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:- dynamic(node/1).
:- dynamic(edge/3).

printMenu :-
    writef('\nMENU\n'),
    writef('1. Add node\n'),
    writef('2. Delete node\n'),
    writef('3. Add edge\n'),
    writef('4. Delete edge\n'),
    writef('5. Show graph\n'),
    writef('6. Show cost\n'),
    writef('0. Exit\n'),
    writef('Select your option\n').

addNode(X) :- node(X),
    writef('Node %d already exists\n', [X]).
addNode(X) :- assert(node(X)).

deleteNode(X) :- not(node(X)),
    writef('Node %d does not exist\n', [X]).
deleteNode(X) :- node(X),
    retractall(edge(X,_,_)),
    retractall(edge(_,X,_)),
    retract(node(X)).

addEdge(X,Y,_) :- not(node(X)) ; not(node(Y)),
    writef('Node %d or %d does not exist\n',[X, Y]).
addEdge(_,_,Z) :- Z < 1,
    writef('Edge distance cannot be 0 or negative\n').
addEdge(X,Y,_) :- edge(X, Y, _),
    writef('Edge already exists from %d to %d\n', [X, Y]).
addEdge(X,Y,Z) :- assert(edge(X,Y,Z)).

deleteEdge(X,Y) :- not(edge(X,Y,_)),
    writef('Edge from %d to %d does not exist\n', [X, Y]).
deleteEdge(X,Y) :-
    retract(edge(X,Y,_)).

showGraph :-
    findall(N,node(N),R1),
    writef('Nodes %s\n', [R1]),
    findall([X,Y,C],edge(X,Y,C), R2),
    write('Edges '), write(R2), writef('\n').

path(X,Y,-1000) :- not(edge(X,Y,_)).
path(X,Y,C) :- edge(X,Y,C).
path(X,Y,C) :- edge(X,A,C1),
    path(A,Y,C2),
    C is C1 + C2.

showCost(X,Y) :- not(node(X)) ; not(node(Y)),
    writef('Node %d or %d does not exist\n', [X,Y]).
showCost(X,Y) :- path(X,Y,C),
    C < 1,
    writef('Path from %d to %d does not exist\n', [X,Y]).
showCost(X,Y) :- path(X,Y,C),
    writef('Cost from %d to %d is %d', [X,Y,C]).


selected(0).
selected(1) :-
    writef('Adding node\n'),
    read(X),
    addNode(X),
    graphExe.
selected(2) :-
    writef('Deleting node\n'),
    read(X),
    deleteNode(X),
    graphExe.
selected(3) :-
    writef('Adding edge\n Insert X, Y and C\n'),
    read(X),
    read(Y),
    read(Z),
    addEdge(X,Y,Z),
    graphExe.
selected(4) :-
    writef('Deleting edge\n Insert X and Y\n'),
    read(X),
    read(Y),
    deleteEdge(X,Y),
    graphExe.
selected(5) :-
    writef('Show graph\n'),
    showGraph,
    graphExe.
selected(6) :-
    writef('Show cost\n'),
    read(X),
    read(Y),
    showCost(X,Y).
selected(X) :-
    writef('Option %d not found!\n',X),
    graphExe.

graphExe :-
    printMenu,
    read(X),
    selected(X).