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use anyhow::Result;
use schist_models::{
budget_update::BudgetUpdate, category::Category, date_utc::DateUtc,
};
use schist_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 schist_models::{budget_update::BudgetUpdate, category::Category, date_utc::DateUtc};
use schist_traits::nowlike::Nowlike;
use super::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());
}
}
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