/* 

  GPS School problem in Picat.

  School problem from Chapter 4 of 
  Peter Norvig's Paradigms of Artificial Intelligence Programming (PAIP)

  The comments in quotes ("...") is also from this book.
   
  Notes: 
  * The order of a rule are
     - name (action)
     - preconditions
     - delete rule
     - add rule
  
  In PAIP, the two last items are in the reversed order.


  For alternative approaches in action/4:
  - http://www.hakank.org/picat/school_problem_planner2.pi
  - http://www.hakank.org/picat/school_problem_planner3.pi

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

*/


import planner.


main => go.

/*
 The plan is:
     [look up number]
     [telephone shop]
     [tell shop problem]
     [give shop money]
     [shop installs battery]
     [drive son to school]

*/
go =>
  %  "Here are some examples of using GPS"
  % "The first example works with a complex chain of steps."
  Init = [[son,at,home], [car,needs,battery],[have,money], [have,phone,book]],
  Final = [[son,at,school]],
  school_problem(Init,Final),
  nl.

go2 =>

  Init= [[freddy,at,home],[car,needs,battery],[have,money],[have,phone,book]],
  Final= [[freddy,at,school]],

  school_problem(Init,Final),
  nl.

go3 =>

  % "The next example fails because there is no way to make the car work,"
  %  "because we can't contact the shop to get the battery fixed."
  Init = [[son,at,home],[car,needs,battery],[have,money]],
  Final= [[son,at, school]],

  school_problem(Init,Final),
  nl.

go4 =>

  % "The third example is easy, because the car is currently working."
  Init = [[son,at,home],[car,works]],
  Final = [[son,at,school]],
  school_problem(Init,Final),
  nl.

go5 =>

  % This has no solution since we spend the money on battery
  Init = [[son,at,home],[have,money],[car,needs,battery]],
  Final = [[have,money],[son,at,school]],
  school_problem(Init,Final),
  nl.


school_problem(Init,Final) =>
  println(init_state=Init),
  println(final_state=Final),
  cl_facts($[final2(Final)],$[final2(-)]),

  best_plan(Init, Plan),
  % println(Plan),
  foreach(Move in Plan)
     println(move=Move)
  end,
  println(len=Plan.length),
  nl.


%
% ensure that all goals in final2/1 are in the list L.
%
final(L) =>
  final2(Final2),
  pre(L,Final2),
  writeln(final=L).


% prerequisite:
%    all elements in X must be in L
pre(L,X) => 
  foreach(M in X)
    member(M, L)
  end.

%
% delete all occurrences of X (a list) in L
%
del(L, X) = L2 =>
   L2 = L,
   foreach(E in X)
      L2 := delete_all(L2,E)
   end.

%
% add X to L (if it's not already there)
%
add(L, X) = L2 =>
  L1 = L,
  foreach(E in X)
    if not member(E,L1) then
       L1 := L1 ++ [E]
    end
  end,
  L2 = L1.

%
% Actions
% 

table

% [[drive ?X to school]
%  [[?X at home] [car works]]
%  [[?X at home]]
%  [[?X at school]]
%  ]
action(From,To,Move,Cost),
 pre(From,[[X,at,home],[car,works]]) ?=>
 To = From.del([[X,at,home]]).add([[X,at,school]]),
 Move = [drive,X,to,scool],
 Cost = 1.

   
% [[shop installs battery]
%  [[car needs battery] [shop knows problem] [shop has money]]
%  [[car needs battery]]
%  [[car works]]
%  ]
action(From,To,Move,Cost),
 pre(From,[[car,needs,battery],[shop,knows,problem],[shop,has,money]]) ?=>
 Move = [shop,installs,battery],
 To = From.del([[car,needs,battery]]).add([[car,works]]),
 Cost = 1.

% [[tell shop problem]
%  [[in communication with shop]]
%  [[in communication with shop]]
%  [[shop knows problem]]
%  ]
action(From,To,Move,Cost),
 pre(From,[[in,communication,with,shop]]) ?=>
 Move = [tell,shop,problem],
 To = From.del([[in,communication,with,shop]]).add([[shop,knows,problem]]),
 Cost = 1.

% [[telephone shop]
%  [[know phone number]]
%  [[know phone number]]  ;;; hakank: must do this for the solver to work
%  [[in communication with shop] [know phone number]] ;;; put the knowledge back
%  ]
action(From,To,Move,Cost),
 pre(From,[[know,phone,number]]) ?=>
 Move = [telephone,shop],
 To = From.del([[know,phone,number]]).add([[in,communication,with,shop],[know,phone,number]]), % put the knowledge back
 Cost = 1.


% [[look up number]
%  [[have phone book]]
%  [[have phone book]]  ;;; hakank: must do this for the solver to work
%  [[know phone number] [have phone book]]  ;;; we still have the phone book...
%  ]
action(From,To,Move,Cost),
 pre(From,[[have,phone,book]]) ?=>
 Move = [look,up,number],
 To = From.del([[have,phone,book]]).add([[know,phone,number],[have,phone,book]]), % we still have the phone book...
 Cost = 1.


% [[give shop money]
%  [[have money]]
%  [[have money]]
%  [[shop has money]]
%  ]
action(From,To,Move,Cost),
 pre(From,[[have,money]]) ?=>
 Move = [give,shop,money],
 To = From.del([[have,money]]).add([[shop,has,money]]),
 Cost = 1.

% % extra rule (from PAIP, page 143)
% action(From,To,Move,Cost),
%  pre(From,[[have,money],[X,at,home]]) ?=>
%  Move = [taxi,X,to,school],
%  To = From.del([[have,money]]).add([[X,at,school]]),
%  Cost = 1.