package app

import (
	"context"
	"errors"
	"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/output"
	"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"`
	Queue            output.QueueStats `json:"queue"`
	RuntimeIndicator RuntimeIndicator  `json:"runtimeIndicator"`
	RuntimeAlert     string            `json:"runtimeAlert,omitempty"`
}

type RuntimeIndicator string

const (
	RuntimeIndicatorNormal        RuntimeIndicator = "normal"
	RuntimeIndicatorDegraded      RuntimeIndicator = "degraded"
	RuntimeIndicatorQueueCritical RuntimeIndicator = "queueCritical"
)

// 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
	frameQueue    *output.FrameQueue

	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,
		frameQueue:    output.NewFrameQueue(cfg.Runtime.FrameQueueCapacity),
	}
}

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 > 10 {
			return fmt.Errorf("outputDrive out of range (0-10)")
		}
	}
	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)

	queue := e.frameQueue.Stats()
	lateBuffers := e.lateBuffers.Load()
	ri := runtimeIndicator(queue.Health, lateBuffers)
	return EngineStats{
		State:            state.String(),
		ChunksProduced:   e.chunksProduced.Load(),
		TotalSamples:     e.totalSamples.Load(),
		Underruns:        e.underruns.Load(),
		LateBuffers:      lateBuffers,
		LastError:        errVal,
		UptimeSeconds:    uptime,
		MaxCycleMs:       durationMs(e.maxCycleNs.Load()),
		MaxGenerateMs:    durationMs(e.maxGenerateNs.Load()),
		MaxUpsampleMs:    durationMs(e.maxUpsampleNs.Load()),
		MaxWriteMs:       durationMs(e.maxWriteNs.Load()),
		Queue:            queue,
		RuntimeIndicator: ri,
		RuntimeAlert:     runtimeAlert(queue.Health, lateBuffers),
	}
}

func runtimeIndicator(queueHealth output.QueueHealth, lateBuffers uint64) RuntimeIndicator {
	switch {
	case queueHealth == output.QueueHealthCritical:
		return RuntimeIndicatorQueueCritical
	case queueHealth == output.QueueHealthLow || lateBuffers > 0:
		return RuntimeIndicatorDegraded
	default:
		return RuntimeIndicatorNormal
	}
}

func runtimeAlert(queueHealth output.QueueHealth, lateBuffers uint64) string {
	switch {
	case queueHealth == output.QueueHealthCritical:
		return "queue health critical"
	case lateBuffers > 0:
		return "late buffers"
	case queueHealth == output.QueueHealthLow:
		return "queue health low"
	default:
		return ""
	}
}

func (e *Engine) run(ctx context.Context) {
	e.wg.Add(1)
	go e.writerLoop(ctx)
	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)
		frame.GeneratedAt = t0
		t1 := time.Now()
		if e.upsampler != nil {
			frame = e.upsampler.Process(frame)
			frame.GeneratedAt = t0
		}
		t2 := time.Now()

		genDur := t1.Sub(t0)
		upDur := t2.Sub(t1)
		updateMaxDuration(&e.maxGenerateNs, genDur)
		updateMaxDuration(&e.maxUpsampleNs, upDur)

		enqueued := cloneFrame(frame)
		if enqueued == nil {
			e.lastError.Store("engine: frame clone failed")
			e.underruns.Add(1)
			continue
		}

		if err := e.frameQueue.Push(ctx, enqueued); err != nil {
			if ctx.Err() != nil {
				return
			}
			if errors.Is(err, output.ErrFrameQueueClosed) {
				return
			}
			e.lastError.Store(err.Error())
			e.underruns.Add(1)
			select {
			case <-time.After(e.chunkDuration):
			case <-ctx.Done():
				return
			}
			continue
		}
	}
}

func (e *Engine) writerLoop(ctx context.Context) {
	defer e.wg.Done()
	for {
		frame, err := e.frameQueue.Pop(ctx)
		if err != nil {
			if ctx.Err() != nil {
				return
			}
			if errors.Is(err, output.ErrFrameQueueClosed) {
				return
			}
			e.lastError.Store(err.Error())
			e.underruns.Add(1)
			continue
		}

		writeStart := time.Now()
		n, err := e.driver.Write(ctx, frame)
		writeDur := time.Since(writeStart)

		cycleDur := writeDur
		if !frame.GeneratedAt.IsZero() {
			cycleDur = time.Since(frame.GeneratedAt)
		}

		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 write=%s over=%s",
					cycleDur, e.chunkDuration, writeDur, cycleDur-e.chunkDuration)
			}
		}

		if err != nil {
			if ctx.Err() != nil {
				return
			}
			e.lastError.Store(err.Error())
			e.underruns.Add(1)
			select {
			case <-time.After(e.chunkDuration):
			case <-ctx.Done():
				return
			}
			continue
		}

		e.chunksProduced.Add(1)
		e.totalSamples.Add(uint64(n))
	}
}

func cloneFrame(src *output.CompositeFrame) *output.CompositeFrame {
	if src == nil {
		return nil
	}
	samples := make([]output.IQSample, len(src.Samples))
	copy(samples, src.Samples)
	return &output.CompositeFrame{
		Samples:      samples,
		SampleRateHz: src.SampleRateHz,
		Timestamp:    src.Timestamp,
		GeneratedAt:  src.GeneratedAt,
		Sequence:     src.Sequence,
	}
}