#ifndef TREETRIE_H_f55a3f6d_ef43_45d3_bec3_496a196b5db1
#define TREETRIE_H_f55a3f6d_ef43_45d3_bec3_496a196b5db1

#ifdef __cplusplus
extern "C" {
#endif

typedef enum tt_tag_t {
  TT_TAG_TAIL = 0,
  TT_TAG_BRANCH,
  TT_TAG_LEAF, /* only case where one of node a or b points to non-node */
  TT_TAG_NODE
} tt_tag_t;

typedef enum tt_reserved_node_idx_t {
  TT_ERROR = 0, /* invalid node index, means "no node at all", not even empty */
  TT_EMPTY, /* empty treetrie */
  TT_OK, /* terminal marker */

  TT_FIRST_VALID_NODE_IDX
} tt_reserved_node_idx_t;

typedef uint32_t tt_node_idx_t; /* N.B. tt_reserved_node_idx_t */

typedef uint32_t tt_atom_t;

typedef union tt_header_t {
  uint32_t next_free;
  struct {
    uint32_t refcount : 24;
    uint32_t index : 6;
    tt_tag_t tag : 2;
  } inuse;
} tt_header_t;

#define TT_REFCOUNT_LIMIT ((1 << 24) - 1)

typedef struct tt_node_t {
  tt_node_idx_t a; /* always a real node idx */
  tt_node_idx_t b; /* a real node idx unless corresponding tag is TT_TAG_LEAF */
} tt_node_t;

typedef struct tt_arena_t {
  /* Fields for the Robin Hood hashset used for hashconsing of tt_nodes */
  unsigned int max_probe;
  unsigned int live_count;
  unsigned int table_length;
  tt_node_idx_t *table;

  tt_header_t *headers;
  tt_node_t *nodes;

  tt_node_idx_t free_chain;
} tt_arena_t;

extern int tt_arena_init(tt_arena_t *a);
extern void tt_arena_done(tt_arena_t *a);

/* Returns 0 if consing failed (because of out-of-memory).
   Otherwise, returns a nonzero index.
   Grabs na and nb (according to tag) IF it needs to allocate a new node, otherwise does not.
   DOES NOT increase the reference count of the returned node. */
extern tt_node_idx_t tt_arena_cons(tt_arena_t *a,
				   uint32_t tag,
				   uint32_t index,
				   tt_node_idx_t na,
				   tt_node_idx_t nb);

extern tt_node_idx_t tt_grab(tt_arena_t *a, tt_node_idx_t i);
extern void tt_drop(tt_arena_t *a, tt_node_idx_t i);

/* WARNING: private, unsafe */
typedef uint32_t tt_hash_t;
extern tt_hash_t tt_hash_node(tt_arena_t *a, tt_node_idx_t i);

#ifdef __cplusplus
}
#endif

#endif