using System;
using System.Diagnostics;
using TakeoutSaaS.Shared.Abstractions.Diagnostics;

namespace TakeoutSaaS.Shared.Abstractions.Results;

/// <summary>
/// 统一的 API 返回结果包装。
/// </summary>
/// <typeparam name="T">数据载荷类型</typeparam>
public sealed record class ApiResponse<T>
{
    /// <summary>
    /// 是否成功。
    /// </summary>
    public bool Success { get; init; }

    /// <summary>
    /// 状态/错误码（默认 200）。
    /// </summary>
    public int Code { get; init; } = 200;

    /// <summary>
    /// 提示信息。
    /// </summary>
    public string? Message { get; init; }

    /// <summary>
    /// 业务数据。
    /// </summary>
    public T? Data { get; init; }

    /// <summary>
    /// 错误详情（如字段验证错误）。
    /// </summary>
    public object? Errors { get; init; }

    /// <summary>
    /// TraceId，便于链路追踪。
    /// </summary>
    public string TraceId { get; init; } = string.Empty;

    /// <summary>
    /// 时间戳（UTC）。
    /// </summary>
    public DateTime Timestamp { get; init; } = DateTime.UtcNow;

    /// <summary>
    /// 成功返回。
    /// </summary>
    public static ApiResponse<T> Ok(T data, string? message = "操作成功")
        => Create(true, 200, message, data);

    /// <summary>
    /// 无数据的成功返回。
    /// </summary>
    public static ApiResponse<T> Ok(string? message = "操作成功")
        => Create(true, 200, message, default);

    /// <summary>
    /// 兼容旧名称：成功结果。
    /// </summary>
    public static ApiResponse<T> SuccessResult(T data, string? message = "操作成功")
        => Ok(data, message);

    /// <summary>
    /// 错误返回。
    /// </summary>
    public static ApiResponse<T> Error(int code, string message, object? errors = null)
        => Create(false, code, message, default, errors);

    /// <summary>
    /// 兼容旧名称：失败结果。
    /// </summary>
    public static ApiResponse<T> Failure(int code, string message)
        => Error(code, message);

    /// <summary>
    /// 附加错误详情。
    /// </summary>
    public ApiResponse<T> WithErrors(object? errors)
        => this with { Errors = errors };

    private static ApiResponse<T> Create(bool success, int code, string? message, T? data, object? errors = null)
        => new()
        {
            Success = success,
            Code = code,
            Message = message,
            Data = data,
            Errors = errors,
            TraceId = ResolveTraceId(),
            Timestamp = DateTime.UtcNow
        };

    private static string ResolveTraceId()
    {
        if (!string.IsNullOrWhiteSpace(TraceContext.TraceId))
        {
            return TraceContext.TraceId!;
        }

        return Activity.Current?.Id ?? Guid.NewGuid().ToString("N");
    }
}