import Foundation

// MARK: - Service Protocol

protocol ChallengeServiceProtocol: Sendable {
    func listChallenges(filter: ChallengeFilter) async throws -> [Challenge]
    func getChallenge(id: String) async throws -> (challenge: Challenge, participants: [ChallengeParticipant])
    func createChallenge(request: CreateChallengeRequest) async throws -> Challenge
    func updateChallenge(id: String, request: UpdateChallengeRequest) async throws -> Challenge
    func joinChallenge(id: String) async throws
    func leaveChallenge(id: String) async throws
    func getLeaderboard(challengeId: String) async throws -> [LeaderboardEntry]
    func submitProgress(challengeId: String, progress: ProgressSubmission) async throws -> (progress: Double, percentage: Double)
}

// MARK: - Default Service

class ChallengeService: ChallengeServiceProtocol {
    private let baseURL: URL
    private let session: URLSession
    private let authToken: String?

    init(
        baseURL: URL = URL(string: "http://localhost:3000")!,
        session: URLSession = .shared,
        authToken: String? = nil
    ) {
        self.baseURL = baseURL
        self.session = session
        self.authToken = authToken
    }

    func listChallenges(filter: ChallengeFilter = ChallengeFilter()) async throws -> [Challenge] {
        var components = URLComponents(url: baseURL.appendingPathComponent("/api/challenges"), resolvingAgainstBaseURL: true)!
        var queryItems: [URLQueryItem] = [
            URLQueryItem(name: "limit", value: String(filter.limit)),
            URLQueryItem(name: "offset", value: String(filter.offset))
        ]
        if let type = filter.challengeType { queryItems.append(URLQueryItem(name: "type", value: type.rawValue)) }
        if let status = filter.status { queryItems.append(URLQueryItem(name: "status", value: status.rawValue)) }
        if let participation = filter.participationStatus { queryItems.append(URLQueryItem(name: "participation", value: participation.rawValue)) }
        if let clubId = filter.clubId { queryItems.append(URLQueryItem(name: "clubId", value: clubId)) }
        components.queryItems = queryItems

        let request = try buildRequest(url: components.url!)
        let (data, response) = try await session.data(for: request)
        try validateResponse(response)

        let decoded = try JSONDecoder().decode(ChallengeListResponse.self, from: data)
        return decoded.challenges
    }

    func getChallenge(id: String) async throws -> (challenge: Challenge, participants: [ChallengeParticipant]) {
        let url = baseURL.appendingPathComponent("/api/challenges/\(id)")
        let request = try buildRequest(url: url)
        let (data, response) = try await session.data(for: request)
        try validateResponse(response)

        let decoded = try JSONDecoder().decode(ChallengeDetailResponse.self, from: data)
        return (decoded.challenge, decoded.participants)
    }

    func createChallenge(request: CreateChallengeRequest) async throws -> Challenge {
        let url = baseURL.appendingPathComponent("/api/challenges")
        var request = try buildRequest(url: url, method: .post)
        request.httpBody = try JSONEncoder().encode(request)

        let (data, response) = try await session.data(for: request)
        try validateResponse(response)

        let decoded = try JSONDecoder().decode(CreateChallengeResponse.self, from: data)
        return decoded.challenge
    }

    func updateChallenge(id: String, request: UpdateChallengeRequest) async throws -> Challenge {
        let url = baseURL.appendingPathComponent("/api/challenges/\(id)")
        var request = try buildRequest(url: url, method: .patch)
        request.httpBody = try JSONEncoder().encode(request)

        let (data, response) = try await session.data(for: request)
        try validateResponse(response)

        let decoded = try JSONDecoder().decode(UpdateChallengeResponse.self, from: data)
        return decoded.challenge
    }

    func joinChallenge(id: String) async throws {
        let url = baseURL.appendingPathComponent("/api/challenges/\(id)/join")
        let request = try buildRequest(url: url, method: .post)

        let (_, response) = try await session.data(for: request)
        try validateResponse(response)
    }

    func leaveChallenge(id: String) async throws {
        let url = baseURL.appendingPathComponent("/api/challenges/\(id)/leave")
        let request = try buildRequest(url: url, method: .post)

        let (_, response) = try await session.data(for: request)
        try validateResponse(response)
    }

    func getLeaderboard(challengeId: String) async throws -> [LeaderboardEntry] {
        let url = baseURL.appendingPathComponent("/api/challenges/\(challengeId)/leaderboard")
        let request = try buildRequest(url: url)
        let (data, response) = try await session.data(for: request)
        try validateResponse(response)

        let decoded = try JSONDecoder().decode(LeaderboardResponse.self, from: data)
        return decoded.entries
    }

    func submitProgress(challengeId: String, progress: ProgressSubmission) async throws -> (progress: Double, percentage: Double) {
        let url = baseURL.appendingPathComponent("/api/challenges/\(challengeId)/progress")
        var request = try buildRequest(url: url, method: .post)
        request.httpBody = try JSONEncoder().encode(progress)

        let (data, response) = try await session.data(for: request)
        try validateResponse(response)

        let decoded = try JSONDecoder().decode(ProgressResponse.self, from: data)
        return (decoded.newProgress, decoded.progressPercentage)
    }

    // MARK: - Helpers

    private func buildRequest(url: URL, method: HTTPMethod = .get, body: Data? = nil) throws -> URLRequest {
        var request = URLRequest(url: url)
        request.httpMethod = method.rawValue
        request.setValue("application/json", forHTTPHeaderField: "Content-Type")

        if let token = authToken {
            request.setValue("Bearer \(token)", forHTTPHeaderField: "Authorization")
        }

        if let body = body {
            request.httpBody = body
        }

        return request
    }

    private func validateResponse(_ response: URLResponse) throws {
        guard let httpResponse = response as? HTTPURLResponse else {
            throw ChallengeError.invalidResponse
        }

        guard (200...299).contains(httpResponse.statusCode) else {
            switch httpResponse.statusCode {
            case 401: throw ChallengeError.unauthorized
            case 403: throw ChallengeError.forbidden
            case 404: throw ChallengeError.notFound
            case 429: throw ChallengeError.rateLimited
            case 500...599: throw ChallengeError.serverError(httpResponse.statusCode)
            default: throw ChallengeError.httpError(httpResponse.statusCode)
            }
        }
    }
}

// MARK: - Error Types

enum ChallengeError: LocalizedError {
    case invalidResponse
    case unauthorized
    case forbidden
    case notFound
    case rateLimited
    case serverError(Int)
    case httpError(Int)

    var errorDescription: String {
        switch self {
        case .invalidResponse: return "Invalid server response"
        case .unauthorized: return "Unauthorized — please log in again"
        case .forbidden: return "Forbidden — check permissions"
        case .notFound: return "Challenge not found"
        case .rateLimited: return "Too many requests — try again shortly"
        case .serverError(let code): return "Server error (\(code))"
        case .httpError(let code): return "HTTP error (\(code))"
        }
    }
}