/* 

  Planning problem in Picat.

  From Ivan Bratko, Prolog Programming for Artifical Intelligence, 4th edition,
  Page 90ff (the Prolog code is on page 94) 

  This Picat model was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/


main => 
  go.


% depth-first
go =>
  plan($state(door,corner2,floor(middle)), $state(_,_,in_basket), Plan),
  println(plan=Plan),
  nl.

% breadth-first
% go(door,middle),pickup,go(middle,corner2),drop]
% [go(door,corner2),push(corner2,middle),pickup,drop]
% [go(door,middle),pickup,go(middle,corner2),drop,push(corner2,_2898)]
% [go(door,middle),pickup,go(middle,corner2),drop,go(corner2,_2898)]
% [go(door,middle),pickup,go(middle,corner2),push(corner2,_2898),drop]
% [go(door,middle),pickup,go(middle,_2918),go(_2918,corner2),drop]
% [go(door,corner2),push(corner2,middle),pickup,drop,push(middle,_2898)]
% ....
go2 => 
  S0 = $state(door,corner2,floor(middle)),
  append(Plan,_,_),  
  plan(S0, $state(_,_,in_basket), Plan),
  println(Plan),
  fail,
  nl.

% ensure that drop is the last action
% [go(door,middle),pickup,go(middle,corner2),drop]
% [go(door,corner2),push(corner2,middle),pickup,drop]
% [go(door,middle),pickup,go(middle,corner2),push(corner2,_28e8),drop]
% [go(door,middle),pickup,go(middle,_2968),go(_2968,corner2),drop]
% [go(door,corner2),push(corner2,middle),pickup,push(middle,_28e8),drop]
% [go(door,corner2),push(corner2,middle),pickup,go(middle,middle),drop]
% [go(door,corner2),push(corner2,_2948),push(_2948,middle),pickup,drop]
% [go(door,corner2),push(corner2,middle),go(middle,middle),pickup,drop]
% [go(door,_2910),go(_2910,middle),pickup,go(middle,corner2),drop]
% [go(door,_2910),go(_2910,corner2),push(corner2,middle),pickup,drop]
% [go(door,middle),pickup,go(middle,corner2),push(corner2,_29d0),push(_29d0,_2918),drop]
% [go(door,middle),pickup,go(middle,corner2),push(corner2,_2918),go(_2918,_2918),drop]
% [go(door,middle),pickup,go(middle,_2998),go(_2998,corner2),push(corner2,_2918),drop]
% [go(door,middle),pickup,go(middle,_2998),go(_2998,_29d0),go(_29d0,corner2),drop]
% ....
go3 => 
  S0 = $state(door,corner2,floor(middle)),
  append(Plan,_,_),
  append(_,[drop],Plan),
  plan(S0, $state(_,_,in_basket), Plan),
  println(Plan),
  fail,
  nl.
  


% """
% State of the robot'2s world = state( RobotLocation, BasketLocation, RubbishLocation)
% action( State, Action, NewState): Action in State produces NewState
% We assume robot never drops rubbish to floor, and never pushes rubbish around
% """

action( State1,               % Robot and rubbish both at Pos1
        Action,               % Pick up rubbish from floor
        State2) ?=>           % Rubbish now held by robot
        State1 = $state( Pos1, Pos2, floor(Pos1)),
        Action = pickup,
        State2 = $state( Pos1, Pos2, held).

action( State1,                 % Robot and basket both at Pos
        Action,                                   % Drop rubbish to basket
        State2) ?=>        % Rubbish now in basket                               
        State1 = $state( Pos, Pos, held),
        Action = drop,
        State2 = $state( Pos, Pos, in_basket).
        

action( State1,                  % Robot and basket both at Pos
        Action,                     % Push basket from Pos to NewPos
        State2) ?=>        % Robot and basket now at NewPos
        State1 = $state( Pos, Pos, Loc),
        Action = $push( Pos, NewPos),
        State2 = $state(NewPos, NewPos, Loc).
        
action( State1,
        Action,                     % Go from Pos1 to NewPos1
        State2) => 
        State1 = $state( Pos1, Pos2, Loc),
        Action = $go( Pos1, NewPos1),
        State2 = $state( NewPos1, Pos2, Loc).
       

% plan( StartState, FinalState, Plan)
plan(State1, State2, Plan) ?=> 
  State1 = State2, Plan = []. % To achieve State from State itself, do nothing

plan( State1, GoalState, Rest)  =>
  Rest = [Action1|RestOfPlan],
  action( State1, Action1, State2),             % Make first action resulting in State2
  plan( State2, GoalState, RestOfPlan).         % Find rest of plan