go-mxl-pattern-generator/internal/audio/runner.go

package audio

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"log"

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

func Run(
	ctx context.Context,
	inst *mxl.Instance,
	cfg Config,
) (runErr error) {
	flowJSON, err := json.Marshal(cfg.Definition)
	if err != nil {
		return fmt.Errorf("marshal audio flow definition: %w", err)
	}

	writer, isCreated, err := inst.NewWriter(string(flowJSON))
	if err != nil {
		return fmt.Errorf("create audio writer: %w", err)
	}
	defer func() {
		if err := writer.Close(); err != nil {
			runErr = errors.Join(
				runErr,
				fmt.Errorf("close audio writer: %w", err),
			)
		}
	}()
	if !isCreated {
		log.Printf("reusing existing audio flow: %s", cfg.ID())
	}

	writerCfg := writer.Config()
	if writerCfg.Common.Format != mxl.FormatAudio {
		return fmt.Errorf(
			"audio writer has format %s, want audio",
			writerCfg.Common.Format,
		)
	}
	if writerCfg.Continuous.ChannelCount != uint32(cfg.Channels()) {
		return fmt.Errorf(
			"audio writer has %d channels, configured generator expects %d",
			writerCfg.Continuous.ChannelCount,
			cfg.Channels(),
		)
	}

	rate := writerCfg.Common.GrainRate
	if rate != cfg.Rate() {
		return fmt.Errorf(
			"audio writer has sample rate %d/%d, configured generator expects %d/%d",
			rate.Num,
			rate.Den,
			cfg.Rate().Num,
			cfg.Rate().Den,
		)
	}

	const baseFrequency = 1000.0

	gen, err := NewSineGenerator(cfg, baseFrequency)
	if err != nil {
		return fmt.Errorf("initialize audio generator: %w", err)
	}

	batch := batchSize(rate)
	maxBatch, err := writer.GetMaxWriteLengthSamples()
	if err != nil {
		return fmt.Errorf("get maximum audio write length: %w", err)
	}
	if maxBatch == 0 {
		return fmt.Errorf("audio writer reported a maximum write length of zero samples")
	}
	if batch > maxBatch {
		batch = maxBatch
	}
	index := mxl.CurrentIndex(rate)
	if index < batch-1 {
		return fmt.Errorf("current audio index %d is too small for batch size %d", index, batch)
	}

	log.Printf(
		"writing audio flow sampleRate=%d/%d channels=%d batch=%d starting at idx=%d",
		rate.Num,
		rate.Den,
		cfg.Channels(),
		batch,
		index,
	)

	var samplesWritten uint64

	for {
		select {
		case <-ctx.Done():
			log.Printf("stopping audio after %d samples", samplesWritten)
			return nil
		default:
		}

		access, err := writer.OpenSamples(index, int(batch))
		if err != nil {
			return fmt.Errorf(
				"open %d audio samples at index %d: %w",
				batch,
				index,
				err,
			)
		}

		firstSample := index - batch + 1
		for channel := uint64(0); channel < access.ChannelCount; channel++ {
			first, second, err := access.ChannelFragments(channel)
			if err != nil {
				return cancelSamples(
					access,
					fmt.Errorf(
						"get fragments for audio channel %d at index %d: %w",
						channel,
						index,
						err,
					),
				)
			}

			if err := gen.Generate(
				uint(channel),
				firstSample,
				first,
				second,
			); err != nil {
				return cancelSamples(
					access, fmt.Errorf(
						"generate audio channel %d at index %d: %w",
						channel,
						index,
						err,
					),
				)
			}
		}

		if err := access.Commit(); err != nil {
			return fmt.Errorf(
				"commit %d audio samples at index %d: %w",
				batch,
				index,
				err,
			)
		}

		samplesWritten += batch
		index += batch
		mxl.SleepNs(mxl.NsUntilIndex(index, rate))
	}
}

func cancelSamples(
	access *mxl.SamplesWriteAccess,
	cause error,
) error {
	if err := access.Cancel(); err != nil {
		return errors.Join(
			cause,
			fmt.Errorf("cancel audio samples: %w", err),
		)
	}
	return cause
}

func batchSize(rate mxl.Rational) uint64 {
	if rate.Num <= 0 || rate.Den <= 0 {
		return 1
	}

	samples := rate.Num / (100 * rate.Den)
	if samples < 1 {
		return 1
	}
	return uint64(samples)
}