QueueCube/ios/QueueCube/Backend/API.swift

//
//  API.swift
//  QueueCube
//
//  Created by James Magahern on 3/3/25.
//

import Foundation

struct MediaItem: Codable
{
    let filename: String?
    let title: String?
    let id: Int

    let current: Bool?
    let playing: Bool?
    let metadata: Metadata?
    let playbackError: String?
    
    var displayTitle: String {
        metadata?.title ?? title ?? displayFilename ?? "item \(id)"
    }
    
    private var displayFilename: String? {
        guard let filename else { return nil }
        if let url = URL(string: filename) {
            return url.lastPathComponent
        }
        
        return filename
    }
    
    // MARK: - Types
    
    struct Metadata: Codable
    {
        let title: String?
        let description: String?
        let siteName: String?
    }
}

struct SearchResultItem: Codable
{
    var type: String
    var title: String
    var author: String
    var mediaUrl: String
    var thumbnailUrl: String
}

struct FetchResult<T: Codable>: Codable
{
    let success: Bool
    let results: T?
    let error: String?
}

struct NowPlayingInfo: Codable
{
    let playingItem: MediaItem?
    let isPaused: Bool
    let volume: Int
    let timePosition: Double?
    let duration: Double?
    let seekable: Bool?
}

actor API
{
    let baseURL: URL
    private let requestTimeout: TimeInterval
    
    private var pingTask: Task<(), any Swift.Error>? = nil
    
    init(baseURL: URL, requestTimeout: TimeInterval = 60) {
        self.baseURL = baseURL
        self.requestTimeout = requestTimeout
    }
    
    public func fetchNowPlayingInfo() async throws -> NowPlayingInfo {
        try await request()
            .path("/nowplaying")
            .json()
    }
    
    public func fetchPlaylist() async throws -> [MediaItem] {
        try await request()
            .path("/playlist")
            .json()
    }
    
    public func fetchFavorites() async throws -> [MediaItem] {
        try await request()
            .path("/favorites")
            .json()
    }
    
    public func play() async throws {
        try await request()
            .path("/play")
            .post()
    }
    
    public func pause() async throws {
        try await request()
            .path("/pause")
            .post()
    }
    
    public func stop() async throws {
        try await request()
            .path("/stop")
            .post()
    }
    
    public func skip(_ to: Int? = nil) async throws {
        let path = if let to { "/skip/\(to)" } else { "/skip" }
        try await request()
            .path(path)
            .post()
    }
    
    public func previous() async throws {
        try await request()
            .path("/previous")
            .post()
    }
    
    public func add(mediaURL: String) async throws {
        try await request()
            .path("/playlist")
            .body([ "url" : mediaURL ])
            .post()
    }
    
    public func replace(mediaURL: String) async throws {
        try await request()
            .path("/playlist/replace")
            .body([ "url" : mediaURL ])
            .post()
    }
    
    public func addFavorite(mediaURL: String) async throws {
        try await request()
            .path("/favorites")
            .body([ "filename" : mediaURL ])
            .post()
    }
    
    public func deleteFavorite(mediaURL: String) async throws {
        try await request()
            .pathString("/favorites/\(mediaURL.uriEncoded())")
            .method(.delete)
            .execute()
    }
    
    public func renameFavorite(mediaURL: String, title: String) async throws {
        try await request()
            .pathString("/favorites/\(mediaURL.uriEncoded())/title")
            .body([ "title": title ])
            .method(.put)
            .execute()
    }
    
    public func delete(index: Int) async throws {
        try await request()
            .path("/playlist/\(index)")
            .method(.delete)
            .execute()
    }
    
    public func setVolume(_ value: Double) async throws {
        try await request()
            .path("/volume")
            .body([ "volume" : Int(value * 100) ])
            .post()
    }

    public func seek(to time: Double) async throws {
        try await request()
            .path("/player/seek")
            .body([ "time" : time ])
            .post()
    }
    
    public func search(query: String) async throws -> FetchResult<[SearchResultItem]> {
        try await request()
            .pathString("/search?q=\(query.uriEncoded())")
            .json()
    }
    
    public func events() async throws -> AsyncStream<StreamEvent> {
        let requestBuilder: () -> RequestBuilder = request
        
        return AsyncStream { continuation in
            let websocketTask: URLSessionWebSocketTask = API.spawnWebsocketTask(requestBuilder: requestBuilder, with: continuation)
            
            Task {
                var pingLoopEnabled = true
                while pingLoopEnabled {
                    try await Task.sleep(for: .seconds(5))
                    
                    websocketTask.sendPing { error in
                        if let error {
                            API.notifyError(error, continuation: continuation)
                            pingLoopEnabled = false 
                        } else {
                            continuation.yield(.event(Event(type: .receivedWebsocketPong)))
                        }
                    }
                }
            }
        }
    }
    
    private static func spawnWebsocketTask(
        requestBuilder: () -> RequestBuilder,
        with continuation: AsyncStream<StreamEvent>.Continuation
    ) -> URLSessionWebSocketTask
    {
        let url = requestBuilder()
            .path("/events")
            .websocket()
        
        let websocketTask = URLSession.shared.webSocketTask(with: url)
        websocketTask.resume()
        
        Task {
            do {
                let event = { (data: Data) in
                    try JSONDecoder().decode(Event.self, from: data)
                }
                
                while websocketTask.state == .running {
                    switch try await websocketTask.receive() {
                    case .string(let string):
                        let event = try event(string.data(using: .utf8)!)
                        continuation.yield(.event(event))
                    case .data(let data):
                        let event = try event(data)
                        continuation.yield(.event(event))
                    default:
                        break
                    }
                }
            } catch {
                notifyError(error, continuation: continuation)
            }
        }
        
        return websocketTask
    }
    
    private static func notifyError(_ error: any Swift.Error, continuation: AsyncStream<StreamEvent>.Continuation) {
        print("Websocket Error: \(error)")

        // Always notify observers of WebSocket errors so reconnection can happen
        // The UI layer can decide whether to show the error to the user
        continuation.yield(.error(.websocketError(error)))
    }
    
    private func request() -> RequestBuilder {
        RequestBuilder(url: baseURL, timeout: requestTimeout)
    }
    
    // MARK: - Types
    
    enum Error: Swift.Error, LocalizedError
    {
        case apiNotConfigured
        case websocketError(Swift.Error)

        var errorDescription: String? {
            switch self {
            case .apiNotConfigured:
                "No server is configured."
            case .websocketError(let error):
                error.localizedDescription
            }
        }
    }
    
    enum StreamEvent {
        case event(Event)
        case error(API.Error)
    }
    
    struct Event: Decodable
    {
        let type: EventType
        
        enum CodingKeys: String, CodingKey {
            case type = "event"
        }
        
        enum EventType: String, Decodable {
            case playlistUpdate      = "playlist_update"
            case nowPlayingUpdate    = "now_playing_update"
            case volumeUpdate        = "volume_update"
            case favoritesUpdate     = "favorites_update"
            case metadataUpdate      = "metadata_update"
            case mpdUpdate           = "mpd_update"
            case playbackError       = "playback_error"
            
            // Private UI events
            case receivedWebsocketPong
            case websocketReconnected
        }
    }
}

extension String
{
    func uriEncoded() -> Self {
        return addingPercentEncoding(withAllowedCharacters: .urlHostAllowed)!
    }
}