#include "freelist.h"
#include "stddef.h"
#include <assert.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>

/* Fiddle these around according to your need. */
#ifdef FREELIST_NOALIGN
#define ALIGN(x) (x)
#else // FREELIST_NOALIGN

/* Align to nearest multiple of sizeof(void*) */
static inline size_t align_up(size_t n) {
    return (n + sizeof(void *) - 1) & ~(sizeof(void *) - 1);
}

#define ALIGN(x) (align_up(x))
#endif // FREELIST_NOALIGN

/* Initialize the FreeList */
int fl_init(FreeList *fl, uintptr_t start, uintptr_t end, size_t itemsize) {
    size_t size = ALIGN(itemsize + sizeof(FreeListBlock));

    if (!fl || end <= start)
        return EXIT_FAILURE;

    fl->start = start;
    fl->end = end;
    fl->size = size;
    fl->allocated = 0;

    FreeListBlock *block = (FreeListBlock *)start;
    for (size_t i = 0; i < fl_capacity(fl); i++) {
        block->next = (FreeListBlock *)((void *)block + size);
        block->block_state = FL_FREE;
        block = block->next;
    }

    block->next = NULL;

    fl->free = (FreeListBlock *)start;
    return EXIT_SUCCESS;
}

/* Allocate some memory from the FreeList */
void *fl_alloc(FreeList *fl) {
    if (!fl->free || fl->free->block_state != FL_FREE)
        return NULL;

    FreeListBlock *m = fl->free;
    m->block_state = FL_USED;

    fl->free = fl->free->next;
    fl->allocated++;

    return ((void *)m) + sizeof(FreeListBlock);
}

/* Return some memory to the FreeList */
int fl_free(FreeList *fl, void *ptr) {
    if (!fl_is_managed(fl, ptr)) {
        return EXIT_FAILURE; /* We cant free memory we do not own */
    }

    FreeListBlock *block = (FreeListBlock *)((uintptr_t)ptr - sizeof(FreeListBlock));

    if (block->block_state != FL_USED) {
        return EXIT_FAILURE; /* Block must be used */
    }

    block->block_state = FL_FREE;
    block->next = fl->free;
    fl->free = block;
    fl->allocated--;

    return EXIT_SUCCESS;
}

/* Returns how many slots are occupied */
size_t fl_allocated(FreeList *fl) {
    return fl->allocated;
}

/* Returns how many free slots are available (O(1)) */
size_t fl_available(FreeList *fl) {
    return fl_capacity(fl) - fl->allocated;
}

/* Returns the total amount of items the freelist will hold */
size_t fl_capacity(FreeList *fl) {
    return (fl->end - fl->start) / fl->size;
}

/* Check if a piece of memory is managed by the FreeList */
int fl_is_managed(FreeList *fl, void *ptr) {
    return ((uintptr_t)ptr >= fl->start && (uintptr_t)ptr < fl->end);
}

/* Returns the ratio of metadata versus data as a scalar in range 0..1 */
float fl_utilization(FreeList *fl, size_t itemsize) {
    return (float)itemsize / fl->size;
}

/* Walks the free pages/slots, returns total count (O(n), given no cycles) */
size_t fl_check(FreeList *fl) {
    int            avail = 0;
    FreeListBlock *cursor = fl->free;

    while (cursor->next != NULL) {
        avail++;
        assert(cursor->block_state == FL_FREE);
        cursor = cursor->next;
    }

    return avail;
}