billing.erl

-module(billing).
-export([print_bill/1]).

database() ->
    [
     {1111, "Hula Hoops", 21},
     {1112, "Hula Hoops (Giant)", 133},
     {1234, "Dry Sherry, 1lt", 540},
     {4719, "Fish Fingers" , 121},
     {5643, "Nappies" , 1010},
     {3814, "Orange Jelly", 56}
    ].

database_map() ->
    maps:from_list(lists:map(
        fun ({Id, Name, Price}) -> {Id, {Name, Price}} end,
        database()
     )).

print_bill(Items) ->
    print(bill(Items)).

bill(Items) ->
    Database = database_map(),

    Entries = lists:map(fun (Id) -> maps:get(Id, Database) end,
                        lists:filter(fun (Id) -> maps:is_key(Id, Database) end,
                                     Items)),

    StrEntries = lists:map(fun ({Name, Price}) -> {Name, integer_to_list(Price)} end,
                           Entries),


    Total = {"Total", integer_to_list(lists:sum(lists:map(fun ({_Name, Price}) -> Price end, Entries)))},

    LineWidth = 3 + lists:max(lists:map(fun ({Name, Price}) -> length(Name) + length(Price) end,
                                        [Total|StrEntries])),

    BillEntries = lists:map(fun ({Name, Price}) -> bill_entry(Name, Price, LineWidth) end,
                            StrEntries),

    header(LineWidth) ++ BillEntries ++ footer(LineWidth, Total).

header(LineWidth) ->
    Title = "Erlang Stores",
    PaddingWidth = LineWidth-length(Title),

    [
        lists:duplicate(PaddingWidth div 2, " ") ++ Title ++ lists:duplicate(PaddingWidth div 2 + PaddingWidth rem 2, " "),
        ""
    ].

footer(LineWidth, {Name, Price}) ->
    [
        "",
        bill_entry(Name,
                   Price,
                   LineWidth)
    ].

bill_entry(Name, Price, LineWidth) when length(Price) > 2 ->
    SeparatorWidth = LineWidth - length(Name) - length(Price) - 1,

    Name ++ lists:duplicate(SeparatorWidth, ".") ++ lists:sublist(Price, length(Price)-2) ++ "." ++ lists:sublist(Price, length(Price)-1, 2);
bill_entry(Name, Price, LineWidth) when length(Price) == 2 ->
    SeparatorWidth = LineWidth - length(Name) - 4,

    Name ++ lists:duplicate(SeparatorWidth, ".")  ++ "0." ++ Price;
bill_entry(Name, Price, LineWidth) ->
    SeparatorWidth = LineWidth - length(Name) - 4,

    Name ++ lists:duplicate(SeparatorWidth, ".")  ++ "0.0" ++ Price.


print([L|Ls]) ->
    io:format("~s~n",[L]),
    print(Ls);
 print([]) ->
    ok.