#include <stdbool.h>
#include <string.h>
#include "memblock.h"

static memblock_region_t init_memory_regions[MEMBLOCK_INIT_MEMORY_REGION_COUNT];
static memblock_region_t init_reserved_regions[MEMBLOCK_INIT_RESERVED_REGION_COUNT];

memblock_t memblock = {
	.memory.regions = init_memory_regions,
	.memory.count = 0,
	.memory.max = MEMBLOCK_INIT_MEMORY_REGION_COUNT,
	.memory.name = "memory",

	.reserved.regions = init_reserved_regions,
	.reserved.count = 0,
	.reserved.max = MEMBLOCK_INIT_RESERVED_REGION_COUNT,
	.reserved.name = "reserved",
};

static int memblock_insert_region(memblock_type_t *type, memblock_region_t *to_add)
{
	unsigned int i = 0;

	for (i = 0; i < type->count; i++) {
		const memblock_region_t *cur = &type->regions[i];

		if (cur->base >= to_add->limit) {
			break;
		}
	}

	memblock_region_t *src = &type->regions[i];
	memblock_region_t *dst = &type->regions[i + 1];
	unsigned int count = type->count - i;

	memmove(dst, src, count * sizeof *src);

	*src = *to_add;
	type->count++;

	return 0;
}

static int memblock_remove_region(memblock_type_t *type, unsigned int i)
{
	if (i >= type->count) {
		return -1;
	}

	memblock_region_t *src = &type->regions[i + 1];
	memblock_region_t *dst = &type->regions[i];
	unsigned int count = type->count - i;

	memmove(dst, src, count * sizeof *src);
	type->count--;
	return 0;
}

int memblock_add_range(memblock_type_t *type, uintptr_t base, size_t size)
{
	if (size == 0) {
		return 0;
	}

	uintptr_t limit = base + size - 1;

	if (type->count == 0) {
		type->regions[0].base = base;
		type->regions[0].limit = limit;
		type->count++;
		return 0;
	}

	memblock_region_t new_region = { .base = base, .limit = limit };
	bool add_new = true;

	for (unsigned int i = 0; i < type->count; i++) {
		memblock_region_t *cur_region = &type->regions[i];

		/* case 1: the region being added and the current region have no connection what-so-ever (no overlaps) */
		if (cur_region->limit + 1 < new_region.base || cur_region->base > new_region.limit) {
			continue;
		}

		/* case 2: the region being added matches a region already in the list. */
		if (cur_region->base == new_region.base && cur_region->limit == new_region.limit) {
			/* nothing needs to be done */
			add_new = false;
			break;
		}


		/* case 3: the region being added completely contains a region already in the list. */
		if (cur_region->base > new_region.base && cur_region->limit <= new_region.limit) {
			memblock_remove_region(type, i);

			/* after memblock_remove_region(), a different region will have moved into the array slot referenced by i.
			 * decrementing i means we'll stay at the current index and process this region. */
			i--;
			continue;
		}


		/* case 4: the region being added meets or partially overlaps a region already in the list. */

		/* there can be an overlap at the beginning and the end of the region being added,
		 * anything else is either a full overlap (case 3) or not within the region being added at all.
		 * to handle this, remove the region that's already in the list and extend the region being added to cover it */
		if (new_region.base > cur_region->base || new_region.base == cur_region->limit - 1) {
			/* the new region overlaps the END of the current region, change the base of the new region to match that of the current region. */
			new_region.base = cur_region->base;
		} else if (new_region.base < cur_region->base || new_region.limit + 1 == cur_region->base){
			/* the new region overlaps the BEGINNING of the current region, change the limit of the new region to match that of the current region. */
			new_region.limit = cur_region->limit;
		} else {
			continue;
		}

		/* with the new region updated to include the current region, we can remove the current region from the list */
		memblock_remove_region(type, i);
		i--;
	}

	if (add_new) {
		memblock_insert_region(type, &new_region);
	}

	return 0;
}

int memblock_add(uintptr_t base, size_t size)
{
	return memblock_add_range(&memblock.memory, base, size);
}

int memblock_reserve(uintptr_t base, size_t size)
{
	return memblock_add_range(&memblock.reserved, base, size);
}

uintptr_t memblock_alloc(size_t size)
{
	return 0;
}