fm-rds-tx/internal/ingest/runtime.go

package ingest

import (
	"context"
	"sync"
	"sync/atomic"
	"time"

	"github.com/jan/fm-rds-tx/internal/audio"
)

type Runtime struct {
	sink      *audio.StreamSource
	source    Source
	started   atomic.Bool
	onTitle   func(string)
	prebuffer time.Duration

	ctx    context.Context
	cancel context.CancelFunc
	wg     sync.WaitGroup

	work            *frameBuffer
	workSampleRate  int
	prebufferFrames int
	gateOpen        bool
	seenChunk       bool
	lastDrainAt     time.Time
	drainAllowance  float64

	mu     sync.RWMutex
	active SourceDescriptor
	stats  RuntimeStats
}

type RuntimeOption func(*Runtime)

func WithStreamTitleHandler(handler func(string)) RuntimeOption {
	return func(r *Runtime) {
		r.onTitle = handler
	}
}

func WithPrebuffer(d time.Duration) RuntimeOption {
	return func(r *Runtime) {
		if d < 0 {
			d = 0
		}
		r.prebuffer = d
	}
}

func WithPrebufferMs(ms int) RuntimeOption {
	return func(r *Runtime) {
		if ms < 0 {
			ms = 0
		}
		r.prebuffer = time.Duration(ms) * time.Millisecond
	}
}

func NewRuntime(sink *audio.StreamSource, src Source, opts ...RuntimeOption) *Runtime {
	sampleRate := 44100
	capacity := 1024
	if sink != nil {
		if sink.SampleRate > 0 {
			sampleRate = sink.SampleRate
		}
		if sinkCap := sink.Stats().Capacity; sinkCap > 0 {
			capacity = sinkCap * 2
		}
	}
	r := &Runtime{
		sink:           sink,
		source:         src,
		work:           newFrameBuffer(capacity),
		workSampleRate: sampleRate,
		stats: RuntimeStats{
			State: "idle",
		},
	}
	for _, opt := range opts {
		if opt != nil {
			opt(r)
		}
	}
	if r.workSampleRate > 0 && r.prebuffer > 0 {
		r.prebufferFrames = int(r.prebuffer.Seconds() * float64(r.workSampleRate))
	}
	minCapacity := 256
	if r.prebufferFrames > 0 && minCapacity < r.prebufferFrames*2 {
		minCapacity = r.prebufferFrames * 2
	}
	if r.work == nil || r.work.capacity() < minCapacity {
		r.work = newFrameBuffer(minCapacity)
	}
	r.updateBufferedStatsLocked()
	return r
}

func (r *Runtime) Start(ctx context.Context) error {
	if r.sink == nil {
		r.mu.Lock()
		r.stats.State = "failed"
		r.mu.Unlock()
		return nil
	}
	if r.source == nil {
		r.mu.Lock()
		r.stats.State = "idle"
		r.mu.Unlock()
		return nil
	}
	if !r.started.CompareAndSwap(false, true) {
		return nil
	}

	r.ctx, r.cancel = context.WithCancel(ctx)
	r.mu.Lock()
	r.active = r.source.Descriptor()
	r.stats.State = "starting"
	r.stats.Prebuffering = false
	r.stats.WriteBlocked = false
	r.gateOpen = false
	r.seenChunk = false
	r.lastDrainAt = time.Now()
	r.drainAllowance = 0
	r.work.reset()
	r.updateBufferedStatsLocked()
	r.mu.Unlock()
	if err := r.source.Start(r.ctx); err != nil {
		r.started.Store(false)
		r.mu.Lock()
		r.stats.State = "failed"
		r.mu.Unlock()
		return err
	}

	r.wg.Add(1)
	go r.run()
	return nil
}

func (r *Runtime) Stop() error {
	if !r.started.CompareAndSwap(true, false) {
		return nil
	}
	if r.cancel != nil {
		r.cancel()
	}
	if r.source != nil {
		_ = r.source.Stop()
	}
	r.wg.Wait()
	r.mu.Lock()
	r.stats.State = "stopped"
	r.mu.Unlock()
	return nil
}

func (r *Runtime) run() {
	defer r.wg.Done()

	ch := r.source.Chunks()
	errCh := r.source.Errors()
	ticker := time.NewTicker(10 * time.Millisecond)
	defer ticker.Stop()
	var titleCh <-chan string
	if src, ok := r.source.(StreamTitleSource); ok && r.onTitle != nil {
		titleCh = src.StreamTitleUpdates()
	}
	for {
		select {
		case <-r.ctx.Done():
			return
		case err, ok := <-errCh:
			if !ok {
				errCh = nil
				continue
			}
			if err == nil {
				continue
			}
			r.mu.Lock()
			r.stats.State = "degraded"
			r.stats.Prebuffering = false
			r.mu.Unlock()
		case chunk, ok := <-ch:
			if !ok {
				r.mu.Lock()
				r.stats.State = "stopped"
				r.stats.Prebuffering = false
				r.mu.Unlock()
				return
			}
			r.handleChunk(chunk)
		case <-ticker.C:
			r.drainWorkingBuffer()
		case title, ok := <-titleCh:
			if !ok {
				titleCh = nil
				continue
			}
			r.onTitle(title)
		}
	}
}

func (r *Runtime) handleChunk(chunk PCMChunk) {
	r.mu.Lock()
	r.seenChunk = true

	// Propagate the actual decoded sample rate to the sink and pacer the
	// first time (or whenever) it differs from our working rate. This fixes
	// the two-part rate-mismatch bug that appears when a native decoder
	// (e.g. go-mp3) decodes a 48000 Hz stream while the StreamSource and
	// StreamResampler were initialised assuming 44100 Hz:
	//
	//  1. The pacer (pacedDrainLimitLocked) was draining at the wrong rate,
	//     causing the work buffer to overflow → glitches.
	//  2. The StreamResampler ratio (inputRate/outputRate) was computed from
	//     the stale sink.SampleRate, so every frame was played at the wrong
	//     pitch → audio too slow (44100/48000 ≈ 91.9 % speed).
	//
	// SetSampleRate writes atomically, so the StreamResampler's NextFrame()
	// picks up the corrected ratio without any additional locking.
	if chunk.SampleRateHz > 0 && chunk.SampleRateHz != r.workSampleRate {
		r.workSampleRate = chunk.SampleRateHz
		if r.sink != nil {
			r.sink.SetSampleRate(chunk.SampleRateHz)
		}
	}

	r.mu.Unlock()

	frames, err := ChunkToFrames(chunk)
	if err != nil {
		r.mu.Lock()
		r.stats.ConvertErrors++
		r.stats.State = "degraded"
		r.mu.Unlock()
		return
	}
	dropped := uint64(0)
	for _, frame := range frames {
		if !r.work.push(frame) {
			dropped++
		}
	}
	r.mu.Lock()
	if chunk.SampleRateHz > 0 {
		r.active.SampleRateHz = chunk.SampleRateHz
	}
	if chunk.Channels > 0 {
		r.active.Channels = chunk.Channels
	}
	r.stats.LastChunkAt = time.Now()
	r.stats.DroppedFrames += dropped
	if dropped > 0 {
		r.stats.State = "degraded"
	}
	r.updateBufferedStatsLocked()
	r.mu.Unlock()
	r.drainWorkingBuffer()
}

func (r *Runtime) drainWorkingBuffer() {
	r.mu.Lock()
	defer r.mu.Unlock()
	now := time.Now()
	if r.sink == nil {
		r.resetDrainPacerLocked(now)
		r.updateBufferedStatsLocked()
		return
	}
	bufferedFrames := r.work.available()
	if !r.gateOpen {
		switch {
		case bufferedFrames == 0:
			if r.stats.State == "degraded" {
				// Keep degraded visible until fresh audio recovers runtime.
			} else if !r.seenChunk {
				r.stats.State = "starting"
			} else if r.stats.State != "degraded" {
				r.stats.State = "running"
			}
			r.stats.Prebuffering = false
			r.stats.WriteBlocked = false
			r.resetDrainPacerLocked(now)
			r.updateBufferedStatsLocked()
			return
		case r.prebufferFrames > 0 && bufferedFrames < r.prebufferFrames:
			r.stats.State = "prebuffering"
			r.stats.Prebuffering = true
			r.stats.WriteBlocked = false
			r.resetDrainPacerLocked(now)
			r.updateBufferedStatsLocked()
			return
		default:
			r.gateOpen = true
			r.resetDrainPacerLocked(now)
		}
	}
	writeBlocked := false
	limit := r.pacedDrainLimitLocked(now, bufferedFrames)
	written := 0
	for written < limit && r.work.available() > 0 {
		frame, ok := r.work.peek()
		if !ok {
			break
		}
		if !r.sink.WriteFrame(frame) {
			writeBlocked = true
			break
		}
		r.work.pop()
		written++
	}
	if written > 0 {
		r.drainAllowance -= float64(written)
		if r.drainAllowance < 0 {
			r.drainAllowance = 0
		}
	}
	if r.work.available() == 0 && r.prebufferFrames > 0 {
		// Re-arm the gate after dry-out to rebuild margin before resuming.
		r.gateOpen = false
		r.resetDrainPacerLocked(now)
	}
	r.stats.Prebuffering = false
	r.stats.WriteBlocked = writeBlocked
	if writeBlocked {
		r.stats.State = "degraded"
	} else {
		r.stats.State = "running"
	}
	r.updateBufferedStatsLocked()
}

func (r *Runtime) pacedDrainLimitLocked(now time.Time, bufferedFrames int) int {
	if bufferedFrames <= 0 {
		return 0
	}
	// Use workSampleRate which is kept in sync with sink.SampleRate via
	// handleChunk. This ensures the pacer drains at the actual decoded rate
	// rather than the initial (potentially wrong) configured rate.
	rate := r.workSampleRate
	if r.sink != nil && r.sink.GetSampleRate() > 0 {
		rate = r.sink.GetSampleRate()
	}
	if rate <= 0 {
		return bufferedFrames
	}
	if !r.lastDrainAt.IsZero() {
		elapsed := now.Sub(r.lastDrainAt)
		if elapsed > 0 {
			r.drainAllowance += elapsed.Seconds() * float64(rate)
		}
	}
	r.lastDrainAt = now
	maxAllowance := maxInt(1, rate/5) // cap accumulated credit at 200 ms
	if r.drainAllowance > float64(maxAllowance) {
		r.drainAllowance = float64(maxAllowance)
	}
	limit := int(r.drainAllowance)
	if limit <= 0 {
		return 0
	}
	maxBurst := maxInt(1, rate/50) // max 20 ms worth of frames per drain call
	if limit > maxBurst {
		limit = maxBurst
	}
	sinkStats := r.sink.Stats()
	headroom := sinkStats.Capacity - sinkStats.Available
	if headroom < 0 {
		headroom = 0
	}
	if limit > headroom {
		limit = headroom
	}
	if limit > bufferedFrames {
		limit = bufferedFrames
	}
	return limit
}

func (r *Runtime) resetDrainPacerLocked(now time.Time) {
	r.lastDrainAt = now
	r.drainAllowance = 0
}

func maxInt(a, b int) int {
	if a > b {
		return a
	}
	return b
}

func (r *Runtime) updateBufferedStatsLocked() {
	available := r.work.available()
	capacity := r.work.capacity()
	buffered := 0.0
	if capacity > 0 {
		buffered = float64(available) / float64(capacity)
	}
	bufferedSeconds := 0.0
	if r.workSampleRate > 0 {
		bufferedSeconds = float64(available) / float64(r.workSampleRate)
	}
	r.stats.Buffered = buffered
	r.stats.BufferedSeconds = bufferedSeconds
}

func (r *Runtime) Stats() Stats {
	r.mu.RLock()
	runtimeStats := r.stats
	active := r.active
	r.mu.RUnlock()

	sourceStats := SourceStats{}
	if r.source != nil {
		sourceStats = r.source.Stats()
	}
	if sourceStats.BufferedSeconds < runtimeStats.BufferedSeconds {
		sourceStats.BufferedSeconds = runtimeStats.BufferedSeconds
	}
	return Stats{
		Active:  active,
		Source:  sourceStats,
		Runtime: runtimeStats,
	}
}

type frameBuffer struct {
	frames []audio.Frame
	head   int
	len    int
}

func newFrameBuffer(capacity int) *frameBuffer {
	if capacity < 1 {
		capacity = 1
	}
	return &frameBuffer{frames: make([]audio.Frame, capacity)}
}

func (b *frameBuffer) capacity() int {
	return len(b.frames)
}

func (b *frameBuffer) available() int {
	return b.len
}

func (b *frameBuffer) reset() {
	b.head = 0
	b.len = 0
}

func (b *frameBuffer) push(frame audio.Frame) bool {
	if b.len >= len(b.frames) {
		return false
	}
	idx := (b.head + b.len) % len(b.frames)
	b.frames[idx] = frame
	b.len++
	return true
}

func (b *frameBuffer) peek() (audio.Frame, bool) {
	if b.len == 0 {
		return audio.Frame{}, false
	}
	return b.frames[b.head], true
}

func (b *frameBuffer) pop() (audio.Frame, bool) {
	if b.len == 0 {
		return audio.Frame{}, false
	}
	frame := b.frames[b.head]
	b.head = (b.head + 1) % len(b.frames)
	b.len--
	return frame, true
}