advent-of-code-2024/day_3/mull_it_over.adb

with Ada.Integer_Text_IO; use Ada.Integer_Text_IO;
with GNAT.Regpat;         use GNAT.Regpat;

with Ada.Text_IO;       use Ada.Text_IO;
with Ada.Strings.Fixed; use Ada.Strings.Fixed;

--  This code reads its input from standard input
--  Use cat _input.txt | Mull_It_Over_ to get the result
procedure Mull_It_Over is

   subtype Operand is Positive;

   --  Use pattern to match mul operations
   Mul_Pattern : constant Pattern_Matcher :=
     Compile ("mul\(([0-9]+),([0-9]+)\)");

   Sum : Natural := 0;

begin
   while not End_Of_File loop
      declare
         Line            : constant String  := Get_Line;
         Remaining       : String  := Line;
         Matches         : Match_Array (0 .. Paren_Count (Mul_Pattern));
      begin
         Match (Mul_Pattern, Remaining, Matches);
         --  Iterate on all match of the line
         while Matches (0) /= No_Match loop
            declare
               Operand_1 : Operand;
               Operand_2 : Operand;
               Last      : Positive;
            begin
               Get
                 (Remaining (Matches (1).First .. Matches (1).Last), Operand_1,
                  Last);
               Get
                 (Remaining (Matches (2).First .. Matches (2).Last), Operand_2,
                  Last);
               Sum := Sum + Operand_1 * Operand_2;
            end;
            --  Copy without last parenthesis
            Move
              (Remaining (Matches (2).Last + 2 .. Remaining'Last), Remaining);
            Match (Mul_Pattern, Remaining, Matches);
         end loop;
      end;
   end loop;

   Put_Line ("The sum is " & Sum'Image);
end Mull_It_Over;