using System.Text.Json;

namespace MyHomePage.Api.Common;

/// <summary>
/// 全局异常处理中间件。
/// 捕获下游抛出的 <see cref="BusinessException"/> 与未处理异常，统一包装为 <see cref="ApiResponse{T}"/>。
/// </summary>
public class ExceptionHandlingMiddleware
{
    private readonly RequestDelegate _next;
    private readonly ILogger<ExceptionHandlingMiddleware> _logger;
    private readonly IHostEnvironment _env;

    public ExceptionHandlingMiddleware(
        RequestDelegate next,
        ILogger<ExceptionHandlingMiddleware> logger,
        IHostEnvironment env)
    {
        _next = next;
        _logger = logger;
        _env = env;
    }

    public async Task InvokeAsync(HttpContext context)
    {
        try
        {
            await _next(context);
        }
        catch (BusinessException ex)
        {
            _logger.LogWarning("Business exception ({Code}): {Message}", ex.Code, ex.Message);
            // 使用 ex.Code 透传业务状态码（默认 400/404/500），不再硬编码 200
            var status = ex.Code is >= 400 and < 600 ? ex.Code : StatusCodes.Status400BadRequest;
            await WriteAsync(context, ApiResponse<object>.Fail(ex.Code, ex.Message), status);
        }
        catch (Exception ex)
        {
            _logger.LogError(ex, "Unhandled exception: {Message}", ex.Message);
            var message = _env.IsDevelopment() ? ex.Message : "服务器内部错误";
            await WriteAsync(context, ApiResponse<object>.Fail(500, message), StatusCodes.Status500InternalServerError);
        }
    }

    private static async Task WriteAsync(HttpContext ctx, object payload, int statusCode)
    {
        ctx.Response.StatusCode = statusCode;
        ctx.Response.ContentType = "application/json; charset=utf-8";
        var json = JsonSerializer.Serialize(payload, new JsonSerializerOptions
        {
            PropertyNamingPolicy = JsonNamingPolicy.CamelCase
        });
        await ctx.Response.WriteAsync(json);
    }
}