package audio

/*
#cgo CFLAGS: -I"${SRCDIR}/../cgo" -march=native -Ofast -std=c99
#include "audio.h"
*/
import "C"
import (
	"fmt"
	"github.com/dh1tw/gosamplerate"
	"log"
)

type Stream struct {
	source           chan []float32
	channels         int
	sampleRate       float64
	samplesProcessed int
	buffer           []float32
	blockSize        int
}

func NewStream(source chan []float32, channels int, sampleRate float64, blockSize int) *Stream {
	return &Stream{
		source:     source,
		channels:   channels,
		sampleRate: sampleRate,
		blockSize:  blockSize,
	}
}

func (s *Stream) GetChannels() int {
	return s.channels
}

func (s *Stream) GetSampleRate() float64 {
	return s.sampleRate
}

func (s *Stream) GetSamplesProcessed() int {
	return s.samplesProcessed
}

func (s *Stream) GetAsChannel() chan float32 {
	newChannel := make(chan float32)
	go func() {
		defer close(newChannel)
		for {
			v, more := s.Get()
			if !more {
				return
			}
			newChannel <- v
			s.samplesProcessed++
		}
	}()
	return newChannel
}

func (s *Stream) GetAsBlockChannel() chan []float32 {
	newChannel := make(chan []float32)

	go func() {
		defer close(newChannel)
		for buf := range s.source {
			s.buffer = append(s.buffer, buf...)
			for len(s.buffer) >= s.blockSize*s.channels {
				newChannel <- s.buffer[0 : s.blockSize*s.channels]
				s.samplesProcessed += s.blockSize * s.channels
				s.buffer = s.buffer[s.blockSize*s.channels:]
			}
		}

		if len(s.buffer) > 0 {
			newChannel <- s.buffer
			s.samplesProcessed += len(s.buffer)
		}
		s.buffer = nil
	}()
	return newChannel
}

func (s *Stream) Get() (float32, bool) {
	var more bool
	if len(s.buffer) == 0 {
		s.buffer, more = <-s.source
		if !more {
			return 0, false
		}
	}
	f := s.buffer[0]
	s.buffer = s.buffer[1:]
	s.samplesProcessed++
	return f, true
}

func (s *Stream) AdvanceSeconds(seconds float64) bool {
	stopAt := s.secondsIndex(seconds)
	for i := 0; i < stopAt; i++ {
		_, more := s.Get()
		if !more {
			return false
		}
	}
	return true
}

func (s *Stream) secondsIndex(seconds float64) int {
	return int(seconds * s.sampleRate)
}

const (
	RESAMPLER_QUALITY_BANDLIMITED_BEST    = gosamplerate.SRC_SINC_BEST_QUALITY
	RESAMPLER_QUALITY_BANDLIMITED_MEDIUM  = gosamplerate.SRC_SINC_MEDIUM_QUALITY
	RESAMPLER_QUALITY_BANDLIMITED_FASTEST = gosamplerate.SRC_SINC_FASTEST
	RESAMPLER_QUALITY_HOLD                = gosamplerate.SRC_ZERO_ORDER_HOLD
	RESAMPLER_QUALITY_LINEAR              = gosamplerate.SRC_LINEAR
)

func (s *Stream) DoResample(channels int, sampleRate float64, quality int) (*Stream, error) {
	if channels != 1 && channels != 2 && s.channels != channels {
		return nil, fmt.Errorf("cannot convert from %d channels to %d", s.channels, channels)
	}

	if channels == s.channels && sampleRate == s.sampleRate {
		return s, nil
	}

	samplerateConverter, err := gosamplerate.New(quality, channels, s.blockSize*s.channels)
	if err != nil {
		return nil, err
	}

	newChannel := make(chan []float32)

	go func() {
		defer gosamplerate.Delete(samplerateConverter)
		defer close(newChannel)
		ratio := sampleRate / s.sampleRate

		for buf := range s.GetAsBlockChannel() {
			if channels != s.channels && channels == 1 {
				if channels == 1 {
					//bring any number of channels to mono, equally weighted, reusing buffer backwards
					C.audio_multiple_channels_to_mono((*C.float)(&buf[0]), C.size_t(len(buf)), C.int(s.channels))
					buf = buf[0:(len(buf) / s.channels)]
				} else if channels == 2 {
					//bring any number of channels to stereo, using downmix formulas when necessary
					out := make([]float32, (len(buf)/s.channels)*2)
					C.audio_multiple_channels_to_stereo((*C.float)(&buf[0]), C.size_t(len(buf)), (*C.float)(&out[0]), C.int(s.channels))
					buf = out
				}
			}

			for len(buf) > 0 {
				n := len(buf)
				if n > s.blockSize*channels {
					n = s.blockSize * channels
				}
				b, err := samplerateConverter.Process(buf[0:n], ratio, false)
				if err != nil {
					log.Panic(err)
				}
				if len(b) > 0 {
					newChannel <- b
				}
				buf = buf[n:]
			}
		}

		b, err := samplerateConverter.Process([]float32{}, ratio, true)
		if err != nil {
			log.Panic(err)
		}
		if len(b) > 0 {
			newChannel <- b
		}
	}()

	return NewStream(newChannel, channels, sampleRate, s.blockSize), nil
}