z".parse();
+        let datetime_utc_8: Result<DatetimeUtc> = "1970-11-23T00:00:61.000Z".parse();
+
+        assert!(datetime_utc_1.is_err());
+        assert!(datetime_utc_2.is_err());
+        assert!(datetime_utc_3.is_err());
+        assert!(datetime_utc_4.is_err());
+        assert!(datetime_utc_5.is_err());
+        assert!(datetime_utc_6.is_err());
+        assert!(datetime_utc_7.is_err());
+        assert!(datetime_utc_8.is_err());
+    }
+}
diff --git a/rust/schist_core/src/models/mod.rs b/rust/schist_core/src/models/mod.rs
new file mode 100644
index 0000000..2eb7ac2
--- /dev/null
+++ b/rust/schist_core/src/models/mod.rs
@@ -0,0 +1,11 @@
+pub mod account;
+pub mod budget;
+pub mod budget_update;
+pub mod category;
+pub mod category_balance;
+pub mod category_budget;
+pub mod category_transfer;
+pub mod date_utc;
+pub mod datetime_utc;
+pub mod transaction;
+pub mod transaction_categorisation;
diff --git a/rust/schist_core/src/models/transaction.rs b/rust/schist_core/src/models/transaction.rs
new file mode 100644
index 0000000..18a4c0e
--- /dev/null
+++ b/rust/schist_core/src/models/transaction.rs
@@ -0,0 +1,18 @@
+use derive_builder::Builder;
+use diesel::prelude::*;
+
+use crate::models::account::Account;
+
+use super::datetime_utc::DatetimeUtc;
+
+#[derive(Builder, Queryable, Identifiable, Selectable, Insertable, Associations, Debug, PartialEq)]
+#[diesel(table_name = crate::schema::transactions)]
+#[diesel(belongs_to(Account))]
+pub struct Transaction {
+    pub id: i32,
+    pub description: String,
+    pub payee: String,
+    pub quantity: i32,
+    pub date: DatetimeUtc,
+    pub account_id: i32,
+}
diff --git a/rust/schist_core/src/models/transaction_categorisation.rs b/rust/schist_core/src/models/transaction_categorisation.rs
new file mode 100644
index 0000000..c6ac6ea
--- /dev/null
+++ b/rust/schist_core/src/models/transaction_categorisation.rs
@@ -0,0 +1,12 @@
+use derive_builder::Builder;
+use diesel::prelude::*;
+
+#[derive(Builder, Queryable, Identifiable, Selectable, Insertable, Debug, PartialEq)]
+#[diesel(table_name = crate::schema::transaction_categorisations)]
+pub struct TransactionCategorisation {
+    pub id: i32,
+    pub description: String,
+    pub quantity: i32,
+    pub transaction_id: i32,
+    pub category_id: i32,
+}
diff --git a/rust/schist_core/src/queries/accounts/delete_all.rs b/rust/schist_core/src/queries/accounts/delete_all.rs
new file mode 100644
index 0000000..84d7bf6
--- /dev/null
+++ b/rust/schist_core/src/queries/accounts/delete_all.rs
@@ -0,0 +1,11 @@
+use anyhow::{Context, Result};
+use diesel::{RunQueryDsl, SqliteConnection};
+
+use crate::schema::accounts::dsl::accounts;
+
+pub fn delete_all_accounts(connection: &mut SqliteConnection) -> Result<usize> {
+    let num_rows_deleted = diesel::delete(accounts)
+        .execute(connection)
+        .with_context(|| "failed to delete all accounts")?;
+    Ok(num_rows_deleted)
+}
diff --git a/rust/schist_core/src/queries/accounts/get_all.rs b/rust/schist_core/src/queries/accounts/get_all.rs
new file mode 100644
index 0000000..ab53729
--- /dev/null
+++ b/rust/schist_core/src/queries/accounts/get_all.rs
@@ -0,0 +1,10 @@
+use anyhow::{Context, Result};
+use crate::{models::account::Account, schema::accounts::dsl::accounts};
+use diesel::{QueryDsl, RunQueryDsl, SelectableHelper, SqliteConnection};
+
+pub fn get_all_accounts(connection: &mut SqliteConnection) -> Result<Vec<Account>> {
+    let all_accounts = accounts.select(Account::as_select())
+        .load(connection)
+        .with_context(|| "failed to get all accounts")?;
+    Ok(all_accounts)
+}
diff --git a/rust/schist_core/src/queries/accounts/insert.rs b/rust/schist_core/src/queries/accounts/insert.rs
new file mode 100644
index 0000000..7020b68
--- /dev/null
+++ b/rust/schist_core/src/queries/accounts/insert.rs
@@ -0,0 +1,28 @@
+use anyhow::{Context, Result};
+use crate::{
+    models::account::Account,
+    schema::accounts::dsl::accounts as accounts_table,
+};
+use diesel::prelude::*;
+
+pub fn insert_accounts(
+    accounts: &[Account],
+    connection: &mut SqliteConnection,
+) -> Result<usize> {
+    let num_accounts_inserted = diesel::insert_into(accounts_table)
+        .values(accounts)
+        .execute(connection)
+        .with_context(|| err_msg(accounts))?;
+    Ok(num_accounts_inserted)
+}
+
+fn err_msg(accounts: &[Account]) -> String {
+    format!(
+        "failed to insert accounts: [{}]",
+        accounts
+            .iter()
+            .map(|a| format!("\"{}\": \"{}\"", a.id, a.name))
+            .collect::<Vec<String>>()
+            .join(", ")
+    )
+}
diff --git a/rust/schist_core/src/queries/accounts/mod.rs b/rust/schist_core/src/queries/accounts/mod.rs
new file mode 100644
index 0000000..222b180
--- /dev/null
+++ b/rust/schist_core/src/queries/accounts/mod.rs
@@ -0,0 +1,7 @@
+mod delete_all;
+mod get_all;
+mod insert;
+
+pub use delete_all::delete_all_accounts;
+pub use get_all::get_all_accounts;
+pub use insert::insert_accounts;
diff --git a/rust/schist_core/src/queries/budget_updates/delete_all.rs b/rust/schist_core/src/queries/budget_updates/delete_all.rs
new file mode 100644
index 0000000..b7ad082
--- /dev/null
+++ b/rust/schist_core/src/queries/budget_updates/delete_all.rs
@@ -0,0 +1,11 @@
+use anyhow::{Context, Result};
+use diesel::{RunQueryDsl, SqliteConnection};
+
+use crate::schema::budget_updates::dsl::budget_updates;
+
+pub fn delete_all_budget_updates(connection: &mut SqliteConnection) -> Result<usize> {
+    let num_rows_deleted = diesel::delete(budget_updates)
+        .execute(connection)
+        .with_context(|| "failed to delete all budget updates")?;
+    Ok(num_rows_deleted)
+}
diff --git a/rust/schist_core/src/queries/budget_updates/get_all.rs b/rust/schist_core/src/queries/budget_updates/get_all.rs
new file mode 100644
index 0000000..9c9310b
--- /dev/null
+++ b/rust/schist_core/src/queries/budget_updates/get_all.rs
@@ -0,0 +1,16 @@
+use anyhow::{Context, Result};
+use crate::{
+    models::budget_update::BudgetUpdate,
+    schema::budget_updates::dsl::budget_updates as budget_updates_table,
+};
+use diesel::{QueryDsl, RunQueryDsl, SelectableHelper, SqliteConnection};
+
+pub fn get_all_budget_updates(
+    connection: &mut SqliteConnection,
+) -> Result<Vec<BudgetUpdate>> {
+    let all_budget_updates = budget_updates_table
+        .select(BudgetUpdate::as_select())
+        .load::<BudgetUpdate>(connection)
+        .with_context(|| "failed to get all budget updates")?;
+    Ok(all_budget_updates)
+}
diff --git a/rust/schist_core/src/queries/budget_updates/get_first_with_date_and_category_id.rs b/rust/schist_core/src/queries/budget_updates/get_first_with_date_and_category_id.rs
new file mode 100644
index 0000000..2d8f97c
--- /dev/null
+++ b/rust/schist_core/src/queries/budget_updates/get_first_with_date_and_category_id.rs
@@ -0,0 +1,25 @@
+use anyhow::{Context, Result};
+use crate::{
+    models::{budget_update::BudgetUpdate, date_utc::DateUtc},
+    schema::budget_updates::{
+        self as budget_updates_schema, dsl::budget_updates as budget_updates_table,
+    },
+};
+use diesel::{
+    ExpressionMethods, OptionalExtension, QueryDsl, RunQueryDsl, SelectableHelper, SqliteConnection
+};
+
+pub fn get_first_budget_update_with_date_and_category_id(
+    date: &DateUtc,
+    category_id: i32,
+    connection: &mut SqliteConnection,
+) -> Result<Option<BudgetUpdate>> {
+    let first_budget_update = budget_updates_table
+        .select(BudgetUpdate::as_select())
+        .filter(budget_updates_schema::date.eq(date.to_string()))
+        .filter(budget_updates_schema::category_id.eq(category_id))
+        .first(connection)
+        .optional()
+        .with_context(|| format!("failed to get first budget update with date {}", date.to_string()))?;
+    Ok(first_budget_update)
+}
diff --git a/rust/schist_core/src/queries/budget_updates/get_most_recent_with_category_id.rs b/rust/schist_core/src/queries/budget_updates/get_most_recent_with_category_id.rs
new file mode 100644
index 0000000..41ef5ec
--- /dev/null
+++ b/rust/schist_core/src/queries/budget_updates/get_most_recent_with_category_id.rs
@@ -0,0 +1,21 @@
+use anyhow::{Context, Result};
+use crate::{
+    models::date_utc::DateUtc,
+    schema::budget_updates::{
+        self as budget_updates_schema, dsl::budget_updates as budget_updates_table,
+    }, traits::nowlike::Nowlike,
+};
+use diesel::{dsl::max, ExpressionMethods, QueryDsl, RunQueryDsl, SqliteConnection};
+
+pub fn get_most_recent_budget_update_date_with_category_id(
+    category_id: i32,
+    connection: &mut SqliteConnection,
+) -> Result<Option<DateUtc>> {
+    let most_recent_date = budget_updates_table
+        .select(max(budget_updates_schema::date))
+        .filter(budget_updates_schema::category_id.eq(category_id))
+        .filter(budget_updates_schema::date.le(DateUtc::now()))
+        .first(connection)
+        .with_context(|| format!("failed to get most recent budget update date with category ID {}", category_id))?;
+    Ok(most_recent_date)
+}
diff --git a/rust/schist_core/src/queries/budget_updates/insert.rs b/rust/schist_core/src/queries/budget_updates/insert.rs
new file mode 100644
index 0000000..e8ae271
--- /dev/null
+++ b/rust/schist_core/src/queries/budget_updates/insert.rs
@@ -0,0 +1,28 @@
+use anyhow::{Context, Result};
+use crate::{
+    models::budget_update::BudgetUpdate,
+    schema::budget_updates::dsl::budget_updates as budget_updates_table,
+};
+use diesel::prelude::*;
+
+pub fn insert_budget_updates(
+    budget_updates: &[BudgetUpdate],
+    connection: &mut SqliteConnection,
+) -> Result<usize> {
+    let num_rows_inserted = diesel::insert_into(budget_updates_table)
+        .values(budget_updates)
+        .execute(connection)
+        .with_context(|| err_msg(budget_updates))?;
+    Ok(num_rows_inserted)
+}
+
+fn err_msg(budget_updates: &[BudgetUpdate]) -> String {
+    format!(
+        "failed to insert budget updates: [{}]",
+        budget_updates
+            .iter()
+            .map(|a| a.id.to_string())
+            .collect::<Vec<String>>()
+            .join(", ")
+    )
+}
diff --git a/rust/schist_core/src/queries/budget_updates/mod.rs b/rust/schist_core/src/queries/budget_updates/mod.rs
new file mode 100644
index 0000000..6fc7de0
--- /dev/null
+++ b/rust/schist_core/src/queries/budget_updates/mod.rs
@@ -0,0 +1,11 @@
+mod delete_all;
+mod get_all;
+mod get_first_with_date_and_category_id;
+mod get_most_recent_with_category_id;
+mod insert;
+
+pub use delete_all::delete_all_budget_updates;
+pub use get_all::get_all_budget_updates;
+pub use get_first_with_date_and_category_id::get_first_budget_update_with_date_and_category_id;
+pub use get_most_recent_with_category_id::get_most_recent_budget_update_date_with_category_id;
+pub use insert::insert_budget_updates;
diff --git a/rust/schist_core/src/queries/categories/delete_all.rs b/rust/schist_core/src/queries/categories/delete_all.rs
new file mode 100644
index 0000000..1fd2581
--- /dev/null
+++ b/rust/schist_core/src/queries/categories/delete_all.rs
@@ -0,0 +1,11 @@
+use anyhow::{Context, Result};
+use diesel::{RunQueryDsl, SqliteConnection};
+
+use crate::schema::categories::dsl::categories;
+
+pub fn delete_all_categories(connection: &mut SqliteConnection) -> Result<usize> {
+    let num_rows_deleted = diesel::delete(categories)
+        .execute(connection)
+        .with_context(|| "failed to delete all categories")?;
+    Ok(num_rows_deleted)
+}
diff --git a/rust/schist_core/src/queries/categories/get_all.rs b/rust/schist_core/src/queries/categories/get_all.rs
new file mode 100644
index 0000000..431ed9c
--- /dev/null
+++ b/rust/schist_core/src/queries/categories/get_all.rs
@@ -0,0 +1,11 @@
+use anyhow::{Context, Result};
+use crate::{models::category::Category, schema::categories::dsl::categories as categories_table};
+use diesel::{QueryDsl, RunQueryDsl, SelectableHelper, SqliteConnection};
+
+pub fn get_all_categories(connection: &mut SqliteConnection) -> Result<Vec<Category>> {
+    let all_categories = categories_table
+        .select(Category::as_select())
+        .load(connection)
+        .with_context(|| "failed to get all categories")?;
+    Ok(all_categories)
+}
diff --git a/rust/schist_core/src/queries/categories/get_all_balances.rs b/rust/schist_core/src/queries/categories/get_all_balances.rs
new file mode 100644
index 0000000..c9a0102
--- /dev/null
+++ b/rust/schist_core/src/queries/categories/get_all_balances.rs
@@ -0,0 +1,47 @@
+use anyhow::{Context, Result};
+use crate::{models::category_balance::CategoryBalance, queries::{
+        budget_updates::get_all_budget_updates,
+        categories::get_all_categories,
+        category_transfers::{
+            sum_category_transfer_quantity_per_from_category_id,
+            sum_category_transfer_quantity_per_to_category_id,
+        },
+        transaction_categorisations::sum_transaction_categorisation_quantity_per_category_id,
+    }, utils::calculate_category_balance};
+use diesel::SqliteConnection;
+
+pub fn get_all_category_balances(
+    connection: &mut SqliteConnection,
+) -> Result<Vec<CategoryBalance>> {
+    get_all_category_balances_without_context(connection)
+        .with_context(|| "failed to get all category balances")
+}
+
+fn get_all_category_balances_without_context(
+    connection: &mut SqliteConnection,
+) -> Result<Vec<CategoryBalance>> {
+    let categories = get_all_categories(connection)?;
+    let transaction_sums = sum_transaction_categorisation_quantity_per_category_id(connection)?;
+    let category_transfer_from_sums =
+        sum_category_transfer_quantity_per_from_category_id(connection)?;
+    let category_transfer_to_sums = sum_category_transfer_quantity_per_to_category_id(connection)?;
+    let budget_updates = get_all_budget_updates(connection)?;
+
+    let mut balances = Vec::<CategoryBalance>::new();
+    for category in categories {
+        let balance = calculate_category_balance(
+            &category,
+            &transaction_sums,
+            &category_transfer_from_sums,
+            &category_transfer_to_sums,
+            &budget_updates,
+        )?;
+
+        balances.push(CategoryBalance {
+            category_id: category.id,
+            balance: balance.try_into().unwrap(),
+        })
+    }
+
+    Ok(balances)
+}
diff --git a/rust/schist_core/src/queries/categories/get_all_ids.rs b/rust/schist_core/src/queries/categories/get_all_ids.rs
new file mode 100644
index 0000000..8505e71
--- /dev/null
+++ b/rust/schist_core/src/queries/categories/get_all_ids.rs
@@ -0,0 +1,11 @@
+use anyhow::{Context, Result};
+use crate::schema::categories::{self as categories_schema, dsl::categories as categories_table};
+use diesel::{QueryDsl, RunQueryDsl, SqliteConnection};
+
+pub fn get_all_category_ids(connection: &mut SqliteConnection) -> Result<Vec<i32>> {
+    let all_category_ids = categories_table
+        .select(categories_schema::id)
+        .load(connection)
+        .with_context(|| "failed to get all category IDs")?;
+    Ok(all_category_ids)
+}
diff --git a/rust/schist_core/src/queries/categories/get_most_recent_budget_per_category_id.rs b/rust/schist_core/src/queries/categories/get_most_recent_budget_per_category_id.rs
new file mode 100644
index 0000000..9f2e4f6
--- /dev/null
+++ b/rust/schist_core/src/queries/categories/get_most_recent_budget_per_category_id.rs
@@ -0,0 +1,52 @@
+use anyhow::{Context, Result};
+use crate::{models::{budget::Budget, category_budget::CategoryBudget}, queries::{
+    budget_updates::{
+        get_first_budget_update_with_date_and_category_id, get_most_recent_budget_update_date_with_category_id,
+    },
+    categories::get_all_category_ids,
+}};
+use diesel::SqliteConnection;
+
+pub fn get_most_recent_category_budget_per_category_id(
+    connection: &mut SqliteConnection,
+) -> Result<Vec<CategoryBudget>> {
+    get_most_recent_category_budget_per_category_id_without_context(connection)
+        .with_context(|| "failed to get most recent category budget per category ID")
+}
+
+fn get_most_recent_category_budget_per_category_id_without_context(
+    connection: &mut SqliteConnection,
+) -> Result<Vec<CategoryBudget>> {
+    let category_ids: Vec<i32> = get_all_category_ids(connection)?;
+
+    let mut budgets = Vec::<CategoryBudget>::new();
+    for category_id in category_ids {
+        let most_recent_budget_update_date =
+            get_most_recent_budget_update_date_with_category_id(category_id, connection)?;
+
+        if most_recent_budget_update_date.is_none() {
+            budgets.push(CategoryBudget {
+                category_id,
+                budget: Option::None,
+            });
+            continue;
+        }
+        let most_recent_budget_update_date = most_recent_budget_update_date.unwrap();
+
+        let most_recent_budget_update = get_first_budget_update_with_date_and_category_id(
+            &most_recent_budget_update_date,
+            category_id,
+            connection,
+        )?;
+        // The fact we found the date by getting the most recent budget update
+        // date guarantees that the Option is Some
+        let most_recent_budget_update = most_recent_budget_update.unwrap();
+
+        budgets.push(CategoryBudget {
+            category_id,
+            budget: Some(Budget::from(&most_recent_budget_update)),
+        });
+    }
+
+    Ok(budgets)
+}
diff --git a/rust/schist_core/src/queries/categories/insert.rs b/rust/schist_core/src/queries/categories/insert.rs
new file mode 100644
index 0000000..bccba72
--- /dev/null
+++ b/rust/schist_core/src/queries/categories/insert.rs
@@ -0,0 +1,28 @@
+use anyhow::{Context, Result};
+use crate::{
+    models::category::Category,
+    schema::categories::dsl::categories as categories_table,
+};
+use diesel::prelude::*;
+
+pub fn insert_categories(
+    categories: &[Category],
+    connection: &mut SqliteConnection,
+) -> Result<usize> {
+    let num_categories_inserted = diesel::insert_into(categories_table)
+        .values(categories)
+        .execute(connection)
+        .with_context(|| err_msg(categories))?;
+    Ok(num_categories_inserted)
+}
+
+fn err_msg(categories: &[Category]) -> String {
+    format!(
+        "failed to insert categories: [{}]",
+        categories
+            .iter()
+            .map(|a| format!("\"{}\": \"{}\"", a.id, a.name))
+            .collect::<Vec<String>>()
+            .join(", ")
+    )
+}
diff --git a/rust/schist_core/src/queries/categories/mod.rs b/rust/schist_core/src/queries/categories/mod.rs
new file mode 100644
index 0000000..edeeebf
--- /dev/null
+++ b/rust/schist_core/src/queries/categories/mod.rs
@@ -0,0 +1,13 @@
+mod delete_all;
+mod get_all;
+mod get_all_balances;
+mod get_all_ids;
+mod get_most_recent_budget_per_category_id;
+mod insert;
+
+pub use delete_all::delete_all_categories;
+pub use get_all::get_all_categories;
+pub use get_all_balances::get_all_category_balances;
+pub use get_all_ids::get_all_category_ids;
+pub use get_most_recent_budget_per_category_id::get_most_recent_category_budget_per_category_id;
+pub use insert::insert_categories;
diff --git a/rust/schist_core/src/queries/category_transfers/delete_all.rs b/rust/schist_core/src/queries/category_transfers/delete_all.rs
new file mode 100644
index 0000000..406b80b
--- /dev/null
+++ b/rust/schist_core/src/queries/category_transfers/delete_all.rs
@@ -0,0 +1,7 @@
+use diesel::{result::Error, RunQueryDsl, SqliteConnection};
+
+use crate::schema::category_transfers::dsl::category_transfers;
+
+pub fn delete_all_category_transfers(connection: &mut SqliteConnection) -> Result<usize, Error> {
+    diesel::delete(category_transfers).execute(connection)
+}
diff --git a/rust/schist_core/src/queries/category_transfers/get_all.rs b/rust/schist_core/src/queries/category_transfers/get_all.rs
new file mode 100644
index 0000000..73d7e10
--- /dev/null
+++ b/rust/schist_core/src/queries/category_transfers/get_all.rs
@@ -0,0 +1,11 @@
+use anyhow::{Context, Result};
+use crate::{models::category_transfer::CategoryTransfer, schema::category_transfers::dsl::category_transfers as category_transfers_table};
+use diesel::{QueryDsl, RunQueryDsl, SelectableHelper, SqliteConnection};
+
+pub fn get_all_category_transfers(connection: &mut SqliteConnection) -> Result<Vec<CategoryTransfer>> {
+    let all_category_transfers = category_transfers_table
+        .select(CategoryTransfer::as_select())
+        .load(connection)
+        .with_context(|| "failed to get all category transfers")?;
+    Ok(all_category_transfers)
+}
diff --git a/rust/schist_core/src/queries/category_transfers/insert.rs b/rust/schist_core/src/queries/category_transfers/insert.rs
new file mode 100644
index 0000000..e1db167
--- /dev/null
+++ b/rust/schist_core/src/queries/category_transfers/insert.rs
@@ -0,0 +1,15 @@
+use crate::{
+    models::category_transfer::CategoryTransfer,
+    schema::category_transfers::dsl::category_transfers as category_transfers_table,
+};
+use diesel::prelude::*;
+use diesel::result::Error;
+
+pub fn insert_category_transfers(
+    category_transfers: &[CategoryTransfer],
+    connection: &mut SqliteConnection,
+) -> Result<usize, Error> {
+    diesel::insert_into(category_transfers_table)
+        .values(category_transfers)
+        .execute(connection)
+}
diff --git a/rust/schist_core/src/queries/category_transfers/mod.rs b/rust/schist_core/src/queries/category_transfers/mod.rs
new file mode 100644
index 0000000..eed7946
--- /dev/null
+++ b/rust/schist_core/src/queries/category_transfers/mod.rs
@@ -0,0 +1,11 @@
+mod delete_all;
+mod get_all;
+mod insert;
+mod sum_quantity_per_from_category_id;
+mod sum_quantity_per_to_category_id;
+
+pub use delete_all::delete_all_category_transfers;
+pub use get_all::get_all_category_transfers;
+pub use insert::insert_category_transfers;
+pub use sum_quantity_per_from_category_id::sum_category_transfer_quantity_per_from_category_id;
+pub use sum_quantity_per_to_category_id::sum_category_transfer_quantity_per_to_category_id;
diff --git a/rust/schist_core/src/queries/category_transfers/sum_quantity_per_from_category_id.rs b/rust/schist_core/src/queries/category_transfers/sum_quantity_per_from_category_id.rs
new file mode 100644
index 0000000..a9c2a8c
--- /dev/null
+++ b/rust/schist_core/src/queries/category_transfers/sum_quantity_per_from_category_id.rs
@@ -0,0 +1,18 @@
+use crate::schema::category_transfers::{
+    self as category_transfers_schema,
+    dsl::category_transfers as category_transfers_table,
+};
+use diesel::{dsl::sum, result::Error, QueryDsl, RunQueryDsl, SqliteConnection};
+
+pub fn sum_category_transfer_quantity_per_from_category_id(
+    connection: &mut SqliteConnection,
+) -> Result<Vec<(i32, i64)>, Error> {
+    category_transfers_table
+        .group_by(category_transfers_schema::from_category_id)
+        .select((
+            category_transfers_schema::from_category_id,
+            sum(category_transfers_schema::quantity),
+        ))
+        .load::<(i32, Option<i64>)>(connection)
+        .map(|result| result.iter().map(|sum| (sum.0, sum.1.unwrap_or(0))).collect())
+}
diff --git a/rust/schist_core/src/queries/category_transfers/sum_quantity_per_to_category_id.rs b/rust/schist_core/src/queries/category_transfers/sum_quantity_per_to_category_id.rs
new file mode 100644
index 0000000..f041477
--- /dev/null
+++ b/rust/schist_core/src/queries/category_transfers/sum_quantity_per_to_category_id.rs
@@ -0,0 +1,18 @@
+use crate::schema::category_transfers::{
+    self as category_transfers_schema,
+    dsl::category_transfers as category_transfers_table,
+};
+use diesel::{dsl::sum, result::Error, QueryDsl, RunQueryDsl, SqliteConnection};
+
+pub fn sum_category_transfer_quantity_per_to_category_id(
+    connection: &mut SqliteConnection,
+) -> Result<Vec<(i32, i64)>, Error> {
+    category_transfers_table
+        .group_by(category_transfers_schema::to_category_id)
+        .select((
+            category_transfers_schema::to_category_id,
+            sum(category_transfers_schema::quantity),
+        ))
+        .load::<(i32, Option<i64>)>(connection)
+        .map(|vec| vec.iter().map(|(id, sum)| (*id, sum.unwrap_or(0))).collect())
+}
diff --git a/rust/schist_core/src/queries/clear.rs b/rust/schist_core/src/queries/clear.rs
new file mode 100644
index 0000000..e704634
--- /dev/null
+++ b/rust/schist_core/src/queries/clear.rs
@@ -0,0 +1,20 @@
+use anyhow::Result;
+use crate::queries::{
+    accounts::delete_all_accounts,
+    budget_updates::delete_all_budget_updates,
+    categories::delete_all_categories,
+    category_transfers::delete_all_category_transfers,
+    transactions::delete_all_transactions,
+    transaction_categorisations::delete_all_transaction_categorisations,
+};
+use diesel::SqliteConnection;
+
+pub fn clear(connection: &mut SqliteConnection) -> Result<()> {
+    delete_all_accounts(connection)?;
+    delete_all_budget_updates(connection)?;
+    delete_all_categories(connection)?;
+    delete_all_category_transfers(connection)?;
+    delete_all_transactions(connection)?;
+    delete_all_transaction_categorisations(connection)?;
+    Ok(())
+}
diff --git a/rust/schist_core/src/queries/mod.rs b/rust/schist_core/src/queries/mod.rs
new file mode 100644
index 0000000..f0852ce
--- /dev/null
+++ b/rust/schist_core/src/queries/mod.rs
@@ -0,0 +1,7 @@
+pub mod accounts;
+pub mod budget_updates;
+pub mod categories;
+pub mod category_transfers;
+pub mod clear;
+pub mod transactions;
+pub mod transaction_categorisations;
diff --git a/rust/schist_core/src/queries/transaction_categorisations/delete_all.rs b/rust/schist_core/src/queries/transaction_categorisations/delete_all.rs
new file mode 100644
index 0000000..e80a0ca
--- /dev/null
+++ b/rust/schist_core/src/queries/transaction_categorisations/delete_all.rs
@@ -0,0 +1,7 @@
+use diesel::{result::Error, RunQueryDsl, SqliteConnection};
+
+use crate::schema::transaction_categorisations::dsl::transaction_categorisations;
+
+pub fn delete_all_transaction_categorisations(connection: &mut SqliteConnection) -> Result<usize, Error> {
+    diesel::delete(transaction_categorisations).execute(connection)
+}
diff --git a/rust/schist_core/src/queries/transaction_categorisations/get_all.rs b/rust/schist_core/src/queries/transaction_categorisations/get_all.rs
new file mode 100644
index 0000000..0cacfe6
--- /dev/null
+++ b/rust/schist_core/src/queries/transaction_categorisations/get_all.rs
@@ -0,0 +1,11 @@
+use anyhow::{Context, Result};
+use crate::{models::transaction_categorisation::TransactionCategorisation, schema::transaction_categorisations::dsl::transaction_categorisations as transaction_categorisations_table};
+use diesel::{QueryDsl, RunQueryDsl, SelectableHelper, SqliteConnection};
+
+pub fn get_all_transaction_categorisations(connection: &mut SqliteConnection) -> Result<Vec<TransactionCategorisation>> {
+    let all_transaction_categorisations = transaction_categorisations_table
+        .select(TransactionCategorisation::as_select())
+        .load(connection)
+        .with_context(|| "failed to get all transaction categorisations")?;
+    Ok(all_transaction_categorisations)
+}
diff --git a/rust/schist_core/src/queries/transaction_categorisations/insert.rs b/rust/schist_core/src/queries/transaction_categorisations/insert.rs
new file mode 100644
index 0000000..3da1c33
--- /dev/null
+++ b/rust/schist_core/src/queries/transaction_categorisations/insert.rs
@@ -0,0 +1,15 @@
+use crate::{
+    models::transaction_categorisation::TransactionCategorisation,
+    schema::transaction_categorisations::dsl::transaction_categorisations as transaction_categorisations_table,
+};
+use diesel::prelude::*;
+use diesel::result::Error;
+
+pub fn insert_transaction_categorisations(
+    transaction_categorisations: &[TransactionCategorisation],
+    connection: &mut SqliteConnection,
+) -> Result<usize, Error> {
+    diesel::insert_into(transaction_categorisations_table)
+        .values(transaction_categorisations)
+        .execute(connection)
+}
diff --git a/rust/schist_core/src/queries/transaction_categorisations/mod.rs b/rust/schist_core/src/queries/transaction_categorisations/mod.rs
new file mode 100644
index 0000000..d383791
--- /dev/null
+++ b/rust/schist_core/src/queries/transaction_categorisations/mod.rs
@@ -0,0 +1,9 @@
+mod delete_all;
+mod get_all;
+mod insert;
+mod sum_quantity_per_category_id;
+
+pub use delete_all::delete_all_transaction_categorisations;
+pub use get_all::get_all_transaction_categorisations;
+pub use insert::insert_transaction_categorisations;
+pub use sum_quantity_per_category_id::sum_transaction_categorisation_quantity_per_category_id;
diff --git a/rust/schist_core/src/queries/transaction_categorisations/sum_quantity_per_category_id.rs b/rust/schist_core/src/queries/transaction_categorisations/sum_quantity_per_category_id.rs
new file mode 100644
index 0000000..61f3492
--- /dev/null
+++ b/rust/schist_core/src/queries/transaction_categorisations/sum_quantity_per_category_id.rs
@@ -0,0 +1,18 @@
+use crate::schema::transaction_categorisations::{
+    self as transaction_categorisations_schema,
+    dsl::transaction_categorisations as transaction_categorisations_table,
+};
+use diesel::{dsl::sum, result::Error, QueryDsl, RunQueryDsl, SqliteConnection};
+
+pub fn sum_transaction_categorisation_quantity_per_category_id(
+    connection: &mut SqliteConnection,
+) -> Result<Vec<(i32, i64)>, Error> {
+    transaction_categorisations_table
+        .group_by(transaction_categorisations_schema::category_id)
+        .select((
+            transaction_categorisations_schema::category_id,
+            sum(transaction_categorisations_schema::quantity),
+        ))
+        .load::<(i32, Option<i64>)>(connection)
+        .map(|vec| vec.iter().map(|(category_id, sum)| (*category_id, sum.unwrap_or(0))).collect())
+}
diff --git a/rust/schist_core/src/queries/transactions/delete_all.rs b/rust/schist_core/src/queries/transactions/delete_all.rs
new file mode 100644
index 0000000..43b7976
--- /dev/null
+++ b/rust/schist_core/src/queries/transactions/delete_all.rs
@@ -0,0 +1,7 @@
+use diesel::{result::Error, RunQueryDsl, SqliteConnection};
+
+use crate::schema::transactions::dsl::transactions;
+
+pub fn delete_all_transactions(connection: &mut SqliteConnection) -> Result<usize, Error> {
+    diesel::delete(transactions).execute(connection)
+}
diff --git a/rust/schist_core/src/queries/transactions/get_all.rs b/rust/schist_core/src/queries/transactions/get_all.rs
new file mode 100644
index 0000000..afb87f4
--- /dev/null
+++ b/rust/schist_core/src/queries/transactions/get_all.rs
@@ -0,0 +1,11 @@
+use anyhow::{Context, Result};
+use crate::{models::transaction::Transaction, schema::transactions::dsl::transactions as transactions_table};
+use diesel::{QueryDsl, RunQueryDsl, SelectableHelper, SqliteConnection};
+
+pub fn get_all_transactions(connection: &mut SqliteConnection) -> Result<Vec<Transaction>> {
+    let all_transactions = transactions_table
+        .select(Transaction::as_select())
+        .load(connection)
+        .with_context(|| "failed to get all category transfers")?;
+    Ok(all_transactions)
+}
diff --git a/rust/schist_core/src/queries/transactions/insert.rs b/rust/schist_core/src/queries/transactions/insert.rs
new file mode 100644
index 0000000..32f3dc2
--- /dev/null
+++ b/rust/schist_core/src/queries/transactions/insert.rs
@@ -0,0 +1,15 @@
+use crate::{
+    models::transaction::Transaction,
+    schema::transactions::dsl::transactions as transactions_table,
+};
+use diesel::prelude::*;
+use diesel::result::Error;
+
+pub fn insert_transactions(
+    transactions: &[Transaction],
+    connection: &mut SqliteConnection,
+) -> Result<usize, Error> {
+    diesel::insert_into(transactions_table)
+        .values(transactions)
+        .execute(connection)
+}
diff --git a/rust/schist_core/src/queries/transactions/mod.rs b/rust/schist_core/src/queries/transactions/mod.rs
new file mode 100644
index 0000000..983e9af
--- /dev/null
+++ b/rust/schist_core/src/queries/transactions/mod.rs
@@ -0,0 +1,7 @@
+mod delete_all;
+mod get_all;
+mod insert;
+
+pub use delete_all::delete_all_transactions;
+pub use get_all::get_all_transactions;
+pub use insert::insert_transactions;
diff --git a/rust/schist_core/src/schema.rs b/rust/schist_core/src/schema.rs
new file mode 100644
index 0000000..372f8f3
--- /dev/null
+++ b/rust/schist_core/src/schema.rs
@@ -0,0 +1,72 @@
+// @generated automatically by Diesel CLI.
+
+diesel::table! {
+    accounts (id) {
+        id -> Integer,
+        name -> Text,
+        opening_balance -> Integer,
+        opening_date -> Text,
+    }
+}
+
+diesel::table! {
+    budget_updates (id) {
+        id -> Integer,
+        category_id -> Integer,
+        date -> Text,
+        new_budget -> Integer,
+        new_period -> Integer,
+    }
+}
+
+diesel::table! {
+    categories (id) {
+        id -> Integer,
+        name -> Text,
+    }
+}
+
+diesel::table! {
+    category_transfers (id) {
+        id -> Integer,
+        description -> Text,
+        quantity -> Integer,
+        from_category_id -> Integer,
+        to_category_id -> Integer,
+    }
+}
+
+diesel::table! {
+    transaction_categorisations (id) {
+        id -> Integer,
+        description -> Text,
+        quantity -> Integer,
+        transaction_id -> Integer,
+        category_id -> Integer,
+    }
+}
+
+diesel::table! {
+    transactions (id) {
+        id -> Integer,
+        description -> Text,
+        payee -> Text,
+        quantity -> Integer,
+        date -> Text,
+        account_id -> Integer,
+    }
+}
+
+diesel::joinable!(budget_updates -> categories (category_id));
+diesel::joinable!(transaction_categorisations -> categories (category_id));
+diesel::joinable!(transaction_categorisations -> transactions (transaction_id));
+diesel::joinable!(transactions -> accounts (account_id));
+
+diesel::allow_tables_to_appear_in_same_query!(
+    accounts,
+    budget_updates,
+    categories,
+    category_transfers,
+    transaction_categorisations,
+    transactions,
+);
diff --git a/rust/schist_core/src/traits/dateable.rs b/rust/schist_core/src/traits/dateable.rs
new file mode 100644
index 0000000..05f2d74
--- /dev/null
+++ b/rust/schist_core/src/traits/dateable.rs
@@ -0,0 +1,5 @@
+pub trait Dateable {
+    fn year(&self) -> i32;
+    fn month(&self) -> u32;
+    fn day(&self) -> u32;
+}
diff --git a/rust/schist_core/src/traits/mod.rs b/rust/schist_core/src/traits/mod.rs
new file mode 100644
index 0000000..ab5caca
--- /dev/null
+++ b/rust/schist_core/src/traits/mod.rs
@@ -0,0 +1,3 @@
+pub mod dateable;
+pub mod nowlike;
+pub mod timeable;
diff --git a/rust/schist_core/src/traits/nowlike.rs b/rust/schist_core/src/traits/nowlike.rs
new file mode 100644
index 0000000..bae2309
--- /dev/null
+++ b/rust/schist_core/src/traits/nowlike.rs
@@ -0,0 +1,3 @@
+pub trait Nowlike {
+    fn now() -> Self;
+}
diff --git a/rust/schist_core/src/traits/timeable.rs b/rust/schist_core/src/traits/timeable.rs
new file mode 100644
index 0000000..f6f9244
--- /dev/null
+++ b/rust/schist_core/src/traits/timeable.rs
@@ -0,0 +1,5 @@
+pub trait Timeable {
+    fn hour(&self) -> u32;
+    fn minute(&self) -> u32;
+    fn second(&self) -> u32;
+}
diff --git a/rust/schist_core/src/utils/calculate_budgets_accrual.rs b/rust/schist_core/src/utils/calculate_budgets_accrual.rs
new file mode 100644
index 0000000..56171ca
--- /dev/null
+++ b/rust/schist_core/src/utils/calculate_budgets_accrual.rs
@@ -0,0 +1,155 @@
+use anyhow::Result;
+use crate::{models::{
+    budget_update::BudgetUpdate, category::Category, date_utc::DateUtc
+}, traits::nowlike::Nowlike};
+
+pub fn calculate_budgets_accrual(category: &Category, budget_updates: &[BudgetUpdate]) -> Result<i64> {
+    let mut budget_updates = budget_updates
+        .iter()
+        .filter(|bu| bu.category_id == category.id)
+        .collect::<Vec<&BudgetUpdate>>();
+    budget_updates.sort_by_key(|bu| bu.date.clone());
+    budget_updates.reverse();
+
+    let mut budgets_accrual = 0.0_f64;
+    let mut calculated_back_to_date = DateUtc::now();
+
+    for budget_update in budget_updates {
+        let days_on_this_budget = calculated_back_to_date.day_diff(&budget_update.date);
+        if days_on_this_budget == 0_u32 {
+            return Err(anyhow::Error::msg(format!(
+                "failed to calculate budgets accrual since two budget updates had the same date ({})",
+                budget_update.date,
+            )));
+        }
+        let budget_per_day = budget_update.new_budget as f64 / budget_update.new_period as f64;
+        budgets_accrual += days_on_this_budget as f64 * budget_per_day;
+        calculated_back_to_date = budget_update.date.clone();
+    }
+
+    Ok(budgets_accrual.floor() as i64)
+}
+
+#[cfg(test)]
+mod test {
+    use chrono::{Days, Utc};
+
+    use crate::{
+        models::{budget_update::BudgetUpdate, category::Category, date_utc::DateUtc}, traits::nowlike::Nowlike, utils::calculate_budgets_accrual
+    };
+
+    #[test]
+    fn when_no_budget_updates_then_return_zero() {
+        let category = Category {
+            id: 0,
+            name: String::from("Groceries"),
+        };
+        let budget_updates = [];
+
+        let result = calculate_budgets_accrual(&category, &budget_updates);
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 0_i64);
+    }
+
+    #[test]
+    fn when_one_budget_update_for_another_category_then_return_zero() {
+        let category = Category {
+            id: 0,
+            name: String::from("Groceries"),
+        };
+        let budget_updates = [BudgetUpdate {
+            id: 0,
+            category_id: 1,
+            date: DateUtc::now(),
+            new_budget: 100,
+            new_period: 1,
+        }];
+
+        let result = calculate_budgets_accrual(&category, &budget_updates);
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 0_i64);
+    }
+
+    #[test]
+    fn when_one_budget_update_then_return_quantity_times_days_in_past() {
+        let category = Category {
+            id: 0,
+            name: String::from("Groceries"),
+        };
+        let budget_updates = [BudgetUpdate {
+            id: 0,
+            category_id: 0,
+            date: DateUtc::from(Utc::now().checked_sub_days(Days::new(120)).unwrap()),
+            new_budget: 100,
+            new_period: 1,
+        }];
+
+        let result = calculate_budgets_accrual(&category, &budget_updates);
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 12_000);
+    }
+
+    #[test]
+    fn when_two_budget_updates_then_calculates_as_expected() {
+        let category = Category {
+            id: 0,
+            name: String::from("Groceries"),
+        };
+        let budget_updates = [
+            BudgetUpdate {
+                id: 0,
+                category_id: 0,
+                date: DateUtc::from(&Utc::now().checked_sub_days(Days::new(60)).unwrap()),
+                new_budget: 200,
+                new_period: 1,
+            },
+            BudgetUpdate {
+                id: 0,
+                category_id: 0,
+                date: DateUtc::from(&Utc::now().checked_sub_days(Days::new(120)).unwrap()),
+                new_budget: 100,
+                new_period: 1,
+            },
+        ];
+
+        let result = calculate_budgets_accrual(&category, &budget_updates);
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 18_000);
+    }
+
+    #[test]
+    fn when_two_budget_updates_on_same_day_then_returns_err() {
+        let category = Category {
+            id: 0,
+            name: String::from("Groceries"),
+        };
+        let budget_updates = [
+            BudgetUpdate {
+                id: 0,
+                category_id: 0,
+                date: DateUtc::from_ymd(2020, 12, 25).unwrap(),
+                new_budget: 200,
+                new_period: 1,
+            },
+            BudgetUpdate {
+                id: 0,
+                category_id: 0,
+                date: DateUtc::from_ymd(2020, 12, 25).unwrap(),
+                new_budget: 100,
+                new_period: 1,
+            },
+        ];
+        let mut budget_updates_reversed = budget_updates.clone();
+        budget_updates_reversed.reverse();
+
+        let result_leftways = calculate_budgets_accrual(&category, &budget_updates);
+        let result_rightways = calculate_budgets_accrual(&category, &budget_updates_reversed);
+
+        assert!(result_leftways.is_err());
+        assert!(result_rightways.is_err());
+    }
+}
diff --git a/rust/schist_core/src/utils/calculate_category_balance.rs b/rust/schist_core/src/utils/calculate_category_balance.rs
new file mode 100644
index 0000000..61b94a8
--- /dev/null
+++ b/rust/schist_core/src/utils/calculate_category_balance.rs
@@ -0,0 +1,153 @@
+use anyhow::Result;
+use crate::{
+    models::{budget_update::BudgetUpdate, category::Category},
+    utils::{calculate_budgets_accrual, find_by_id_or},
+};
+
+pub fn calculate_category_balance(
+    category: &Category,
+    transaction_sums: &[(i32, i64)],
+    category_transfer_from_sums: &[(i32, i64)],
+    category_transfer_to_sums: &[(i32, i64)],
+    budget_updates: &[BudgetUpdate],
+) -> Result<i64> {
+    let transaction_sum = find_by_id_or(transaction_sums, category.id, 0);
+    let category_transfer_from_sum = find_by_id_or(category_transfer_from_sums, category.id, 0);
+    let category_transfer_to_sum = find_by_id_or(category_transfer_to_sums, category.id, 0);
+    let budget_accruals_sum = calculate_budgets_accrual(category, budget_updates)?;
+
+    Ok(
+        transaction_sum
+            + budget_accruals_sum
+            + category_transfer_to_sum
+            - category_transfer_from_sum
+    )
+}
+
+#[cfg(test)]
+mod test {
+    use chrono::{Days, Utc};
+
+    use crate::{
+        models::{budget_update::BudgetUpdate, category::Category, date_utc::DateUtc},
+        utils::calculate_category_balance
+    };
+
+    #[test]
+    fn when_no_data_then_returns_zero() {
+        let category = Category {
+            id: 0,
+            name: String::new(),
+        };
+
+        let result = calculate_category_balance(&category, &[], &[], &[], &[]);
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 0_i64);
+    }
+
+    #[test]
+    fn when_data_only_for_another_category_then_returns_zero() {
+        let category = Category {
+            id: 0,
+            name: String::new(),
+        };
+        let transaction_sums = [(1, 100)];
+        let category_transfer_from_sums = [(1, 91)];
+        let category_transfer_to_sums = [(2, 79)];
+        let budget_updates = [BudgetUpdate {
+            id: 0,
+            category_id: 1,
+            date: DateUtc::from(Utc::now().checked_sub_days(Days::new(120)).unwrap()),
+            new_budget: 77,
+            new_period: 1,
+        }];
+
+        let result = calculate_category_balance(
+            &category,
+            &transaction_sums,
+            &category_transfer_from_sums,
+            &category_transfer_to_sums,
+            &budget_updates,
+        );
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 0_i64);
+    }
+
+    #[test]
+    fn when_transaction_sum_is_zero_then_returns_zero() {
+        let category = Category {
+            id: 0,
+            name: String::new(),
+        };
+        let transaction_sums = [(0, 0)];
+        let category_transfer_from_sums = [];
+        let category_transfer_to_sums = [];
+        let budget_updates = [];
+
+        let result = calculate_category_balance(
+            &category,
+            &transaction_sums,
+            &category_transfer_from_sums,
+            &category_transfer_to_sums,
+            &budget_updates,
+        );
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 0_i64);
+    }
+
+    #[test]
+    fn when_category_transfers_are_zero_then_returns_zero() {
+        let category = Category {
+            id: 0,
+            name: String::new(),
+        };
+        let transaction_sums = [];
+        let category_transfer_from_sums = [(0, 0)];
+        let category_transfer_to_sums = [(0, 0)];
+        let budget_updates = [];
+
+        let result = calculate_category_balance(
+            &category,
+            &transaction_sums,
+            &category_transfer_from_sums,
+            &category_transfer_to_sums,
+            &budget_updates,
+        );
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 0_i64);
+    }
+
+    #[test]
+    fn when_some_data_then_calculates_as_expected() {
+        let category = Category {
+            id: 0,
+            name: String::new(),
+        };
+        let transaction_sums = [(0, 100)];
+        let category_transfer_from_sums = [(0, 91)];
+        let category_transfer_to_sums = [(0, 79)];
+        let budget_updates = [BudgetUpdate {
+            id: 0,
+            category_id: 0,
+            date: DateUtc::from(&Utc::now().checked_sub_days(Days::new(120)).unwrap()),
+            new_budget: 77,
+            new_period: 1,
+        }];
+
+        let result = calculate_category_balance(
+            &category,
+            &transaction_sums,
+            &category_transfer_from_sums,
+            &category_transfer_to_sums,
+            &budget_updates,
+        );
+
+        let expected_result = 100 + (-91) + 79 + 77 * 120;
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), expected_result);
+    }
+}
diff --git a/rust/schist_core/src/utils/find_by_id_or.rs b/rust/schist_core/src/utils/find_by_id_or.rs
new file mode 100644
index 0000000..8335e5c
--- /dev/null
+++ b/rust/schist_core/src/utils/find_by_id_or.rs
@@ -0,0 +1,41 @@
+pub fn find_by_id_or<Id: PartialEq, Val: Copy>(
+    arr: &[(Id, Val)],
+    id: Id,
+    default: Val,
+) -> Val {
+    arr.iter()
+        .find(|(elem_id, _)| *elem_id == id)
+        .map_or(default, |row| row.1)
+}
+
+#[cfg(test)]
+mod test {
+    use super::find_by_id_or;
+
+    #[test]
+    fn when_no_elements_then_return_default() {
+        let arr = [];
+
+        let result = find_by_id_or(&arr, 1, 42);
+
+        assert_eq!(result, 42);
+    }
+
+    #[test]
+    fn when_id_not_in_elements_then_return_default() {
+        let arr = [(0, 100), (2, 200)];
+
+        let result = find_by_id_or(&arr, 1, 42);
+
+        assert_eq!(result, 42);
+    }
+
+    #[test]
+    fn when_id_in_elements_then_return_value() {
+        let arr = [(1, 67)];
+
+        let result = find_by_id_or(&arr, 1, 42);
+
+        assert_eq!(result, 67);
+    }
+}
diff --git a/rust/schist_core/src/utils/mod.rs b/rust/schist_core/src/utils/mod.rs
new file mode 100644
index 0000000..84a27af
--- /dev/null
+++ b/rust/schist_core/src/utils/mod.rs
@@ -0,0 +1,7 @@
+mod calculate_budgets_accrual;
+mod calculate_category_balance;
+mod find_by_id_or;
+
+pub use calculate_budgets_accrual::calculate_budgets_accrual;
+pub use calculate_category_balance::calculate_category_balance;
+pub use find_by_id_or::find_by_id_or;