#include "world.h"
#include "entity.h"

/* ========================== *
 * World allocation
 * ========================== */

void world_alloc(struct world *world)
{
    MEMZERO_STRUCT(world);
    world->entities_arena = arena_alloc(GIGABYTE(64));
    world->entities = (struct entity *)world->entities_arena.base;
}

void world_copy_replace(struct world *dest, struct world *src)
{
    __prof;

    /* Copy non-arena fields */
    MEMCPY(dest, src, FIELD_OFFSETOF(struct world, _copy_barrier));

    /* Copy arena contents */
    arena_copy_replace(&dest->entities_arena, &src->entities_arena);
}

/* ========================== *
 * Entity allocation
 * ========================== */

struct entity *world_alloc_entity(struct world *world)
{
    struct entity *entity = NULL;
    struct entity_handle handle;
    if (world->first_free_entity.gen) {
        /* Reuse from free list */
        entity = world_entity_from_handle(world, world->first_free_entity);
        world->first_free_entity = entity->next_free;
        handle = entity->handle;
    } else {
        /* Make new */
        u64 idx = world->entities_count++;
        entity = arena_push(&world->entities_arena, struct entity);
        handle = (struct entity_handle) { .gen = 1, .idx = idx };
    }
    *entity = *entity_nil();
    entity->handle = handle;
    return entity;
}

void world_release_entity(struct world *world, struct entity *entity)
{
    struct entity_handle next_free = world->first_free_entity;
    world->first_free_entity = entity->handle;
    *entity = (struct entity) {
        .handle.gen = entity->handle.gen + 1,
        .next_free = next_free
    };
}

/* ========================== *
 * Queries
 * ========================== */

/* Returns a valid entity or nil entity. Always safe to read result, need to check to write. */
struct entity *world_entity_from_handle(struct world *world, struct entity_handle handle)
{
    if (handle.idx < world->entities_count) {
        struct entity *entities = world->entities;
        struct entity *entity = &entities[handle.idx];
        if (entity->handle.gen == handle.gen) {
            return entity;
        }
    }
    return entity_nil();
}

/* ========================== *
 * Tree
 * ========================== */

void world_link_entities(struct world *world, struct entity *parent, struct entity *child)
{
    struct entity *first_child = world_entity_from_handle(world, parent->first);
    struct entity *last_child = world_entity_from_handle(world, parent->last);

    child->prev = last_child->handle;
    child->parent = parent->handle;

    if (last_child->valid) {
        last_child->next = child->handle;
    }
    parent->last = child->handle;

    if (!first_child->valid) {
        parent->first = child->handle;
    }
}