#ifdef HAVE_CONFIG_H
#include "config.h"
#endif

#include "shmalloc.h"

#include <stdio.h>
#include <string.h>
#include <assert.h>

struct _ShmAllocSpace
{
  size_t size;

  ShmAllocBlock *blocks;
};

struct _ShmAllocBlock
{
  int use_count;

  ShmAllocSpace *space;

  unsigned long offset;
  unsigned long size;

  ShmAllocBlock *next;
};


ShmAllocSpace *
shm_alloc_space_new (size_t size)
{
  ShmAllocSpace *self = spalloc_new (ShmAllocSpace);

  memset (self, 0, sizeof (ShmAllocSpace));

  self->size = size;

  return self;
}

void
shm_alloc_space_free (ShmAllocSpace * self)
{
  assert (self && self->blocks == NULL);
  spalloc_free (ShmAllocSpace, self);
}


ShmAllocBlock *
shm_alloc_space_alloc_block (ShmAllocSpace * self, unsigned long size)
{
  ShmAllocBlock *block;
  ShmAllocBlock *item = NULL;
  ShmAllocBlock *prev_item = NULL;
  unsigned long prev_end_offset = 0;


  for (item = self->blocks; item; item = item->next) {
    unsigned long max_size = 0;

    max_size = item->offset - prev_end_offset;

    if (max_size >= size)
      break;

    prev_end_offset = item->offset + item->size;
    prev_item = item;
  }

  /* Did not find space before an existing block */
  if (self->blocks && !item) {
    /* Return NULL if there is no big enough space, otherwise, there is space
     * at the end */
    if (self->size - prev_end_offset < size)
      return NULL;
  }

  block = spalloc_new (ShmAllocBlock);
  memset (block, 0, sizeof (ShmAllocBlock));
  block->offset = prev_end_offset;
  block->size = size;
  block->use_count = 1;
  block->space = self;

  if (prev_item)
    prev_item->next = block;
  else
    self->blocks = block;

  block->next = item;

  return block;
}

unsigned long
shm_alloc_space_alloc_block_get_offset (ShmAllocBlock * block)
{
  return block->offset;
}

static void
shm_alloc_space_free_block (ShmAllocBlock * block)
{
  ShmAllocBlock *item = NULL;
  ShmAllocBlock *prev_item = NULL;
  ShmAllocSpace *self = block->space;

  for (item = self->blocks; item; item = item->next) {
    if (item == block) {
      if (prev_item)
        prev_item->next = item->next;
      else
        self->blocks = item->next;
      break;
    }
    prev_item = item;
  }

  spalloc_free (ShmAllocBlock, block);
}

ShmAllocBlock *
shm_alloc_space_block_get (ShmAllocSpace * self, unsigned long offset)
{
  ShmAllocBlock *block = NULL;

  for (block = self->blocks; block; block = block->next) {
    if (block->offset <= offset && (block->offset + block->size) > offset)
      return block;
  }

  return NULL;
}


void
shm_alloc_space_block_inc (ShmAllocBlock * block)
{
  block->use_count++;
}

void
shm_alloc_space_block_dec (ShmAllocBlock * block)
{
  block->use_count--;

  if (block->use_count <= 0)
    shm_alloc_space_free_block (block);
}