#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include "audio.h"
#include "system.h"

#define BUFFER_INC_RES 1000000000UL

audio *alloc_audio(uint32_t master_clock, uint32_t clock_div, int sample_rate, int buffer_size)
{
	size_t alloc_size = sizeof(audio) + buffer_size * sizeof(int16_t) * 2;
	audio *context = malloc(alloc_size);
	memset(context, 0, alloc_size);
	context->writebuffer = context->buffer;
	context->playbuffer = context->buffer + buffer_size;
	
	context->buffer_size = buffer_size;
	context->clock_inc = clock_div;
	context->buffer_inc = ((BUFFER_INC_RES * (uint64_t)sample_rate) / (uint64_t)master_clock) * clock_div;
	for (int i = 0; i < NUM_CHANNELS; i++)
	{
		context->value[i] = context->volume[i] << 5;
	}
	return context;
}

void audio_run(audio *context, uint32_t target)
{
	while (context->cycles < target)
	{
		for (int i = 0; i < 4; i++)
		{
			if (context->timer_cur[i]) {
				context->timer_cur[i]--;
				if (!context->timer_cur[i]) {
					context->value[i] = context->value[i] ? 0 : (context->volume[i] << 5);
				}
			} else {
				context->timer_cur[i] = context->timer_load[i];
			}
		}
		context->buffer_fraction += context->buffer_inc;
		if (context->buffer_fraction >= BUFFER_INC_RES) {
			context->buffer_fraction -= BUFFER_INC_RES;
			context->writebuffer[context->buffer_pos++] = 
				context->value[0] + context->value[1] + context->value[2] + context->value[3];
			if (context->buffer_pos == context->buffer_size) {
				int16_t *tmp = context->playbuffer;
				context->playbuffer = context->writebuffer;
				context->writebuffer = tmp;
				system_present_audio(context->playbuffer);
				context->buffer_pos = 0;
			}
		}
		context->cycles += context->clock_inc;
	}
}

void audio_write_freq(audio *context, int channel, uint16_t value)
{
	context->timer_cur[channel] = context->timer_load[channel] = value;
}

void audio_write_vol(audio *context, int pair, uint16_t value)
{
	int channel = pair * 2;
	context->value[channel] = context->volume[channel] = value >> 8;
	channel++;
	context->value[channel] = context->volume[channel] = value;
}