#include "entity.h"

static int entity_collide_with(struct Entity *restrict, struct Entity *restrict,
                               int mask);

struct Entity *
entity_collide(void *restrict entity, int mask)
{
	struct Entity *const e = entity;
	int i;

	i = ENTITY_GRID_SIZE;
	while (i-- > 0)
		if (entity_collide_with(e, g_entity_grid[i], mask))
			return g_entity_grid[i];

	return NULL;
}

/* axis aligned bounding box collision checking */
static int
entity_collide_with(struct Entity *restrict self, struct Entity *restrict other,
                    int mask)
{
	const int sx = self->x + self->hb_x;
	const int sy = self->y + self->hb_y;
	const int ox = other->x + other->hb_x;
	const int oy = other->y + other->hb_y;

	if (self == NULL || other == NULL || self == other ||
	    !(mask & other->layer))
		return 0;

	return sx < ox + other->hb_w && sx + self->hb_w > ox &&
	       sy < oy + other->hb_h && sy + self->hb_h > oy;
}