EmailBill/Service/Budget/BudgetItemCalculator.cs

namespace Service.Budget;

/// <summary>
/// 预算明细项计算辅助类
/// 用于计算单个预算项的有效金额（计算用金额）
/// </summary>
public static class BudgetItemCalculator
{
    /// <summary>
    /// 计算预算项的有效金额
    /// </summary>
    /// <param name="category">预算类别（收入/支出）</param>
    /// <param name="budgetLimit">预算金额</param>
    /// <param name="actualAmount">实际金额</param>
    /// <param name="isMandatory">是否为硬性消费</param>
    /// <param name="isArchived">是否为归档数据</param>
    /// <param name="referenceDate">参考日期</param>
    /// <param name="periodType">预算周期类型（月度/年度）</param>
    /// <returns>有效金额（用于计算的金额）</returns>
    public static decimal CalculateEffectiveAmount(
        BudgetCategory category,
        decimal budgetLimit,
        decimal actualAmount,
        bool isMandatory,
        bool isArchived,
        DateTime referenceDate,
        BudgetPeriodType periodType)
    {
        // 归档数据直接返回实际值
        if (isArchived)
        {
            return actualAmount;
        }

        // 收入：实际>0取实际，否则取预算
        if (category == BudgetCategory.Income)
        {
            return actualAmount > 0 ? actualAmount : budgetLimit;
        }

        // 支出（硬性且实际=0）：按天数折算
        if (category == BudgetCategory.Expense && isMandatory && actualAmount == 0)
        {
            return CalculateMandatoryAmount(budgetLimit, referenceDate, periodType);
        }

        // 支出（普通）：取MAX
        if (category == BudgetCategory.Expense)
        {
            return Math.Max(budgetLimit, actualAmount);
        }

        return budgetLimit;
    }

    /// <summary>
    /// 计算硬性消费按天数折算的金额
    /// </summary>
    private static decimal CalculateMandatoryAmount(
        decimal limit,
        DateTime date,
        BudgetPeriodType periodType)
    {
        if (periodType == BudgetPeriodType.Month)
        {
            var daysInMonth = DateTime.DaysInMonth(date.Year, date.Month);
            return limit / daysInMonth * date.Day;
        }
        else // Year
        {
            var daysInYear = DateTime.IsLeapYear(date.Year) ? 366 : 365;
            return limit / daysInYear * date.DayOfYear;
        }
    }

    /// <summary>
    /// 生成计算说明
    /// </summary>
    /// <param name="category">预算类别</param>
    /// <param name="budgetLimit">预算金额</param>
    /// <param name="actualAmount">实际金额</param>
    /// <param name="effectiveAmount">有效金额</param>
    /// <param name="isMandatory">是否为硬性消费</param>
    /// <param name="isArchived">是否为归档数据</param>
    /// <returns>计算说明文本</returns>
    public static string GenerateCalculationNote(
        BudgetCategory category,
        decimal budgetLimit,
        decimal actualAmount,
        decimal effectiveAmount,
        bool isMandatory,
        bool isArchived)
    {
        if (isArchived)
        {
            return "归档实际";
        }

        if (category == BudgetCategory.Income)
        {
            return actualAmount > 0 ? "使用实际" : "使用预算";
        }

        if (category == BudgetCategory.Expense)
        {
            if (isMandatory && actualAmount == 0)
            {
                return "按天折算";
            }

            if (actualAmount > budgetLimit)
            {
                return "使用实际（超支）";
            }

            return effectiveAmount == actualAmount ? "使用实际" : "使用预算";
        }

        return "使用预算";
    }
}