#include <stdio.h>
#include <SDL/SDL.h>
#include <math.h>
#include "s3m_header.h"
#include "helpers.h"

typedef struct
{
    const signed short *src;

    unsigned int pos;

    float frac;
    float rate;

    unsigned int length;
    unsigned int loopEnd;
    unsigned int loopLength;

    unsigned int vol;

    float volL, volR;
} MIXERCHANNEL;

MIXERCHANNEL mixerChn[NUM_MIX_CHANNELS];

static signed int mixBufL[SOUND_BUFFER_SIZE], mixBufR[SOUND_BUFFER_SIZE];

int generateFrame(int numSamples);

int audioRunning = 0;

void mixerClrChn(int ch)
{
    memset(&mixerChn[ch], 0, sizeof (MIXERCHANNEL));

    return;
}

void mixerClrAllChn(void)
{
    memset(mixerChn, 0, NUM_MIX_CHANNELS * sizeof (MIXERCHANNEL));

    return;
}

void mixerSetChnSrc(int ch, const signed short *src, unsigned int length, unsigned int loopLength, unsigned int loopEnd)
{
    mixerChn[ch].src = src;
    mixerChn[ch].frac = 0.0f;
    mixerChn[ch].pos = 0;

    mixerChn[ch].length = length;
    mixerChn[ch].loopEnd = loopEnd;
    mixerChn[ch].loopLength = loopLength;

    return;
}

void mixerSetChnPos(int ch, unsigned int pos)
{
    if (pos <= mixerChn[ch].length)
    {
        if (mixerChn[ch].loopLength > 0)
        {
            if (pos > mixerChn[ch].loopEnd)
            {
                pos -= mixerChn[ch].loopLength;
            }
        }

        mixerChn[ch].frac = 0.0f;
        mixerChn[ch].pos = pos;
    }

    return;
}

void mixerSetChn(int ch, float vol, int pan)
{
    mixerChn[ch].volL = vol * (float)(0xFF - pan);
    mixerChn[ch].volR = vol * (float)(       pan);

    return;
}

void mixerSetChnRate(int ch, float rate)
{
    mixerChn[ch].rate = 1.0f / ((float)SOUND_FREQUENCY / rate);
    mixerChn[ch].frac = 0.0f;

    return;
}

void mixAudio(signed short *target, int numSamples)
{
    memset(mixBufL, 0, numSamples * sizeof (int));
    memset(mixBufR, 0, numSamples * sizeof (int));

    {
        int ch;
        for (ch = 0; ch < NUM_MIX_CHANNELS; ch++)
        {
            int s;
            for (s = 0; s < numSamples; s++)
            {
                if (mixerChn[ch].src != NULL)
                {
                    mixBufL[s] += (signed int)((float)mixerChn[ch].src[mixerChn[ch].pos] * mixerChn[ch].volL);
                    mixBufR[s] += (signed int)((float)mixerChn[ch].src[mixerChn[ch].pos] * mixerChn[ch].volR);

                    mixerChn[ch].frac += mixerChn[ch].rate;

                    if (mixerChn[ch].frac >= 1.0f)
                    {
                        mixerChn[ch].pos  += (int)mixerChn[ch].frac;
                        mixerChn[ch].frac -= (int)mixerChn[ch].frac;
                    }

                    if (mixerChn[ch].loopLength > 0)
                    {
                        if (mixerChn[ch].pos >= mixerChn[ch].loopEnd)
                        {
                            mixerChn[ch].pos -= mixerChn[ch].loopLength;
                        }
                    }
                    else if (mixerChn[ch].pos >= mixerChn[ch].length)
                    {
                        mixerChn[ch].src = NULL;

                        break;
                    }
                }
            }
        }
    }

    {
        signed short *out = target;

        int s;
        for (s = 0; s < numSamples; s++)
        {
            *out++ = (signed short)clamp((signed int)(mixBufL[s] / 0x8000), -0x8000, 0x7FFF);
            *out++ = (signed short)clamp((signed int)(mixBufR[s] / 0x8000), -0x8000, 0x7FFF);
        }
    }

    return;
}

static void SDLMixAudioCallback(void *userdata, unsigned char *stream, int len)
{
    signed short *out = (signed short *)stream;
    int numSamples = len / 4;

    while (numSamples)
    {
        int gen = generateFrame(numSamples);
        mixAudio(out, gen);

        out += (gen * 2);
        numSamples -= gen;
    }

    return;
}

int openMixer(void)
{
    SDL_AudioSpec fmt;

    mixerClrAllChn();

    fmt.freq = SOUND_FREQUENCY;
    fmt.format = AUDIO_S16SYS;
    fmt.channels = 2;
    fmt.samples = SOUND_BUFFER_SIZE;
    fmt.callback = SDLMixAudioCallback;
    fmt.userdata = NULL;

    if (SDL_OpenAudio(&fmt, NULL) < 0)
    {
        printf("Unable to open audio: %s\n", SDL_GetError());

        return 0;
    }

    SDL_PauseAudio(0);

    audioRunning = 1;

    return 1;
}

void closeMixer(void)
{
    mixerClrAllChn();

    SDL_PauseAudio(1);
    SDL_CloseAudio();

    return;
}