#include <kernel/arch/generic.h>
#include <kernel/malloc.h>
#include <kernel/panic.h>
#include <kernel/util.h>
#include <shared/mem.h>
#include <stdbool.h>
#include <stdint.h>

extern uint8_t pbitmap[]; /* linker.ld */
static size_t pbitmap_len; /* in bytes */
static void *memtop;
static void *firstfreepage; /* not necessarily actually free */

static size_t
toindex(void *p)
{
	assert((void*)pbitmap <= p);
	return ((uintptr_t)p - (uintptr_t)pbitmap) / PAGE_SIZE;
}

static bool
pbitmap_get(void *p)
{
	size_t i = toindex(p);
	size_t b = i / 8;
	uint8_t m = 1 << (i&7);
	assert(b < pbitmap_len); // TODO the bitmap should be a tad longer
	return (pbitmap[b]&m) != 0;
}

static bool
pbitmap_set(void *p, bool v)
{
	size_t i = toindex(p);
	size_t b = i / 8;
	uint8_t m = 1 << (i&7);
	assert(b < pbitmap_len);
	bool prev = (pbitmap[b]&m) != 0;
	if (v) {
		pbitmap[b] |= m;
	} else {
		pbitmap[b] &= ~m;
	}
	return prev;
}

void
mem_init(void *p)
{
	memtop = p;
	kprintf("memory   %8x -> %8x\n", &_bss_end, memtop);
	pbitmap_len = toindex(memtop) / 8;
	memset(pbitmap, 0, pbitmap_len);
	mem_reserve(pbitmap, pbitmap_len);
	firstfreepage = pbitmap;
}

void
mem_reserve(void *addr, size_t len)
{
	kprintf("reserved %8x -> %8x\n", addr, addr + len);

	void *top = min(addr + len, memtop);
	addr = (void*)((uintptr_t)addr & ~PAGE_MASK); /* round down to page */
	for (void *p = max(addr, (void*)pbitmap); p < top; p += PAGE_SIZE) {
		/* this doesn't allow overlapping reserved regions, but, more
		 * importantly, it prevents reserving an already allocated page */
		if (pbitmap_get(p)) {
			panic_invalid_state();
		}
		pbitmap_set(p, true);
	}
}

void *
page_zalloc(size_t pages)
{
	void *p = page_alloc(pages);
	memset(p, 0, pages * PAGE_SIZE);
	return p;
}

void *
page_alloc(size_t pages)
{
	assert(pages == 1);
	for (void *p = firstfreepage; p < memtop; p += PAGE_SIZE) {
		if (!pbitmap_get(p)) {
			pbitmap_set(p, true);
			firstfreepage = p + PAGE_SIZE;
			return p;
		}
	}
	kprintf("we ran out of memory :(\ngoodbye.\n");
	panic_unimplemented();
}

void
page_free(void *addr, size_t pages)
{
	assert((void*)pbitmap <= addr);
	for (size_t i = 0; i < pages; i++) {
		if (pbitmap_set(addr + i*PAGE_SIZE, false) == false) {
			panic_invalid_state();
		}
	}
	firstfreepage = min(firstfreepage, addr);
}