import Foundation

// MARK: - Service Protocol

protocol CommunityEventServiceProtocol: Sendable {
    func listEvents(filter: EventFilter) async throws -> [CommunityEvent]
    func getEvent(id: String) async throws -> (event: CommunityEvent, participants: [EventParticipant])
    func createEvent(request: CreateEventRequest) async throws -> CommunityEvent
    func updateEvent(id: String, request: UpdateEventRequest) async throws -> CommunityEvent
    func RSVP(eventId: String, status: RSVPStatus) async throws
}

// MARK: - Default Service

class CommunityEventService: CommunityEventServiceProtocol {
    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 listEvents(filter: EventFilter = EventFilter()) async throws -> [CommunityEvent] {
        var components = URLComponents(url: baseURL.appendingPathComponent("/api/events"), resolvingAgainstBaseURL: true)!
        var queryItems: [URLQueryItem] = [
            URLQueryItem(name: "limit", value: String(filter.limit)),
            URLQueryItem(name: "offset", value: String(filter.offset))
        ]
        if let type = filter.eventType { queryItems.append(URLQueryItem(name: "type", value: type.rawValue)) }
        if let startDate = filter.startDate { queryItems.append(URLQueryItem(name: "startDate", value: ISO8601DateFormatter().string(from: startDate))) }
        if let endDate = filter.endDate { queryItems.append(URLQueryItem(name: "endDate", value: ISO8601DateFormatter().string(from: endDate))) }
        if let location = filter.location { queryItems.append(URLQueryItem(name: "location", value: location)) }
        if let radius = filter.radiusKm { queryItems.append(URLQueryItem(name: "radius", value: String(radius))) }
        if let rsvp = filter.rsvpStatus { queryItems.append(URLQueryItem(name: "rsvp", value: rsvp.rawValue)) }
        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(EventListResponse.self, from: data)
        return decoded.events
    }

    func getEvent(id: String) async throws -> (event: CommunityEvent, participants: [EventParticipant]) {
        let url = baseURL.appendingPathComponent("/api/events/\(id)")
        let request = try buildRequest(url: url)
        let (data, response) = try await session.data(for: request)
        try validateResponse(response)

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

    func createEvent(request: CreateEventRequest) async throws -> CommunityEvent {
        let url = baseURL.appendingPathComponent("/api/events")
        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(CreateEventResponse.self, from: data)
        return decoded.event
    }

    func updateEvent(id: String, request: UpdateEventRequest) async throws -> CommunityEvent {
        let url = baseURL.appendingPathComponent("/api/events/\(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(UpdateEventResponse.self, from: data)
        return decoded.event
    }

    func RSVP(eventId: String, status: RSVPStatus) async throws {
        let url = baseURL.appendingPathComponent("/api/events/\(eventId)/rsvp")
        var request = try buildRequest(url: url, method: .post)
        request.httpBody = try JSONEncoder().encode(["status": status.rawValue])

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

    // 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 CommunityEventError.invalidResponse
        }

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

// MARK: - Error Types

enum CommunityEventError: 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 "Event 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))"
        }
    }
}