package sine

import (
	"bytes"
	"encoding/binary"
	"math"
	"time"
)

type SineStream struct {
	Frequency  float64
	Samplerate int
	State      uint64
	Beep       bool
	Timestamp  time.Time
}

func makeSample(channelValues ...float64) (ret []byte) {
	// target format: s16le
	buf := new(bytes.Buffer)
	for _, value := range channelValues {
		intValue := int16(value * math.MaxInt16)
		binary.Write(buf, binary.LittleEndian, intValue)
	}
	return buf.Bytes()
}

func (stream *SineStream) Read(data []byte) (n int, err error) {
	n = 0
	for (len(data) - n) >= 4 { // at least 2 bytes per channel need to be available
		var sampleValue float64
		if stream.Beep && stream.State%uint64(stream.Samplerate) > uint64(float64(stream.Samplerate)*0.15) {
			sampleValue = 0
		} else {
			sampleValue = math.Sin(stream.Frequency * 2. * math.Pi * (float64(stream.State) / float64(stream.Samplerate)))
		}

		b := makeSample(sampleValue, sampleValue)
		copy(data[n:], b)

		n += len(b)

		targetTime := stream.Timestamp.
			Add(time.Duration(float64(time.Second) * float64(stream.State) / float64(stream.Samplerate)))
		delay := targetTime.Sub(time.Now())
		/*log.Println("state", stream.State, "value", sampleValue, "time", targetTime, "delay", delay)
		time.Sleep(time.Second)*/
		if delay > 0 {
			<-time.After(delay)
		}

		/*if stream.State%uint64(stream.Samplerate) == 0 {
			log.Println("state", stream.State, "value", sampleValue, "time", targetTime, "delay", delay)
		}*/

		stream.State++
	}

	return
}