%% -*- Prolog -*-

/**
 * @file   bhash.yap
 * @author VITOR SANTOS COSTA <vsc@VITORs-MBP.lan>
 * @date   Tue Nov 17 01:11:29 2015
 * 
 * @brief  Backtrackable Hash Tables
 * 
 * 
*/

:- source.
:- yap_flag(unknown,error).
:- style_check(all).

:- module(b_hash, [   b_hash_new/1,
		      b_hash_new/2,
		      b_hash_new/4,
		      b_hash_lookup/3,
		      b_hash_update/3,
		      b_hash_update/4,
		      b_hash_insert_new/4,
		      b_hash_insert/4,
		      b_hash_size/2,
		      b_hash_code/2,
		      is_b_hash/1,
        	      b_hash_to_list/2,
		      b_hash_values_to_list/2,
		      b_hash_keys_to_list/2
		    ]).

/**
 * @defgroup bhash Backtrackable Hash Tables
 * @ingroup library

@{

This library implements hash-arrays.
It requires the hash key to be a ground term. The library can
be loaded as

:- use_module( library( bhash ) ).

This code relies on backtrackable updates. The default hash key is
generated by term_hash/4.

*/

:- use_module(library(terms), [ term_hash/4 ]).


:- meta_predicate(b_hash_new(-,+,3,2)).

array_default_size(2048).

/** @pred is_b_hash( +Hash )

Term _Hash_ is a hash table.
*/
is_b_hash(V) :- var(V), !, fail.
is_b_hash(hash(_,_,_,_,_)).

/** @pred b_hash_new( -NewHash )

Create a empty hash table _NewHash_, with size 2048 entries.
*/
b_hash_new(hash(Keys, Vals, Size, N, _, _)) :-
	array_default_size(Size),
	array(Keys, Size),
	array(Vals, Size),
	create_mutable(0, N).

/** @pred b_hash_new( -_NewHash_, +_Size_ )

Create a empty hash table, with size _Size_ entries.
*/
b_hash_new(hash(Keys, Vals, Size, N, _, _), Size) :-
	array(Keys, Size),
	array(Vals, Size),
	create_mutable(0, N).

/** @pred b_hash_new( -_NewHash_, +_Size_, :_Hash_, :_Cmp_ )

Create a empty hash table, with size _Size_ entries.
_Hash_ defines a partition function, and _Cmp_ defined a comparison function.
*/
b_hash_new(hash(Keys,Vals, Size, N, HashF, CmpF), Size, HashF, CmpF) :-
	array(Keys, Size),
	array(Vals, Size),
	create_mutable(0, N).

/**
  @pred  b_hash_size( +_Hash_, -_Size_ )

_Size_ unifies with the size of the hash table _Hash_.
*/
b_hash_size(hash(_, _, Size, _, _, _), Size).

/**
  @pred b_hash_lookup( +_Key_, ?_Val_, +_Hash_ )

Search the ground term _Key_ in table _Hash_ and unify _Val_ with the associated entry.
*/
b_hash_lookup(Key, Val, hash(Keys, Vals, Size, _, F, CmpF)):-
	hash_f(Key, Size, Index, F),
	fetch_key(Keys, Index, Size, Key, CmpF, ActualIndex),
	array_element(Vals, ActualIndex, Mutable),
	get_mutable(Val, Mutable).

fetch_key(Keys, Index, Size, Key, CmpF, ActualIndex) :-
	array_element(Keys, Index, El),
	nonvar(El),
	(
	    cmp_f(CmpF, El, Key)
	->
	    Index = ActualIndex
	;
	    I1 is (Index+1) mod Size,
	    fetch_key(Keys, I1, Size, Key, CmpF, ActualIndex)
	).

/**
  @pred b_hash_update( +_Key_, +_Hash_, +NewVal )

Update to the value associated with the ground term _Key_ in table _Hash_ to _NewVal_.
*/
b_hash_update(Hash, Key, NewVal):-
	Hash = hash(Keys, Vals, Size, _, F, CmpF),
	hash_f(Key,Size,Index,F),
	fetch_key(Keys, Index, Size, Key, CmpF, ActualIndex),
	array_element(Vals, ActualIndex, Mutable),
	update_mutable(NewVal, Mutable).

/**
  @pred b_hash_update( +_Key_, -_OldVal_, +_Hash_, +NewVal )

Update to the value associated with the ground term _Key_ in table _Hash_ to _NewVal_, and unify _OldVal_ with the current value.
*/
b_hash_update(Hash, Key, OldVal, NewVal):-
	Hash = hash(Keys, Vals, Size, _, F, CmpF),
	hash_f(Key,Size,Index,F),
	fetch_key(Keys, Index, Size, Key, CmpF, ActualIndex),
	array_element(Vals, ActualIndex, Mutable),
	get_mutable(OldVal, Mutable),
	update_mutable(NewVal, Mutable).

/** b_hash_insert(+_Hash_, +_Key_, _Val_, +_NewHash_ )

Insert the term _Key_-_Val_ in table _Hash_ and unify _NewHash_ with the result. If ground term _Key_ exists, update the dictionary.
*/
b_hash_insert(Hash, Key, NewVal, NewHash):-
	Hash = hash(Keys, Vals, Size, N, F, CmpF),
	hash_f(Key,Size,Index,F),
	find_or_insert(Keys, Index, Size, N, CmpF, Vals, Key, NewVal, Hash, NewHash).

find_or_insert(Keys, Index, Size, N, CmpF, Vals, Key, NewVal, Hash, NewHash) :-
	array_element(Keys, Index, El),
	(
	    var(El)
	->
	    add_element(Keys, Index, Size, N, Vals, Key, NewVal, Hash, NewHash)
	;
	    cmp_f(CmpF, El, Key)
	->
	     % do rb_update
	    array_element(Vals, Index, Mutable),
	    update_mutable(NewVal, Mutable),
	    Hash = NewHash
        ;
	    I1 is (Index+1) mod Size,
	    find_or_insert(Keys, I1, Size, N, CmpF, Vals, Key, NewVal, Hash, NewHash)
	).

/**
  @pred b_hash_insert_new(+_Hash_, +_Key_, _Val_, +_NewHash_ )

Insert the term _Key_-_Val_ in table _Hash_ and unify _NewHash_ with the result. If ground term _Key_ exists, fail.
*/
b_hash_insert_new(Hash, Key, NewVal, NewHash):-
	Hash = hash(Keys, Vals, Size, N, F, CmpF),
	hash_f(Key,Size,Index,F),
	find_or_insert_new(Keys, Index, Size, N, CmpF, Vals, Key, NewVal, Hash, NewHash).

find_or_insert_new(Keys, Index, Size, N, CmpF, Vals, Key, NewVal, Hash, NewHash) :-
	array_element(Keys, Index, El),
	(
	    var(El)
	->
	    add_element(Keys, Index, Size, N, Vals, Key, NewVal, Hash, NewHash)
	;
	    cmp_f(CmpF, El, Key)
	->
	    fail
        ;
	    I1 is (Index+1) mod Size,
	    find_or_insert_new(Keys, I1, Size, N, CmpF, Vals, Key, NewVal, Hash, NewHash)
	).

add_element(Keys, Index, Size, N, Vals, Key, NewVal, Hash, NewHash) :-
	get_mutable(NEls, N),
	NN is NEls+1,
	update_mutable(NN, N),
	array_element(Keys, Index, Key),
	update_mutable(NN, N),
	array_element(Vals, Index, Mutable),
	create_mutable(NewVal, Mutable),
	(
	    NN > Size/3
	->
	    expand_array(Hash, NewHash)
	;
	    Hash = NewHash
	).

expand_array(Hash, NewHash) :-
	Hash == NewHash, !,
	Hash = hash(Keys, Vals, Size, _X, F, _CmpF),
	new_size(Size, NewSize),
	array(NewKeys, NewSize),
	array(NewVals, NewSize),
	copy_hash_table(Size, Keys, Vals, F, NewSize, NewKeys, NewVals),
	/* overwrite in place */
	setarg(1, Hash, NewKeys),
	setarg(2, Hash, NewVals),
	setarg(3, Hash, NewSize).

expand_array(Hash, hash(NewKeys, NewVals, NewSize, X, F, CmpF)) :-
	Hash = hash(Keys, Vals, Size, X, F, CmpF),
	new_size(Size, NewSize),
	array(NewKeys, NewSize),
	array(NewVals, NewSize),
	copy_hash_table(Size, Keys, Vals, F, NewSize, NewKeys, NewVals).

new_size(Size, NewSize) :-
	Size > 1048576, !,
	NewSize is Size+1048576.
new_size(Size, NewSize) :-
	NewSize is Size*2.

copy_hash_table(0, _, _, _, _, _, _) :- !.
copy_hash_table(I1, Keys, Vals, F, Size, NewKeys, NewVals) :-
	I is I1-1,
	array_element(Keys, I, Key),
	nonvar(Key), !,
	array_element(Vals, I, Val),
	insert_el(Key, Val, Size, F, NewKeys, NewVals),
	copy_hash_table(I, Keys, Vals, F, Size, NewKeys, NewVals).
copy_hash_table(I1, Keys, Vals, F, Size, NewKeys, NewVals) :-
	I is I1-1,
	copy_hash_table(I, Keys, Vals, F, Size, NewKeys, NewVals).

insert_el(Key, Val, Size, F, NewKeys, NewVals) :-
	hash_f(Key,Size,Index, F),
	find_free(Index, Size, NewKeys, TrueIndex),
	array_element(NewKeys, TrueIndex, Key),
	array_element(NewVals, TrueIndex, Val).

find_free(Index, Size, Keys, NewIndex) :-
	array_element(Keys, Index, El),
	(
	    var(El)
	->
	    NewIndex = Index
	;
	    I1 is (Index+1) mod Size,
	    find_free(I1, Size, Keys, NewIndex)
	).

hash_f(Key, Size, Index, F) :-
	var(F), !,
	term_hash(Key,-1,Size,Index).
hash_f(Key, Size, Index, F) :-
	call(F, Key, Size, Index).

cmp_f(F, A, B) :-
	var(F), !,
	A == B.
cmp_f(F, A, B) :-
	call(F, A, B).

/**
  @pred b_hash_to_list(+_Hash_, -_KeyValList_ )

The term _KeyValList_ unifies with a list containing all terms _Key_-_Val_ in the hash table.
*/
b_hash_to_list(hash(Keys, Vals, _, _, _, _), LKeyVals) :-
	Keys =.. (_.LKs),
	Vals =.. (_.LVs),
	mklistpairs(LKs, LVs, LKeyVals).

/**
  @pred b_key_to_list(+_Hash_, -_KeyList_ )

The term _KeyList_ unifies with a list containing all keys in the hash table.
*/
b_hash_keys_to_list(hash(Keys, _, _, _, _, _), LKeys) :-
	Keys =.. (_.LKs),
	mklistels(LKs, LKeys).

/**
  @pred b_key_to_list(+_Hash_, -_ValList_ )

The term _`valList_ unifies with a list containing all values in the hash table.
*/
b_hash_values_to_list(hash(_, Vals, _, _, _, _), LVals) :-
	Vals =.. (_.LVs),
	mklistvals(LVs, LVals).

mklistpairs([], [], []).
mklistpairs(V.LKs, _.LVs, KeyVals) :- var(V), !,
	mklistpairs(LKs, LVs, KeyVals).
mklistpairs(K.LKs, V.LVs, (K-VV).KeyVals) :- 
        get_mutable(VV, V),
	mklistpairs(LKs, LVs, KeyVals).

mklistels([],  []).
mklistels(V.Els, NEls) :- var(V), !,
	mklistels(Els, NEls).
mklistels(K.Els, K.NEls) :- 
	mklistels(Els, NEls).

mklistvals([],  []).
mklistvals(V.Vals, NVals) :- var(V), !,
	mklistvals(Vals, NVals).
mklistvals(K.Vals, KK.NVals) :- 
	get_mutable(KK, K),
	mklistvals(Vals, NVals).

/**
@}
*/