// Copyright 2021 The Ebiten Authors
//
// 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.

package audio

import (
	"io"
	"runtime"
	"sync"
	"time"
)

// player is exactly same as the interface oto.Player.
// This is defined in order to remove the dependency on Oto from this file.
type player interface {
	Pause()
	Play()
	IsPlaying() bool
	Reset()
	Volume() float64
	SetVolume(volume float64)
	UnplayedBufferSize() int
	Err() error
	SetBufferSize(bufferSize int)
	io.Closer
}

type context interface {
	NewPlayer(io.Reader) player
	Suspend() error
	Resume() error
	Err() error
}

type playerFactory struct {
	context    context
	sampleRate int

	m sync.Mutex
}

var driverForTesting context

func newPlayerFactory(sampleRate int) *playerFactory {
	f := &playerFactory{
		sampleRate: sampleRate,
	}
	if driverForTesting != nil {
		f.context = driverForTesting
	}
	// TODO: Consider the hooks.
	return f
}

type playerImpl struct {
	context        *Context
	player         player
	src            io.Reader
	stream         *timeStream
	factory        *playerFactory
	initBufferSize int
	m              sync.Mutex
}

func (f *playerFactory) newPlayer(context *Context, src io.Reader) (*playerImpl, error) {
	f.m.Lock()
	defer f.m.Unlock()

	p := &playerImpl{
		src:     src,
		context: context,
		factory: f,
	}
	runtime.SetFinalizer(p, (*playerImpl).Close)
	return p, nil
}

func (f *playerFactory) suspend() error {
	f.m.Lock()
	defer f.m.Unlock()

	if f.context == nil {
		return nil
	}
	return f.context.Suspend()
}

func (f *playerFactory) resume() error {
	f.m.Lock()
	defer f.m.Unlock()

	if f.context == nil {
		return nil
	}
	return f.context.Resume()
}

func (f *playerFactory) error() error {
	f.m.Lock()
	defer f.m.Unlock()

	if f.context == nil {
		return nil
	}
	return f.context.Err()
}

func (f *playerFactory) initContextIfNeeded() (<-chan struct{}, error) {
	f.m.Lock()
	defer f.m.Unlock()

	if f.context != nil {
		return nil, nil
	}

	c, ready, err := newContext(f.sampleRate, channelNum, bitDepthInBytes)
	if err != nil {
		return nil, err
	}
	f.context = c
	return ready, nil
}

func (p *playerImpl) ensurePlayer() error {
	// Initialize the underlying player lazily to enable calling NewContext in an 'init' function.
	// Accessing the underlying player functions requires the environment to be already initialized,
	// but if Ebitengine is used for a shared library, the timing when init functions are called
	// is unexpectable.
	// e.g. a variable for JVM on Android might not be set.
	ready, err := p.factory.initContextIfNeeded()
	if err != nil {
		return err
	}
	if ready != nil {
		go func() {
			<-ready
			p.context.setReady()
		}()
	}

	if p.stream == nil {
		s, err := newTimeStream(p.src, p.factory.sampleRate)
		if err != nil {
			return err
		}
		p.stream = s
	}
	if p.player == nil {
		p.player = p.factory.context.NewPlayer(p.stream)
		if p.initBufferSize != 0 {
			p.player.SetBufferSize(p.initBufferSize)
			p.initBufferSize = 0
		}
	}
	return nil
}

func (p *playerImpl) Play() {
	p.m.Lock()
	defer p.m.Unlock()

	if err := p.ensurePlayer(); err != nil {
		p.context.setError(err)
		return
	}
	if p.player.IsPlaying() {
		return
	}
	p.player.Play()
	p.context.addPlayer(p)
}

func (p *playerImpl) Pause() {
	p.m.Lock()
	defer p.m.Unlock()

	if p.player == nil {
		return
	}
	if !p.player.IsPlaying() {
		return
	}

	p.player.Pause()
	p.context.removePlayer(p)
}

func (p *playerImpl) IsPlaying() bool {
	p.m.Lock()
	defer p.m.Unlock()

	if p.player == nil {
		return false
	}
	return p.player.IsPlaying()
}

func (p *playerImpl) Volume() float64 {
	p.m.Lock()
	defer p.m.Unlock()

	if err := p.ensurePlayer(); err != nil {
		p.context.setError(err)
		return 0
	}
	return p.player.Volume()
}

func (p *playerImpl) SetVolume(volume float64) {
	p.m.Lock()
	defer p.m.Unlock()

	if err := p.ensurePlayer(); err != nil {
		p.context.setError(err)
		return
	}
	p.player.SetVolume(volume)
}

func (p *playerImpl) Close() error {
	p.m.Lock()
	defer p.m.Unlock()
	runtime.SetFinalizer(p, nil)

	if p.player != nil {
		defer func() {
			p.player = nil
		}()
		p.player.Pause()
		return p.player.Close()
	}
	return nil
}

func (p *playerImpl) Current() time.Duration {
	p.m.Lock()
	defer p.m.Unlock()
	if err := p.ensurePlayer(); err != nil {
		p.context.setError(err)
		return 0
	}

	samples := (p.stream.Current() - int64(p.player.UnplayedBufferSize())) / bytesPerSample
	return time.Duration(samples) * time.Second / time.Duration(p.factory.sampleRate)
}

func (p *playerImpl) Rewind() error {
	return p.Seek(0)
}

func (p *playerImpl) Seek(offset time.Duration) error {
	p.m.Lock()
	defer p.m.Unlock()

	if err := p.ensurePlayer(); err != nil {
		return err
	}

	if p.player.IsPlaying() {
		defer func() {
			p.player.Play()
		}()
	}
	p.player.Reset()
	return p.stream.Seek(offset)
}

func (p *playerImpl) Err() error {
	p.m.Lock()
	defer p.m.Unlock()

	if p.player == nil {
		return nil
	}
	return p.player.Err()
}

func (p *playerImpl) SetBufferSize(bufferSize time.Duration) {
	p.m.Lock()
	defer p.m.Unlock()

	bufferSizeInBytes := int(bufferSize * bytesPerSample * time.Duration(p.factory.sampleRate) / time.Second)
	bufferSizeInBytes = bufferSizeInBytes / bytesPerSample * bytesPerSample
	if p.player == nil {
		p.initBufferSize = bufferSizeInBytes
		return
	}
	p.player.SetBufferSize(bufferSizeInBytes)
}

func (p *playerImpl) source() io.Reader {
	return p.src
}

type timeStream struct {
	r          io.Reader
	sampleRate int
	pos        int64

	// m is a mutex for this stream.
	// All the exported functions are protected by this mutex as Read can be read from a different goroutine than Seek.
	m sync.Mutex
}

func newTimeStream(r io.Reader, sampleRate int) (*timeStream, error) {
	s := &timeStream{
		r:          r,
		sampleRate: sampleRate,
	}
	if seeker, ok := s.r.(io.Seeker); ok {
		// Get the current position of the source.
		pos, err := seeker.Seek(0, io.SeekCurrent)
		if err != nil {
			return nil, err
		}
		s.pos = pos
	}
	return s, nil
}

func (s *timeStream) Read(buf []byte) (int, error) {
	s.m.Lock()
	defer s.m.Unlock()

	n, err := s.r.Read(buf)
	s.pos += int64(n)
	return n, err
}

func (s *timeStream) Seek(offset time.Duration) error {
	s.m.Lock()
	defer s.m.Unlock()

	o := int64(offset) * bytesPerSample * int64(s.sampleRate) / int64(time.Second)

	// Align the byte position with the samples.
	o -= o % bytesPerSample
	o += s.pos % bytesPerSample

	seeker, ok := s.r.(io.Seeker)
	if !ok {
		panic("audio: the source must be io.Seeker when seeking but not")
	}
	pos, err := seeker.Seek(o, io.SeekStart)
	if err != nil {
		return err
	}

	s.pos = pos
	return nil
}

func (s *timeStream) Current() int64 {
	s.m.Lock()
	defer s.m.Unlock()

	return s.pos
}