#include <math.h>
#include <stdlib.h>
#include <SDL/SDL.h>
#include <SDL/SDL_mixer.h>

#define CHUNK_SIZE 4096
#if 1
#define FLANGER_BUFFER_SIZE 88200
#else
#define FLANGER_BUFFER_SIZE 2000
#endif

void handle_exit(void)
{
    Mix_Quit();
    SDL_Quit();
    puts("Shutdown complete.");
}

static struct flanger {
    int samples;
    int frequency;
    int
        start_ms,
        stop_ms;
    int cur_delay;
    int sweep_dir;
    int sweep_speed;
    Sint16 buf[FLANGER_BUFFER_SIZE];
} flange_chan;

/* Perform flanging effect */
void flanger_func(int chan, void *stream, int len, void *udata)
{
    int i;
    Sint16 *sbuf = stream;
    struct flanger *flanger = udata;
    int local_len = len / sizeof(Sint16);

    /*printf("Samples: %d, Local Len: %d, Len: %d\n", flanger->samples, local_len, len);*/
    for (i = 0; i < local_len; i++) {
        flanger->buf[(flanger->samples + i) %
            FLANGER_BUFFER_SIZE] = sbuf[i];
        sbuf[i] = sbuf[i] / 2 + flanger->buf[(flanger->samples +
            (FLANGER_BUFFER_SIZE - flanger->cur_delay / 1000 * 2) + i) %
            FLANGER_BUFFER_SIZE] / 2;
        if (!(i%2)) {
            if (flanger->cur_delay >= flanger->frequency /
                    (1000 / flanger->stop_ms) * 1000) {
                flanger->sweep_dir = -flanger->sweep_speed;
            } else if (flanger->cur_delay <= flanger->frequency /
                    (1000 / flanger->start_ms) * 1000) {
                flanger->sweep_dir = flanger->sweep_speed;
            }
            flanger->cur_delay += flanger->sweep_dir;
        }
        /*sbuf[i] = 0;*/
    }

    flanger->samples = (flanger->samples + local_len) % FLANGER_BUFFER_SIZE;

    return;
}

int main(int argc, char *argv[])
{
    char *mp3_file;
    Mix_Music *mp3_stream;

    /* Audio settings */
    int frequency = 44100;
    Uint16 format = AUDIO_S16;
    int channels = 2;

    if (argc != 2) {
        printf("Usage %s: <mp3-file>\n", argv[0]);
        return EXIT_SUCCESS;
    }

    mp3_file = argv[1];

    /* Setup shutdown sequence */
    atexit(handle_exit);

    /* Setup SDL & friends */
    SDL_Init(SDL_INIT_AUDIO);
    Mix_Init(MIX_INIT_MP3);

    /* Open audio */
    if (Mix_OpenAudio(frequency, format, channels, CHUNK_SIZE)) {
        printf("Mix_OpenAudio failed: %s\n", Mix_GetError());
        /* Mix_FreeMusic(mp3_stream); */
        return EXIT_FAILURE;
    }

    /* Verify audio compatibility */
    Mix_QuerySpec(&frequency, &format, &channels);
    printf("Device settings are: %d, %hd, %d\n", frequency, format, channels);
    if (format != AUDIO_S16) {
        puts("Selected device format incompatible :-(\n");
        return EXIT_FAILURE;
    }

    /* Load MP3 file */
    mp3_stream = Mix_LoadMUS(mp3_file);
    if (!mp3_stream) {
        printf("Mix_LoadMUS failed: %s\n", Mix_GetError());
        return EXIT_FAILURE;
    }

    /* Setup flangers */
    memset(flange_chan.buf, 0x0, sizeof(short) * FLANGER_BUFFER_SIZE);
    flange_chan.frequency = frequency;
    flange_chan.samples = 0;
    flange_chan.start_ms = 1;
    flange_chan.stop_ms = 20;
    flange_chan.sweep_speed = 5;
    flange_chan.cur_delay = 0;
    flange_chan.sweep_dir = 1;
    if (!Mix_RegisterEffect(MIX_CHANNEL_POST, flanger_func, NULL, &flange_chan)) {
        printf("Mix_RegisterEffect failed: %s\n", Mix_GetError());
        return EXIT_FAILURE;
    }

    /* Start playback */
    if (Mix_PlayMusic(mp3_stream, 0) < 0) {
        printf("Mix_PlayMusic failed: %s\n", Mix_GetError());
        Mix_FreeMusic(mp3_stream);
        return EXIT_FAILURE;
    }

    while (Mix_PlayingMusic())
        SDL_Delay(100);

    return EXIT_SUCCESS;
}