package sfx

import (
	"encoding/binary"
	"fmt"
	"io"
	"math"
)

// WriteWAV encodes samples ([-1,1] floats) as a 16-bit mono PCM WAV.
func WriteWAV(w io.Writer, samples []float64, sampleRate int) error {
	dataLen := len(samples) * 2
	var hdr [44]byte
	copy(hdr[0:4], "RIFF")
	binary.LittleEndian.PutUint32(hdr[4:8], uint32(36+dataLen))
	copy(hdr[8:12], "WAVE")
	copy(hdr[12:16], "fmt ")
	binary.LittleEndian.PutUint32(hdr[16:20], 16)                   // fmt chunk size
	binary.LittleEndian.PutUint16(hdr[20:22], 1)                    // PCM
	binary.LittleEndian.PutUint16(hdr[22:24], 1)                    // mono
	binary.LittleEndian.PutUint32(hdr[24:28], uint32(sampleRate))   // sample rate
	binary.LittleEndian.PutUint32(hdr[28:32], uint32(sampleRate*2)) // byte rate
	binary.LittleEndian.PutUint16(hdr[32:34], 2)                    // block align
	binary.LittleEndian.PutUint16(hdr[34:36], 16)                   // bits per sample
	copy(hdr[36:40], "data")
	binary.LittleEndian.PutUint32(hdr[40:44], uint32(dataLen))
	if _, err := w.Write(hdr[:]); err != nil {
		return err
	}
	buf := make([]byte, 2*len(samples))
	for i, s := range samples {
		v := int16(math.Round(s * 32767))
		binary.LittleEndian.PutUint16(buf[i*2:], uint16(v))
	}
	_, err := w.Write(buf)
	return err
}

// ReadWAVHeader sanity-parses a WAV header (used in tests and info).
func ReadWAVHeader(r io.Reader) (sampleRate, bits, channels, dataBytes int, err error) {
	var hdr [44]byte
	if _, err = io.ReadFull(r, hdr[:]); err != nil {
		return
	}
	if string(hdr[0:4]) != "RIFF" || string(hdr[8:12]) != "WAVE" {
		err = fmt.Errorf("not a WAV file")
		return
	}
	channels = int(binary.LittleEndian.Uint16(hdr[22:24]))
	sampleRate = int(binary.LittleEndian.Uint32(hdr[24:28]))
	bits = int(binary.LittleEndian.Uint16(hdr[34:36]))
	dataBytes = int(binary.LittleEndian.Uint32(hdr[40:44]))
	return
}