import AVFoundation

final class VideoReader {
    var sampleRead: ((CMSampleBuffer) -> Void)?
    
    private let assetReader: AVAssetReader
    private let output: AVAssetReaderTrackOutput
    private let nominalFrameRate: Float
    private var timer: Timer?

    init?() {
        guard
            let url = Bundle.main.url(forResource: "2", withExtension: "MOV")
        else { return nil }
        let urlAsset = AVURLAsset(url: url, options: [AVURLAssetPreferPreciseDurationAndTimingKey: true])
        guard let track = urlAsset.tracks(withMediaType: .video).first else { return nil }

        nominalFrameRate = 1 / track.nominalFrameRate

        do {
            guard let asset = track.asset else { return nil }
            assetReader = try AVAssetReader(asset: asset)
        } catch {
            print(error)
            return nil
        }

        let settings: [String: Any] = [
            String(kCVPixelBufferPixelFormatTypeKey): kCVPixelFormatType_32BGRA,
            String(kCVPixelBufferMetalCompatibilityKey): true
        ]

        output = AVAssetReaderTrackOutput(track: track, outputSettings: settings)
        output.alwaysCopiesSampleData = false
        guard assetReader.canAdd(output) else { return nil }
        assetReader.add(output)
    }

    func readSamples() {
        timer = Timer.scheduledTimer(withTimeInterval: Double(nominalFrameRate), repeats: true, block: { [weak self] currentTimer in
            guard let self = self else {
                currentTimer.invalidate()
                return
            }

            guard self.assetReader.status == .reading else { return }

            guard let sample = self.output.copyNextSampleBuffer() else {
                print("output.copyNextSampleBuffer() is nil")
                currentTimer.invalidate()
                self.timer?.invalidate()
                self.timer = nil
                return
            }

            self.sampleRead?(sample)
        })

        if !assetReader.startReading() {
            timer?.invalidate()
            timer = nil
        }
    }

    private func printAssetReaderStatus() {
        switch self.assetReader.status {
        case .reading: print("reading")
        case .cancelled: print("canceled")
        case .completed: print("completed")
        case .failed: print("failed")
        case .unknown: print("unknown")
        @unknown default:
            print("@unknown default")
        }
    }
}