Program Laba3_1;
Uses
    System.SysUtils;
Const
    Min = 1;
    Max = 50;
Procedure Condition();
Begin
    Writeln('This program converts a string according to the rule: ');
    Writeln('1)If the string length > N, then the program will discard the first characters.');
    Writeln('2)If the string length < N, then the program will add "."');
    Writeln;
End;
Function ChoiseInput(): Char;
Var
    Input: Char;
    IsCorrect: Boolean;
Begin
    Repeat
        Readln(Input);
        Input := UpCase(Input);
        if ((Input = 'Y') or (Input = 'N')) then
            IsCorrect := True
        else
        Begin
            IsCorrect := False;
            Writeln('Incorrect input. Enter Y(Yes) or N(No): ');
        End;
    Until IsCorrect;
    ChoiseInput := Input;
End;
Function InputFromFile(): String;
Var
    Sentence: String;
    FileName: String;
    IsCorrect: Boolean;
    InputFile: Text;
begin
    Repeat
        Writeln('Enter the name of the file you want to read from: ');
        Readln(FileName);
        FileName := FileName + '.txt';
        IsCorrect := True;
        Assign(InputFile, FileName);
        {$I-}
        Reset(InputFile);
        {$I+}
        if IOResult <> 0 then
        begin
            Writeln('File ',FileName,' does not exist!');
            IsCorrect := False;
        end
        else
        begin
            Read(InputFile, Sentence);
            if length(Sentence) = 0 then
            begin
                Writeln('File ',FileName,' is empty!');
                IsCorrect := False;
            end;
            if ((Length(Sentence) < Min) or (Length(Sentence) > Max)) then
            Begin
                Writeln('Check the file! String length must be in the interval [',Min,'...',Max,']: ');
                IsCorrect := False;
            End;
        end;
    Until IsCorrect;
    Writeln('Source string: ',Sentence);
    Close(InputFile);
    InputFromFile := Sentence;
end;
Function CheckInputString(): String;
Var
    IsCorrect: Boolean;
    Sentence: String;
Begin
    Repeat
        Readln(Sentence);
        if ((Length(Sentence) >= Min) and (Length(Sentence) <= Max)) then
            IsCorrect := True
        else
        Begin
            Writeln('Enter string length from interval [',Min,'...',Max,']: ');
            IsCorrect := False;
        End;
    Until IsCorrect;
    CheckInputString := Sentence;
End;
Function InputFromConsole(): String;
Var
    Sentence: String;
Begin
    Writeln('Please, enter a string: ');
    Sentence := CheckInputString();
    InputFromConsole := Sentence;
End;
Function CheckInput(): Integer;
Var
    N: Integer;
    IsCorrect: Boolean;
Begin
    IsCorrect := False;
    Repeat
        Try
            Readln(N);
            if ((N >= Min) and (N <= Max)) then
                IsCorrect := True
            else
                Writeln('Enter number from interval [',Min,'...',Max,']: ');
        Except
            Writeln('Check entered data. Enter number from interval [',Min,'...',Max,']: ');
        End;
    Until IsCorrect;
    CheckInput := N;
End;
Procedure StringConversion(Var Sentence: String; N: integer);
Var
    i, Len: integer;
Begin
    Len := Length(Sentence);
    if ((Len > N) and (Len mod 2 = 0)) then
    Begin
        Sentence := copy (Sentence,len - N + 1,Len - n );
        Writeln ('Final string: ',Sentence);
    End
    else
        if ((Len > N) and (Len mod 2 <> 0)) then
        Begin
            Sentence := copy(Sentence, Len - N + 1, Len - N + 1);
            Writeln ('Final string: ',Sentence);
        End;
    if Len < N then
    Begin
        for i := Len + 1 to N do
            Insert('.',Sentence,1);
        Writeln ('Final string: ',Sentence);
    End;
    if Len = N then
        Writeln ('Final string: ',Sentence);
End;
Procedure OutputInFile(Sentence: String);
Var
    NameOfFile: String;
    OutputFile: Text;
Begin
    Writeln('Enter the file name for the entry: ');
    Readln(NameOfFile);
    NameOfFile := NameOfFile + '.txt';
    Assign(OutputFile,NameOfFile);
    Rewrite(OutputFile);
    Writeln(OutputFile,'Final string: ');
    Writeln(OutputFile,Sentence);
    Close(OutputFile);
    Writeln('String successfully written to file ',NameOfFile);
End;
Procedure Main();
Var
    Sentence: String;
    N: Integer;
begin
    Condition();
    Writeln('Would you like to use File input instead of Console input?',
                'Enter Y(Yes) or N(No): ');
    if ChoiseInput = 'Y' then
        Sentence := InputFromFile()
    else
        Sentence := InputFromConsole();
    Writeln('Enter N: ');
    N := CheckInput();
    StringConversion(Sentence,N);
    Write('Would you like to write down the answer to File? Enter Y(Yes) or N(No): ');
    if ChoiseInput = 'Y' then
        OutputInFile(Sentence);
    Writeln('Press "Enter" to exit.');
    Readln;
end;
Begin
    Main();
End.