#include <string.h>
#include "filesys/file.h"
#include "threads/thread.h"
#include "threads/vaddr.h"
#include "threads/malloc.h"
#include "threads/palloc.h"
#include "vm/mmap.h"
#include "vm/page.h"

static struct mmap_table_entry *mmap_table_get (struct mmap_table *table,
    mapid_t mapid);

/* initialize memory mapped files table */
bool
mmap_table_init (struct mmap_table *table)
{
  table->ids = palloc_get_page (PAL_ZERO);
  if (table->ids == NULL)
    return false;
  table->id_cap  = PGSIZE / sizeof (table->ids[0]);
  table->id_free = 0;
  table->id_max  = -1;
  return true;
}

/* frees the content of mmap table */
void
mmap_table_free (struct mmap_table *table)
{
  //TODO
  palloc_free_page (table->ids);
}

/* inserts a new mmap entry in the mmap table
   returns -1 if entry is invalid or already in the table */
mapid_t
mmap_table_insert (struct mmap_table *table, void *addr, struct file *file,
    off_t len)
{
  off_t ofs = 0;
  size_t page_read_bytes;
  struct mmap_table_entry *mme;
  mapid_t mapid;

  /* no more entries left */
  if (table->id_free >= table->id_cap)
    return -1;

  mme = malloc (sizeof *mme);
  if (mme == NULL)
    return -1;

  mapid = table->id_free++;
  mme->addr  = addr;
  mme->file  = file;
  table->ids[mapid] = mme;

  /* create needed pages in page table */
  while (len > 0)
    {
      page_read_bytes = (len < PGSIZE) ? len : PGSIZE;

      if (!page_table_insert_segment (&thread_current ()->page_table, file, ofs,
            addr, page_read_bytes, true))
        return -1;

      /* Advance. */
      len  -= PGSIZE;
      ofs  += page_read_bytes;
      addr += PGSIZE;
    }

  /* update index of free/max mapid index */
  if (mapid > table->id_max)
    table->id_max = mapid;
  while (table->ids[table->id_free] != NULL)
  {
    table->id_free++;
    if (table->id_free >= table->id_cap)
      break;
  }

  return mapid;
}

static struct mmap_table_entry *
mmap_table_get (struct mmap_table *table, mapid_t mapid)
{
  if (mapid < 0 || mapid >= table->id_cap || !table->ids[mapid])
    return NULL;
  return table->ids[mapid];
}

bool
mmap_table_remove (struct mmap_table *table, mapid_t mapid)
{
  struct mmap_table_entry *mme = mmap_table_get(table, mapid);
  if (mme == NULL)
    return false;

  table->ids[mapid] = NULL;

  //TODO

  /* update index of free/max file descriptor index */
  if (mapid < table->id_free)
    table->id_free = mapid;
  while (table->ids[table->id_max] == NULL)
  {
    table->id_max--;
    if (table->id_max < 0)
      break;
  }

  return true;
}