/*
 * @author  xamidev <xamidev@riseup.net>
 * @brief   Physical memory manager from freelist
 * @license GPL-3.0-only
 */

/*
pmm - Physical Memory Manager
will manage 4kb pages physically
it will probably need to get some info from Limine,
to see which pages are used by kernel/bootloader/mmio/fb etc.
*/

#include "paging.h"
#include <limine.h>
#include <stddef.h>
#include <stdint.h>
#include <kernel.h>
#include "mem/misc/utils.h"
#include "pmm.h"

/*
First we'll have to discover the physical memory layout,
and for that we can use a Limine request.
*/

/*
We will look for the biggest usable physical memory region
and use this for the bitmap. The reserved memory will be ignored.
*/

struct limine_memmap_entry* biggest_entry;

static void pmm_find_biggest_usable_region(struct limine_memmap_response* memmap, struct limine_hhdm_response* hhdm)
{
    // Max length of a usable memory region
    uint64_t length_max = 0;
    uint64_t offset = hhdm->offset;

    DEBUG("Usable Memory:");
    for (size_t i=0; i<memmap->entry_count; i++)
    {
        struct limine_memmap_entry* entry = memmap->entries[i];

        if (entry->type == LIMINE_MEMMAP_USABLE)
        {
            DEBUG("0x%p-0x%p mapped at 0x%p-0x%p", entry->base, entry->base+entry->length,
                        entry->base+offset, entry->base+entry->length+offset);
            if (entry->length > length_max)
            {
                length_max = entry->length;
                biggest_entry = entry;
            }
        }
    }

    DEBUG("Biggest usable memory region:");
    DEBUG("0x%p-0x%p mapped at 0x%p-0x%p", biggest_entry->base, biggest_entry->base + biggest_entry->length,
            biggest_entry->base+offset, biggest_entry->base+biggest_entry->length+offset);
}

// Offset from Higher Half Direct Map
uint64_t hhdm_off;

static uintptr_t g_freelist = 0;

uintptr_t pmm_alloc()
{
    if (!g_freelist)
	{
		panic(NULL, "PMM is out of memory!");		
	}
    uintptr_t addr = g_freelist;
    g_freelist = *(uintptr_t*) PHYS_TO_VIRT(g_freelist);
    return addr;
}

void pmm_free(uintptr_t addr)
{
    *(uintptr_t*) PHYS_TO_VIRT(addr) = g_freelist;
    g_freelist = addr;
}

static void pmm_init_freelist()
{
    // We simply call pmm_free() on each page that is marked USABLE
    // in our big memory region.
    uint64_t base = ALIGN_UP(biggest_entry->base, PAGE_SIZE);
    uint64_t end = ALIGN_DOWN(biggest_entry->base + biggest_entry->length, PAGE_SIZE);

    uint64_t page_count=0;
    for (uint64_t addr = base; addr < end; addr += PAGE_SIZE)
    {
        pmm_free(addr);
        //DEBUG("page %u lives at phys 0x%p (virt 0x%p)", page_count, addr, PHYS_TO_VIRT(addr));
        page_count++;
    }
    DEBUG("%u frames in freelist, available for use (%u bytes)", page_count, page_count*PAGE_SIZE);
}

void pmm_init(struct limine_memmap_response* memmap, struct limine_hhdm_response* hhdm)
{
    hhdm_off = hhdm->offset;
    pmm_find_biggest_usable_region(memmap, hhdm);
    //pmm_allocate_bitmap(hhdm); too complicated for my small brain
    
    // Now we have biggest USABLE region,
    // so to populate the free list we just iterate through it
    pmm_init_freelist();
}