#include "SDL_FPSCounter.h"

#include <SDL3/SDL.h>
#include <stdlib.h>

int SDL_CreateFPSCounter(SDL_FPSCounter* counter, uint32_t window_length)
{
	counter->window = malloc(sizeof(uint64_t) * window_length);
	if (counter->window == NULL) {
		SDL_OutOfMemory();
		return -1;
	}
	memset(counter->window, 0, window_length * sizeof(uint64_t));
	counter->frequency = SDL_GetPerformanceFrequency();
	counter->window_index = 0;
	counter->window_length = window_length;

	return EXIT_SUCCESS;
}

void SDL_DestroyFPSCounter(SDL_FPSCounter* counter)
{
	free(counter->window);
	memset(counter, 0, sizeof *counter);
}

int SDL_FPSCounterTick(SDL_FPSCounter* counter)
{
	counter->window[counter->window_index] = SDL_GetPerformanceCounter();
	counter->window_index++;
	counter->window_index = counter->window_index % counter->window_length;

	return EXIT_SUCCESS;
}

uint64_t SDL_FPSCounterFPS(SDL_FPSCounter* counter)
{
	uint64_t last = counter->window[counter->window_index];
	uint64_t current;
	uint64_t acc_difference = 0;

	for (uint32_t i = (counter->window_index + 1) % counter->window_length; i != counter->window_index; i = (i + 1) % counter->window_length) {
		current = counter->window[i];
		acc_difference += current - last;

		last = current;
	}

	uint64_t average_difference = acc_difference / (counter->window_length - 1);
	return counter->frequency / average_difference;
}