package transcode

import (
    "context"

    "github.com/gopxl/beep"
    "github.com/gopxl/beep/effects"
)

func buildPipeline(streamer beep.Streamer, format beep.Format, opt Options) (beep.Streamer, beep.Format) {
    out := streamer
    if opt.SampleRate > 0 && format.SampleRate != beep.SampleRate(opt.SampleRate) {
        out = beep.Resample(4, format.SampleRate, beep.SampleRate(opt.SampleRate), out)
        format.SampleRate = beep.SampleRate(opt.SampleRate)
    }
    if opt.Channels == 1 {
        out = effects.Mono(out)
        format.NumChannels = 1
    }
    return out, format
}

func drainSamples(ctx context.Context, s beep.Streamer) ([]float64, error) {
    buf := make([][2]float64, 4096)
    var samples []float64
    for {
        if err := ctx.Err(); err != nil {
            return nil, err
        }
        n, ok := s.Stream(buf)
        if !ok {
            if err := s.Err(); err != nil {
                return nil, err
            }
            break
        }
        for i := 0; i < n; i++ {
            samples = append(samples, buf[i][0])
        }
    }
    return samples, nil
}