unit SelctGui;

(************************************************)
(* SELCTGUI.PAS                                 *)
(* Author:   Daniel Marschall                   *)
(* Revision: 2020-09-07                         *)
(* License:  Apache 2.0                         *)
(* This file contains:                          *)
(* - A list box control GUI                     *)
(************************************************)

interface

uses
  StrList;

function DoScreenSelectionList(X, Y, ListWidth, ListHeight: integer; items: PStringList): integer;

implementation

uses
  Crt;

(* MISC FUNCTIONS *)

function FillRight(str: string; len: integer; c: char): string;
var
  s: string;
  i: integer;
begin
  s := str;
  for i := Length(str) to len-1 do
  begin
    s := s + c;
  end;
  FillRight := s;
end;

(* GRAPHICAL USER INTERFACE (GUI) *)

function DoScreenSelectionList(X, Y, ListWidth, ListHeight: integer; items: PStringList): integer;
var
  i: integer;
  itemIndex: integer;
  sc: char;
  iStartScope, iEndScope: integer;
label
  doAgain;
begin
  ClrScr;

  itemIndex := 0;
  iStartScope := itemIndex;
  iEndScope := itemIndex + ListHeight;

doAgain:

  if itemIndex < 0 then
    itemIndex := 0;
  if itemIndex > ListCount(items)-1 then
    itemIndex := ListCount(items)-1;

  if itemIndex < iStartScope then
  begin
    Dec(iEndScope);
    Dec(iStartScope);
  end;

  if itemIndex > iEndScope then
  begin
    Inc(iEndScope);
    Inc(iStartScope);
  end;

  for i := iStartScope to iEndScope-1 do
  begin
    if itemIndex = i then
    begin
      TextColor(Black);
      TextBackground(White);
    end
    else
    begin
      TextColor(White);
      TextBackground(Black);
    end;
    GotoXY(x,y+i-iStartScope);
    if i > ListCount(items)-1 then
      Write(FillRight('', ListWidth, ' '))
    else
      Write(FillRight(ListGetElement(items, i), ListWidth, ' '));
    TextColor(White);
    TextBackground(Black);
  end;

  repeat
    sc := ReadKey;
    if sc = #0 then
    begin
      sc := ReadKey;
      if sc = #72 then
      begin
        dec(itemIndex);
        goto doAgain;
      end;
      if sc = #80 then
      begin
        inc(itemIndex);
        goto doAgain;
      end;
    end;

    if sc = #13(*Return*) then
    begin
      DoScreenSelectionList := itemIndex;
      exit;
    end;

    if sc = #27(*ESC*) then
    begin
      DoScreenSelectionList := -1;
      exit;
    end;
  until false;
end;

end.