// Copyright 2015 Hajime Hoshi
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

// +build js

package audio

import (
	"io"
	"io/ioutil"

	"github.com/gopherjs/gopherjs/js"
)

var context *js.Object

type audioProcessor struct {
	src        io.ReadSeeker
	sampleRate int
	position   float64
}

func toLR(data []byte) ([]int16, []int16) {
	l := make([]int16, len(data)/4)
	r := make([]int16, len(data)/4)
	for i := 0; i < len(data)/4; i++ {
		l[i] = int16(data[4*i]) | int16(data[4*i+1])<<8
		r[i] = int16(data[4*i+2]) | int16(data[4*i+3])<<8
	}
	return l, r
}

func (a *audioProcessor) play() error {
	// TODO: Reading all data at once is temporary implemntation. Treat this as stream.
	buf, err := ioutil.ReadAll(a.src)
	if err != nil {
		return err
	}
	if len(buf) == 0 {
		return nil
	}
	const channelNum = 2
	const bytesPerSample = channelNum * 16 / 8
	b := context.Call("createBuffer", channelNum, len(buf)/bytesPerSample, a.sampleRate)
	l := b.Call("getChannelData", 0)
	r := b.Call("getChannelData", 1)
	il, ir := toLR(buf)
	const max = 1 << 15
	for i := 0; i < len(il); i++ {
		l.SetIndex(i, float64(il[i])/max)
		r.SetIndex(i, float64(ir[i])/max)
	}
	s := context.Call("createBufferSource")
	s.Set("buffer", b)
	s.Call("connect", context.Get("destination"))
	s.Call("start", a.position)
	a.position += b.Get("duration").Float()
	return nil
}

func play(src io.ReadSeeker, sampleRate int) error {
	a := &audioProcessor{
		src:        src,
		sampleRate: sampleRate,
		position:   context.Get("currentTime").Float(),
	}
	return a.play()
}

func initialize() {
	// Do nothing in node.js.
	if js.Global.Get("require") != js.Undefined {
		return
	}

	class := js.Global.Get("AudioContext")
	if class == js.Undefined {
		class = js.Global.Get("webkitAudioContext")
	}
	if class == js.Undefined {
		return
	}
	context = class.New()
}