internal
void accum_dt_ms(Delta_Time_Accum &accum, f32 dt)
{
	if (accum.count < accum.max) {
		assert(accum.start == 0);
		accum.base[accum.count++] = dt;
	} else {
		accum.base[accum.start++] = dt;
		if (accum.start == accum.max)
			accum.start = 0;
	}
}

internal
f32 calc_avg_dt_ms(const Delta_Time_Accum &accum)
{
	f32 res = 0;
	for (u16 idx = 0; idx < accum.count; ++idx)
		res += accum.base[idx];
	if (accum.count) res /= accum.count;
	return res;
}

internal
String8 to_pretty_size(Arena *arena, u64 bytes)
{
	if (bytes >= GiB(1)) return push_str8f(arena, "%.1f GiB", (f32)bytes / GiB(1));
	if (bytes >= MiB(1)) return push_str8f(arena, "%.1f MiB", (f32)bytes / MiB(1));
	if (bytes >= KiB(1)) return push_str8f(arena, "%.1f KiB", (f32)bytes / KiB(1));
	return push_str8f(arena, "%zu B", bytes);
}

internal
u32 mem_edit_bg_color_fn(const u8 *data, u64 off, const void *user_data)
{
  const App_State *app = reinterpret_cast<const App_State *>(user_data);
  const RNTuple_Info &rinfo = app->rntinfo;
  u64 rblob_sz = rinfo.rblob_header_size;

#define COL(c) (ImColor((c)[0], (c)[1], (c)[2]))
  if (off <= rinfo.root_file_header_size) return COL(app->vsettings.col_tfile);
  if (rinfo.rng_anchor_key.start <= off && off <= rinfo.rng_anchor_key.end()) return COL(app->vsettings.col_key);
  if (rinfo.rng_header.start - rblob_sz <= off && off <= rinfo.rng_header.start) return COL(app->vsettings.col_key);
  if (rinfo.rng_footer.start - rblob_sz <= off && off <= rinfo.rng_footer.start) return COL(app->vsettings.col_key);
  if (rinfo.rng_anchor.start <= off && off <= rinfo.rng_anchor.end()) return COL(app->vsettings.col_anchor);
  if (rinfo.rng_header.start <= off && off <= rinfo.rng_header.end()) return COL(app->vsettings.col_header);
  if (rinfo.rng_footer.start <= off && off <= rinfo.rng_footer.end()) return COL(app->vsettings.col_footer);
#undef COL

  return IM_COL32(0, 0, 0, 0);
}

internal
MemoryEditor make_memory_editor(const App_State &app)
{
  MemoryEditor mem_edit;
  // mem_edit.ReadOnly = true;
  mem_edit.Cols = 32;
  mem_edit.OptShowDataPreview = true;
  mem_edit.BgColorFn = mem_edit_bg_color_fn;
  mem_edit.BgColorFnUserData = &app;
  return mem_edit;
}

internal
Viewer_Settings make_viewer_settings()
{
  Viewer_Settings settings {};
#define COL(c, r, g, b) settings.c[0] = r/255.0, settings.c[1] = g/255.0, settings.c[2] = b/255.0
  COL(col_anchor, 150, 150, 0);
  COL(col_header, 150, 0, 50);
  COL(col_footer, 50, 0, 150);
  COL(col_key,    0, 100, 50);
  COL(col_tfile,  90, 90, 90);
#undef COL
  return settings;
}

internal
void update_and_render(Arena *arena, App_State &app, f32 delta_time_ms)
{
  accum_dt_ms(app.delta_time_accum, delta_time_ms);
  
  ImGui::SetNextWindowPos({ 0, 0 });
  ImGui::SetNextWindowSize({ (f32)app.win_data.width, (f32)app.win_data.height });

  Temp scratch = temp_begin(arena);
  defer { temp_end(scratch); };

  const u64 inspected_max_size = 2048;
  u64 text_buf_size = min(app.inspected_file_size * 2, inspected_max_size);
  char *text_buf = arena_push_array_no_zero<char>(scratch.arena, text_buf_size + 1);
  // Convert file content to human readable
  // @Speed: maybe do this only when the file changes
  for (u64 i = 0; i < text_buf_size / 2; ++i)
    sprintf(&text_buf[2 * i], "%02X", app.inspected_fmem[i]);
  text_buf[text_buf_size] = 0;
  
  const auto main_win_flags = ImGuiWindowFlags_NoResize | ImGuiWindowFlags_NoTitleBar | ImGuiWindowFlags_NoDecoration;
  if (ImGui::Begin("main", nullptr, main_win_flags)) {
        
    String8 ntpl_desc = rntuple_description(scratch.arena, app.rntinfo.anchor);
    ImGui::Text("RNTuple '%s' (%s) from file \"%s\"", app.ntpl_name, ntpl_desc.c(), app.inspected_fname);

    // Draw stats
    {
      ImGui::SameLine();

      u64 mem_used = arena_mem_used(arena);
      f32 avg_dt = calc_avg_dt_ms(app.delta_time_accum);

      String8 stat_txt = push_str8f(scratch.arena, "mem used: %s | avg dt: %.1f", 
                                    to_pretty_size(scratch.arena, mem_used), avg_dt);

      f32 pos_x = (ImGui::GetCursorPosX() + ImGui::GetColumnWidth() - ImGui::CalcTextSize(stat_txt.c()).x 
        - ImGui::GetScrollX() - 2 * ImGui::GetStyle().ItemSpacing.x);
      if (pos_x > ImGui::GetCursorPosX())
        ImGui::SetCursorPosX(pos_x);

      ImGui::Text("%s", stat_txt.c());
    }

    ImGui::Separator();

    // Draw main content
    {
      static MemoryEditor mem_edit = make_memory_editor(app);
      ImGui::BeginTable("Hex View", 2);

      ImGui::TableNextColumn();
      mem_edit.DrawContents(app.inspected_fmem, app.inspected_file_size);

      ImGui::TableNextColumn();
      ImGui::ColorEdit3("TFile",          app.vsettings.col_tfile,  ImGuiColorEditFlags_NoInputs);
      ImGui::ColorEdit3("RNTuple Anchor", app.vsettings.col_anchor, ImGuiColorEditFlags_NoInputs);
      ImGui::ColorEdit3("RNTuple Header", app.vsettings.col_header, ImGuiColorEditFlags_NoInputs);
      ImGui::ColorEdit3("RNTuple Footer", app.vsettings.col_footer, ImGuiColorEditFlags_NoInputs);
      ImGui::ColorEdit3("TKey Header",    app.vsettings.col_key,    ImGuiColorEditFlags_NoInputs);

      ImGui::EndTable();
    }

    ImGui::End();
  }
}