program stack;

uses crt;

type
  Subscriber = record
    name: string[255];
    adress : string[255];
    number_phone : string[255];
  end;

type
  T = Subscriber;

type
  PNode = ^ Node;
  Node = record
    data: T;
    next: PNode;
  end;

type List = class

  private

    head: PNode;
    size: Integer;

  public

    constructor Create();
    function get_size() : integer;
    function get_el(pos:integer) : PNode;
    procedure push_front(el: T);
    procedure erase(pos:Integer);
    procedure out_list();

end;

constructor List.Create();
begin
  head:=nil;
  size:=0;
end;

function List.get_size() : integer;
begin
  get_size:=size;
end;

function List.get_el(pos:integer) : PNode;
var
  current : PNode = head;
begin
  for i:integer:=0 to size-1 do
  begin
    if(pos=i) then
    begin
      get_el:=current;
      break;
    end;
    current:=current^.next;
  end;
end;

procedure List.push_front(el: T);
var
  current: PNode;
begin
  new(current);
  current^ .data := el;
  current^ .next := head;
  head := current;
  size+=1;
end;

procedure List.erase(pos:Integer);
var
  current:PNode=head;
  previous:PNode=nil;
  found : boolean = false;
begin
  if(pos<0) then
  begin
    writeln('Incorrect position entered');
    exit;
  end;
  for i: Integer :=0 to size-1 do
  begin
    if(i=pos) then
    begin
      found:=true;
      if(previous = nil) then
      begin
        head := current^.next;
        dispose(current);
        break;
      end
      else
      begin
        previous^.next := current^.next;
        dispose(current);
        break;
      end;
    end;
    previous:=current;
    current:=current^.next;
  end;

  if(found) then
    size-=1
  else
    writeln('The entered position is larger than the size of the List');
end;

procedure List.out_list();
var
  current: PNode;
begin
  current := head;
  write('List = {');
  while (current <> nil) do
  begin
    write(current^.data:3, ';');
    current:=current^.next;
  end;
  write('}');
  writeln();
  write('Size = ',size);
  writeln();
end;

var a : List;
    quit, buf_string : string;
    number_command, pos, n_subscribers :integer;
    data : T;
    element : PNode;
    f : file of Subscriber;

begin
  a := new List;
  Assign(f,'C:\PABCWork.NET\My Work\Subscribers.data');
  Rewrite(f);
  Writeln('Enter number of subscribers:');
  Readln(n_subscribers);
  for i:integer:=1 to n_subscribers do
  begin
    ClrScr();
    writeln('Entered name:');
    Readln(data.name);
    writeln('Entered adress:');
    Readln(data.adress);
    writeln('Entered number phone:');
    Readln(data.number_phone);
    Write(f,data);
  end;
  Close(f);

  Reset(f);
  while not Eof(f) do
  begin
    Read(f,data);
    a.push_front(data);
  end;
  Close(f);

  while(quit<>'q') do
  begin
    ClrScr();
    writeln('Choose a command:');
    writeln('1) Push front');
    writeln('2) Erase');
    Writeln('3) Edit');
    writeln('4) Out List');
    writeln('5) Quit');
    readln(number_command);
    case number_command of
      1:
      begin
        ClrScr();
        writeln('Entered name:');
        Readln(data.name);
        writeln('Entered adress:');
        Readln(data.adress);
        writeln('Entered number phone:');
        Readln(data.number_phone);
        a.push_front(data);
      end;
      2:
      begin
        ClrScr();
        writeln('Enter the position of the element to be deleted:');
        Readln(pos);
        a.erase(pos);
        if((pos<0) or (pos>=a.get_size())) then
          Readln();
      end;

      3:
      begin
        ClrScr();
        writeln('Enter the position of the element to be edit:');
        Readln(pos);
        if((pos<0) or (pos>=a.get_size())) then
          Writeln('Incorrect position entered')
        else
        begin
          element:=a.get_el(pos);
          Writeln('Choose a command:');
          Writeln('1)Edit name');
          Writeln('2)Edit adress');
          Writeln('3)Edit number phone');
          Readln(number_command);
          case number_command of
            1:
            begin
              Writeln('Entered new name:');
              Readln(buf_string);
              element^.data.name:=buf_string;
            end;

            2:
            begin
              Writeln('Entered new adress:');
              Readln(buf_string);
              element^.data.adress:=buf_string;
            end;

            3:
            begin
              Writeln('Entered new number phone:');
              Readln(buf_string);
              element^.data.number_phone:=buf_string;
            end;

            else
            begin
              ClrScr();
              writeln('Command not found.');
              readln();
            end;
          end;
        end;
      end;

      4:
      begin
        ClrScr();
        a.out_list();
        Readln();
      end;
      5: quit:='q';
      else
      begin
        ClrScr();
        writeln('Command not found. Please try again.');
        readln();
      end;
    end;
  end;
end.