Nelua

require 'libs.nuklear'
require 'libs.sokol_app'
require 'libs.sokol_gfx'
require 'libs.sokol_glue'
require 'libs.sokol_nuklear'

require 'string'

local set: boolean = false
local prev: integer, op: integer = 0, 0
local numbers: *[9]cchar = (@*[9]cchar)("789456123"_cstring)
local ops: [4]byte = {'+'_byte, '-'_byte, '*'_byte, '/'_byte}
local a: number, b: number = 0.0, 0.0
local current: *number = &a

local function calculator(ctx: *NK_context)
  if nk_begin(ctx, "Calculator", nk_rect(10, 10, 180, 250),
     NK_WINDOW_BORDER|NK_WINDOW_NO_SCROLLBAR|NK_WINDOW_TITLE|NK_WINDOW_MOVABLE) == nk_true then
    local solve: boolean = false
    do
      nk_layout_row_dynamic(ctx, 35, 1)
      local sb: stringbuilder <close>
      sb:prepare(256)
      local ok: boolean, len: cint = sb:writef('%.2f', $current)
      nk_edit_string(ctx, NK_EDIT_SIMPLE, &sb.data[0], &len, #sb, nk_filter_float)
      sb:resize(len)
      if len > 0 then
        $current = tonumber(sb:view())
      else
        $current = 0
      end
    end

    nk_layout_row_dynamic(ctx, 35, 4)
    for i=0,<16 do
      if i >= 12 and i < 15  then
          if i > 12 then continue end
          if nk_button_label(ctx, "C") == nk_true then
            a, b, op = 0, 0, 0
            current = &a
            set = false
          end
          if nk_button_label(ctx, "0") == nk_true then
            $current = $current * 10.0
            set = false
          end
          if nk_button_label(ctx, "=") == nk_true then
            solve = true
            prev = op
            op = 0
          end
      elseif ((i+1) % 4) ~= 0 then
        if nk_button_text(ctx, &numbers[(i//4)*3+i%4], 1) == nk_true then
          $current = $current * 10.0 + numbers[(i//4)*3+i%4] - '0'_byte
          set = false
        end
      elseif nk_button_text(ctx, &ops[i//4], 1) == nk_true then
        if not set then
          if current ~= &b then
            current = &b
          else
            prev = op
            solve = true
          end
        end
        op = ops[i//4]
        set = true
      end
    end
    if solve then
      if     prev == '+'_byte then a = a + b
      elseif prev == '-'_byte then a = a - b
      elseif prev == '*'_byte then a = a * b
      elseif prev == '/'_byte then a = a / b end
      current = &a
      if set then current = &b end
      b, set = 0, false
    end
  end
  nk_end(ctx)
end

local function init()
  local sgdesc: sg_desc = {context = sapp_sgcontext()}
  sg_setup(&sgdesc)
  local snkdesc: snk_desc_t = {dpi_scale = sapp_dpi_scale()}
  snk_setup(&snkdesc)
end

local function frame()
  local nkctx: *NK_context = snk_new_frame()
  calculator(nkctx)
  local pass_action: sg_pass_action
  pass_action.colors[0] = {action=SG_ACTION_CLEAR, value={0.0, 0.0, 0.0, 1.0}}
  sg_begin_default_pass(&pass_action, sapp_width(), sapp_height())
  snk_render(sapp_width(), sapp_height())
  sg_end_pass()
  sg_commit()
end

local function input(event: *sapp_event)
  snk_handle_event(event)
end

local function cleanup()
  snk_shutdown()
  sg_shutdown()
end

local app_desc: sapp_desc = {
  init_cb = init,
  frame_cb = frame,
  event_cb = input,
  cleanup_cb = cleanup,
  width = 512,
  height = 512,
  window_title = "Sokol Nuklear",
  enable_clipboard = true,
  html5_canvas_resize = true,
}
sapp_run(&app_desc)