#include "stars.h"
#include "conf.h"
#include "raygint/display.h"
#include <stdlib.h>

struct Star {
	int x;
	float y;
	float spd;
	int stretch;
};

static struct Star stars[STARS_COUNT];

static void star_rand(struct Star *);
static void star_update(struct Star *);
static void star_draw(struct Star *);

void
stars_init(void)
{
	int i = STARS_COUNT;
	while (i-- > 0) {
		stars[i].y = (float)(rand() % DHEIGHT);
		star_rand(&stars[i]);
	}
}

void
stars_update(void)
{
	int i = STARS_COUNT;
	while (i-- > 0)
		star_update(&stars[i]);
}

void
stars_draw(void)
{
	int i = STARS_COUNT;
	while (i-- > 0)
		star_draw(&stars[i]);
}

static void
star_rand(struct Star *s)
{
	s->x = STARS_MIN_X + rand() % (STARS_MAX_X - STARS_MIN_X);
	s->spd = STARS_BASE_SPEED +
	         (float)(rand() & 0xff) / 0xff * STARS_SPEED_VARIATION;
	s->stretch = s->spd * STARS_STRETCH * STARS_SIZE - 1.0f;
}

static void
star_update(struct Star *s)
{
	s->y -= s->spd;
	if (s->y < -STARS_SIZE - STARS_MAX_SPEED * STARS_STRETCH) {
		s->y = DHEIGHT - STARS_SIZE;
		star_rand(s);
	}
}

static void
star_draw(struct Star *s)
{
	const int x = s->x;
	const int y = s->y;
	const int x2 = x + STARS_SIZE - 1;
	const int y2 = y + s->stretch;
	drect(x, y, x2, y2, STARS_COLOR);
}