/*
NAME
  alsa.go

AUTHOR
  Alan Noble <alan@ausocean.org>
  Trek Hopton <trek@ausocean.org>

LICENSE
  This file is Copyright (C) 2019 the Australian Ocean Lab (AusOcean)

  It is free software: you can redistribute it and/or modify them
  under the terms of the GNU General Public License as published by the
  Free Software Foundation, either version 3 of the License, or (at your
  option) any later version.

  It is distributed in the hope that it will be useful, but WITHOUT
  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
  for more details.

  You should have received a copy of the GNU General Public License in gpl.txt.
  If not, see http://www.gnu.org/licenses.
*/

// Package alsa provides access to input from ALSA audio devices.
package alsa

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"sync"
	"time"

	yalsa "github.com/yobert/alsa"

	"bitbucket.org/ausocean/av/codec/adpcm"
	"bitbucket.org/ausocean/av/codec/codecutil"
	"bitbucket.org/ausocean/av/codec/pcm"
	"bitbucket.org/ausocean/av/device"
	"bitbucket.org/ausocean/av/revid/config"
	"bitbucket.org/ausocean/utils/logging"
	"bitbucket.org/ausocean/utils/pool"
)

const (
	pkg           = "alsa: "
	rbTimeout     = 100 * time.Millisecond
	rbNextTimeout = 2000 * time.Millisecond
	rbLen         = 200
)

// "running" means the input goroutine is reading from the ALSA device and writing to the ringbuffer.
// "paused" means the input routine is sleeping until unpaused or stopped.
// "stopped" means the input routine is stopped and the ALSA device is closed.
const (
	running = iota + 1
	paused
	stopped
)

const (
	defaultSampleRate = 48000
	defaultBitDepth   = 16
	defaultChannels   = 1
	defaultRecPeriod  = 1.0
	defaultCodec      = codecutil.PCM
)

// Configuration field errors.
var (
	errInvalidSampleRate = errors.New("invalid sample rate, defaulting")
	errInvalidChannels   = errors.New("invalid number of channels, defaulting")
	errInvalidBitDepth   = errors.New("invalid bitdepth, defaulting")
	errInvalidRecPeriod  = errors.New("invalid record period, defaulting")
	errInvalidCodec      = errors.New("invalid audio codec, defaulting")
)

// An ALSA device holds everything we need to know about the audio input stream and implements io.Reader and device.AVDevice.
type ALSA struct {
	l      logging.Logger        // Logger for device's routines to log to.
	mode   uint8         // Operating mode, either running, paused, or stopped.
	mu     sync.Mutex    // Provides synchronisation when changing modes concurrently.
	title  string        // Name of audio title, or empty for the default title.
	dev    *yalsa.Device // ALSA device's Audio input device.
	pb     pcm.Buffer    // Buffer to contain the direct audio from ALSA.
	buf    *pool.Buffer  // Ring buffer to contain processed audio ready to be read.
	Config               // Configuration parameters for this device.
}

// Config provides parameters used by the ALSA device.
type Config struct {
	SampleRate uint
	Channels   uint
	BitDepth   uint
	RecPeriod  float64
	Codec      string
}

// New initializes and returns an ALSA device which has its logger set as the given logger.
func New(l logging.Logger) *ALSA { return &ALSA{l: l} }

// Name returns the name of the device.
func (d *ALSA) Name() string {
	return "ALSA"
}

// Setup will take a Config struct, check the validity of the relevant fields
// and then perform any configuration necessary. If fields are not valid,
// an error is added to the multiError and a default value is used.
// It then initialises the ALSA device which can then be started, read from, and stopped.
func (d *ALSA) Setup(c config.Config) error {
	var errs device.MultiError
	if c.SampleRate <= 0 {
		errs = append(errs, errInvalidSampleRate)
		c.SampleRate = defaultSampleRate
	}
	if c.Channels <= 0 {
		errs = append(errs, errInvalidChannels)
		c.Channels = defaultChannels
	}
	if c.BitDepth <= 0 {
		errs = append(errs, errInvalidBitDepth)
		c.BitDepth = defaultBitDepth
	}
	if c.RecPeriod <= 0 {
		errs = append(errs, errInvalidRecPeriod)
		c.RecPeriod = defaultRecPeriod
	}
	if c.InputCodec != codecutil.ADPCM && c.InputCodec != codecutil.PCM {
		errs = append(errs, errInvalidCodec)
		c.InputCodec = defaultCodec
	}
	d.Config = Config{
		SampleRate: c.SampleRate,
		Channels:   c.Channels,
		BitDepth:   c.BitDepth,
		RecPeriod:  c.RecPeriod,
		Codec:      c.InputCodec,
	}

	// Open the requested audio device.
	err := d.open()
	if err != nil {
		return fmt.Errorf("failed to open device: %w", err)
	}

	// Setup the device to record with desired period.
	ab := d.dev.NewBufferDuration(time.Duration(d.RecPeriod * float64(time.Second)))
	sf, err := pcm.SFFromString(ab.Format.SampleFormat.String())
	if err != nil {
		return fmt.Errorf("unable to get sample format from string: %w", err)
	}
	cf := pcm.BufferFormat{
		SFormat:  sf,
		Channels: uint(ab.Format.Channels),
		Rate:     uint(ab.Format.Rate),
	}
	d.pb = pcm.Buffer{
		Format: cf,
		Data:   ab.Data,
	}

	// Create pool buffer with appropriate chunk size.
	cs := d.DataSize()
	d.buf = pool.NewBuffer(rbLen, cs, rbTimeout)

	// Start device in paused mode.
	d.mode = paused
	go d.input()

	if len(errs) != 0 {
		return errs
	}
	return nil
}

// Set exists to satisfy the implementation of the Device interface that revid uses.
// Everything that would usually be in Set is in the Setup function.
// This is because an ALSA device is different to other devices in that it
// outputs binary non-packetised data and it requires a different configuration procedure.
func (d *ALSA) Set(c config.Config) error {
	return nil
}

// Start will start recording audio and writing to the ringbuffer.
// Once an ALSA device has been stopped it cannot be started again. This is likely to change in future.
func (d *ALSA) Start() error {
	d.mu.Lock()
	mode := d.mode
	d.mu.Unlock()
	switch mode {
	case paused:
		d.mu.Lock()
		d.mode = running
		d.mu.Unlock()
		return nil
	case stopped:
		// TODO(Trek): Make this reopen device and start recording.
		return errors.New("device is stopped")
	case running:
		return nil
	default:
		return fmt.Errorf("invalid mode: %d", mode)
	}
}

// Stop will stop recording audio and close the device.
// Once an ALSA device has been stopped it cannot be started again. This is likely to change in future.
func (d *ALSA) Stop() error {
	d.mu.Lock()
	d.mode = stopped
	d.mu.Unlock()
	return nil
}

// open the recording device with the given name and prepare it to record.
// If name is empty, the first recording device is used.
func (d *ALSA) open() error {
	// Close any existing device.
	if d.dev != nil {
		d.l.Debug( "closing device", "title", d.title)
		d.dev.Close()
		d.dev = nil
	}

	// Open sound card and open recording device.
	d.l.Debug( "opening sound card")
	cards, err := yalsa.OpenCards()
	if err != nil {
		return err
	}
	defer yalsa.CloseCards(cards)

	d.l.Debug( "finding audio device")
	for _, card := range cards {
		devices, err := card.Devices()
		if err != nil {
			continue
		}
		for _, dev := range devices {
			if dev.Type != yalsa.PCM || !dev.Record {
				continue
			}
			if dev.Title == d.title || d.title == "" {
				d.dev = dev
				break
			}
		}
	}
	if d.dev == nil {
		return errors.New("no ALSA device found")
	}

	d.l.Debug( "opening ALSA device", "title", d.dev.Title)
	err = d.dev.Open()
	if err != nil {
		return err
	}

	// Try to configure device with chosen channels.
	channels, err := d.dev.NegotiateChannels(int(d.Channels))
	if err != nil && d.Channels == 1 {
		d.l.Info( "device is unable to record in mono, trying stereo", "error", err)
		channels, err = d.dev.NegotiateChannels(2)
	}
	if err != nil {
		return fmt.Errorf("device is unable to record with requested number of channels: %w", err)
	}
	d.l.Debug( "alsa device channels set", "channels", channels)

	// Try to negotiate a rate to record in that is divisible by the wanted rate
	// so that it can be easily downsampled to the wanted rate.
	// rates is a slice of common sample rates including the standard for CD (44100Hz) and standard for professional audio recording (48000Hz).
	// Note: if a card thinks it can record at a rate but can't actually, this can cause a failure.
	// Eg. the audioinjector sound card is supposed to record at 8000Hz and 16000Hz but it can't due to a firmware issue,
	// a fix for this is to remove 8000 and 16000 from the rates slice.
	var rates = [8]int{8000, 16000, 32000, 44100, 48000, 88200, 96000, 192000}

	var rate int
	foundRate := false
	for r := range rates {
		if r < int(d.SampleRate) {
			continue
		}
		if r%int(d.SampleRate) == 0 {
			rate, err = d.dev.NegotiateRate(r)
			if err == nil {
				foundRate = true
				d.l.Debug( "alsa device sample rate set", "rate", rate)
				break
			}
		}
	}

	// If no easily divisible rate is found, then use the default rate.
	if !foundRate {
		d.l.Warning( "unable to sample at requested rate, default used.", "rateRequested", d.SampleRate)
		rate, err = d.dev.NegotiateRate(defaultSampleRate)
		if err != nil {
			return err
		}
		d.l.Debug( "alsa device sample rate set", "rate", rate)
	}

	var aFmt yalsa.FormatType
	switch d.BitDepth {
	case 16:
		aFmt = yalsa.S16_LE
	case 32:
		aFmt = yalsa.S32_LE
	default:
		return fmt.Errorf("unsupported sample bits %v", d.BitDepth)
	}
	devFmt, err := d.dev.NegotiateFormat(aFmt)
	if err != nil {
		return err
	}
	var bitdepth int
	switch devFmt {
	case yalsa.S16_LE:
		bitdepth = 16
	case yalsa.S32_LE:
		bitdepth = 32
	default:
		return fmt.Errorf("unsupported sample bits %v", d.BitDepth)
	}
	d.l.Debug( "alsa device bit depth set", "bitdepth", bitdepth)

	// A 50ms period is a sensible value for low-ish latency. (this could be made configurable if needed)
	// Some devices only accept even period sizes while others want powers of 2.
	// So we will find the closest power of 2 to the desired period size.
	const wantPeriod = 0.05 //seconds
	bytesPerSecond := rate * channels * (bitdepth / 8)
	wantPeriodSize := int(float64(bytesPerSecond) * wantPeriod)
	nearWantPeriodSize := nearestPowerOfTwo(wantPeriodSize)

	// At least two period sizes should fit within the buffer.
	bufSize, err := d.dev.NegotiateBufferSize(nearWantPeriodSize * 2)
	if err != nil {
		return err
	}
	d.l.Debug( "alsa device buffer size set", "buffersize", bufSize)

	if err = d.dev.Prepare(); err != nil {
		return err
	}

	d.l.Debug( "successfully negotiated device params")
	return nil
}

// input continously records audio and writes it to the ringbuffer.
// Re-opens the device and tries again if the ASLA device returns an error.
func (d *ALSA) input() {
	for {
		// Check mode.
		d.mu.Lock()
		mode := d.mode
		d.mu.Unlock()
		switch mode {
		case paused:
			time.Sleep(time.Duration(d.RecPeriod) * time.Second)
			continue
		case stopped:
			if d.dev != nil {
				d.l.Debug( "closing ALSA device", "title", d.title)
				d.dev.Close()
				d.dev = nil
			}
			err := d.buf.Close()
			if err != nil {
				d.l.Error( "unable to close pool buffer", "error", err)
			}
			return
		}

		// Read from audio device.
		d.l.Debug( "recording audio for period", "seconds", d.RecPeriod)
		err := d.dev.Read(d.pb.Data)
		if err != nil {
			d.l.Debug( "read failed", "error", err.Error())
			err = d.open() // re-open
			if err != nil {
				d.l.Fatal( "reopening device failed", "error", err.Error())
				return
			}
			continue
		}

		// Process audio.
		d.l.Debug( "processing audio")
		toWrite := d.formatBuffer()

		// Write audio to ringbuffer.
		n, err := d.buf.Write(toWrite.Data)
		switch err {
		case nil:
			d.l.Debug( "wrote audio to ringbuffer", "length", n)
		case pool.ErrDropped:
			d.l.Warning( "old audio data overwritten")
		default:
			d.l.Error( "unexpected ringbuffer error", "error", err.Error())
		}
	}
}

// Read reads from the ringbuffer, returning the number of bytes read upon success.
func (d *ALSA) Read(p []byte) (int, error) {
	// Ready ringbuffer for read.
	d.l.Debug( pkg+"getting next chunk ready")
	_, err := d.buf.Next(rbNextTimeout)
	if err != nil {
		switch err {
		case io.EOF:
			d.l.Debug( pkg+"EOF from Next")
			return 0, err
		case pool.ErrTimeout:
			d.l.Debug( pkg+"pool buffer timeout")
			return 0, err
		default:
			d.l.Error( pkg+"unexpected error from Next", "error", err.Error())
			return 0, err
		}
	}

	// Read from pool buffer.
	d.l.Debug( pkg+"reading from buffer")
	n, err := d.buf.Read(p)
	if err != nil {
		switch err {
		case io.EOF:
			d.l.Debug( pkg+"EOF from Read")
			return n, err
		default:
			d.l.Error( pkg+"unexpected error from Read", "error", err.Error())
			return n, err
		}
	}
	d.l.Debug( fmt.Sprintf("%v read %v bytes", pkg, n))
	return n, nil
}

// formatBuffer returns audio that has been converted to the desired format.
func (d *ALSA) formatBuffer() pcm.Buffer {
	var err error

	// If nothing needs to be changed, return the original.
	if d.pb.Format.Channels == d.Channels && d.pb.Format.Rate == d.SampleRate {
		return d.pb
	}
	var formatted pcm.Buffer
	if d.pb.Format.Channels != d.Channels {
		// Convert channels.
		// TODO(Trek): Make this work for conversions other than stereo to mono.
		if d.pb.Format.Channels == 2 && d.Channels == 1 {
			formatted, err = pcm.StereoToMono(d.pb)
			if err != nil {
				d.l.Fatal( "channel conversion failed", "error", err.Error())
			}
		}
	}

	if d.pb.Format.Rate != d.SampleRate {
		// Convert rate.
		formatted, err = pcm.Resample(formatted, d.SampleRate)
		if err != nil {
			d.l.Fatal( "rate conversion failed", "error", err.Error())
		}
	}

	switch d.Codec {
	case codecutil.PCM:
	case codecutil.ADPCM:
		b := bytes.NewBuffer(make([]byte, 0, adpcm.EncBytes(len(formatted.Data))))
		enc := adpcm.NewEncoder(b)
		_, err = enc.Write(formatted.Data)
		if err != nil {
			d.l.Fatal( "unable to encode", "error", err.Error())
		}
		formatted.Data = b.Bytes()
	default:
		d.l.Error( "unhandled audio codec")
	}

	return formatted
}

// DataSize returns the size in bytes of the data ALSA device d will
// output in the duration of a single recording period.
func (d *ALSA) DataSize() int {
	s := pcm.DataSize(d.SampleRate, d.Channels, d.BitDepth, d.RecPeriod)
	if d.Codec == codecutil.ADPCM {
		s = adpcm.EncBytes(s)
	}
	return s
}

// nearestPowerOfTwo finds and returns the nearest power of two to the given integer.
// If the lower and higher power of two are the same distance, it returns the higher power.
// For negative values, 1 is returned.
// Source: https://stackoverflow.com/a/45859570
func nearestPowerOfTwo(n int) int {
	if n <= 0 {
		return 1
	}
	if n == 1 {
		return 2
	}
	v := n
	v--
	v |= v >> 1
	v |= v >> 2
	v |= v >> 4
	v |= v >> 8
	v |= v >> 16
	v++         // higher power of 2
	x := v >> 1 // lower power of 2
	if (v - n) > (n - x) {
		return x
	}
	return v
}

// IsRunning is used to determine if the ALSA device is running.
func (d *ALSA) IsRunning() bool {
	return d.mode == running
}