%%
%% %CopyrightBegin%
%%
%% Copyright Ericsson AB 1996-2010. All Rights Reserved.
%%
%% The contents of this file are subject to the Erlang Public License,
%% Version 1.1, (the "License"); you may not use this file except in
%% compliance with the License. You should have received a copy of the
%% Erlang Public License along with this software. If not, it can be
%% retrieved online at http://www.erlang.org/.
%%
%% Software distributed under the License is distributed on an "AS IS"
%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
%% the License for the specific language governing rights and limitations
%% under the License.
%%
%% %CopyrightEnd%
%%
-module(digraph).

-export([new/0, new/1, delete/1, info/1]).

-export([add_vertex/1, add_vertex/2, add_vertex/3]).
-export([del_vertex/2, del_vertices/2]).
-export([vertex/2, no_vertices/1, vertices/1]).
-export([source_vertices/1, sink_vertices/1]).

-export([add_edge/3, add_edge/4, add_edge/5]).
-export([del_edge/2, del_edges/2, del_path/3]).
-export([edge/2, no_edges/1, edges/1]).

-export([out_neighbours/2, in_neighbours/2]).
-export([out_edges/2, in_edges/2, edges/2]).
-export([out_degree/2, in_degree/2]).
-export([get_path/3, get_cycle/2]).

-export([get_short_path/3, get_short_cycle/2]).

-export_type([d_type/0, vertex/0]).

-record(digraph, {vtab = notable :: ets:tab(),
		  etab = notable :: ets:tab(),
		  ntab = notable :: ets:tab(),
	          cyclic = true  :: boolean()}).
%% A declaration equivalent to the following one is hard-coded in erl_types.
%% That declaration contains hard-coded information about the #digraph{}
%% record and the types of its fields.  So, please make sure that any
%% changes to its structure are also propagated to erl_types.erl.
%%
%% -opaque digraph() :: #digraph{}.

-type edge()    :: term().
-type label()   :: term().
-type vertex()  :: term().

-type add_edge_err_rsn() :: {'bad_edge', [vertex()]} | {'bad_vertex', vertex()}.

%%
%% Type is a list of
%%  protected | private
%%  acyclic | cyclic
%%
%%  default is [cyclic,protected]
%%
-type d_protection() :: 'private' | 'protected'.
-type d_cyclicity()  :: 'acyclic' | 'cyclic'.
-type d_type()       :: d_cyclicity() | d_protection().

-spec new() -> digraph().

new() -> new([]).

-spec new([d_type()]) -> digraph().

new(Type) ->
    case check_type(Type, protected, []) of
	{Access, Ts} ->
	    V = ets:new(vertices, [set, Access]),
	    E = ets:new(edges, [set, Access]),
	    N = ets:new(neighbours, [bag, Access]),
	    ets:insert(N, [{'$vid', 0}, {'$eid', 0}]),
	    set_type(Ts, #digraph{vtab=V, etab=E, ntab=N});
	error ->
	    erlang:error(badarg)
    end.

%%
%% Check type of graph
%%
%-spec check_type([d_type()], d_protection(), [{'cyclic', boolean()}]) ->
%       	{d_protection(), [{'cyclic', boolean()}]}.

check_type([acyclic|Ts], A, L) ->
    check_type(Ts, A,[{cyclic,false} | L]);
check_type([cyclic | Ts], A, L) ->
    check_type(Ts, A, [{cyclic,true} | L]);
check_type([protected | Ts], _, L) ->
    check_type(Ts, protected, L);
check_type([private | Ts], _, L) ->
    check_type(Ts, private, L);
check_type([], A, L) -> {A, L};
check_type(_, _, _) -> error.

%%
%% Set graph type
%%
-spec set_type([{'cyclic', boolean()}], digraph()) -> digraph().

set_type([{cyclic,V} | Ks], G) ->
    set_type(Ks, G#digraph{cyclic = V});
set_type([], G) -> G.


%% Data access functions

-spec delete(digraph()) -> 'true'.

delete(G) ->
    ets:delete(G#digraph.vtab),
    ets:delete(G#digraph.etab),
    ets:delete(G#digraph.ntab).

-spec info(digraph()) -> [{'cyclicity', d_cyclicity()} |
			  {'memory', non_neg_integer()} |
			  {'protection', d_protection()}].
info(G) ->
    VT = G#digraph.vtab,
    ET = G#digraph.etab,
    NT = G#digraph.ntab,
    Cyclicity = case G#digraph.cyclic of
		    true  -> cyclic;
		    false -> acyclic
		end,
    Protection = ets:info(VT, protection),
    Memory = ets:info(VT, memory) + ets:info(ET, memory) + ets:info(NT, memory),
    [{cyclicity, Cyclicity}, {memory, Memory}, {protection, Protection}].

-spec add_vertex(digraph()) -> vertex().

add_vertex(G) ->
    do_add_vertex({new_vertex_id(G), []}, G).

-spec add_vertex(digraph(), vertex()) -> vertex().

add_vertex(G, V) ->
    do_add_vertex({V, []}, G).

-spec add_vertex(digraph(), vertex(), label()) -> vertex().

add_vertex(G, V, D) ->
    do_add_vertex({V, D}, G).

-spec del_vertex(digraph(), vertex()) -> 'true'.

del_vertex(G, V) ->
    do_del_vertex(V, G).

-spec del_vertices(digraph(), [vertex()]) -> 'true'.

del_vertices(G, Vs) -> 
    do_del_vertices(Vs, G).

-spec vertex(digraph(), vertex()) -> {vertex(), label()} | 'false'.

vertex(G, V) ->
    case ets:lookup(G#digraph.vtab, V) of
	[] -> false;
	[Vertex] -> Vertex
    end.

-spec no_vertices(digraph()) -> non_neg_integer().

no_vertices(G) ->
    ets:info(G#digraph.vtab, size).

-spec vertices(digraph()) -> [vertex()].

vertices(G) ->
    ets:select(G#digraph.vtab, [{{'$1', '_'}, [], ['$1']}]).

-spec source_vertices(digraph()) -> [vertex()].

source_vertices(G) ->
    collect_vertices(G, in).

-spec sink_vertices(digraph()) -> [vertex()].

sink_vertices(G) ->
    collect_vertices(G, out).

-spec in_degree(digraph(), vertex()) -> non_neg_integer().

in_degree(G, V) ->
    length(ets:lookup(G#digraph.ntab, {in, V})).

-spec in_neighbours(digraph(), vertex()) -> [vertex()].

in_neighbours(G, V) ->
    ET = G#digraph.etab,
    NT = G#digraph.ntab,
    collect_elems(ets:lookup(NT, {in, V}), ET, 2).

-spec in_edges(digraph(), vertex()) -> [edge()].

in_edges(G, V) ->
    ets:select(G#digraph.ntab, [{{{in, V}, '$1'}, [], ['$1']}]).

-spec out_degree(digraph(), vertex()) -> non_neg_integer().

out_degree(G, V) ->
    length(ets:lookup(G#digraph.ntab, {out, V})).

-spec out_neighbours(digraph(), vertex()) -> [vertex()].

out_neighbours(G, V) ->
    ET = G#digraph.etab,
    NT = G#digraph.ntab,
    collect_elems(ets:lookup(NT, {out, V}), ET, 3).

-spec out_edges(digraph(), vertex()) -> [edge()].

out_edges(G, V) ->
    ets:select(G#digraph.ntab, [{{{out, V}, '$1'}, [], ['$1']}]).

-spec add_edge(digraph(), vertex(), vertex()) ->
	 edge() | {'error', add_edge_err_rsn()}.

add_edge(G, V1, V2) ->
    do_add_edge({new_edge_id(G), V1, V2, []}, G).

-spec add_edge(digraph(), vertex(), vertex(), label()) ->
	 edge() | {'error', add_edge_err_rsn()}.

add_edge(G, V1, V2, D) ->
    do_add_edge({new_edge_id(G), V1, V2, D}, G).

-spec add_edge(digraph(), edge(), vertex(), vertex(), label()) ->
	 edge() | {'error', add_edge_err_rsn()}.

add_edge(G, E, V1, V2, D) ->
    do_add_edge({E, V1, V2, D}, G).

-spec del_edge(digraph(), edge()) -> 'true'.

del_edge(G, E) ->
    do_del_edges([E], G).

-spec del_edges(digraph(), [edge()]) -> 'true'.

del_edges(G, Es) ->
    do_del_edges(Es, G).

-spec no_edges(digraph()) -> non_neg_integer().

no_edges(G) ->
    ets:info(G#digraph.etab, size).

-spec edges(digraph()) -> [edge()].

edges(G) ->
    ets:select(G#digraph.etab, [{{'$1', '_', '_', '_'}, [], ['$1']}]).

-spec edges(digraph(), vertex()) -> [edge()].

edges(G, V) ->
    ets:select(G#digraph.ntab, [{{{out, V},'$1'}, [], ['$1']},
				{{{in, V}, '$1'}, [], ['$1']}]).

-spec edge(digraph(), edge()) -> {edge(),vertex(),vertex(),label()} | 'false'.

edge(G, E) ->
    case ets:lookup(G#digraph.etab,E) of
	[] -> false;
	[Edge] -> Edge
    end.

%%
%% Generate a "unique" edge identifier (relative to this graph)
%%
-spec new_edge_id(digraph()) -> nonempty_improper_list('$e', non_neg_integer()).

new_edge_id(G) ->
    NT = G#digraph.ntab,
    [{'$eid', K}] = ets:lookup(NT, '$eid'),
    true = ets:delete(NT, '$eid'),
    true = ets:insert(NT, {'$eid', K+1}),
    ['$e' | K].

%%
%% Generate a "unique" vertex identifier (relative to this graph)
%%
-spec new_vertex_id(digraph()) -> nonempty_improper_list('$v', non_neg_integer()).

new_vertex_id(G) ->
    NT = G#digraph.ntab,
    [{'$vid', K}] = ets:lookup(NT, '$vid'),
    true = ets:delete(NT, '$vid'),
    true = ets:insert(NT, {'$vid', K+1}),
    ['$v' | K].

%%
%% Collect elements for a index in a tuple
%%
collect_elems(Keys, Table, Index) ->
    collect_elems(Keys, Table, Index, []).

collect_elems([{_,Key}|Keys], Table, Index, Acc) ->
    collect_elems(Keys, Table, Index,
		  [ets:lookup_element(Table, Key, Index)|Acc]);
collect_elems([], _, _, Acc) -> Acc.

-spec do_add_vertex({vertex(), label()}, digraph()) -> vertex().

do_add_vertex({V, _Label} = VL, G) ->
    ets:insert(G#digraph.vtab, VL),
    V.

%%
%% Collect either source or sink vertices.
%%
collect_vertices(G, Type) ->
    Vs = vertices(G),
    lists:foldl(fun(V, A) ->
			case ets:member(G#digraph.ntab, {Type, V}) of
			    true -> A;
			    false -> [V|A]
			end
		end, [], Vs).

%%
%% Delete vertices
%%
do_del_vertices([V | Vs], G) ->
    do_del_vertex(V, G),
    do_del_vertices(Vs, G);
do_del_vertices([], #digraph{}) -> true.

do_del_vertex(V, G) ->
    do_del_nedges(ets:lookup(G#digraph.ntab, {in, V}), G),
    do_del_nedges(ets:lookup(G#digraph.ntab, {out, V}), G),
    ets:delete(G#digraph.vtab, V).

do_del_nedges([{_, E}|Ns], G) ->
    case ets:lookup(G#digraph.etab, E) of
	[{E, V1, V2, _}] ->
	    do_del_edge(E, V1, V2, G),
	    do_del_nedges(Ns, G);
	[] -> % cannot happen
	    do_del_nedges(Ns, G)
    end;
do_del_nedges([], #digraph{}) -> true.

%%
%% Delete edges
%%
do_del_edges([E|Es], G) ->
    case ets:lookup(G#digraph.etab, E) of
	[{E,V1,V2,_}] ->
	    do_del_edge(E,V1,V2,G),
	    do_del_edges(Es, G);
	[] ->
	    do_del_edges(Es, G)
    end;
do_del_edges([], #digraph{}) -> true.

do_del_edge(E, V1, V2, G) ->
    ets:select_delete(G#digraph.ntab, [{{{in, V2}, E}, [], [true]},
				       {{{out,V1}, E}, [], [true]}]),
    ets:delete(G#digraph.etab, E).

-spec rm_edges([vertex(),...], digraph()) -> 'true'.

rm_edges([V1, V2|Vs], G) ->
    rm_edge(V1, V2, G),
    rm_edges([V2|Vs], G);
rm_edges(_, _) -> true.

-spec rm_edge(vertex(), vertex(), digraph()) -> 'ok'.

rm_edge(V1, V2, G) ->
    Es = out_edges(G, V1),
    rm_edge_0(Es, V1, V2, G).
    
rm_edge_0([E|Es], V1, V2, G) ->
    case ets:lookup(G#digraph.etab, E) of
	[{E, V1, V2, _}]  ->
            do_del_edge(E, V1, V2, G),
	    rm_edge_0(Es, V1, V2, G);
	_ ->
	    rm_edge_0(Es, V1, V2, G)
    end;
rm_edge_0([], _, _, #digraph{}) -> ok.
    
%%
%% Check that endpoints exist
%%
-spec do_add_edge({edge(), vertex(), vertex(), label()}, digraph()) ->
	edge() | {'error', add_edge_err_rsn()}.

do_add_edge({E, V1, V2, Label}, G) ->
    case ets:member(G#digraph.vtab, V1) of
	false -> {error, {bad_vertex, V1}};
	true  ->
	    case ets:member(G#digraph.vtab, V2) of
		false -> {error, {bad_vertex, V2}};
                true ->
                    case other_edge_exists(G, E, V1, V2) of
                        true -> {error, {bad_edge, [V1, V2]}};
                        false when G#digraph.cyclic =:= false ->
                            acyclic_add_edge(E, V1, V2, Label, G);
                        false ->
                            do_insert_edge(E, V1, V2, Label, G)
                    end
	    end
    end.

other_edge_exists(#digraph{etab = ET}, E, V1, V2) ->
    case ets:lookup(ET, E) of
        [{E, Vert1, Vert2, _}] when Vert1 =/= V1; Vert2 =/= V2 ->
            true;
        _ ->
            false
    end.

-spec do_insert_edge(edge(), vertex(), vertex(), label(), digraph()) -> edge().

do_insert_edge(E, V1, V2, Label, #digraph{ntab=NT, etab=ET}) ->
    ets:insert(NT, [{{out, V1}, E}, {{in, V2}, E}]),
    ets:insert(ET, {E, V1, V2, Label}),
    E.

-spec acyclic_add_edge(edge(), vertex(), vertex(), label(), digraph()) ->
	edge() | {'error', {'bad_edge', [vertex()]}}.

acyclic_add_edge(_E, V1, V2, _L, _G) when V1 =:= V2 ->
    {error, {bad_edge, [V1, V2]}};
acyclic_add_edge(E, V1, V2, Label, G) ->
    case get_path(G, V2, V1) of
	false -> do_insert_edge(E, V1, V2, Label, G);
	Path -> {error, {bad_edge, Path}}
    end.

%%
%% Delete all paths from vertex V1 to vertex V2
%%

-spec del_path(digraph(), vertex(), vertex()) -> 'true'.

del_path(G, V1, V2) ->
    case get_path(G, V1, V2) of
	false -> true;
	Path ->
	    rm_edges(Path, G),
	    del_path(G, V1, V2)
    end.

%%
%% Find a cycle through V
%% return the cycle as list of vertices [V ... V]
%% if no cycle exists false is returned
%% if only a cycle of length one exists it will be
%% returned as [V] but only after longer cycles have
%% been searched.
%%

-spec get_cycle(digraph(), vertex()) -> [vertex(),...] | 'false'.

get_cycle(G, V) ->
    case one_path(out_neighbours(G, V), V, [], [V], [V], 2, G, 1) of
	false ->
	    case lists:member(V, out_neighbours(G, V)) of
		true -> [V];
		false -> false
	    end;
	Vs -> Vs
    end.

%%
%% Find a path from V1 to V2
%% return the path as list of vertices [V1 ... V2]
%% if no path exists false is returned
%%

-spec get_path(digraph(), vertex(), vertex()) -> [vertex(),...] | 'false'.

get_path(G, V1, V2) ->
    one_path(out_neighbours(G, V1), V2, [], [V1], [V1], 1, G, 1).

%%
%% prune_short_path (evaluate conditions on path)
%% short : if path is too short
%% ok    : if path is ok
%%
prune_short_path(Counter, Min) when Counter < Min ->
    short;
prune_short_path(_Counter, _Min) ->
    ok.

one_path([W|Ws], W, Cont, Xs, Ps, Prune, G, Counter) ->
    case prune_short_path(Counter, Prune) of
	short -> one_path(Ws, W, Cont, Xs, Ps, Prune, G, Counter);
	ok -> lists:reverse([W|Ps])
    end;
one_path([V|Vs], W, Cont, Xs, Ps, Prune, G, Counter) ->
    case lists:member(V, Xs) of
	true ->  one_path(Vs, W, Cont, Xs, Ps, Prune, G, Counter);
	false -> one_path(out_neighbours(G, V), W, 
			  [{Vs,Ps} | Cont], [V|Xs], [V|Ps], 
			  Prune, G, Counter+1)
    end;
one_path([], W, [{Vs,Ps}|Cont], Xs, _, Prune, G, Counter) ->
    one_path(Vs, W, Cont, Xs, Ps, Prune, G, Counter-1);
one_path([], _, [], _, _, _, _, _Counter) -> false.

%%
%% Like get_cycle/2, but a cycle of length one is preferred.
%%

-spec get_short_cycle(digraph(), vertex()) -> [vertex(),...] | 'false'.

get_short_cycle(G, V) ->
    get_short_path(G, V, V).

%%
%% Like get_path/3, but using a breadth-first search makes it possible
%% to find a short path.
%%

-spec get_short_path(digraph(), vertex(), vertex()) -> [vertex(),...] | 'false'.

get_short_path(G, V1, V2) ->
    T = new(),
    add_vertex(T, V1),
    Q = queue:new(),
    Q1 = queue_out_neighbours(V1, G, Q),
    L = spath(Q1, G, V2, T),
    delete(T),
    L.
    
spath(Q, G, Sink, T) ->
    case queue:out(Q) of
	{{value, E}, Q1} ->
	    {_E, V1, V2, _Label} = edge(G, E),
	    if 
		Sink =:= V2 ->
		    follow_path(V1, T, [V2]);
		true ->
		    case vertex(T, V2) of
			false ->
			    add_vertex(T, V2),
			    add_edge(T, V2, V1),
			    NQ = queue_out_neighbours(V2, G, Q1),
			    spath(NQ, G, Sink, T);
			_V ->
			    spath(Q1, G, Sink, T)
		    end
	    end;
	{empty, _Q1} ->
	    false
    end.

follow_path(V, T, P) ->
    P1 = [V | P],
    case out_neighbours(T, V) of
	[N] ->
	    follow_path(N, T, P1);
	[] ->
	    P1
    end.

queue_out_neighbours(V, G, Q0) ->
    lists:foldl(fun(E, Q) -> queue:in(E, Q) end, Q0, out_edges(G, V)).
