program LabWork31;

{$APPTYPE CONSOLE}

uses
  SysUtils;

type
   TCharSet = set of Char;

const
   LenModOrDiv = 2;          // because 5-3 = 2 +1 = 3 (+1 because we include third index)

function UserChooce(): Boolean;
var
   IsCorrect: Boolean;
   Choice: Char;
begin
   IsCorrect := False;
   repeat
      Write('Y/N: ');
      Readln(Choice);
      Choice := UpCase(Choice);
      case Ord(Choice) of
         Ord('Y'):
            begin
               IsCorrect := True;
               UserChooce := True;
            end;
         Ord('N'):
            begin
               IsCorrect := True;
               UserChooce := False;
            end
      else
         Writeln('You made an incorrect choice, please, try again clearly following the instructions.');
      end;
   until IsCorrect;
end;


function CorrectFormatOfTheFile(FileName: String): String;
const
   FormatLen = 4;
begin
   if AnsiCompareStr(copy(FileName, length(FileName) - FormatLen, FormatLen), '.txt') <> 0 then
      FileName := FileName + '.txt';
   CorrectFormatOfTheFile := FileName;
end;

function InputFileName(): String;
var
   FileName: String;
   IsCorrect: Boolean;
begin
   Writeln('Please, enter name of the file or way to the file.');
   Writeln('Example: F:\Programming\Lab\3_1\Delphi\Input.txt');
   IsCorrect := False;
   repeat
      Readln(FileName);
      FileName := CorrectFormatOfTheFile(FileName);
      if FileExists(FileName) then
      begin
         IsCorrect := True;
         InputFileName := FileName;
      end
      else
         Writeln('File with the same name does not exist, please, enter name of the file again.');
   until IsCorrect;
end;


function EnterStringFromFile(): String;
var
   Input: TextFile;
   UserString: String;
begin
   AssignFile(Input, InputFileName);
   Reset(Input);
   while seekEOF(Input) do
   begin
      Writeln('Your file haven''t strings.');
      Writeln;
      AssignFile(Input, InputFileName);
      Reset(Input);
   end;
   Readln(Input, UserString);
   Close(Input);
   EnterStringFromFile := UserString;
end;


function EnterStringFromConsole(): String;
var
   UserString: String;
begin
   Write('Please, enter your string: ');
   Readln(UserString);
   EnterStringFromConsole := UserString;
end;


function ModOrDiv(const UserString: String; const Index: Integer): Boolean;
var
   StringLen: Integer;
   Assumption: String;
   IsCorrectAssumption: Boolean;
begin
   IsCorrectAssumption := False;
   StringLen := length(UserString);
   if StringLen - Index >= LenModOrDiv then
      Assumption := copy(UserString, Index, LenModOrDiv + 1);
      if (AnsiCompareStr(Assumption, 'mod') = 0)or(AnsiCompareStr(Assumption, 'div') = 0) then
         IsCorrectAssumption := True;
   ModOrDiv := IsCorrectAssumption;
end;


function CreateSet(const UserString: String): TCharSet;
var
   Symbol: Char;
   Symbols: TCharSet;
   StringIndex, StringLen: Integer;
const
   SetNumbers = ['0', '2', '4', '6', '8'];
   OperationsAndParentheses =
      ['(', ')', '{', '}', '[', ']', '+', '-', '*', '/'];
begin
   Symbols := [];
   StringLen := Length(UserString);
   StringIndex := 1;
   while StringIndex <= StringLen do
   begin
      Symbol := UserString[StringIndex];
      if not (Symbol in Symbols) then
         if Symbol in OperationsAndParentheses then
            Include(Symbols, Symbol)
         else
            if Symbol in SetNumbers then
               Include(Symbols, Symbol)
            else
               if ModOrDiv(UserString, StringIndex) then
                  begin
                     Include(Symbols, UpCase(Symbol));
                     StringIndex := StringIndex + LenModOrDiv;  // +2 because we inc(stringIndex) in next line
                  end;
      inc(StringIndex);
   end;
   CreateSet := Symbols;
end;


function SetToStr(const Symbols: TCharSet): String;
var
   CurrentChar: Char;
   StringFromSet: String;
   i: Integer;
begin
   StringFromSet := '';
   for i := 0 to 255 do
   begin
      CurrentChar := Chr(i);
      if CurrentChar in Symbols then
         case Ord(CurrentChar) of
            Ord('M'):
               StringFromSet := StringFromSet + 'mod ';
            Ord('D'):
               StringFromSet := StringFromSet + 'div ';
         else
            StringFromSet := StringFromSet + CurrentChar + ' ';
         end;
   end;
   SetToStr := StringFromSet;
end;


procedure OutputInf(const Symbols: TCharSet);
var
   Output: TextFile;
   FileName, StringFromSet: String;
begin
   Writeln;
   StringFromSet := SetToStr(Symbols);
   if AnsiCompareStr(StringFromSet, '') = 0 then
      Writeln('Your string haven''t symbols which can be append to set')
   else
   begin
      Writeln('Your set: ', StringFromSet);
      Writeln('Do you want to output data to a file?');
      if UserChooce() then
      begin
         Writeln('Please, enter name of the file.');
         Writeln('Example: Text.txt');
         Readln(FileName);
         FileName := CorrectFormatOfTheFile(FileName);
         AssignFile(Output, FileName);
         try
            if FileExists(FileName) then
            begin
               Write('A file with this name already exists, ');
               Writeln('do you want to append information(otherwise rewrite)?');
               if UserChooce() then
                  Append(Output)
               else
                  Rewrite(Output);
               end
               else
                  Rewrite(Output);
         except
            Writeln('Error writing to file.');
         end;
         Write(Output, 'Set from your string: ', StringFromSet);
         CloseFile(Output);
         Writeln('Write was successfully.');
      end;
   end;
end;


procedure Main();
var
   UserString: String;
begin
   Writeln('Hello, this program extracts integers from a string.');
   repeat
      Writeln('Do you want to enter data through a file? (otherwise via console).');
      if UserChooce then
      begin
         UserString := EnterStringFromFile();
         Writeln('Your string: ', UserString);
      end
      else
         UserString := EnterStringFromConsole();
      UserString := StringReplace(UserString, ' ', '', [rfReplaceAll]);
      if UserString = '' then
         Writeln('Your string is empty.')
      else
         OutputInf(CreateSet(UserString));
      Writeln('Do you want enter another string?');
   until not UserChooce();
   Writeln('Press enter to exit...');
   Readln;
end;


begin
   Main;
end.