import Foundation

/// DTO helper structures matching Go backend API schema
private struct BackendResponse<T: Decodable>: Decodable {
    let code: Int
    let message: String
    let data: T?
}

private struct BackendAuthData: Decodable {
    let user: BackendUser
    let token: String
}

private struct BackendUser: Decodable {
    let id: String
    let username: String
    let email: String?
    let phoneNumber: String?
    let avatarURL: String?
    let registeredAt: Date
    
    func toUserAccount(token: String) -> UserAccount {
        return UserAccount(
            id: id,
            username: username,
            email: email,
            phoneNumber: phoneNumber,
            avatarURL: avatarURL,
            token: token,
            registeredAt: registeredAt
        )
    }
}

/// Remote server adapter implementing `AuthServiceProtocol`.
/// Connects to the CelestiaTrace Go backend server at https://celestia-trace.ccdw.life/v1
final class RemoteAuthServiceStub: AuthServiceProtocol {
    private let baseURL: URL
    private let session: URLSession
    private var cachedUser: UserAccount?
    
    init(baseURL: URL = URL(string: "https://celestia-trace.ccdw.life/v1")!, session: URLSession = .shared) {
        self.baseURL = baseURL
        self.session = session
    }
    
    private var decoder: JSONDecoder {
        let dec = JSONDecoder()
        dec.dateDecodingStrategy = .custom { decoder in
            let container = try decoder.singleValueContainer()
            let dateStr = try container.decode(String.self)
            
            let formatter = ISO8601DateFormatter()
            formatter.formatOptions = [.withInternetDateTime, .withFractionalSeconds]
            if let date = formatter.date(from: dateStr) {
                return date
            }
            formatter.formatOptions = [.withInternetDateTime]
            if let date = formatter.date(from: dateStr) {
                return date
            }
            throw DecodingError.dataCorruptedError(in: container, debugDescription: "Invalid date format: \(dateStr)")
        }
        return dec
    }
    
    func login(request: LoginRequest, completion: @escaping (AuthResult<UserAccount>) -> Void) {
        let endpoint = baseURL.appendingPathComponent("auth/login")
        var urlReq = URLRequest(url: endpoint)
        urlReq.httpMethod = "POST"
        urlReq.setValue("application/json", forHTTPHeaderField: "Content-Type")
        
        let body: [String: Any] = [
            "identifier": request.identifier,
            "password": request.password
        ]
        urlReq.httpBody = try? JSONSerialization.data(withJSONObject: body)
        
        performRequest(urlReq, completion: completion)
    }
    
    func register(request: RegisterRequest, completion: @escaping (AuthResult<UserAccount>) -> Void) {
        let endpoint = baseURL.appendingPathComponent("auth/register")
        var urlReq = URLRequest(url: endpoint)
        urlReq.httpMethod = "POST"
        urlReq.setValue("application/json", forHTTPHeaderField: "Content-Type")
        
        let body: [String: Any] = [
            "username": request.username,
            "identifier": request.identifier,
            "password": request.password
        ]
        urlReq.httpBody = try? JSONSerialization.data(withJSONObject: body)
        
        performRequest(urlReq, completion: completion)
    }
    
    func updateProfile(request: UpdateProfileRequest, completion: @escaping (AuthResult<UserAccount>) -> Void) {
        guard let token = cachedUser?.token else {
            completion(.failure(.userNotFound))
            return
        }
        
        let endpoint = baseURL.appendingPathComponent("user/profile")
        var urlReq = URLRequest(url: endpoint)
        urlReq.httpMethod = "PUT"
        urlReq.setValue("application/json", forHTTPHeaderField: "Content-Type")
        urlReq.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
        
        var body: [String: Any] = [:]
        if let username = request.username { body["username"] = username }
        if let email = request.email { body["email"] = email }
        if let phone = request.phoneNumber { body["phoneNumber"] = phone }
        if let avatar = request.avatarURL { body["avatarURL"] = avatar }
        
        urlReq.httpBody = try? JSONSerialization.data(withJSONObject: body)
        
        let task = session.dataTask(with: urlReq) { [weak self] data, response, error in
            guard let self = self else { return }
            if let error = error {
                completion(.failure(.networkError(error.localizedDescription)))
                return
            }
            guard let data = data else {
                completion(.failure(.networkError("未收到服务器响应数据")))
                return
            }
            
            do {
                let resp = try self.decoder.decode(BackendResponse<BackendUser>.self, from: data)
                if resp.code == 0, let bUser = resp.data {
                    let userAccount = bUser.toUserAccount(token: token)
                    self.cachedUser = userAccount
                    completion(.success(userAccount))
                } else {
                    completion(.failure(.networkError(resp.message)))
                }
            } catch {
                completion(.failure(.networkError("响应解析失败: \(error.localizedDescription)")))
            }
        }
        task.resume()
    }
    
    func changePassword(request: ChangePasswordRequest, completion: @escaping (AuthResult<Bool>) -> Void) {
        guard let token = cachedUser?.token else {
            completion(.failure(.userNotFound))
            return
        }
        
        let endpoint = baseURL.appendingPathComponent("user/change-password")
        var urlReq = URLRequest(url: endpoint)
        urlReq.httpMethod = "POST"
        urlReq.setValue("application/json", forHTTPHeaderField: "Content-Type")
        urlReq.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
        
        let body: [String: Any] = [
            "oldPassword": request.oldPassword,
            "newPassword": request.newPassword
        ]
        urlReq.httpBody = try? JSONSerialization.data(withJSONObject: body)
        
        let task = session.dataTask(with: urlReq) { data, response, error in
            if let error = error {
                completion(.failure(.networkError(error.localizedDescription)))
                return
            }
            guard let data = data else {
                completion(.failure(.networkError("未收到服务器响应数据")))
                return
            }
            
            do {
                if let json = try JSONSerialization.jsonObject(with: data) as? [String: Any],
                   let code = json["code"] as? Int {
                    if code == 0 {
                        completion(.success(true))
                    } else {
                        let msg = json["message"] as? String ?? "密码修改失败"
                        completion(.failure(.incorrectPassword))
                    }
                } else {
                    completion(.failure(.networkError("非法服务器响应格式")))
                }
            } catch {
                completion(.failure(.networkError(error.localizedDescription)))
            }
        }
        task.resume()
    }
    
    func logout(completion: @escaping () -> Void) {
        if let token = cachedUser?.token {
            let endpoint = baseURL.appendingPathComponent("auth/logout")
            var urlReq = URLRequest(url: endpoint)
            urlReq.httpMethod = "POST"
            urlReq.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
            let task = session.dataTask(with: urlReq) { _, _, _ in }
            task.resume()
        }
        cachedUser = nil
        completion()
    }
    
    func getCurrentUser() -> UserAccount? {
        return cachedUser
    }
    
    private func performRequest(_ urlReq: URLRequest, completion: @escaping (AuthResult<UserAccount>) -> Void) {
        let task = session.dataTask(with: urlReq) { [weak self] data, response, error in
            guard let self = self else { return }
            if let error = error {
                completion(.failure(.networkError(error.localizedDescription)))
                return
            }
            guard let data = data else {
                completion(.failure(.networkError("未收到服务器响应数据")))
                return
            }
            
            do {
                let resp = try self.decoder.decode(BackendResponse<BackendAuthData>.self, from: data)
                if resp.code == 0, let authData = resp.data {
                    let userAccount = authData.user.toUserAccount(token: authData.token)
                    self.cachedUser = userAccount
                    completion(.success(userAccount))
                } else {
                    if resp.code == 409 {
                        completion(.failure(.userAlreadyExists))
                    } else if resp.code == 401 {
                        completion(.failure(.invalidCredentials))
                    } else {
                        completion(.failure(.networkError(resp.message)))
                    }
                }
            } catch {
                completion(.failure(.networkError("响应解析失败: \(error.localizedDescription)")))
            }
        }
        task.resume()
    }
}