// 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.

// Package vorbis provides Ogg/Vorbis decoder.
package vorbis

import (
	"fmt"
	"io"

	"github.com/jfreymuth/oggvorbis"

	"github.com/hajimehoshi/ebiten/v2/audio"
	"github.com/hajimehoshi/ebiten/v2/audio/internal/convert"
)

// Stream is a decoded audio stream.
type Stream struct {
	decoded io.ReadSeeker
	size    int64
}

// Read is implementation of io.Reader's Read.
func (s *Stream) Read(p []byte) (int, error) {
	return s.decoded.Read(p)
}

// Seek is implementation of io.Seeker's Seek.
//
// Note that Seek can take long since decoding is a relatively heavy task.
func (s *Stream) Seek(offset int64, whence int) (int64, error) {
	return s.decoded.Seek(offset, whence)
}

// Length returns the size of decoded stream in bytes.
func (s *Stream) Length() int64 {
	return s.size
}

type decoder interface {
	Read([]float32) (int, error)
	SetPosition(int64) error
	Length() int64
	Channels() int
	SampleRate() int
}

type decoded struct {
	totalBytes int
	posInBytes int
	decoder    decoder
	decoderr   io.Reader
}

func (d *decoded) Read(b []byte) (int, error) {
	if d.decoderr == nil {
		d.decoderr = convert.NewReaderFromFloat32Reader(d.decoder)
	}

	l := d.totalBytes - d.posInBytes
	if l > len(b) {
		l = len(b)
	}
	if l < 0 {
		return 0, io.EOF
	}

retry:
	n, err := d.decoderr.Read(b[:l])
	if err != nil && err != io.EOF {
		return 0, err
	}
	if n == 0 && l > 0 && err != io.EOF {
		// When l is too small, decoder's Read might return 0 for a while. Let's retry.
		goto retry
	}

	d.posInBytes += n
	if d.posInBytes == d.totalBytes || err == io.EOF {
		return n, io.EOF
	}
	return n, nil
}

func (d *decoded) Seek(offset int64, whence int) (int64, error) {
	next := int64(0)
	switch whence {
	case io.SeekStart:
		next = offset
	case io.SeekCurrent:
		next = int64(d.posInBytes) + offset
	case io.SeekEnd:
		next = int64(d.totalBytes) + offset
	}
	// pos should be always even
	next = next / 2 * 2
	d.posInBytes = int(next)
	d.decoder.SetPosition(next / int64(d.decoder.Channels()) / 2)
	d.decoderr = nil
	return next, nil
}

func (d *decoded) Length() int64 {
	return int64(d.totalBytes)
}

// decode accepts an ogg stream and returns a decorded stream.
func decode(in io.ReadSeeker) (*decoded, int, int, error) {
	r, err := oggvorbis.NewReader(in)
	if err != nil {
		return nil, 0, 0, err
	}
	d := &decoded{
		// TODO: r.Length() returns 0 when the format is unknown.
		// Should we check that?
		totalBytes: int(r.Length()) * r.Channels() * 2, // 2 means 16bit per sample.
		posInBytes: 0,
		decoder:    r,
	}
	if _, err := d.Read(make([]byte, 65536)); err != nil && err != io.EOF {
		return nil, 0, 0, err
	}
	if _, err := d.Seek(0, io.SeekStart); err != nil {
		return nil, 0, 0, err
	}
	return d, r.Channels(), r.SampleRate(), nil
}

// Decode decodes Ogg/Vorbis data to playable stream.
//
// Decode returns error when decoding fails or IO error happens.
//
// Decode automatically resamples the stream to fit with the audio context if necessary.
//
// A Stream doesn't close src even if src implements io.Closer.
// Closing the source is src owner's responsibility.
func Decode(context *audio.Context, src io.ReadSeeker) (*Stream, error) {
	decoded, channelNum, sampleRate, err := decode(src)
	if err != nil {
		return nil, err
	}
	if channelNum != 1 && channelNum != 2 {
		return nil, fmt.Errorf("vorbis: number of channels must be 1 or 2 but was %d", channelNum)
	}
	var s io.ReadSeeker = decoded
	size := decoded.Length()
	if channelNum == 1 {
		s = convert.NewStereo16(s, true, false)
		size *= 2
	}
	if sampleRate != context.SampleRate() {
		r := convert.NewResampling(s, size, sampleRate, context.SampleRate())
		s = r
		size = r.Length()
	}
	stream := &Stream{decoded: s, size: size}
	return stream, nil
}