unit Unit3;

interface

uses WebCore, WebUI, WebForms, WebCtrls, WebCtnrs, WebLabels, AlbumItem, WebBtns,
   WebData, WebGrids, WebEdits;

type

   TForm3 = class(TForm)
      ScrollBox: TScrollPanel;
      Label1: TLabel;
      lbScrollTop: TLabel;
      Label2: TLabel;
      lbUpperRow: TLabel;
      PanelDummy: TBasicPanel;
      Label3: TLabel;
      lbLowerRow: TLabel;
      Albums: TDataSet;
      procedure Form3Create(Sender: TObject);
      procedure ScrollBoxScroll(Sender: TObject);
      procedure AlbumsAfterLoad(Sender: TObject);
      function GetItemWidth(AColumns: integer): integer;
   private
      { Private declarations }   
      RowsDone: Array of integer; 
      RowsTotal: integer;
      procedure CreateAlbumItems(AFirstRow, ALastRow: integer);
      function RowExists(ARow: integer): Boolean;
   public
      { Public declarations }
   end;

var
   Form3: TForm3; 

const
   ROW_HEIGHT     = 150;
   VISIBLE_ROWS   = 4;
   VISIBLE_SCOPE  = 5;
   COLUMNS        = 2;
implementation

procedure TForm3.Form3Create(Sender: TObject);
begin
   PanelDummy.Left := ScrollBox.Width;
   SetLength(RowsDone,0); 
   Database.DatabaseName := 'MySpotify';
   Database.BaseURL := 'databases';
   Database.LoadRows(Albums);
end;

function TForm3.GetItemWidth(AColumns: integer): integer;
begin
   Result := (Scrollbox.Width
             - Scrollbox.VertScrollbar.Width - Scrollbox.VertScrollbar.Margins.Right 
             - Scrollbox.VertScrollbar.Margins.Left) div AColumns;
end;

procedure TForm3.ScrollBoxScroll(Sender: TObject);  
var
   TempScrollTop: Integer;
   TempUpperRow, TempLowerRow: integer;
begin
   TempScrollTop := ScrollBox.ScrollTop;
   lbScrollTop.Caption := IntToStr(TempScrollTop);
   TempUpperRow := Floor(TempScrollTop / ROW_HEIGHT);
   TempLowerRow := TempUpperRow + VISIBLE_SCOPE;

   lbUpperRow.Caption := IntToStr(TempUpperRow);
   lbLowerRow.Caption := IntToStr(TempLowerRow);
   if TempLowerRow > RowsTotal -1 then
      TempLowerRow := RowsTotal -1;
   CreateAlbumItems(TempUpperRow, TempLowerRow);
end; 

procedure TForm3.CreateAlbumItems(AFirstRow, ALastRow: integer);
var
   i, z, Temp, TempItemWidth: integer;
   TempItem: TAlbumItem; 
begin 
   TempItemWidth := GetItemWidth(COLUMNS);
   ScrollBox.BeginUpdate;
   try
      for i := AFirstRow to ALastRow do
      begin
         if i = 0 then
            Albums.MoveTo(1)
         else
            Albums.MoveTo((i * 2) + 1);
         if not RowExists(i) then 
         begin
            for z := 0 to 1 do
            begin 
               if not Albums.EOF then
               begin
                  TempItem := TAlbumItem.Create(ScrollBox);
                  with TempItem do
                  begin
                     Width  := TempItemWidth;
                     Height := ROW_HEIGHT;
                     Top := i * ROW_HEIGHT;
                     if z = 0 then
                        Left := 0
                     else
                        Left := TempItemWidth;
                     AlbumName := Albums.Columns['Name'].asString;
                     AlbumArtists := Albums.Columns['Artists'].asString;
                     AlbumURL := Albums.Columns['ImageURL_Medium'].asString;
                     Animations.Visible.Duration := 200;
                     Animations.Visible.Style := asLinear;
                  end;
                  Albums.Next;
               end;
            end; 
            Temp := Length(RowsDone);
            Inc(Temp);
            SetLength(RowsDone,Temp);
            RowsDone[Temp] := i;
         end;
      end;
   finally
      ScrollBox.EndUpdate;
   end;
end; 

function TForm3.RowExists(ARow: integer): Boolean;  
var
   i: integer;
begin 
   Result := false;
   for i := 0 to Length(RowsDone) -1 do
   begin
      if RowsDone[i] = ARow then
      begin
         Result := true;
         Break; 
      end;
   end;
end;

procedure TForm3.AlbumsAfterLoad(Sender: TObject);
begin 
   RowsTotal := Ceil(Albums.RowCount / 2);
   PanelDummy.Height := RowsTotal * ROW_HEIGHT;
   CreateAlbumItems(0,VISIBLE_ROWS);
end;

end.