4 files changed, 251 insertions, 0 deletions
diff --git a/schist_queries/src/utils/calculate_budgets_accrual.rs b/schist_queries/src/utils/calculate_budgets_accrual.rs
new file mode 100644
index 0000000..ca82953
--- /dev/null
+++ b/schist_queries/src/utils/calculate_budgets_accrual.rs
@@ -0,0 +1,72 @@
+use anyhow::Result;
+use schist_models::{
+    budget_drip::BudgetDrip,
+    category::Category,
+};
+
+pub fn calculate_budgets_accrual(category: &Category, budget_drips: &[BudgetDrip]) -> Result<i64> {
+    Ok(budget_drips
+        .iter()
+        .filter(|bd| bd.category_id == category.id)
+        .map(|bd| Into::<i64>::into(bd.quantity))
+        .sum()
+    )
+}
+
+#[cfg(test)]
+mod test {
+    use schist_fakes::{budget_drip::make_fake_budget_drip_builder, category::make_fake_category};
+
+    use super::calculate_budgets_accrual;
+
+    #[test]
+    fn when_no_budget_drips_then_return_zero() {
+        let category = make_fake_category(0);
+        let budget_drips = [];
+
+        let result = calculate_budgets_accrual(&category, &budget_drips);
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 0_i64);
+    }
+
+    #[test]
+    fn when_one_budget_drip_for_another_category_then_return_zero() {
+        let category = make_fake_category(0);
+        let budget_drips = [
+            make_fake_budget_drip_builder(0).quantity(100).category_id(1).build().unwrap(),
+        ];
+
+        let result = calculate_budgets_accrual(&category, &budget_drips);
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 0_i64);
+    }
+
+    #[test]
+    fn when_one_budget_drip_then_return_quantity() {
+        let category = make_fake_category(0);
+        let budget_drips = [
+            make_fake_budget_drip_builder(0).quantity(100).category_id(0).build().unwrap(),
+        ];
+
+        let result = calculate_budgets_accrual(&category, &budget_drips);
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 100);
+    }
+
+    #[test]
+    fn when_two_budget_drips_then_return_sum() {
+        let category = make_fake_category(0);
+        let budget_drips = [
+            make_fake_budget_drip_builder(0).quantity(100).category_id(0).build().unwrap(),
+            make_fake_budget_drip_builder(1).quantity(120).category_id(0).build().unwrap(),
+        ];
+
+        let result = calculate_budgets_accrual(&category, &budget_drips);
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 220);
+    }
+}
diff --git a/schist_queries/src/utils/calculate_category_balance.rs b/schist_queries/src/utils/calculate_category_balance.rs
new file mode 100644
index 0000000..73e80cd
--- /dev/null
+++ b/schist_queries/src/utils/calculate_category_balance.rs
@@ -0,0 +1,130 @@
+use anyhow::Result;
+use schist_models::{budget_drip::BudgetDrip, category::Category};
+
+use super::{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_drips: &[BudgetDrip],
+) -> 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_drips)?;
+
+    Ok(
+        transaction_sum
+            + budget_accruals_sum
+            + category_transfer_to_sum
+            - category_transfer_from_sum
+    )
+}
+
+#[cfg(test)]
+mod test {
+    use schist_fakes::{budget_drip::make_fake_budget_drip_builder, category::make_fake_category};
+
+    use super::calculate_category_balance;
+
+    #[test]
+    fn when_no_data_then_returns_zero() {
+        let category = make_fake_category(0);
+
+        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 = make_fake_category(0);
+        let transaction_sums = [(1, 100)];
+        let category_transfer_from_sums = [(1, 91)];
+        let category_transfer_to_sums = [(2, 79)];
+        let budget_drips = [
+            make_fake_budget_drip_builder(0).quantity(100).category_id(1).build().unwrap(),
+        ];
+
+        let result = calculate_category_balance(
+            &category,
+            &transaction_sums,
+            &category_transfer_from_sums,
+            &category_transfer_to_sums,
+            &budget_drips,
+        );
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 0_i64);
+    }
+
+    #[test]
+    fn when_transaction_sum_is_zero_then_returns_zero() {
+        let category = make_fake_category(0);
+        let transaction_sums = [(0, 0)];
+        let category_transfer_from_sums = [];
+        let category_transfer_to_sums = [];
+        let budget_drips = [];
+
+        let result = calculate_category_balance(
+            &category,
+            &transaction_sums,
+            &category_transfer_from_sums,
+            &category_transfer_to_sums,
+            &budget_drips,
+        );
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 0_i64);
+    }
+
+    #[test]
+    fn when_category_transfers_are_zero_then_returns_zero() {
+        let category = make_fake_category(0);
+        let transaction_sums = [];
+        let category_transfer_from_sums = [(0, 0)];
+        let category_transfer_to_sums = [(0, 0)];
+        let budget_drips = [];
+
+        let result = calculate_category_balance(
+            &category,
+            &transaction_sums,
+            &category_transfer_from_sums,
+            &category_transfer_to_sums,
+            &budget_drips,
+        );
+
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), 0_i64);
+    }
+
+    #[test]
+    fn when_some_data_then_calculates_as_expected() {
+        let category = make_fake_category(0);
+        let transaction_sums = [(0, 100)];
+        let category_transfer_from_sums = [(0, 91)];
+        let category_transfer_to_sums = [(0, 79)];
+        let budget_drips = [
+            make_fake_budget_drip_builder(0).quantity(77).category_id(0).build().unwrap(),
+            make_fake_budget_drip_builder(0).quantity(77).category_id(0).build().unwrap(),
+            make_fake_budget_drip_builder(0).quantity(77).category_id(0).build().unwrap(),
+            make_fake_budget_drip_builder(0).quantity(77).category_id(0).build().unwrap(),
+            make_fake_budget_drip_builder(0).quantity(77).category_id(0).build().unwrap(),
+        ];
+
+        let result = calculate_category_balance(
+            &category,
+            &transaction_sums,
+            &category_transfer_from_sums,
+            &category_transfer_to_sums,
+            &budget_drips,
+        );
+
+        let expected_result = 100 + (-91) + 79 + 77 * 5;
+        assert!(result.is_ok());
+        assert_eq!(result.unwrap(), expected_result);
+    }
+}
diff --git a/schist_queries/src/utils/find_by_id_or.rs b/schist_queries/src/utils/find_by_id_or.rs
new file mode 100644
index 0000000..8335e5c
--- /dev/null
+++ b/schist_queries/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/schist_queries/src/utils/mod.rs b/schist_queries/src/utils/mod.rs
new file mode 100644
index 0000000..f2653d8
--- /dev/null
+++ b/schist_queries/src/utils/mod.rs
@@ -0,0 +1,8 @@
+mod calculate_budgets_accrual;
+mod calculate_category_balance;
+mod find_by_id_or;
+
+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;