/*
	(c) 2003 Martin Voelkle & Stephane Magnenat
*/
#include <SDL/SDL.h>
#include <SDL/SDL_audio.h>
#include <vorbis/codec.h>
#include <vorbis/vorbisfile.h>
#include <stdlib.h>

Sint16 minsint16 = (1 << (sizeof(Sint16)*8-1));
Sint16 maxsint16 = minsint16 - 1;

struct Tracks
{
	int ntracks;
	int *gains;
	int *indexes;
	OggVorbis_File *files;
};
int run;

#define CLAMP(val, min, max) { if ((val)<(min)) (val)=(min); else if ((val)>(max)) (val)=(max); }

void mixaudio(void *tracks, Uint8 *stream, int len)
{
	Tracks *t = (Tracks *)tracks;
	int nsamples = len >> 1;
	Sint16 track[nsamples];
	Sint16 *mix = (Sint16 *)stream;

	// init buffer
	for (int j = 0; j < nsamples; j++)
	{
		mix[j] = 0;
	}

	for (int i = 0; i < t->ntracks; i++)
	{
		// read ogg
		long rest = len;
		char *p = (char *)track;
		while(rest > 0)
		{
			long ret = ov_read(&t->files[i], p, rest, 0, 2, 1, &t->indexes[i]);
			if (ret == 0) // EOF
			{
				ov_pcm_seek(&t->files[i], 0);
			}
			else if (ret < 0) // stream error
			{
			}
			else
			{
				rest -= ret;
				p += ret;
			}
		}

		// sum sample
		for (int j = 0; j < nsamples; j++)
		{
			mix[j] = minsint16 >? (mix[j] + ((track[j] * t->gains[i])>>8)) <? maxsint16;
		}
	}

}

void redisplay(SDL_Surface *s, Tracks *t)
{
	for (int i=0; i<t->ntracks; i++)
	{
		SDL_Rect sel = {i*30, 255-t->gains[i], 30, t->gains[i]};
		SDL_FillRect(s, &sel, SDL_MapRGB(s->format, 255, 20, 20));
		SDL_Rect black = {i*30, 0, 30, 255-t->gains[i]};
		SDL_FillRect(s, &black, SDL_MapRGB(s->format, 50, 50, 50));
	}
	SDL_Flip(s);
}

void handle_gain_change(SDL_Event *event, Tracks *t)
{
	int id = event->button.x/30;
	int gain = 255-event->button.y;
	CLAMP(id, 0, t->ntracks-1);
	CLAMP(gain, 0, 255);
	t->gains[id] = gain;
}

int main(int argc, char **argv)
{

	if (argc==1)
	{
		printf("Usage: %s file.ogg {file.ogg}\n", argv[0]);
		exit(1);
	}

	SDL_Init(SDL_INIT_VIDEO|SDL_INIT_AUDIO);

	Tracks t;
	t.ntracks = argc - 1;
	t.gains = new int[t.ntracks];
	t.indexes = new int[t.ntracks];
	t.files = new OggVorbis_File[t.ntracks];

	for (int i = 0; i < t.ntracks; i++)
	{
		t.gains[i] = 255/t.ntracks;
		FILE* file = fopen(argv[i+1], "rb");
		if (ov_open(file, &t.files[i], NULL, 0) < 0)
		{
			fprintf(stderr, "File does not appear to be an Ogg bitstream.\n");
			exit(1);
		}
	}

	SDL_AudioSpec as;
	// Set 16-bit stereo audio at 44Khz
	as.freq = 44100;
	as.format = AUDIO_S16;
	as.channels = 2;
	as.samples = 512;
	as.callback = mixaudio;
	as.userdata = &t;

	// Open the audio device and start playing sound!
	if (SDL_OpenAudio(&as, NULL) < 0)
	{
		fprintf(stderr, "Unable to open audio: %s\n", SDL_GetError());
		exit(1);
	}

	// Init video
	SDL_Surface *screen;
	screen = SDL_SetVideoMode(t.ntracks*30, 256, 32, SDL_HWSURFACE|SDL_DOUBLEBUF);
	if (screen == NULL)
	{
		fprintf(stderr, "Unable to set %dx256 video: %s\n", t.ntracks, SDL_GetError());
		exit(1);
	}

	redisplay(screen, &t);

	SDL_PauseAudio(0);

	SDL_Event event;
	while (SDL_WaitEvent(&event))
	{
		if (event.type == SDL_QUIT)
		{
			break;
		}
		else if ((event.type == SDL_MOUSEBUTTONDOWN) || ((event.type == SDL_MOUSEMOTION) && (event.motion.state)))
		{
			handle_gain_change(&event, &t);
			redisplay(screen, &t);
		}
	}

	SDL_PauseAudio(1);

	for(int i=0; i<t.ntracks; i++)
	{
		ov_clear(&t.files[i]);
	}

	SDL_CloseAudio();
	SDL_Quit();

}