% Rename this file as "grad.pl" and use SWI-Prolog to run it

% Database for students and graduation info -Expert System

/* Syntax: grad(SSN) to check if the student can graduate or not */

%student(name,ssn,address,gpa)

student('st1',1000,'street1, city1, state1, zip1',3.75).
student('st2',1001,'street2, city2, state2, zip2',4.0).

%coursetaken(ssn,course#,sem,year,grade)

coursetaken(1000,no1,fall,2002,'A').
coursetaken(1000,no2,fall,2002,'B').
coursetaken(1000,no3,fall,2002,'A').

coursetaken(1000,in1,fall,2002,'A').
coursetaken(1000,in2,fall,2002,'A').
coursetaken(1000,in3,fall,2002,'A').
coursetaken(1000,no7,fall,2002,'A').

coursetaken(1000,c1,spring,2002,'A').
coursetaken(1000,c2,spring,2002,'A').
coursetaken(1000,c3,spring,2002,'A').

coursetaken(1001,no8,fall,2002,'A').
coursetaken(1001,no9,fall,2002,'B').
coursetaken(1001,no10,fall,2002,'A').
coursetaken(1001,no4,fall,2002,'A').
coursetaken(1001,no5,fall,2002,'A').
coursetaken(1001,no6,fall,2002,'B').


%course(course#,coursename,type,creditHrs).. type = core or elective or thesis or independent

course(c1,_,core,3).
course(c2,_,core,3).
course(c3,_,core,3).

course(no1,cs1,core,6).
course(no2,cs2,elective,3).
course(no3,cs3,thesis,6).

course(no7,cocs7,core,3).
course(no8,cocs8,core,3).
course(no9,cocs9,core,3).
course(no10,cocs10,core,3).

course(in1,inn1,independent,3).
course(in2,inn2,independent,3).
%course(in3,inn3,independent,3).

course(no4,cs4,core,3).
course(no5,cs5,elective,3).
course(no6,cs6,thesis,3).

%thesis(ssn#) means that the person with the particular ssn# is in the thesis option

thesis(1000).

dept(1000, cs).
dept(1001, cs).
dept(1002, cs).

%====================================================================

%list_courses(ssn#, outputList) -Output list contains the list of courses that are taken by ssn#

list_courses(Sid, L):-list_courses(Sid,[],L). 
list_courses(Sid, Acc, L):-coursetaken(Sid,Cno,_,_,_), \+member(Cno,Acc), append([Cno],Acc,L1), list_courses(Sid,L1, L), !. 
list_courses(_, Acc,Acc). 


%collect_hrs(Sid,N):- N is the list of the courses that the student with Sid has already taken
collect_hrs(Sid,N):-collect_hrs(Sid,[],N).
collect_hrs(Sid,L,N):-coursetaken(Sid,Cno,_,_,_), \+member(Cno,L),append([Cno],L,L1), collect_hrs(Sid,L1,N),!.
collect_hrs(_,Acc,Acc).

%sum_hrs(ssn#,result) -result contains the sum of the credit hrs of the courses taken by ssn#

sum_hrs(Sid,N):-sum_hrs(Sid,0,[],N).
sum_hrs(Sid,Acc,L,N):-coursetaken(Sid,Cno,_,_,_),course(Cno,_,_,Hrs),\+member(Cno,L),append([Cno],L,L1),A is Acc+Hrs, sum_hrs(Sid,A,L1,N),!.
sum_hrs(_,Acc,_,Acc).

%sum_hrs_type(ssn#,type, result) -result contains the sum of the credit hrs of the courses taken by ssn# of the gvn type = thesis, independent, core, elective

sum_hrs_type(Sid,Ty,N):-sum_hrs_type(Sid,0,[],Ty,N,Li).
sum_hrs_type(Sid,Acc,L,Ty,N,Li):-coursetaken(Sid,Cno,_,_,_),course(Cno,_,Ty,Hrs),\+member(Cno,L),append([Cno],L,L1),A is Acc+Hrs, sum_hrs_type(Sid,A,L1,Ty,N,Li),!.
sum_hrs_type(_,Acc,Li,_,Acc,Li).

%calculate GPA -gpa(Sid,G) stores the gpa of Sid in G
gpa(Sid,G):-gpa1(Sid,0,[],N,Len), G is N/Len.
gpa1(Sid,Acc,L,N,Len):-coursetaken(Sid,Cid,_,_,G), \+member(Cid,L), append([Cid],L,L1), G='A', Acc1 is Acc+4,gpa1(Sid,Acc1,L1,N,Len),!.
gpa1(Sid,Acc,L,N,Len):-coursetaken(Sid,Cid,_,_,G), \+member(Cid,L), append([Cid],L,L1), G='B', Acc1 is Acc+3,gpa1(Sid,Acc1,L1,N,Len),!.
gpa1(_,Acc1,L,Acc1,Len):-length(L,Len).

%ind_study_ok(sid):- checks if the student with "Sid" has taken more than 2 independent studies or not.
ind_study_ok(Sid):-sum_hrs_type(Sid,0,[],independent,_,Li),length(Li,Le),Le=<2. 

%core_study_ok(sid)- checks if the student has taken 5 core courses or not
core_study_ok(Sid):-sum_hrs_type(Sid,0,[],core,_,Li),length(Li,Le),Le>=5.

%thesis_study_ok- checks to see if the student has taken less than <6 or >6 hrs as thesis hrs.
thesis_study_ok(Sid):-sum_hrs_type(Sid,thesis,N),N=<6.

%grad(ssn) : can the student with ssn graduate
grad(Sid,_):-thesis(Sid),sum_hrs(Sid,N),N>=30,thesis_study_ok(Sid),ind_study_ok(Sid),gpa(Sid,Gpa),Gpa>=3,core_study_ok(Sid).
grad(Sid):- \+thesis(Sid),sum_hrs(Sid,N),N>=33,ind_study_ok(Sid),gpa(Sid,Gpa),Gpa>=3,core_study_ok(Sid).
% The remaining courses are assigned assuming that all the courses are for 3 credit hrs.. Just for simplicity
grad(Sid,L):- dept(Sid, Dept), sum_hrs(Sid,Num), collect_hrs(Sid, Taken), Num1 is 33-Num, Num1\==0, Num2 is Num1/3, print('To graduate # courses the student needs to take is '), print(Num2), nl, print('Courses already taken ==> '), print(Taken), nl, print('For graduation the student has the following choice of courses'),nl,chooseN(Dept, Num2, L, Taken).


subsequence([X|Xs],[X|Ys]):-subsequence(Xs,Ys).
subsequence(Xs,[Y|Ys]):-subsequence(Xs,Ys).
subsequence([],Ys).

%=======================================

% this program aims at finding the # choices that are possible i.e N C K (N choose K)

% cantake(dept, course) denotes that the student of this dept can take this course

cantake(cs, no1).
cantake(cs, no2).
cantake(cs, no3).
cantake(cs, no4).
cantake(cs, no5).
cantake(cs, no6).
cantake(cs, no7).
cantake(cs, no8).
cantake(cs, no9).
cantake(cs, no10).
cantake(cs, no11).
cantake(cs, no12).

%assign(cs,6,0,[],L,[]). gives L = [no6, no5, no4, no3, no2, no1] 

assign(Dept,N,N,L,L,_).
assign(Dept,N,A,L,R,Taken):- cantake(Dept,Course), \+member(Course, Taken), \+member(Course, L), append([Course], L, L1), A1 is A+1, assign(Dept, N, A1, L1, R,Taken). 


%chooseN(Dept, N, L, Taken) where N is the # courses that we are trying to select and L is the List that will contain the list of the courses (of length N) that the student can take and Taken is the list of courses that the student has already taken
chooseN(Dept, N, L, Taken):- assign(Dept,N,0,[],L,Taken).

% R will store a list of lists which will contain all the possible combinations in which the "N" courses can be taken
%my_setof(Dept,N,R):- setof(L,chooseN(Dept,N,L),R).