package mxladapter

import (
	"context"
	"errors"
	"fmt"
	"math/bits"
	"time"

	"mxl-player/internal/playback"
	"mxl-player/internal/source"

	mxl "github.com/qvest-digital/go-mxl/mxl"
)

const (
	DefaultAudioReadTimeout      = 20 * time.Millisecond
	DefaultAudioBatchDuration    = 10 * time.Millisecond
	DefaultAudioUnavailableAfter = 2 * time.Second
	DefaultAudioTemporaryDelay   = 10 * time.Millisecond
)

var ErrInvalidAudioBatch = errors.New("invalid audio batch configuration")

type AudioFactory struct {
	ReadTimeout      time.Duration
	BatchDuration    time.Duration
	UnavailableAfter time.Duration
}

type localAudioSource interface {
	ReadAudioOnceCtx(context.Context, uint64, time.Duration) (source.AudioFrame, error)
	Rate() mxl.Rational
	Channels() uint64
	Close() error
}

type audioReader struct {
	source           localAudioSource
	readTimeout      time.Duration
	batch            uint64
	channels         uint64
	rateNumerator    int64
	rateDenominator  int64
	unavailableAfter time.Duration
	retryDelay       time.Duration
	now              func() time.Time
	wait             temporaryWaitFunc
}

var _ playback.AudioReaderFactory = AudioFactory{}
var _ playback.AudioReader = (*audioReader)(nil)

func audioBatchSize(
	rateNumerator int64,
	rateDenominator int64,
	duration time.Duration,
) (uint64, error) {
	if rateNumerator <= 0 || rateDenominator <= 0 || duration <= 0 {
		return 0, fmt.Errorf(
			"%w: rate=%d/%d duration=%s",
			ErrInvalidAudioBatch,
			rateNumerator,
			rateDenominator,
			duration,
		)
	}

	denominator := uint64(rateDenominator)
	seconds := uint64(time.Second)
	if denominator > ^uint64(0)/seconds {
		return 0, fmt.Errorf("%w: denominator overflow", ErrInvalidAudioBatch)
	}
	denominator *= seconds

	high, low := bits.Mul64(uint64(rateNumerator), uint64(duration))
	if high >= denominator {
		return 0, fmt.Errorf("%w: sample count overflow", ErrInvalidAudioBatch)
	}
	batch, _ := bits.Div64(high, low, denominator)
	if batch == 0 {
		batch = 1
	}
	return batch, nil
}

func (f AudioFactory) OpenAudio(
	ctx context.Context,
	config playback.FeedConfig,
) (playback.AudioReader, error) {
	if err := ctx.Err(); err != nil {
		return nil, err
	}
	if err := config.Validate(); err != nil {
		return nil, &source.SourceError{
			Op:   "validate audio feed",
			Kind: source.ErrorKindInvalidConfig,
			Err:  err,
		}
	}
	if !config.IsConfigured() {
		return nil, &source.SourceError{
			Op:   "validate audio feed",
			Kind: source.ErrorKindInvalidConfig,
			Err:  errors.New("audio feed is not configured"),
		}
	}

	src, err := source.OpenAudio(config.Domain, config.UUID)
	if err != nil {
		return nil, fmt.Errorf("open local MXL audio: %w", err)
	}
	closeOnError := true
	defer func() {
		if closeOnError {
			_ = src.Close()
		}
	}()

	if err := ctx.Err(); err != nil {
		return nil, err
	}

	readTimeout := f.ReadTimeout
	if readTimeout <= 0 {
		readTimeout = DefaultAudioReadTimeout
	}
	batchDuration := f.BatchDuration
	if batchDuration <= 0 {
		batchDuration = DefaultAudioBatchDuration
	}
	unavailableAfter := f.UnavailableAfter
	if unavailableAfter <= 0 {
		unavailableAfter = DefaultAudioUnavailableAfter
	}

	rate := src.Rate()
	batch, err := audioBatchSize(rate.Num, rate.Den, batchDuration)
	if err != nil {
		return nil, &source.SourceError{
			Op:   "calculate audio batch",
			Kind: source.ErrorKindInvalidConfig,
			Err:  err,
		}
	}

	reader := &audioReader{
		source:           src,
		readTimeout:      readTimeout,
		batch:            batch,
		channels:         src.Channels(),
		rateNumerator:    rate.Num,
		rateDenominator:  rate.Den,
		unavailableAfter: unavailableAfter,
		retryDelay:       DefaultAudioTemporaryDelay,
		now:              time.Now,
		wait:             waitForTemporaryRetry,
	}
	closeOnError = false
	return reader, nil
}

func (r *audioReader) ReadAudio(ctx context.Context) (playback.AudioFrame, error) {
	var unavailableSince time.Time

	for {
		frame, err := r.source.ReadAudioOnceCtx(ctx, r.batch, r.readTimeout)
		if err == nil {
			return playback.AudioFrame{
				Index:                 frame.Index,
				SampleCount:           frame.SampleCount,
				Channels:              frame.Channels,
				Label:                 frame.Label,
				SampleRateNumerator:   r.rateNumerator,
				SampleRateDenominator: r.rateDenominator,
				Samples:               frame.Samples,
			}, nil
		}
		if ctx.Err() != nil {
			return playback.AudioFrame{}, ctx.Err()
		}
		if source.KindOf(err) != source.ErrorKindTemporary {
			return playback.AudioFrame{}, err
		}

		now := r.now()
		if unavailableSince.IsZero() {
			unavailableSince = now
		} else if now.Sub(unavailableSince) >= r.unavailableAfter {
			return playback.AudioFrame{}, &source.SourceError{
				Op:   "read local MXL audio",
				Kind: source.ErrorKindUnavailable,
				Err: fmt.Errorf(
					"no audio data for %s: %w",
					r.unavailableAfter,
					err,
				),
			}
		}

		if err := r.wait(ctx, r.retryDelay); err != nil {
			if ctx.Err() != nil {
				return playback.AudioFrame{}, ctx.Err()
			}
			return playback.AudioFrame{}, err
		}
	}
}

func (r *audioReader) Close() error {
	return r.source.Close()
}