//
//  APIEnvelope.swift
//  suixinkan
//

import Foundation

/// 后端统一响应包裹实体，承载业务 code、msg 和真实 data。
struct APIEnvelope<T: Decodable>: Decodable {
    let data: T?
    let code: Int
    let msg: String?

    /// 判断后端业务 code 是否代表成功。
    var isSuccess: Bool {
        code == 100000
    }

    /// 后端统一 Envelope 的 JSON 字段映射。
    enum CodingKeys: String, CodingKey {
        case data
        case code
        case msg
    }

    /// 自定义解码逻辑，兼容成功响应、空 data 和 EmptyPayload。
    init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        code = try container.decodeIfPresent(Int.self, forKey: .code) ?? 0
        msg = try container.decodeIfPresent(String.self, forKey: .msg)

        guard code == 100000 else {
            data = nil
            return
        }

        guard container.contains(.data), try !container.decodeNil(forKey: .data) else {
            data = nil
            return
        }

        if T.self == EmptyPayload.self {
            data = EmptyPayload() as? T
            return
        }

        data = try container.decode(T.self, forKey: .data)
    }
}

/// 空响应实体，用于表示接口成功但不返回业务 data。
struct EmptyPayload: Codable {}

/// 错误响应实体，用于从 HTTP 错误体中提取服务端文案。
struct ErrorEnvelope: Decodable {
    let code: Int?
    let msg: String?
    let message: String?
    let error: String?
}