package app

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

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

func updateMaxDuration(dst *atomic.Uint64, d time.Duration) {
	v := uint64(d)
	for {
		cur := dst.Load()
		if v <= cur {
			return
		}
		if dst.CompareAndSwap(cur, v) {
			return
		}
	}
}

func durationMs(ns uint64) float64 {
	return float64(ns) / float64(time.Millisecond)
}

type EngineStats struct {
	State          string  `json:"state"`
	ChunksProduced uint64  `json:"chunksProduced"`
	TotalSamples   uint64  `json:"totalSamples"`
	Underruns      uint64  `json:"underruns"`
	LateBuffers    uint64  `json:"lateBuffers,omitempty"`
	LastError      string  `json:"lastError,omitempty"`
	UptimeSeconds  float64 `json:"uptimeSeconds"`
	MaxCycleMs     float64 `json:"maxCycleMs,omitempty"`
	MaxGenerateMs  float64 `json:"maxGenerateMs,omitempty"`
	MaxUpsampleMs  float64 `json:"maxUpsampleMs,omitempty"`
	MaxWriteMs     float64 `json:"maxWriteMs,omitempty"`
}

// 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
	lateBuffers    atomic.Uint64
	maxCycleNs     atomic.Uint64
	maxGenerateNs  atomic.Uint64
	maxUpsampleNs  atomic.Uint64
	maxWriteNs     atomic.Uint64
	lastError      atomic.Value // string

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

	// Live audio stream (optional)
	streamSrc *audio.StreamSource
}

// SetStreamSource configures a live audio stream as the audio source.
// Must be called before Start(). The StreamResampler is created internally
// to convert from the stream's sample rate to the DSP composite rate.
func (e *Engine) SetStreamSource(src *audio.StreamSource) {
	e.streamSrc = src
	compositeRate := float64(e.cfg.FM.CompositeRateHz)
	if compositeRate <= 0 {
		compositeRate = 228000
	}
	resampler := audio.NewStreamResampler(src, compositeRate)
	e.generator.SetExternalSource(resampler)
	log.Printf("engine: live audio stream — %d Hz → %.0f Hz (buffer %d frames)",
		src.SampleRate, compositeRate, src.Stats().Capacity)
}

// StreamSource returns the live audio stream source, or nil.
// Used by the control server for stats and HTTP audio ingest.
func (e *Engine) StreamSource() *audio.StreamSource {
	return e.streamSrc
}

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
		}
		// mpxGain scales the FM deviation to compensate for hardware
		// DAC/SDR scaling factors. DSP chain stays at logical 0-1.0 levels.
		if cfg.FM.MpxGain > 0 && cfg.FM.MpxGain != 1.0 {
			maxDev *= cfg.FM.MpxGain
		}
		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(),
		LateBuffers:    e.lateBuffers.Load(),
		LastError:      errVal,
		UptimeSeconds:  uptime,
		MaxCycleMs:     durationMs(e.maxCycleNs.Load()),
		MaxGenerateMs:  durationMs(e.maxGenerateNs.Load()),
		MaxUpsampleMs:  durationMs(e.maxUpsampleNs.Load()),
		MaxWriteMs:     durationMs(e.maxWriteNs.Load()),
	}
}

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)
			}
		}

		t0 := time.Now()
		frame := e.generator.GenerateFrame(e.chunkDuration)
		t1 := time.Now()
		if e.upsampler != nil {
			frame = e.upsampler.Process(frame)
		}
		t2 := time.Now()
		n, err := e.driver.Write(ctx, frame)
		t3 := time.Now()

		genDur := t1.Sub(t0)
		upDur := t2.Sub(t1)
		writeDur := t3.Sub(t2)
		cycleDur := t3.Sub(t0)

		updateMaxDuration(&e.maxGenerateNs, genDur)
		updateMaxDuration(&e.maxUpsampleNs, upDur)
		updateMaxDuration(&e.maxWriteNs, writeDur)
		updateMaxDuration(&e.maxCycleNs, cycleDur)

		if cycleDur > e.chunkDuration {
			late := e.lateBuffers.Add(1)
			if late <= 5 || late%20 == 0 {
				log.Printf("TX LATE: cycle=%s budget=%s gen=%s up=%s write=%s over=%s",
					cycleDur, e.chunkDuration, genDur, upDur, writeDur, cycleDur-e.chunkDuration)
			}
		}

		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))
	}
}