program Project1;

{$APPTYPE CONSOLE}
{$R *.res}

uses
  System.SysUtils;

Function CheckExtension(Path: String): Boolean; forward;

Function InputNumber(MinNumber, MaxNumber: Integer): Integer;

var
    IsCorrect: Boolean;
    Number: Integer;

begin
    repeat
        IsCorrect := true;
        try
            Readln(Number);
        except
            Writeln('Нужно ввести целое число, которое не меньше ', MinNumber,
                    ' и не больше ', MaxNumber);
            IsCorrect := false;
        end;
        if IsCorrect and ((Number < MinNumber) or (Number > MaxNumber)) then
        begin
            Writeln('Нужно ввести целое число, которое не меньше ', MinNumber,
                    ' и не больше ', MaxNumber);
            IsCorrect := false;
        end;
    until IsCorrect;
    InputNumber := Number;
end;

Function ChooseWayOfInputOrOutput(): Integer;

const
    CONSOLE_WAY = 1;
    FILE_WAY = 2;

var
    UserWay: Integer;

begin
    Repeat
        UserWay := InputNumber(1, 2);
    Until (UserWay = CONSOLE_WAY) or (UserWay = FILE_WAY);
    ChooseWayOfInputOrOutput := UserWay;
end;

Function InputPathToFile(): String;

var
    Path: String;
    IsCorrect: Boolean;
    NewFile: TextFile;
begin
    Writeln('Введите путь к файлу:');
    repeat
        Readln(Path);
        IsCorrect := CheckExtension(Path);
    until IsCorrect;
    InputPathToFile := Path;
end;

Function CheckPermissionForReading(Path: String): Boolean;

var
    OutputFile: TextFile;
    RightPermission: Boolean;

begin
    Assign(OutputFile, Path);
    RightPermission := true;
    try
        Reset(OutputFile);
        Close(OutputFile);
    except
        Writeln('Файл закрыт для чтения.');
        RightPermission := false;
    end;
    CheckPermissionForReading := RightPermission;
end;

Function ReceiveTextFromConsole(): String;

var
    XStart, XEnd: Integer;
    Text: String;

begin
    Writeln('Введите строку:');
    Readln(Text);
    ReceiveTextFromConsole := Text;
end;

Function ReceiveTextFromFile(Path: String): String;

var
    InputFile: TextFile;
    Text: String;
    IsCorrect: Boolean;

begin;
    IsCorrect := true;
    Assign(InputFile, Path);
    Reset(InputFile);
    Read(InputFile, Text);
    Close(InputFile);
    ReceiveTextFromFile := Text;
end;

Function FindPlusOrMinus(Text: String): Integer;

var
    i: Integer;
    NumberOfElement: Integer;
    IsCorrect: Boolean;

begin
    NumberOfELement := 0;
    IsCorrect := True;
    i := 1;
    while (i < length(Text)) and IsCorrect do
    begin
        if (Text[i] = '+') or (Text[i] = '-') then
        begin
           NumberOfElement := i;
           IsCorrect := False;
        end;
        Inc(i);
    end;
    FindPlusOrMinus := NumberOfElement;
end;

Function CheckText(Text: String): Boolean;
var
    IsCorrect, IsStringCorrect: Boolean;
    i, Index, EndNumber: Integer;
begin
    IsCorrect := True;
    Index := FindPlusOrMinus(Text);
    if Index = 0 then
        IsStringCorrect := false
    else
    begin
        IsStringCorrect := true;
        Inc(Index);
        i := Index;
        EndNumber:= length(Text) + 1;
        while (i < EndNumber) and IsCorrect do
        begin
            if (Ord(Text[i]) > 47) and (Ord(Text[i]) < 58) then
            begin
                IsCorrect := false;
                IsStringCorrect := true;
            end
            else
                IsStringCorrect := false;
            Inc(i);
        end;
    end;
    CheckText := IsStringCorrect;
end;

Function ReceiveString(): String;

const
    CONSOLE_WAY = 1;
    FILE_WAY = 2;

var
    Path: String;
    Text: String;
    UserWay: Integer;
    IsTextCorrect: Boolean;
    IsCorrect: Boolean;

begin;
    repeat
    begin
    Writeln('Выберите способ ввода:'#13#10'Нажмите "1", если хотите ввести число с консоли.'#13#10'Нажмите "2", если хотите считать строку из файла.');
    UserWay := ChooseWayOfInputOrOutput();
    case UserWay of
        CONSOLE_WAY:
            begin
                Text := ReceiveTextFromConsole();
            end;
         FILE_WAY:
            begin
                repeat
                Path := InputPathToFile();
                IsCorrect:= CheckPermissionForReading(Path);
                until IsCorrect;
                Text := ReceiveTextFromFile(Path);
            end;
    end;
    IsTextCorrect := CheckText(Text);
    if not IsTextCorrect then
       Writeln('Нет знака или последующих за ним цифр.');
    end;
    until IsTextCorrect;
    ReceiveString := Text;
end;

Function ReceiveNumber(Text: String): String;

var
    i, EndNumber: Integer;
    ResultNumber: String;
    IsCorrect : Boolean;

begin
    IsCorrect := False;
    i := FindPlusOrMinus(Text);
    ResultNumber := Text[i];
    Inc(i);
    EndNumber := Length(Text) + 1;
    while i < EndNumber do
    begin
        if (Ord(Text[i]) > 47) and (Ord(Text[i]) <58) then
        begin
            ResultNumber := ResultNumber + Copy(Text, I, 1);
        end;
        Inc(i);
    end;
    ReceiveNumber := ResultNumber;
end;

Function CheckExtension(Path: String): Boolean;

var
    RigthExtension: Boolean;

begin
    if (ExtractFileExt(Path) = '.txt') then
        RigthExtension := true
    else
    begin
        Writeln('Неверное расширение файла.');
        RigthExtension := false;
    end;
    CheckExtension := RigthExtension;
end;

Function CheckPermissionForWriting(Path: String): Boolean;

var
    OutputFile: TextFile;
    RightPermission: Boolean;

begin
    Assign(OutputFile, Path);
    RightPermission := true;
    try
        Rewrite(OutputFile);
        Close(OutputFile);
    except
        Writeln('Файл закрыт для записи.');
        RightPermission := false;
    end;
    CheckPermissionForWriting := RightPermission;
end;

Procedure PrintResultToFile(Path: String; ResultString: String);

var
    OutputFile: TextFile;

begin
    Assign(OutputFile, Path);
    Rewrite(OutputFile);
    Writeln(OutputFile,'Полученное число: ', ResultString);
    Close(OutputFile);
end;

Procedure PrintResultInConsole(ResultString: String);

begin;
    Writeln('Полученное число: ', ResultString);
end;

Procedure PrintResult(ResultString: String);

const
    CONSOLE_WAY = 1;
    FILE_WAY = 2;

var
    UserWay: Integer;
    Path: String;
    IsCorrect: Boolean;

begin;
    Writeln('Выберите способ вывода:'#13#10'Нажмите "1", если хотите вывести число в консоль.'#13#10'Нажмите "2", если хотите вывести число в файл.');
    UserWay := ChooseWayOfInputOrOutput();
    case UserWay of
        CONSOLE_WAY:
            begin
                PrintResultInConsole(ResultString);
            end;
         FILE_WAY:
            begin
                repeat
                Path := InputPathToFile;
                IsCorrect := CheckPermissionForWriting(Path);
                until IsCorrect;
                PrintResultToFile(Path, ResultString);
            end;
    end;
end;

Procedure Main();

var
    Text, ResultNumber: String;
    MaxFunctionValue: Double;

begin
    Writeln('Программа выделяет из строки подстроку, которая соответствует целому числу, начинающемуся с ''+'' или ''-''.');
    Text := ReceiveString();
    ResultNumber := ReceiveNumber(Text);
    PrintResult(ResultNumber);
    Writeln('Программа завершена.');
    Readln;
end;

begin
    Main();
end.