//
//  RESTManager.swift
//  IOS_study
//
//  Created by CC-star on 2025/7/3.
//

import Foundation

final class RESTManager {
   static let shared = RESTManager()
   private init() {}//让RESTManager只在这个class在内部被实例化，不在外部实例化，只能在这个作用域里面被调用
   //通过REST API获取一条数据
   func findOne<T: Decodable>(form urlStr: String) async throws -> T {
      guard let url = URL(string: urlStr) else { throw URLError(.badURL) }
      
      var request = URLRequest(url: url)
      request.httpMethod = "GET"
      request.setValue("application/json", forHTTPHeaderField: "Content-Type")
      request.setValue(kAppID, forHTTPHeaderField: "X-LC-Id")
      request.setValue(kAppKey, forHTTPHeaderField: "X-LC-Key")

      let (data, response) = try await URLSession.shared.data(for: request)
      //print(String(data: data, encoding: .utf8) ?? "Invalid data")
      
      guard let httpRespsonse = response as? HTTPURLResponse, 200..<300 ~= httpRespsonse.statusCode else { throw URLError(.badServerResponse) }
      
      let decoder = JSONDecoder()
      //decoder.keyDecodingStrategy = .convertFromSnakeCase//数据库字段是下划线写法的时候
      //把数据库里面的时间戳字符串转换成Date类型（了解）
      decoder.dateDecodingStrategy = .custom { decoder -> Date in
         let container = try decoder.singleValueContainer()
         let dateString = try container.decode(String.self)
         let isoFormatter = ISO8601DateFormatter()
         isoFormatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds] // 支持毫秒
         if let date = isoFormatter.date(from: dateString) { return date }
         throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid date format: \(dateString)")
      }
     return try  decoder.decode( T.self, from: data)
   }
   
   
   //通过REST API获取数组数据
   func find<T: Decodable>(form urlStr: String) async throws ->[T] {
      guard let url = URL(string: urlStr) else { throw URLError(.badURL) }
      
      var request = URLRequest(url: url)
      request.httpMethod = "GET"
      request.setValue("application/json", forHTTPHeaderField: "Content-Type")
      request.setValue(kAppID, forHTTPHeaderField: "X-LC-Id")
      request.setValue(kAppKey, forHTTPHeaderField: "X-LC-Key")

      let (data,_) = try await URLSession.shared.data(for: request)
      //print(String(data: data, encoding: .utf8) ?? "Invalid data")
      
      guard let json = try JSONSerialization.jsonObject(with: data) as? [String: Any],
            let results = json["results"] as? [[String: Any]] else {
         throw URLError(.cannotParseResponse)
      }
      
      let decoder = JSONDecoder()
      //decoder.keyDecodingStrategy = .convertFromSnakeCase//数据库字段是下划线写法的时候
      //把数据库里面的时间戳字符串转换成Date类型（了解）
      decoder.dateDecodingStrategy = .custom { decoder -> Date in
         let container = try decoder.singleValueContainer()
         let dateString = try container.decode(String.self)
         let isoFormatter = ISO8601DateFormatter()
         isoFormatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds] // 支持毫秒
         if let date = isoFormatter.date(from: dateString) { return date }
         throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid date format: \(dateString)")
      }
      
     let tData = try JSONSerialization.data(withJSONObject: results)
     return try  decoder.decode([T].self, from: tData)
   }
   
   
   //通过REST API上传数据
   func save<T: Encodable>(to urlStr: String, object: T) async throws {//T：代表通用类型，泛型，Encodable编码
      guard let url = URL(string: urlStr) else { throw NetworkError.invalidURL//抛出问题 -> 无效网址
      }//有值则赋值给url，没有则进入else
      
      var request = URLRequest(url: url)
      request.httpMethod = "POST"
      request.setValue("application/json", forHTTPHeaderField: "Content-Type")
      request.setValue(kAppID, forHTTPHeaderField: "X-LC-Id")
      request.setValue(kAppKey, forHTTPHeaderField: "X-LC-Key")
      
      let encoder = JSONEncoder()
//      encoder.keyEncodingStrategy = .convertToSnakeCase//数据字段是下划线的写法的时候
      request.httpBody = try encoder.encode(object)//注意：使用链接的方式请求LeanCloud REST需要去掉Date字段（或其他处理）
      
      let (data, response) = try await URLSession.shared.data(for: request)//向服务器请求数据，并返回一个元组类型【一个数据，一个响应】
      
      guard let httpRespsonse = response as? HTTPURLResponse else { throw NetworkError.notHTTPResponse }
      
      if !(200..<300).contains(httpRespsonse.statusCode) {//如果不是 2开头的响应码 -> [200,300)
        let errRespsonse = try JSONSerialization.jsonObject(with: data) as? [String: Any]//Any：字典类型
         let errMsg = errRespsonse?["error"] as? String ?? "响应数据类型转换失败"
         //如果errRespsonse没有值，则返回error
         //如果上面的errRespsonse?["error"] as? String都不满足则返回：响应数据类型转换失败，【??】空壳运算符
         
         throw NetworkError.requestFailed("错误码：\(httpRespsonse.statusCode)，错误信息：\(errMsg)")
      }
   }
}