use axum::{
    Json,
    http::StatusCode,
    response::{IntoResponse, Response},
};
use serde::{Deserialize, Serialize};
use thiserror::Error;

/// 业务状态码 (Business Code)
/// 前端根据此 Code 进行逻辑跳转
#[derive(Debug, Clone, Copy, Serialize, Deserialize, PartialEq)]
#[repr(u32)]
pub enum BizCode {
    Success = 0,

    // 10xxx: 服务端通用错误
    ServerError = 10000,          // 未知/兜底错误
    DbError = 10001,              // 数据库操作失败
    CacheError = 10002,           // Redis/缓存失败
    SerializationError = 10003,   // JSON 解析/序列化失败
    ExternalServiceError = 10004, // 调用第三方/下游服务失败
    ConfigError = 10005,          // 配置加载失败

    // 20xxx: 认证授权相关 (双 Token 核心逻辑)
    Unauthorized = 20000,        // 未认证 (通用)
    AccessTokenExpired = 20001,  // [前端触发] 静默刷新
    RefreshTokenExpired = 20002, // [前端触发] 强制登出
    PermissionDenied = 20003,    // 无权限 (403)
    AccountDisabled = 20004,     // 账号被禁用/锁定
    InvalidCredentials = 20005,  // 账号或密码错误
    MissingHeader = 20006,       // 缺少必要的 Header (如 x-trace-id, Authorization)

    // === 30xxx: 客户端输入错误 ===
    BadRequest = 30000,            // 通用请求参数错误
    ValidationError = 30001,       // 字段校验不通过 (Validation)
    ResourceNotFound = 30002,      // 资源不存在 (404)
    ResourceAlreadyExists = 30003, // 资源冲突/重复 (409)
    MethodNotAllowed = 30004,      // HTTP 方法不支持

    // === 40xxx: 业务流控/状态 ===
    RateLimitExceeded = 40000,  // 请求过于频繁 (429)
    PreconditionFailed = 40001, // 业务前置条件不满足 (如：余额不足无法支付)
}

/// 全局应用错误枚举
#[derive(Error, Debug)]
pub enum AppError {
    // --- 基础设施错误 ---
    #[cfg(feature = "with-sqlx")]
    #[error("Database error: {0}")]
    DbError(sqlx::Error),

    #[cfg(feature = "with-redis")]
    #[error("Cache error: {0}")]
    CacheError(#[from] redis::RedisError),

    // 外部服务调用错误 (如调用其他微服务失败)
    #[error("External service error: {0}")]
    ExternalReqError(String), // 对应 reqwest::Error

    // 消息队列错误
    #[error("MQ error: {0}")]
    MqError(String),

    #[error("IO error: {0}")]
    IoError(#[from] std::io::Error),

    // 序列化/反序列化错误
    #[error("Serialization error: {0}")]
    SerdeError(#[from] serde_json::Error),

    // 任意未预期错误 (兜底)
    #[cfg(feature = "with-anyhow")]
    #[error("Unexpected error: {0}")]
    AnyhowError(#[from] anyhow::Error),

    // ======================================================
    // 2. 认证与授权层 (Auth) - 双 Token 核心
    // ======================================================
    #[error("Authentication failed: {0}")]
    AuthError(String), // 通用认证失败 (签名错误、格式错误)

    #[error("Missing authorization header")]
    MissingAuthHeader,

    #[error("Access token has expired")]
    AccessTokenExpired, // 触发 refresh

    #[error("Refresh token has expired")]
    RefreshTokenExpired, // 触发 logout

    #[error("Permission denied: {0}")]
    PermissionDenied(String), // 403

    #[error("Account is disabled or locked")]
    AccountLocked,

    // ======================================================
    // 3. 客户端输入层 (Client Side)
    // ======================================================
    #[error("Resource not found: {0}")]
    NotFound(String), // 404

    #[error("Resource already exists: {0}")]
    AlreadyExists(String), // 409 Conflict

    #[error("Invalid request parameters: {0}")]
    BadRequest(String), // 400

    #[cfg(feature = "with-validator")]
    #[error("Validation error: {0}")]
    ValidationError(String),

    // ======================================================
    // 4. 业务逻辑层 (Business Logic)
    // ======================================================
    #[error("Rate limit exceeded, please try again later")]
    RateLimitExceeded, // 429

    #[error("Business precondition failed: {0}")]
    BusinessLogicError(String), // 业务状态冲突 (例如：订单已支付不能取消)
}

/// 响应给前端的 JSON 结构
#[derive(Serialize)]
pub struct ErrorResponse {
    pub code: u32,
    pub message: String,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub trace_id: Option<String>, // 可选：返回 trace_id 方便排查
}

// 1. 实现 sqlx::Error -> AppError
#[cfg(feature = "with-sqlx")]
impl From<sqlx::Error> for AppError {
    fn from(e: sqlx::Error) -> Self {
        match e {
            // 将 "查不到数据" 转换为 "NotFound" 业务错误
            sqlx::Error::RowNotFound => AppError::NotFound("Database row not found".into()),
            // 其他错误保持为 DbError
            other => AppError::DbError(other),
        }
    }
}

// 2. 实现 validator::ValidationErrors -> AppError
#[cfg(feature = "with-validator")]
impl From<validator::ValidationErrors> for AppError {
    fn from(e: validator::ValidationErrors) -> Self {
        // 将复杂的校验错误结构体转为字符串供前端显示
        // 你也可以选择在这里只取第一个错误，或者转为 JSON 字符串
        AppError::ValidationError(e.to_string())
    }
}

impl AppError {
    // 映射 HTTP 状态码 (给网关/浏览器看)
    fn http_status(&self) -> StatusCode {
        match self {
            AppError::DbError(_)
            | AppError::CacheError(_)
            | AppError::ExternalReqError(_)
            | AppError::MqError(_)
            | AppError::IoError(_)
            | AppError::SerdeError(_)
            | AppError::AnyhowError(_) => StatusCode::INTERNAL_SERVER_ERROR,
            // 401 Unauthorized
            AppError::AuthError(_)
            | AppError::MissingAuthHeader
            | AppError::AccessTokenExpired
            | AppError::RefreshTokenExpired
            | AppError::AccountLocked => StatusCode::UNAUTHORIZED,

            // 403 Forbidden
            AppError::PermissionDenied(_) => StatusCode::FORBIDDEN,

            // 404 Not Found
            AppError::NotFound(_) => StatusCode::NOT_FOUND,

            // 409 Conflict
            AppError::AlreadyExists(_) => StatusCode::CONFLICT,

            // 429 Too Many Requests
            AppError::RateLimitExceeded => StatusCode::TOO_MANY_REQUESTS,

            // 400 Bad Request (默认)
            _ => StatusCode::BAD_REQUEST,
        }
    }

    // 映射业务状态码 (给前端代码看)
    fn biz_code(&self) -> BizCode {
        match self {
            // Infra
            AppError::DbError(_) => BizCode::DbError,
            AppError::CacheError(_) => BizCode::CacheError,
            AppError::ExternalReqError(_) => BizCode::ExternalServiceError,
            AppError::MqError(_) | AppError::IoError(_) | AppError::AnyhowError(_) => {
                BizCode::ServerError
            }
            AppError::SerdeError(_) => BizCode::SerializationError,

            // Auth
            AppError::AuthError(_) => BizCode::Unauthorized,
            AppError::MissingAuthHeader => BizCode::MissingHeader,
            AppError::AccessTokenExpired => BizCode::AccessTokenExpired,
            AppError::RefreshTokenExpired => BizCode::RefreshTokenExpired,
            AppError::PermissionDenied(_) => BizCode::PermissionDenied,
            AppError::AccountLocked => BizCode::AccountDisabled,

            // Client
            AppError::NotFound(_) => BizCode::ResourceNotFound,
            AppError::AlreadyExists(_) => BizCode::ResourceAlreadyExists,
            AppError::BadRequest(_) => BizCode::BadRequest,
            AppError::ValidationError(_) => BizCode::ValidationError,

            // Biz
            AppError::RateLimitExceeded => BizCode::RateLimitExceeded,
            AppError::BusinessLogicError(_) => BizCode::PreconditionFailed,
        }
    }
}

// 核心：实现 Axum 的 IntoResponse
impl IntoResponse for AppError {
    fn into_response(self) -> Response {
        let status = self.http_status();
        let biz_code = self.biz_code();
        // 生产环境通常不把详细的 DB 报错返回给前端，防止泄露表结构
        // 但这里为了演示，我们先直接使用 self.to_string()
        // 建议：在生产环境针对 DbError/AnyhowError 返回统一的 "Internal Server Error"
        let message = match self {
            AppError::DbError(_) | AppError::AnyhowError(_) => {
                // 如果是生产环境(release模式)，隐藏敏感信息
                #[cfg(not(debug_assertions))]
                {
                    "Internal server error".to_string()
                }
                #[cfg(debug_assertions)]
                {
                    self.to_string()
                }
            }
            _ => self.to_string(),
        };

        // 1. 自动打印 Error 日志 (带上 Trace)
        // 只有开启 telemetry feature 时才打印
        #[cfg(feature = "telemetry")]
        {
            tracing::error!(
                %status,
                code = ?biz_code, // 打印枚举名
                error_msg = %self, // 打印详细错误信息
                "Request failed"
            );
        }

        // 2. 构建 JSON
        let body = Json(ErrorResponse {
            code: biz_code as u32,
            message,
            trace_id: None, // 实际项目中从 tracing context 获取
        });

        (status, body).into_response()
    }
}