% order_for_delivery is the top-level goal
order_for_delivery(Customer_ID,Product,Quantity) :-
    print('processing order from ',Customer_ID),
	product_available(Product,Quantity,From_Location),
	bill_customer(Customer_ID,Product,Quantity,Fee),
	check_credit(Customer_ID,Fee),
	pick_inventory(Product,Quantity,From_Location),
	ship_inventory(Product,Quantity,Customer_ID),
    print('* order complete *'),!.

% product availability check (us only)
product_available(Product,Quantity,From_Location) :-
	product_availability(From_Location,Product,_,Quantity_on_Hand,
	Quantity_Committed,_),
    factory_location(From_location,[_,_,_,_,us]),
	Quantity_Available is Quantity_on_Hand - Quantity_Committed,
	Quantity_Available >= Quantity,
    print('product is available (',Quantity_Available,') from ',From_Location),!.

% customer billing
bill_customer(Customer,Product,Quantity,Fee) :-
	get_product_price(Customer,Product,Price),
    Fee is Quantity * Price,
	compute_sales_tax(Customer,Product,Sales_Tax),
	compute_discount(Customer,Discount),
    prepare_bill(Customer,Product,Quantity,Price,Sales_Tax,Discount).

% product pricing
get_product_price(Customer,Product,Price) :-
    product_price(Product,Customer,Price,_,_),!.

% sales tax - customer and product both non-exempt and location is dc
compute_sales_tax(Customer,Product,Sales_Tax) :-
    customer_location(Customer,[_,_,dc,_,_]),
    customer_info(Customer,_,non_exempt),
    product_stax_type(Product,non_exempt),
    sales_tax(dc,Sales_Tax).
compute_sales_tax(Customer,Product,Sales_Tax) :- Sales_Tax = '0%',!.

% compute_discount(Customer,Discount).
compute_discount(Customer,Discount) :-
    customer_location(Customer,[_,_,_,_,euro]),
    euro_discount(Discount),!.
compute_discount(Customer,Discount) :- Discount = '0%',!.

prepare_bill(Customer,Product,Quantity,Price,Sales_Tax,Discount) :-
    print('***Customer Billing***'),
    print('customer  ',Customer),
    print('product   ',Product),
    print('quantity  ',Quantity),
    print('price     ',Price),
    print('sales tax ',Sales_Tax),
    print('discount  ',Discount),!.

% check_credit(Customer,Fee).
check_credit(Customer_ID,Fee) :-
    print('credit required: ',Fee),
    customer_location(Customer_ID,[_,_,_,_,Area]),
    check_credit_1(Customer_ID,Area).
check_credit_1(Customer_ID,us) :-
	check_customer_inhouse_credit(Customer_ID,us),!.
check_credit_1(Customer_ID,euro) :-
	check_customer_letter_of_credit(Customer_ID,euro),!.
check_customer_inhouse_credit(Customer_ID,us) :-
    print('checking customer inhouse credit for ',Customer_ID),!.
check_customer_letter_of_credit(Customer_ID,euro) :-
    print('checking customer letter of credit for ',Customer_ID),!.

pick_inventory(Product,Quantity,From_Location) :-
    print(From_Location,' pick inventory: ',Product,' quantity: ',
    Quantity).
    
ship_inventory(Product,Quantity,Customer_ID) :-
    customer_location(Customer_ID,[_,_,_,_,euro]),
    print('print customs declaration'),
    print('ship inventory: ',Product,' to customer ',Customer_ID),!.
ship_inventory(Product,Quantity,Customer_ID) :-
    print('ship inventory: ',Product,' to customer ',Customer_ID).

% us sales_tax info
sales_tax(dc,'5.75%').

% discount info
euro_discount('5%').

% customer_info(Customer_ID,Customer_Type,STax_Type).
customer_info(gu,ext_cust,exempt).
customer_info(org_a,ext_cust,non_exempt).
customer_info(dc_org,ext_cust,non_exempt).

% customer_location(Customer_ID,[Street,City,State,Region,Area])
customer_location(gu,['225rsb',wash,dc,east_coast,us]).
customer_location(org_a,[_,paris,france,_,euro]).
customer_location(dc_org,[_,wash,dc,east_coast,us]).

% product_price(Product,Customer,Unit_Price,Unit_Measure,Time_Period).
product_price(abc486,gu,1250,each,q1_1994).
product_price(abc486,exempt,1500,each,cy_1994).
product_price(abc486,_,1750,each,cy_1994).
% product_storage_type(Product,Storage_Conditions). 
product_storage_type(abc486,room_temp).
product_storage_type(chem_b,frozen).
% product_stax_type(Product,Classification).
product_stax_type(abc486,non_exempt).

%factory_location(Factory_ID,[Street,City,State,Region,Area]).
factory_location(factory1,[_,_,_,_,us]).

% product_availability(Factory,Product,Location,Qty_on_Hand,Qty_Comm,Reorder_Pt).
product_availability(factory1,abc486,bin01,50,20,15).
product_availability(factory1,abc486,bin15,150,100,15).

% test specification
order_for_delivery(gu,abc486,2)?
order_for_delivery(org_a,abc486,1)?
order_for_delivery(dc_org,abc486,4)?