grid = {};
iodispatch = {};
vspacing = 4;
hspacing = 4;
cursor = 0;
cellcount = 0;
pageofs = 0;

function gridle()
    system_load("scripts/keyconf.lua")();
    games = list_games( {} );
    if (#games == 0) then
        error "No games found";
        shutdown();
    end

    keyconfig = keyconf_create(0, { "rMENU_ESCAPE", "rMENU_LEFT", "rMENU_RIGHT", "rMENU_UP", "rMENU_DOWN", "rMENU_SELECT" } );
    keyconfig.iofun = gridle_input;
    if (keyconfig.active == false) then
        gridle_input = function(iotbl)
            if (keyconfig:input(iotbl) == true) then
              gridle_input = keyconfig.iofun;
            end
        end
    end

    iodispatch["MENU_UP"]      = function(iotbl) move_cursor( -1 * ncw); end
    iodispatch["MENU_DOWN"]    = function(iotbl) move_cursor( ncw ); end
    iodispatch["MENU_LEFT"]    = function(iotbl) move_cursor( -1 ); end
    iodispatch["MENU_RIGHT"]   = function(iotbl) move_cursor( 1 ); end
    iodispatch["MENU_ESCAPE"]  = function(iotbl) shutdown(); end
    iodispatch["MENU_SELECT"]  = function(iotbl) if (games[cursor + 1]) then
  launch_target( games[cursor + pageofs + 1].title, LAUNCH_EXTERNAL); end end

    cursorvid = fill_surface(34, 34, 255, 255, 255);
    build_grid(64, 64);
end

function cell_coords(x, y)
    return (0.5 * borderw) + x * (cell_width + hspacing), (0.5 * borderh) + y * (cell_height + vspacing);
end

function move_cursor( ofs )
    local pageofs_cur = pageofs;
    cursor = cursor + ofs;

-- paging calculations
    if (ofs > 0) then -- right/forward
        if (cursor >= ncc) then -- move right or "forward"
            cursor = cursor - ncc;
            pageofs_cur = pageofs_cur + ncc;
        end

        -- wrap around on overflow
        if (pageofs_cur + cursor >= #games) then
            pageofs_cur = 0;
            cursor = 0;
        end
    elseif (ofs < 0) then -- left/backward
        if (cursor < 0) then -- step back a page
            pageofs_cur = pageofs_cur - ncc;
            cursor = ncc - ( -1 * cursor);

            if (pageofs_cur < 0) then -- wrap page around
                pageofs_cur = math.floor(#games / ncc) * ncc;
            end

            if (cursor < 0 or cursor >= #games - pageofs_cur) then
                cursor = #games - pageofs_cur - 1;
            end
        end
    end

    local x,y = cell_coords(math.floor(cursor % ncw), math.floor(cursor / ncw));
    move_image(cursorvid, x - hspacing, y - vspacing);

-- reload images of the page has changed
    if (pageofs_cur ~= pageofs) then
        erase_grid();
        pageofs = pageofs_cur;
        build_grid(cell_width, cell_height);
    end
end

function get_image(romset)
    local rvid = BADID;

    if resource("screenshots/" .. romset .. ".png") then
        rvid = load_image("screenshots/" .. romset .. ".png");
    end

    if (rvid == BADID) then
        rvid = render_text( [[\ffonts/default.ttf,96 ]] .. romset );
    end

    return rvid;
end

function erase_grid()
    cellcount = 0;

    for row=0, nch-1 do
     for col=0, ncw-1 do
      if (grid[row][col]) then
       delete_image(grid[row][col]);
       grid[row][col] = nil;
      end
     end
    end

end

function build_grid(width, height)
--  figure out how many full cells we can fit with the current resolution
    ncw = math.floor(VRESW / (width + hspacing));
    nch = math.floor(VRESH / (height + vspacing));
    ncc = ncw * nch;
    cell_width = width;
    cell_height = height;

--  figure out how much "empty" space we'll have to pad with
    borderw = VRESW % (width + hspacing);
    borderh = VRESH % (height + vspacing);

    for row=0, nch-1 do
        grid[row] = {};
        for col=0, ncw-1 do
            local gameno = (row * ncw + col + pageofs + 1); -- games is 1 indexed
            if (games[gameno] == nil) then break; end
            local vid = get_image(games[gameno]["setname"]);
            resize_image(vid, cell_width, cell_height);
            move_image(vid,cell_coords(col, row));
            order_image(vid, 2);
            show_image(vid);
            grid[row][col] = vid;
            cellcount = cellcount + 1;
        end
    end

-- reset the cursor
    delete_image(cursorvid);
    cursorvid = fill_surface(width + 2 * hspacing, height + 2 * vspacing, 255, 255, 255);
    show_image(cursorvid);
    order_image(cursorvid, 0);
    move_cursor(0);
end

function gridle_input(iotbl)
 local restbl = keyconfig:match(iotbl);
 if (restbl and iotbl.active) then
  for ind,val in pairs(restbl) do
   if (iodispatch[val]) then
     iodispatch[val](restbl);
   end
  end
 end
end