#include "framer.h"

/* Installs a MemFramer at the specified address */
MemFramer *mem_framer_install(void *addr, usize end, uint blksz) {
	MemFramer *self = addr;
	usize selfend = (usize)(self + 1);
	usize next = ALIGN_UP(selfend, blksz);

	*self = (MemFramer) {
		.allocator = (MemAllocator) {
			.alloc = mem_framer_alloc,
			.free = mem_framer_free
		},
		.next = next,
		.end = end,
		.blksz = blksz
	};

	return self;
}

/* Allocates a frame */
void *mem_framer_alloc(MemAllocator *inner, usize n) {
	/* When allocating a frame, we have two paths:
	      1. The freelist is not empty: give away
	         the last freed frame
	      2. The freelist is empty: bump away the next
	         frame (pointed at by the next member)
	   The alloc must fail the freelist is empty and that
	   the next is beyond the end of the region */
	
	MemFramer *self = (MemFramer*)inner;

	/* The implementation does not support more than
	   one frame */
	if (n == 0 || n > self->blksz)
		return nil;

	void *ptr = nil;

	if (self->free) {
		ptr = self->free;
		self->free = self->free->next;
	} else if (self->next + self->blksz <= self->end) {
		ptr = (void*)self->next;
		self->next += self->blksz;
	}

	return ptr;
}

/* Frees a frame */
void mem_framer_free(MemAllocator *inner, void *ptr) {
	/* NOTE: this implementation does make the assumption
	         that the given pointer is the base of the allocated
	         region without correction */

	MemFramer *self = (MemFramer*)inner;

	MemFramerFreed *freed = ptr;
	freed->next = self->free;
	self->free = freed;
}