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());
    }
}