using MediatR;
using System.Text.Json;
using TakeoutSaaS.Application.App.Billings.Commands;
using TakeoutSaaS.Application.App.Billings.Dto;
using TakeoutSaaS.Domain.Tenants.Entities;
using TakeoutSaaS.Domain.Tenants.Enums;
using TakeoutSaaS.Domain.Tenants.Repositories;
using TakeoutSaaS.Shared.Abstractions.Constants;
using TakeoutSaaS.Shared.Abstractions.Exceptions;
using TakeoutSaaS.Shared.Abstractions.Ids;

namespace TakeoutSaaS.Application.App.Billings.Handlers;

/// <summary>
/// 创建账单命令处理器。
/// </summary>
public sealed class CreateBillingCommandHandler(
    ITenantRepository tenantRepository,
    ITenantBillingRepository billingRepository,
    IIdGenerator idGenerator)
    : IRequestHandler<CreateBillingCommand, BillingDetailDto>
{
    /// <inheritdoc />
    public async Task<BillingDetailDto> Handle(CreateBillingCommand request, CancellationToken cancellationToken)
    {
        // 1. 校验租户存在
        var tenant = await tenantRepository.FindByIdAsync(request.TenantId, cancellationToken);
        if (tenant is null)
        {
            throw new BusinessException(ErrorCodes.NotFound, "租户不存在");
        }

        // 2. 构建账单实体
        var now = DateTime.UtcNow;
        var statementNo = $"BIL-{now:yyyyMMdd}-{idGenerator.NextId()}";
        var lineItemsJson = JsonSerializer.Serialize(request.LineItems);

        var billing = new TenantBillingStatement
        {
            TenantId = request.TenantId,
            StatementNo = statementNo,
            BillingType = request.BillingType,
            SubscriptionId = null,
            PeriodStart = now,
            PeriodEnd = now,
            AmountDue = request.AmountDue,
            DiscountAmount = 0m,
            TaxAmount = 0m,
            AmountPaid = 0m,
            Currency = "CNY",
            Status = TenantBillingStatus.Pending,
            DueDate = request.DueDate,
            LineItemsJson = lineItemsJson,
            Notes = request.Notes
        };

        // 3. 持久化账单
        await billingRepository.AddAsync(billing, cancellationToken);
        await billingRepository.SaveChangesAsync(cancellationToken);

        // 4. 返回详情 DTO
        return billing.ToBillingDetailDto([], tenant.Name);
    }
}