import Foundation
import Speech
import AVFoundation

/// Live dictation wrapper around `SFSpeechRecognizer` + `AVAudioEngine`. It
/// publishes an incrementally-updated `transcript` while recording so users can
/// speak a dish name — or a whole list of ingredients in one go — instead of
/// typing. Prefers on-device recognition when the locale supports it (private,
/// offline); otherwise falls back to Apple's server recognition.
@MainActor
final class SpeechDictationService: ObservableObject {
    enum State: Equatable {
        case idle
        case recording
        case denied        // microphone or speech-recognition permission refused
        case unavailable   // no recognizer available for the requested locale
    }

    @Published private(set) var state: State = .idle
    @Published private(set) var transcript: String = ""

    private let audioEngine = AVAudioEngine()
    private var recognizer: SFSpeechRecognizer?
    private var request: SFSpeechAudioBufferRecognitionRequest?
    private var task: SFSpeechRecognitionTask?

    var isRecording: Bool { state == .recording }

    /// Requests permissions and, on success, starts live transcription in the
    /// given locale. Partial results stream into `transcript`.
    func start(localeIdentifier: String) {
        guard state != .recording else { return }
        transcript = ""

        SFSpeechRecognizer.requestAuthorization { [weak self] speechAuth in
            guard let self else { return }
            Task { @MainActor in
                guard speechAuth == .authorized else { self.state = .denied; return }
                self.requestMicAndStart(localeIdentifier: localeIdentifier)
            }
        }
    }

    private func requestMicAndStart(localeIdentifier: String) {
        AVAudioApplication.requestRecordPermission { [weak self] granted in
            guard let self else { return }
            Task { @MainActor in
                guard granted else { self.state = .denied; return }
                self.beginSession(localeIdentifier: localeIdentifier)
            }
        }
    }

    private func beginSession(localeIdentifier: String) {
        guard let recognizer = SFSpeechRecognizer(locale: Locale(identifier: localeIdentifier)),
              recognizer.isAvailable else {
            state = .unavailable
            return
        }
        self.recognizer = recognizer

        do {
            let session = AVAudioSession.sharedInstance()
            try session.setCategory(.record, mode: .measurement, options: .duckOthers)
            try session.setActive(true, options: .notifyOthersOnDeactivation)

            let request = SFSpeechAudioBufferRecognitionRequest()
            request.shouldReportPartialResults = true
            if recognizer.supportsOnDeviceRecognition {
                request.requiresOnDeviceRecognition = true
            }
            self.request = request

            let inputNode = audioEngine.inputNode
            let format = inputNode.outputFormat(forBus: 0)
            inputNode.removeTap(onBus: 0)
            inputNode.installTap(onBus: 0, bufferSize: 1024, format: format) { [weak self] buffer, _ in
                self?.request?.append(buffer)
            }

            audioEngine.prepare()
            try audioEngine.start()
            state = .recording

            task = recognizer.recognitionTask(with: request) { [weak self] result, error in
                guard let self else { return }
                Task { @MainActor in
                    if let result {
                        self.transcript = result.bestTranscription.formattedString
                    }
                    if error != nil || (result?.isFinal ?? false) {
                        self.teardownAudio()
                        if self.state == .recording { self.state = .idle }
                    }
                }
            }
        } catch {
            CrashlyticsService.record(error, context: "speech_dictation_start")
            teardownAudio()
            state = .idle
        }
    }

    /// Stops capture, keeping the last transcript, and returns the final text.
    @discardableResult
    func stop() -> String {
        teardownAudio()
        if state == .recording { state = .idle }
        return transcript
    }

    private func teardownAudio() {
        if audioEngine.isRunning {
            audioEngine.stop()
            audioEngine.inputNode.removeTap(onBus: 0)
        }
        request?.endAudio()
        task?.cancel()
        request = nil
        task = nil
        try? AVAudioSession.sharedInstance().setActive(false, options: .notifyOthersOnDeactivation)
    }
}