#ifndef NVIM_MEMFILE_DEFS_H
#define NVIM_MEMFILE_DEFS_H

#include <stdint.h>
#include <stdbool.h>

#include "nvim/types.h"

/// A block number.
///
/// Blocks numbered from 0 upwards have been assigned a place in the actual
/// file. The block number is equal to the page number in the file. The blocks
/// with negative numbers are currently in memory only.
typedef int64_t blocknr_T;

/// A hash item.
///
/// Items' keys are block numbers.
/// Items in the same bucket are organized into a doubly-linked list.
///
/// Therefore, items can be arbitrary data structures beginning with pointers
/// for the list and and a block number key.
typedef struct mf_hashitem {
  struct mf_hashitem *mhi_next;
  struct mf_hashitem *mhi_prev;
  blocknr_T mhi_key;
} mf_hashitem_T;

/// Initial size for a hashtable.
#define MHT_INIT_SIZE 64

/// A chained hashtable with block numbers as keys and arbitrary data structures
/// as items.
///
/// This is an intrusive data structure: we require that items begin with
/// mf_hashitem_T which contains the key and linked list pointers. List of items
/// in each bucket is doubly-linked.
typedef struct mf_hashtab {
  size_t mht_mask;              /// mask used to mod hash value to array index
                                /// (nr of items in array is 'mht_mask + 1')
  size_t mht_count;             /// number of items inserted
  mf_hashitem_T **mht_buckets;  /// points to the array of buckets (can be
                                /// mht_small_buckets or a newly allocated array
                                /// when mht_small_buckets becomes too small)
  mf_hashitem_T *mht_small_buckets[MHT_INIT_SIZE];     /// initial buckets
} mf_hashtab_T;

/// A block header.
///
/// There is a block header for each previously used block in the memfile.
///
/// The block may be linked in the used list OR in the free list.
/// The used blocks are also kept in hash lists.
///
/// The used list is a doubly linked list, most recently used block first.
/// The blocks in the used list have a block of memory allocated.
/// mf_used_count is the number of pages in the used list.
/// The hash lists are used to quickly find a block in the used list.
/// The free list is a single linked list, not sorted.
/// The blocks in the free list have no block of memory allocated and
/// the contents of the block in the file (if any) is irrelevant.
typedef struct bhdr {
  mf_hashitem_T bh_hashitem;         /// header for hash table and key
#define bh_bnum bh_hashitem.mhi_key  /// block number, part of bh_hashitem

  struct bhdr *bh_next;              /// next block header in free or used list
  struct bhdr *bh_prev;              /// previous block header in used list
  void *bh_data;                     /// pointer to memory (for used block)
  unsigned bh_page_count;            /// number of pages in this block

#define BH_DIRTY    1U
#define BH_LOCKED   2U
  unsigned bh_flags;                 // BH_DIRTY or BH_LOCKED
} bhdr_T;

/// A block number translation list item.
///
/// When a block with a negative number is flushed to the file, it gets
/// a positive number. Because the reference to the block is still the negative
/// number, we remember the translation to the new positive number in the
/// double linked trans lists. The structure is the same as the hash lists.
typedef struct mf_blocknr_trans_item {
  mf_hashitem_T nt_hashitem;             /// header for hash table and key
#define nt_old_bnum nt_hashitem.mhi_key  /// old, negative, number
  blocknr_T nt_new_bnum;                 /// new, positive, number
} mf_blocknr_trans_item_T;

/// A memory file.
typedef struct memfile {
  char_u *mf_fname;                  /// name of the file
  char_u *mf_ffname;                 /// idem, full path
  int mf_fd;                         /// file descriptor
  bhdr_T *mf_free_first;             /// first block header in free list
  bhdr_T *mf_used_first;             /// mru block header in used list
  bhdr_T *mf_used_last;              /// lru block header in used list
  unsigned mf_used_count;            /// number of pages in used list
  unsigned mf_used_count_max;        /// maximum number of pages in memory
  mf_hashtab_T mf_hash;              /// hash lists
  mf_hashtab_T mf_trans;             /// trans lists
  blocknr_T mf_blocknr_max;          /// highest positive block number + 1
  blocknr_T mf_blocknr_min;          /// lowest negative block number - 1
  blocknr_T mf_neg_count;            /// number of negative blocks numbers
  blocknr_T mf_infile_count;         /// number of pages in the file
  unsigned mf_page_size;             /// number of bytes in a page
  bool mf_dirty;                      /// TRUE if there are dirty blocks
} memfile_T;

#endif  // NVIM_MEMFILE_DEFS_H
