import Foundation
import UniformTypeIdentifiers

/// Handles uploading local audio files to the Chad Music server.
/// Uses URLSession upload task with progress tracking via delegate.
///
/// @unchecked Sendable: Required because self is passed as URLSessionTaskDelegate
/// across actor boundaries. Safe because delegate methods only dispatch back to
/// MainActor via Task to update observable properties.
@MainActor
@Observable
final class UploadService: NSObject, @unchecked Sendable {

    static let shared = UploadService()

    // MARK: - State

    enum State: Equatable {
        case idle
        case uploading(fileName: String)
        case success(tracksAdded: Int, albumsUpdated: Int)
        case error(String)
    }

    var state: State = .idle
    var progress: Double = 0.0

    // MARK: - Allowed File Types

    static let allowedTypes: [UTType] = {
        var types: [UTType] = [.mp3, .wav, .aiff, .mpeg4Audio]
        if let flac = UTType(filenameExtension: "flac") {
            types.append(flac)
        }
        if let ogg = UTType(filenameExtension: "ogg") {
            types.append(ogg)
        }
        return types
    }()

    // MARK: - Private

    @ObservationIgnored private var uploadTask: Task<Void, Never>?

    // MARK: - Public API

    /// Start uploading a track's local file. Cancels any in-progress upload first.
    func startUpload(track: Track, apiClient: ChadMusicAPIClient) {
        cancel()
        track.uploadState = .uploading
        uploadTask = Task {
            await performUpload(track: track, fileURL: URL(fileURLWithPath: track.filePath), apiClient: apiClient)
        }
    }

    /// Start uploading a file from a URL (file picker / drag-and-drop, no Track object).
    func startUpload(fileURL: URL, apiClient: ChadMusicAPIClient) {
        cancel()
        uploadTask = Task {
            await performUpload(track: nil, fileURL: fileURL, apiClient: apiClient)
        }
    }

    /// Upload a batch of tracks sequentially.
    func uploadBatch(tracks: [Track], apiClient: ChadMusicAPIClient) {
        cancel()
        uploadTask = Task {
            for track in tracks {
                guard !Task.isCancelled else { break }
                guard track.uploadState != .uploaded else { continue }
                guard track.hasLocalFile, FileManager.default.fileExists(atPath: track.filePath) else { continue }
                track.uploadState = .uploading
                await performUpload(track: track, fileURL: URL(fileURLWithPath: track.filePath), apiClient: apiClient)
            }
        }
    }

    /// Cancel the current upload.
    func cancel() {
        uploadTask?.cancel()
        uploadTask = nil
        state = .idle
        progress = 0.0
    }

    /// Reset state after success/error dismissal.
    func dismiss() {
        state = .idle
        progress = 0.0
    }

    // MARK: - Upload Implementation

    private func performUpload(track: Track?, fileURL: URL, apiClient: ChadMusicAPIClient) async {
        guard apiClient.isConfigured else {
            state = .error("Chad Music not configured")
            track?.uploadState = .error
            return
        }

        let fileName = fileURL.lastPathComponent
        state = .uploading(fileName: fileName)
        progress = 0.0

        guard let contentType = Self.contentType(for: fileURL) else {
            state = .error("Unsupported format: .\(fileURL.pathExtension)")
            track?.uploadState = .error
            return
        }

        // Build request URL
        let base = apiClient.serverURL.trimmingCharacters(in: .whitespacesAndNewlines)
        let normalized = base.hasSuffix("/") ? base : base + "/"
        guard let url = URL(string: normalized + "api/upload") else {
            state = .error("Invalid server URL")
            track?.uploadState = .error
            return
        }

        var request = URLRequest(url: url)
        request.httpMethod = "PUT"
        request.timeoutInterval = 600
        for (key, value) in apiClient.authHeaders {
            request.setValue(value, forHTTPHeaderField: key)
        }
        request.setValue(contentType, forHTTPHeaderField: "Content-Type")
        // Sanitize filename for HTTP header (strip CR/LF to prevent header injection)
        let safeFileName = fileName
            .replacingOccurrences(of: "\r", with: "")
            .replacingOccurrences(of: "\n", with: "")
        request.setValue(safeFileName, forHTTPHeaderField: "X-Filename")

        do {
            // Security-scoped access for files from NSOpenPanel
            let accessing = fileURL.startAccessingSecurityScopedResource()
            defer { if accessing { fileURL.stopAccessingSecurityScopedResource() } }

            let config = URLSessionConfiguration.default
            config.timeoutIntervalForResource = 600
            let session = URLSession(configuration: config)
            defer { session.finishTasksAndInvalidate() }

            let (data, response) = try await session.upload(
                for: request, fromFile: fileURL, delegate: self
            )

            guard !Task.isCancelled else { return }

            guard let http = response as? HTTPURLResponse else {
                state = .error("Invalid server response")
                track?.uploadState = .error
                return
            }

            switch http.statusCode {
            case 200..<300:
                let result = try? JSONDecoder().decode(UploadResult.self, from: data)
                state = .success(
                    tracksAdded: result?.tracksAdded ?? 0,
                    albumsUpdated: result?.albumsUpdated ?? 0
                )
                track?.uploadState = .uploaded
            case 401:
                state = .error("Unauthorized — check your API key")
                track?.uploadState = .error
            case 413:
                state = .error("File too large (max 200 MB)")
                track?.uploadState = .error
            default:
                let result = try? JSONDecoder().decode(UploadResult.self, from: data)
                state = .error(
                    result?.message ?? "Server error (HTTP \(http.statusCode))"
                )
                track?.uploadState = .error
            }
        } catch is CancellationError {
            // User cancelled — state already reset by cancel()
            if track?.uploadState == .uploading { track?.uploadState = .none }
        } catch {
            if !Task.isCancelled {
                if (error as NSError).code == NSURLErrorCancelled {
                    if track?.uploadState == .uploading { track?.uploadState = .none }
                } else {
                    state = .error(error.localizedDescription)
                    track?.uploadState = .error
                }
            } else {
                if track?.uploadState == .uploading { track?.uploadState = .none }
            }
        }
    }

    // MARK: - Response Model

    private struct UploadResult: Decodable {
        let status: String
        let tracksAdded: Int?
        let albumsUpdated: Int?
        let message: String?

        enum CodingKeys: String, CodingKey {
            case status
            case tracksAdded = "tracks_added"
            case albumsUpdated = "albums_updated"
            case message
        }
    }

    // MARK: - Content Type Mapping

    private static func contentType(for url: URL) -> String? {
        switch url.pathExtension.lowercased() {
        case "mp3": "audio/mpeg"
        case "flac": "audio/flac"
        case "wav": "audio/wav"
        case "aiff", "aif": "audio/aiff"
        case "m4a", "aac": "audio/mp4"
        case "ogg": "audio/ogg"
        default: nil
        }
    }
}

// MARK: - URLSessionTaskDelegate (progress tracking)

extension UploadService: URLSessionTaskDelegate {
    nonisolated func urlSession(
        _ session: URLSession,
        task: URLSessionTask,
        didSendBodyData bytesSent: Int64,
        totalBytesSent: Int64,
        totalBytesExpectedToSend: Int64
    ) {
        guard totalBytesExpectedToSend > 0 else { return }
        let p = Double(totalBytesSent) / Double(totalBytesExpectedToSend)
        Task { @MainActor in
            self.progress = p
        }
    }
}