import Foundation

// MARK: - Service Protocol

protocol NotificationsServiceProtocol: Sendable {
    func list(params: NotificationListParams) async throws -> [NotificationItem]
    func markAsRead(id: String) async throws
    func markAllAsRead() async throws
}

// MARK: - Default Service

class NotificationsService: NotificationsServiceProtocol {
    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 list(params: NotificationListParams = NotificationListParams()) async throws -> [NotificationItem] {
        var components = URLComponents(url: baseURL.appendingPathComponent("/api/notifications"), resolvingAgainstBaseURL: true)!
        var queryItems: [URLQueryItem] = [
            URLQueryItem(name: "limit", value: String(params.limit)),
            URLQueryItem(name: "offset", value: String(params.offset))
        ]
        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(NotificationListResponse.self, from: data)
        return decoded.notifications
    }

    func markAsRead(id: String) async throws {
        let url = baseURL.appendingPathComponent("/api/notifications/\(id)/read")
        let request = try buildRequest(url: url, method: .patch)

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

        _ = try JSONDecoder().decode(NotificationMarkAsReadResponse.self, from: data)
    }

    func markAllAsRead() async throws {
        let url = baseURL.appendingPathComponent("/api/notifications/read-all")
        let request = try buildRequest(url: url, method: .patch)

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

        _ = try JSONDecoder().decode(NotificationMarkAllReadResponse.self, from: data)
    }

    // 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 NotificationError.invalidResponse
        }

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

// MARK: - Error Types

enum NotificationError: LocalizedError {
    case invalidResponse
    case unauthorized
    case forbidden
    case notFound
    case rateLimited
    case serverError(Int)
    case httpError(Int)
    case decodingError(Error)

    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 "Notification 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))"
        case .decodingError(let error): return "Decoding error: \(error.localizedDescription)"
        }
    }
}

// MARK: - HTTP Method

enum HTTPMethod: String {
    case get = "GET"
    case post = "POST"
    case patch = "PATCH"
    case delete = "DELETE"
}