% FASB SFAC 6, Elements of Financial Statements, in Prolog %
% https://www.fasb.org/pdf/con6.pdf %
% Created by Charles Hoffman, CPA (charles.hoffman@me.com). %
% Public domain: https://creativecommons.org/publicdomain/zero/1.0/ %
% Run SWI-Prolog using https://swish.swi-prolog.org/ %

term(asset).
term(liability).
term(equity).
term(comprehensiveIncome).
term(investmentsByOwners).
term(distributionsToOwners).
term(revenues).
term(expenses).
term(gains).
term(losses).

structure(statementOfFinancialPosition).
structure(statementOfIncome).
structure(statementOfChangesInEquity).

entity(abc_company).
period(2020).
period(2019).

assertion(does_balance_sheet_balance).
assertion(does_income_statement_foot).
assertion(does_equity_roll_forward).

fact(term(asset), entity(abc_company), period(2020), 3500).
fact(term(asset), entity(abc_company), period(2019), 0).
fact(term(liability), entity(abc_company), period(2020),0).
fact(term(liability), entity(abc_company), period(2019),0).
fact(term(equity), entity(abc_company), period(2020),3500).
fact(term(equity), entity(abc_company), period(2019),0).

fact(term(investmentsByOwners), entity(abc_company), period(2020),1000).
fact(term(distributionsToOwners), entity(abc_company), period(2020),500).

fact(term(revenues), entity(abc_company), period(2020),7000).
fact(term(expenses), entity(abc_company), period(2020),3000).
fact(term(gains), entity(abc_company), period(2020),1000).
fact(term(losses), entity(abc_company), period(2020),2000).
fact(term(comprehensiveIncome), entity(abc_company), period(2020),3000).

% rule Assets = Liabilities + Equity %
does_balance_sheet_balance(Entity, Period) :-
    fact(term(asset),entity(Entity),period(Period),Asset),
    fact(term(liability),entity(Entity),period(Period),Liability),
    fact(term(equity),entity(Entity),period(Period),Equity),
    Asset is Liability + Equity.

% rule ComprehensiveIncome = Revenues - Expenses + Gains - Losses %
does_income_statement_foot(Entity, Period) :-
    fact(term(comprehensiveIncome),entity(Entity),period(Period),ComprehensiveIncome),
    fact(term(revenues),entity(Entity),period(Period),Revenues),
    fact(term(expenses),entity(Entity),period(Period),Expenses),
    fact(term(gains),entity(Entity),period(Period),Gains),
    fact(term(losses),entity(Entity),period(Period),Losses),
    ComprehensiveIncome is Revenues - Expenses + Gains - Losses.

% rule EndingEquity = BeginningEquity + ComprehensiveIncome + InvestmentsByOwners - DistributionsToOwners %
does_equity_roll_forward(Entity, Period) :-
   fact(term(equity),entity(Entity),period(2019),BeginningEquity),
   fact(term(comprehensiveIncome),entity(Entity),period(Period),ComprehensiveIncome),
   fact(term(equity),entity(Entity),period(Period),EndingEquity),
   fact(term(distributionsToOwners),entity(Entity),period(Period),DistributionsToOwners),
   EndingEquity is BeginningEquity + ComprehensiveIncome - DistributionsToOwners.


% rule EndingEquity = BeginningEquity + ComprehensiveIncome + InvestmentsByOwners - DistributionsToOwners %
does_equity_roll_forward(Entity, period_range(BeginningPeriod,EndPeriod)) :-
   fact(term(equity),entity(Entity),period(BeginningPeriod),BeginningEquity),
   fact(term(comprehensiveIncome),entity(Entity),period(EndPeriod),ComprehensiveIncome),
   fact(term(equity),entity(Entity),period(EndPeriod),EndingEquity),
   fact(term(investmentsByOwners),entity(Entity),period(EndPeriod),InvestmentsByOwners),
   fact(term(distributionsToOwners),entity(Entity),period(EndPeriod),DistributionsToOwners),
   EndingEquity is BeginningEquity + ComprehensiveIncome + InvestmentsByOwners - DistributionsToOwners.
   
/** <examples>

?- fact(Term, Entity, Period, Value).
?- does_balance_sheet_balance(abc_company, 2020).
?- does_income_statement_foot(abc_company, 2020).
?- does_equity_roll_forward(abc_company, period_range(2019, 2020)).
?- does_equity_roll_forward(abc_company, period_range(2018, 2020)).

*/