import AVFoundation
import Darwin
import os
import VoiceCatCore

private let logger = Logger(subsystem: "cat.voice.VoiceCatiOS", category: "IOSVoiceProcessingEngine")

/// In-process single-producer/single-consumer int16 PCM ring for the VPIO playback path.
///
///   producer = the core's mixer-timer thread (the `vc_set_mixed_output_sink` callback)
///   consumer = the `AVAudioSourceNode` render thread
///
/// Heap-backed (not shared memory like `BroadcastAudioRing`), but the same discipline: aligned
/// 64-bit monotonic indices with `OSMemoryBarrier` for acquire/release ordering. Both the C
/// callback and the render block are real-time — they only do index math + a memcpy here, never
/// lock or allocate.
final class PCMRing {
    private let data: UnsafeMutablePointer<Int16>
    private let capacity: Int
    private var writeIdx: UInt64 = 0
    private var readIdx: UInt64 = 0

    init(capacitySamples: Int) {
        capacity = capacitySamples
        data = UnsafeMutablePointer<Int16>.allocate(capacity: capacitySamples)
        data.initialize(repeating: 0, count: capacitySamples)
    }
    deinit { data.deallocate() }

    /// Producer: append `count` interleaved int16 samples. Drops the chunk if it doesn't fit
    /// (better to skip than tear). Single producer only (the core mixer-timer thread).
    func write(_ src: UnsafePointer<Int16>, count: Int) {
        guard count > 0, count <= capacity else { return }
        let w = writeIdx
        OSMemoryBarrier()
        let r = readIdx
        if capacity - Int(w &- r) < count { return }  // full: drop
        var idx = Int(w % UInt64(capacity))
        var off = 0
        var rem = count
        while rem > 0 {
            let chunk = min(rem, capacity - idx)
            (data + idx).update(from: src + off, count: chunk)
            idx = (idx + chunk) % capacity
            off += chunk
            rem -= chunk
        }
        OSMemoryBarrier()
        writeIdx = w &+ UInt64(count)
    }

    /// Consumer: read up to `count` interleaved int16 samples into `dst`; returns the number
    /// read (the rest is the caller's to silence-fill). Single consumer only (render thread).
    func read(into dst: UnsafeMutablePointer<Int16>, count: Int) -> Int {
        let r = readIdx
        OSMemoryBarrier()
        let w = writeIdx
        let available = Int(w &- r)
        if available <= 0 { return 0 }
        let n = min(available, count)
        var idx = Int(r % UInt64(capacity))
        var off = 0
        var rem = n
        while rem > 0 {
            let chunk = min(rem, capacity - idx)
            (dst + off).update(from: data + idx, count: chunk)
            idx = (idx + chunk) % capacity
            off += chunk
            rem -= chunk
        }
        OSMemoryBarrier()
        readIdx = r &+ UInt64(n)
        return n
    }

    /// Discard everything buffered — call before (re)starting so stale pre-roll isn't played.
    func reset() { OSMemoryBarrier(); readIdx = writeIdx }

    /// Diagnostics: monotonic total samples written / read since the ring was created. The
    /// indices are already cumulative, so these are free. Only read them when both threads are
    /// quiesced (e.g. at teardown after the engine + mixer sink are stopped) — they are not
    /// synchronized for live cross-thread reads. Lets us tell "core never delivered PCM" (Bug 1
    /// core path) apart from "PCM arrived but produced no sound" (AVAudioEngine output graph).
    var debugTotalWritten: UInt64 { writeIdx }
    var debugTotalRead: UInt64 { readIdx }
}

/// Native iOS voice-processing audio path (docs/voice.md §8 "iOS voice processing").
///
/// Real iOS echo cancellation / noise suppression / AGC come ONLY from Apple's Voice-Processing
/// I/O unit (VPIO), which `AVAudioEngine.setVoiceProcessingEnabled(true)` enables. For VPIO to
/// cancel echo it must own BOTH the mic capture and the remote-audio playback (it subtracts the
/// played-back signal from the mic), so on the AEC presets this engine drives both directions and
/// the core runs in external mode (no hardware devices):
///   - **Mic → core:** a tap on the VPIO input node → 48 kHz int16 → `client.feedPcm(micStreamId)`.
///   - **core → speaker:** the core's mixed-output sink fills `ring`; an `AVAudioSourceNode` pulls
///     from it and renders through the VPIO output, giving AEC its reference signal.
///
/// Lifecycle is driven by `SessionState` join/leave. The Stereo Mic / Studio / A2DP presets keep
/// the core's miniaudio path instead (they want raw / stereo / no-AEC routing VPIO can't provide).
@MainActor
final class IOSVoiceProcessingEngine {
    static let shared = IOSVoiceProcessingEngine()

    private(set) var isRunning = false

    private let engine = AVAudioEngine()
    private var sourceNode: AVAudioSourceNode?
    private weak var client: VoiceCatClient?
    private var micStreamId: UInt32 = 0

    // 48 kHz stereo Float32 (deinterleaved) — the format the source node renders and the engine
    // processes in. The core delivers 48 kHz stereo int16 via the mixed-output sink.
    private let outFormat = AVAudioFormat(
        commonFormat: .pcmFormatFloat32, sampleRate: 48000, channels: 2, interleaved: false)!

    // Playback ring (mixed remote audio): ~0.5 s of 48 kHz stereo int16. Filled by the core's
    // mixer-timer thread, drained by the source-node render thread.
    private let ring = PCMRing(capacitySamples: 48000 * 2 / 2)
    // Render-thread scratch for deinterleaving — pre-allocated so the render block never allocates.
    private let renderScratchFrames = 8192
    private let renderScratch: UnsafeMutablePointer<Int16>

    // Mic-feed converter (input-node format → 48 kHz int16) and its target buffer. Owned here so
    // the (background) tap block reuses them instead of allocating per callback.
    private var micConverter: AVAudioConverter?
    private var micTargetFormat: AVAudioFormat?

    private init() {
        renderScratch = UnsafeMutablePointer<Int16>.allocate(capacity: renderScratchFrames * 2)
        renderScratch.initialize(repeating: 0, count: renderScratchFrames * 2)
    }

    /// Start the VPIO engine for an active mic stream. The caller must have already enabled
    /// external playback on the core (`client.setExternalPlayback(true)` + `audioRestart()`) and
    /// started the MIC stream with `externalFeed: true`.
    func start(client: VoiceCatClient, micStreamId: UInt32, captureChannels: UInt32) {
        guard !isRunning else { return }
        self.client = client
        self.micStreamId = micStreamId
        ring.reset()

        // Enable the voice-processing I/O unit (AEC/NS/AGC) on the shared input+output unit.
        do {
            try engine.inputNode.setVoiceProcessingEnabled(true)
        } catch {
            logger.error("setVoiceProcessingEnabled failed: \(error.localizedDescription) — AEC unavailable")
        }

        // ── Playback: source node pulls mixed PCM from the ring through the VPIO output. ──
        let ring = self.ring
        let scratch = self.renderScratch
        let scratchFrames = self.renderScratchFrames
        let src = AVAudioSourceNode(format: outFormat) { _, _, frameCount, ablPtr in
            let frames = Int(frameCount)
            let abl = UnsafeMutableAudioBufferListPointer(ablPtr)
            let n = min(frames, scratchFrames)
            let got = ring.read(into: scratch, count: n * 2) / 2  // interleaved stereo → frames
            // Deinterleave int16 → Float32 per channel; silence-fill any underrun tail.
            let scale: Float = 1.0 / 32768.0
            for ch in 0..<abl.count {
                guard let base = abl[ch].mData?.assumingMemoryBound(to: Float.self) else { continue }
                for i in 0..<frames {
                    if i < got {
                        let s = scratch[i * 2 + min(ch, 1)]
                        base[i] = Float(s) * scale
                    } else {
                        base[i] = 0
                    }
                }
            }
            return noErr
        }
        sourceNode = src
        engine.attach(src)
        engine.connect(src, to: engine.mainMixerNode, format: outFormat)

        // ── Mic: tap the VPIO input node, convert to 48 kHz int16, feed the core. ──
        let inFormat = engine.inputNode.outputFormat(forBus: 0)
        let targetCh = max(1, min(2, captureChannels))
        let target = AVAudioFormat(commonFormat: .pcmFormatInt16, sampleRate: 48000,
                                   channels: AVAudioChannelCount(targetCh), interleaved: true)
        micTargetFormat = target
        micConverter = (target != nil && inFormat.sampleRate > 0)
            ? AVAudioConverter(from: inFormat, to: target!) : nil
        if micConverter == nil {
            logger.error("mic converter unavailable (in=\(inFormat)) — mic will not transmit")
        }

        let c = client
        let sid = micStreamId
        let converter = micConverter
        let tgt = micTargetFormat
        engine.inputNode.installTap(onBus: 0, bufferSize: 960, format: inFormat) { buffer, _ in
            guard let converter, let tgt else { return }
            // Convert this tap buffer to 48 kHz int16. Output capacity scaled for any upsample.
            let ratio = tgt.sampleRate / buffer.format.sampleRate
            let outCap = AVAudioFrameCount(Double(buffer.frameLength) * ratio + 16)
            guard let outBuf = AVAudioPCMBuffer(pcmFormat: tgt, frameCapacity: outCap) else { return }
            var fed = false
            let status = converter.convert(to: outBuf, error: nil) { _, outStatus in
                if fed { outStatus.pointee = .noDataNow; return nil }
                fed = true
                outStatus.pointee = .haveData
                return buffer
            }
            guard status != .error, outBuf.frameLength > 0,
                  let chData = outBuf.int16ChannelData else { return }
            let spc = Int(outBuf.frameLength)
            // int16 interleaved → channelData[0] is the interleaved buffer for interleaved formats.
            c.feedPcm(streamId: sid, pcm: chData[0], samplesPerChannel: spc, channels: targetCh)
        }

        // ── Wire the core's mixed-output sink into the ring (C function pointer, no captures). ──
        let ringPtr = Unmanaged.passUnretained(self.ring).toOpaque()
        client.setMixedOutputSink({ user, pcm, spc, ch, _ in
            guard let user, let pcm else { return }
            let ring = Unmanaged<PCMRing>.fromOpaque(user).takeUnretainedValue()
            ring.write(pcm, count: spc * Int(ch))
        }, user: ringPtr)

        engine.prepare()
        do {
            try engine.start()
            isRunning = true
            // Diagnostics: capture the negotiated graph formats and the live output route so a
            // silent-playback report can be triaged (format/rate mismatch vs. routing vs. the
            // core not delivering PCM — see the ring stats logged in teardown()).
            let outFmt = engine.outputNode.outputFormat(forBus: 0)
            let mixFmt = engine.mainMixerNode.outputFormat(forBus: 0)
            let route = AVAudioSession.sharedInstance().currentRoute.outputs
                .map { "\($0.portName)[\($0.portType.rawValue)]" }.joined(separator: ", ")
            logger.info("""
                VPIO engine started — inFormat=\(inFormat), captureCh=\(targetCh), \
                outputNode=\(outFmt), mainMixer=\(mixFmt), outputRoute=[\(route)]
                """)
        } catch {
            logger.error("VPIO engine start failed: \(error.localizedDescription)")
            teardown()
        }
    }

    /// Stop the VPIO engine. The caller is responsible for restoring the core's hardware playback
    /// afterwards (`client.setExternalPlayback(false)` + `audioRestart()`).
    func stop() {
        guard isRunning else { return }
        teardown()
        logger.info("VPIO engine stopped")
    }

    private func teardown() {
        client?.setMixedOutputSink(nil, user: nil)
        engine.inputNode.removeTap(onBus: 0)
        if engine.isRunning { engine.stop() }
        // Diagnostics (threads now quiesced): how much mixed PCM the core delivered into the ring
        // vs. how much the render thread consumed. written==0 ⇒ the core never delivered (Bug 1
        // core/lifecycle path); written>0 with no audible output ⇒ the AVAudioEngine output graph.
        logger.info("VPIO ring stats — written=\(self.ring.debugTotalWritten) read=\(self.ring.debugTotalRead) samples")
        try? engine.inputNode.setVoiceProcessingEnabled(false)
        if let src = sourceNode {
            engine.detach(src)
            sourceNode = nil
        }
        micConverter = nil
        micTargetFormat = nil
        ring.reset()
        isRunning = false
    }
}