family_budget/backend/src/services/expense_service.rs

use sea_orm::*;
use sea_orm::prelude::Decimal;
use chrono::{Utc, Datelike};
use std::collections::HashMap;
use crate::models::expense::{self, Entity as Expense, Model as ExpenseModel};
use crate::models::category::{Entity as Category};

#[derive(Debug, Clone)]
pub struct MonthlyExpenseGroup {
    pub year: i32,
    pub month: u32,
    pub total_amount: Decimal,
    pub expenses: Vec<ExpenseModel>,
}

pub struct ExpenseService;

impl ExpenseService {
    pub async fn create(
        db: &DatabaseConnection,
        category_id: i32,
        amount: Decimal,
        description: Option<String>,
    ) -> Result<ExpenseModel, DbErr> {
        let expense = expense::ActiveModel {
            category_id: Set(category_id),
            amount: Set(amount),
            description: Set(description),
            created_at: Set(Utc::now().naive_utc()),
            active: Set(true),
            ..Default::default()
        };

        expense.insert(db).await
    }

    pub async fn find_by_id(db: &DatabaseConnection, id: i32) -> Result<Option<ExpenseModel>, DbErr> {
        Expense::find_by_id(id).one(db).await
    }

    pub async fn find_all(db: &DatabaseConnection) -> Result<Vec<ExpenseModel>, DbErr> {
        Expense::find().all(db).await
    }

    pub async fn find_by_category_id(
        db: &DatabaseConnection,
        category_id: i32,
    ) -> Result<Vec<ExpenseModel>, DbErr> {
        Expense::find()
            .filter(expense::Column::CategoryId.eq(category_id))
            .filter(expense::Column::Active.eq(true))
            .all(db)
            .await
    }

    pub async fn find_all_by_category_id(
        db: &DatabaseConnection,
        category_id: i32,
    ) -> Result<Vec<ExpenseModel>, DbErr> {
        Expense::find()
            .filter(expense::Column::CategoryId.eq(category_id))
            .all(db)
            .await
    }

    pub async fn find_inactive_by_category_id(
        db: &DatabaseConnection,
        category_id: i32,
    ) -> Result<Vec<ExpenseModel>, DbErr> {
        Expense::find()
            .filter(expense::Column::CategoryId.eq(category_id))
            .filter(expense::Column::Active.eq(false))
            .all(db)
            .await
    }

    pub async fn update(
        db: &DatabaseConnection,
        id: i32,
        amount: Option<Decimal>,
        description: Option<String>,
    ) -> Result<ExpenseModel, DbErr> {
        let expense = Expense::find_by_id(id)
            .one(db)
            .await?
            .ok_or(DbErr::RecordNotFound("Expense not found".to_string()))?;

        let mut expense: expense::ActiveModel = expense.into();

        if let Some(amount) = amount {
            expense.amount = Set(amount);
        }

        if let Some(desc) = description {
            expense.description = Set(Some(desc));
        }

        expense.update(db).await
    }

    pub async fn delete(db: &DatabaseConnection, id: i32) -> Result<ExpenseModel, DbErr> {
        let expense = Expense::find_by_id(id)
            .one(db)
            .await?
            .ok_or(DbErr::RecordNotFound("Expense not found".to_string()))?;

        let mut expense: expense::ActiveModel = expense.into();
        expense.active = Set(false);
        expense.update(db).await
    }

    pub async fn calculate_remaining_limit(
        db: &DatabaseConnection,
        category_id: i32,
    ) -> Result<Decimal, DbErr> {
        let category = Category::find_by_id(category_id)
            .one(db)
            .await?
            .ok_or(DbErr::RecordNotFound("Category not found".to_string()))?;

        let expenses = Self::find_by_category_id(db, category_id).await?;

        let total_spent: Decimal = expenses.iter().map(|e| e.amount).sum();
        let remaining = category.limit_amount - total_spent;

        Ok(remaining)
    }

    pub async fn get_expense_history(
        db: &DatabaseConnection,
        category_id: i32,
        sort_order: Option<String>,
        show_archive: bool,
    ) -> Result<Vec<MonthlyExpenseGroup>, DbErr> {
        let expenses = if show_archive {
            Self::find_inactive_by_category_id(db, category_id).await?
        } else {
            Self::find_by_category_id(db, category_id).await?
        };

        let mut grouped: HashMap<(i32, u32), Vec<ExpenseModel>> = HashMap::new();

        for expense in expenses {
            let year = expense.created_at.year();
            let month = expense.created_at.month();
            grouped.entry((year, month))
                .or_insert_with(Vec::new)
                .push(expense);
        }

        let mut result: Vec<MonthlyExpenseGroup> = grouped
            .into_iter()
            .map(|((year, month), expenses)| {
                let total_amount: Decimal = expenses
                    .iter()
                    .map(|e| e.amount)
                    .sum();
                MonthlyExpenseGroup {
                    year,
                    month,
                    total_amount,
                    expenses,
                }
            })
            .collect();

        let sort_desc = sort_order
            .as_deref()
            .map(|s| s.to_lowercase() == "desc")
            .unwrap_or(true);

        result.sort_by(|a, b| {
            let cmp = a.year.cmp(&b.year).then(a.month.cmp(&b.month));
            if sort_desc {
                cmp.reverse()
            } else {
                cmp
            }
        });

        Ok(result)
    }
}