// ampler.c

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>

#include <SDL2/SDL.h>

#define SAMPLE_RATE (44100)
#define CHANNELS (2)
#define FRAME_SAMPLES (SAMPLE_RATE / 60)

typedef uint8_t s8;
typedef uint16_t s16;

typedef struct Ampler_state Ampler_state;
struct Ampler_state {
	int size;
	SDL_AudioDeviceID playdev;
	s8 track_l[SAMPLE_RATE * 120]; // 2 minutes
	s8 track_r[SAMPLE_RATE * 120]; // 2 minutes
};

int audio_frame(Ampler_state *state) {
	int queued = SDL_GetQueuedAudioSize(state -> playdev);
	queued /= sizeof s16; // queued is in bytes

	if(queued > FRAME_SAMPLES * CHANNELS * 2) return 0;
	// else puts("queued audio.");

	s16 silence[FRAME_SAMPLES * CHANNELS] = { 0 };
	for (int i = 0; i < FRAME_SAMPLES; i += CHANNELS) {
		int vol = 10;
		silence[i] = (i/2) * vol - FRAME_SAMPLES / 2;
		silence[i + 1] = (i/2) * vol - FRAME_SAMPLES / 2;
	}
	if(SDL_QueueAudio(state -> playdev, silence, sizeof silence))
		puts(SDL_GetError());

	return 1; // audio was qued
}

Ampler_state *init() {
	Ampler_state *state = malloc(sizeof Ampler_state);
	SDL_memset(state, 0, sizeof Ampler_state);

	state -> size = sizeof Ampler_state;

	SDL_AudioSpec want = { 0 }, have = { 0 };
	want.freq = SAMPLE_RATE;
	want.format = AUDIO_S16;
	want.channels = CHANNELS;
	want.samples = 512;
	want.callback = NULL; // use que funcs
	want.userdata = NULL;

	state -> playdev = SDL_OpenAudioDevice(
		NULL, // default device
		0, // not capture
		&want,
		&have,
		0 // no changes allowed
	);
	if(!(state -> playdev))
		puts(SDL_GetError());

	puts("init.");
	return state;
}

int ampler_main(SDL_Window *w, SDL_Renderer *r, Ampler_state **u_data) {
	if(*u_data == NULL) *u_data = init();

	int old_size = (*u_data) -> size, new_size = sizeof Ampler_state;
	if(old_size < new_size) {
		printf("increasing size. %i to %i\n", old_size, new_size);
		Ampler_state *nu = malloc(new_size);
		SDL_memset(nu, 0, new_size);
		SDL_memcpy(nu, *u_data, old_size);
		nu -> size = new_size;
		free(*u_data);
		*u_data = nu;
	}

	Ampler_state *state = *u_data;

	SDL_PauseAudioDevice(state -> playdev, 0); // unpause audio
	while (1) {
		SDL_Event e;
		while(SDL_PollEvent(&e))
			if (e.type == SDL_QUIT)
				return 1;

		audio_frame(state);
		// draw_frame(w, r, state);

		SDL_RenderPresent(r);
		SDL_Delay(1);

		if (!remove("reload-trigger")) {
			SDL_PauseAudioDevice(state -> playdev, 1); // pause audio
			puts("removed reload-trigger, reloading...");
			return 0;
		}
	}
}