fm-rds-tx/internal/app/engine.go

package app

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

	cfgpkg "github.com/jan/fm-rds-tx/internal/config"
	"github.com/jan/fm-rds-tx/internal/dsp"
	offpkg "github.com/jan/fm-rds-tx/internal/offline"
	"github.com/jan/fm-rds-tx/internal/platform"
)

type EngineState int

const (
	EngineIdle EngineState = iota
	EngineRunning
	EngineStopping
)

func (s EngineState) String() string {
	switch s {
	case EngineIdle:
		return "idle"
	case EngineRunning:
		return "running"
	case EngineStopping:
		return "stopping"
	default:
		return "unknown"
	}
}

type EngineStats struct {
	State          string  `json:"state"`
	ChunksProduced uint64  `json:"chunksProduced"`
	TotalSamples   uint64  `json:"totalSamples"`
	Underruns      uint64  `json:"underruns"`
	LastError      string  `json:"lastError,omitempty"`
	UptimeSeconds  float64 `json:"uptimeSeconds"`
}

// Engine is the continuous TX loop. It generates composite IQ in chunks,
// resamples to device rate, and pushes to hardware in a tight loop.
// The hardware buffer_push call is blocking — it returns when the hardware
// has consumed the previous buffer and is ready for the next one.
// This naturally paces the loop to real-time without a ticker.
type Engine struct {
	cfg           cfgpkg.Config
	driver        platform.SoapyDriver
	generator     *offpkg.Generator
	upsampler     *dsp.FMUpsampler // nil = same-rate, non-nil = split-rate
	chunkDuration time.Duration
	deviceRate    float64

	mu        sync.Mutex
	state     EngineState
	cancel    context.CancelFunc
	startedAt time.Time
	wg        sync.WaitGroup

	chunksProduced atomic.Uint64
	totalSamples   atomic.Uint64
	underruns      atomic.Uint64
	lastError      atomic.Value // string

	// Live config: pending frequency change, applied between chunks
	pendingFreq atomic.Pointer[float64]
}

func NewEngine(cfg cfgpkg.Config, driver platform.SoapyDriver) *Engine {
	deviceRate := cfg.EffectiveDeviceRate()
	compositeRate := float64(cfg.FM.CompositeRateHz)
	if compositeRate <= 0 {
		compositeRate = 228000
	}

	var upsampler *dsp.FMUpsampler

	if deviceRate > compositeRate*1.001 {
		// Split-rate: DSP chain runs at compositeRate (typ. 228 kHz),
		// FMUpsampler handles FM modulation + interpolation to deviceRate.
		// This halves CPU load compared to running all DSP at deviceRate.
		cfg.FM.FMModulationEnabled = false
		maxDev := cfg.FM.MaxDeviationHz
		if maxDev <= 0 {
			maxDev = 75000
		}
		upsampler = dsp.NewFMUpsampler(compositeRate, deviceRate, maxDev)
		log.Printf("engine: split-rate mode — DSP@%.0fHz → upsample@%.0fHz (ratio %.2f)",
			compositeRate, deviceRate, deviceRate/compositeRate)
	} else {
		// Same-rate: entire DSP chain runs at deviceRate.
		// Used when deviceRate ≈ compositeRate (e.g. LimeSDR at 228 kHz).
		if deviceRate > 0 {
			cfg.FM.CompositeRateHz = int(deviceRate)
		}
		cfg.FM.FMModulationEnabled = true
		log.Printf("engine: same-rate mode — DSP@%dHz", cfg.FM.CompositeRateHz)
	}

	return &Engine{
		cfg:           cfg,
		driver:        driver,
		generator:     offpkg.NewGenerator(cfg),
		upsampler:     upsampler,
		chunkDuration: 50 * time.Millisecond,
		deviceRate:    deviceRate,
		state:         EngineIdle,
	}
}

func (e *Engine) SetChunkDuration(d time.Duration) {
	e.chunkDuration = d
}

// LiveConfigUpdate carries hot-reloadable parameters from the control API.
// nil pointers mean "no change". Validated before applying.
type LiveConfigUpdate struct {
	FrequencyMHz   *float64
	OutputDrive    *float64
	StereoEnabled  *bool
	PilotLevel     *float64
	RDSInjection   *float64
	RDSEnabled     *bool
	LimiterEnabled *bool
	LimiterCeiling *float64
	PS             *string
	RadioText      *string
}

// UpdateConfig applies live parameter changes without restarting the engine.
// DSP params take effect at the next chunk boundary (~50ms max).
// Frequency changes are applied between chunks via driver.Tune().
// RDS text updates are applied at the next RDS group boundary (~88ms).
func (e *Engine) UpdateConfig(u LiveConfigUpdate) error {
	// --- Validate ---
	if u.FrequencyMHz != nil {
		if *u.FrequencyMHz < 65 || *u.FrequencyMHz > 110 {
			return fmt.Errorf("frequencyMHz out of range (65-110)")
		}
	}
	if u.OutputDrive != nil {
		if *u.OutputDrive < 0 || *u.OutputDrive > 3 {
			return fmt.Errorf("outputDrive out of range (0-3)")
		}
	}
	if u.PilotLevel != nil {
		if *u.PilotLevel < 0 || *u.PilotLevel > 0.2 {
			return fmt.Errorf("pilotLevel out of range (0-0.2)")
		}
	}
	if u.RDSInjection != nil {
		if *u.RDSInjection < 0 || *u.RDSInjection > 0.15 {
			return fmt.Errorf("rdsInjection out of range (0-0.15)")
		}
	}
	if u.LimiterCeiling != nil {
		if *u.LimiterCeiling < 0 || *u.LimiterCeiling > 2 {
			return fmt.Errorf("limiterCeiling out of range (0-2)")
		}
	}

	// --- Frequency: store for run loop to apply via driver.Tune() ---
	if u.FrequencyMHz != nil {
		freqHz := *u.FrequencyMHz * 1e6
		e.pendingFreq.Store(&freqHz)
	}

	// --- RDS text: forward to encoder atomics ---
	if u.PS != nil || u.RadioText != nil {
		if enc := e.generator.RDSEncoder(); enc != nil {
			ps, rt := "", ""
			if u.PS != nil { ps = *u.PS }
			if u.RadioText != nil { rt = *u.RadioText }
			enc.UpdateText(ps, rt)
		}
	}

	// --- DSP params: build new LiveParams from current + patch ---
	// Read current, apply deltas, store new
	current := e.generator.CurrentLiveParams()
	next := current // copy

	if u.OutputDrive != nil { next.OutputDrive = *u.OutputDrive }
	if u.StereoEnabled != nil { next.StereoEnabled = *u.StereoEnabled }
	if u.PilotLevel != nil { next.PilotLevel = *u.PilotLevel }
	if u.RDSInjection != nil { next.RDSInjection = *u.RDSInjection }
	if u.RDSEnabled != nil { next.RDSEnabled = *u.RDSEnabled }
	if u.LimiterEnabled != nil { next.LimiterEnabled = *u.LimiterEnabled }
	if u.LimiterCeiling != nil { next.LimiterCeiling = *u.LimiterCeiling }

	e.generator.UpdateLive(next)
	return nil
}

func (e *Engine) Start(ctx context.Context) error {
	e.mu.Lock()
	if e.state != EngineIdle {
		e.mu.Unlock()
		return fmt.Errorf("engine already in state %s", e.state)
	}

	if err := e.driver.Start(ctx); err != nil {
		e.mu.Unlock()
		return fmt.Errorf("driver start: %w", err)
	}

	runCtx, cancel := context.WithCancel(ctx)
	e.cancel = cancel
	e.state = EngineRunning
	e.startedAt = time.Now()
	e.wg.Add(1)
	e.mu.Unlock()

	go e.run(runCtx)
	return nil
}

func (e *Engine) Stop(ctx context.Context) error {
	e.mu.Lock()
	if e.state != EngineRunning {
		e.mu.Unlock()
		return nil
	}
	e.state = EngineStopping
	e.cancel()
	e.mu.Unlock()

	// Wait for run() goroutine to exit — deterministic, no guessing
	e.wg.Wait()

	if err := e.driver.Flush(ctx); err != nil {
		return err
	}
	if err := e.driver.Stop(ctx); err != nil {
		return err
	}

	e.mu.Lock()
	e.state = EngineIdle
	e.mu.Unlock()
	return nil
}

func (e *Engine) Stats() EngineStats {
	e.mu.Lock()
	state := e.state
	startedAt := e.startedAt
	e.mu.Unlock()

	var uptime float64
	if state == EngineRunning {
		uptime = time.Since(startedAt).Seconds()
	}
	errVal, _ := e.lastError.Load().(string)

	return EngineStats{
		State:          state.String(),
		ChunksProduced: e.chunksProduced.Load(),
		TotalSamples:   e.totalSamples.Load(),
		Underruns:      e.underruns.Load(),
		LastError:      errVal,
		UptimeSeconds:  uptime,
	}
}

func (e *Engine) run(ctx context.Context) {
	defer e.wg.Done()
	for {
		if ctx.Err() != nil {
			return
		}

		// Apply pending frequency change between chunks
		if pf := e.pendingFreq.Swap(nil); pf != nil {
			if err := e.driver.Tune(ctx, *pf); err != nil {
				e.lastError.Store(fmt.Sprintf("tune: %v", err))
			} else {
				log.Printf("engine: tuned to %.3f MHz", *pf/1e6)
			}
		}

		frame := e.generator.GenerateFrame(e.chunkDuration)
		if e.upsampler != nil {
			frame = e.upsampler.Process(frame)
		}
		n, err := e.driver.Write(ctx, frame)
		if err != nil {
			if ctx.Err() != nil { return }
			e.lastError.Store(err.Error())
			e.underruns.Add(1)
			// Back off to avoid pegging CPU on persistent errors
			select {
			case <-time.After(e.chunkDuration):
			case <-ctx.Done():
				return
			}
			continue
		}
		e.chunksProduced.Add(1)
		e.totalSamples.Add(uint64(n))
	}
}