#ifndef WORLD_GRID_H
#define WORLD_GRID_H

/*
 * Where things are, by ground cell: asking "what's around here" looks at the
 * few things in the cells round about instead of everything on the site.
 * Built once a frame (things moving a little in between don't matter: each
 * thing sits in every cell its footprint touches, plus a margin).
 */

#include <stdbool.h>

#include "world/object.h"

#define NEAR_CELL 2.0f   /* meters */

typedef struct Grid {
    int      n;          /* cells along a side */
    int     *start;      /* cell k's things: items[start[k] .. start[k+1]) */
    int     *items;      /* indices into the world's objects */
    int      items_cap;
    unsigned *seen;      /* (each thing once per question) */
    int      seen_cap;
    unsigned stamp;
    int      built_count; /* how many things it was built for */
} Grid;

void Grid_build(Grid *g, Object *const *objects, int count);
void Grid_free(Grid *g);
/* Indices of things whose footprint comes within r of (x, z); returns how many,
   or -1 if they don't fit (or the grid isn't built for count things: look at all). */
int  Grid_near(Grid *g, int count, float x, float z, float r, int *out, int max);

/* Like Grid_near, but the things themselves, in the order they have in objects
   (so answers don't depend on the grid): returns how many, or -1 (look at all). */
int  Grid_nearObjects(Grid *g, Object *const *objects, int count, float x, float z, float r, Object **out, int max);

#endif /* WORLD_GRID_H */