with Ada.Text_IO;
with GNAT.Regpat;

procedure Regular_Expressions is
   use Ada.Text_IO;
   use GNAT.Regpat;

   Pattern : constant String := "p([a-z]+)ch";
   Matcher : Pattern_Matcher := Compile(Pattern);
   Matches : Match_Array(0..1);
begin
   -- This tests whether a pattern matches a string.
   if Match(Pattern, "peach") then
      Put_Line("true");
   else
      Put_Line("false");
   end if;

   -- Many operations are available using the Pattern_Matcher.
   -- Here's a match test like we saw earlier.
   if Match(Matcher, "peach") then
      Put_Line("true");
   else
      Put_Line("false");
   end if;

   -- This finds the match for the regexp.
   Match(Matcher, "peach punch", Matches);
   if Matches(0) /= No_Match then
      Put_Line(Slice("peach punch", Matches(0)));
   end if;

   -- This also finds the first match but returns the
   -- start and end indexes for the match instead of the
   -- matching text.
   Match(Matcher, "peach punch", Matches);
   if Matches(0) /= No_Match then
      Put_Line("idx: " & Matches(0).First'Image & " " & Matches(0).Last'Image);
   end if;

   -- The submatch variant includes information about
   -- both the whole-pattern matches and the submatches
   -- within those matches.
   Match(Matcher, "peach punch", Matches);
   if Matches(0) /= No_Match then
      Put_Line(Slice("peach punch", Matches(0)) & " " & Slice("peach punch", Matches(1)));
   end if;

   -- Ada doesn't have a direct equivalent to Go's FindAllString,
   -- but we can implement similar functionality using a loop.
   declare
      Input : constant String := "peach punch pinch";
      Start : Positive := Input'First;
   begin
      Put("All matches: ");
      loop
         Match(Matcher, Input(Start..Input'Last), Matches);
         exit when Matches(0) = No_Match;
         Put(Slice(Input, Matches(0)) & " ");
         Start := Matches(0).Last + 1;
      end loop;
      New_Line;
   end;

   -- The GNAT.Regpat package doesn't provide a direct equivalent to
   -- Go's ReplaceAllString, but we can implement similar functionality.
   declare
      function Replace_Match (S : String) return String is
      begin
         return "<fruit>";
      end Replace_Match;

      Input : constant String := "a peach";
      Output : String := Input;
      Last : Natural := Input'Last;
   begin
      Loop_Replace :
      loop
         Match(Matcher, Output(Output'First..Last), Matches);
         exit Loop_Replace when Matches(0) = No_Match;
         Output(Matches(0).First..Last) := Replace_Match(Slice(Output, Matches(0))) & Output(Matches(0).Last+1..Last);
         Last := Last + Replace_Match(Slice(Output, Matches(0)))'Length - (Matches(0).Last - Matches(0).First + 1);
      end loop Loop_Replace;
      Put_Line(Output);
   end;
end Regular_Expressions;