constexpr f32 max3(f32 a, f32 b, f32 c)
{
  return (a > b) ? (a > c) ? a : (b > c) ? b : c : (b > c) ? b : c; 
}

struct Color_Rgb { f32 r, g, b; };

// https://stackoverflow.com/questions/141855/programmatically-lighten-a-color
internal
Color_Rgb redist_rgb(Color_Rgb c)
{
  f32 r = c.r;
  f32 g = c.g;
  f32 b = c.b;
  f32 threshold = 255.999;
  f32 m = max3(r, g, b);
  if (m <= threshold)
      return { r, g, b };
  f32 total = r + g + b;
  if (total >= 3 * threshold)
      return { threshold, threshold, threshold };
  f32 x = (3 * threshold - total) / (3 * m - total);
  f32 gray = threshold - x * m;
  return { gray + x * r, gray + x * g, gray + x * b };
}

internal
Color_Rgb brighten(Color_Rgb c, f32 amt)
{
  f32 a = 1.f + amt;
  Color_Rgb cb = { c.r * a, c.g * a, c.b * a };
  cb = redist_rgb(cb);
  return cb;  
}

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
ImColor imcol(const f32 col[3], f32 brighten_amt = 0)
{
  Color_Rgb c = { col[0], col[1], col[2] };
  if (brighten_amt != 0)
    c = brighten(c, brighten_amt);
  
  return ImColor(c.r, c.g, c.b);
}

internal
u32 highlight_zstd_header(const u8 *data, u64 off, App_State &app, f32 brighten)
{
  if (app.viewer.highlight_zstd_headers) {
    static const u32 ZSTD_HEADER = 0xFD2FB528;

    if (app.viewer.last_seen_zstd_header_start > 0) {
      if (off - app.viewer.last_seen_zstd_header_start <= sizeof(ZSTD_HEADER)) {
        return imcol(app.viewer.col_highlight, brighten);
      }
      app.viewer.last_seen_zstd_header_start = 0;
    }
  
    if (off < app.inspected_file.size - sizeof(ZSTD_HEADER) && data[off] == 0x28) {
      u32 bytes;
      memcpy(&bytes, data + off, sizeof(ZSTD_HEADER));
      if (bytes == ZSTD_HEADER) {
        app.viewer.last_seen_zstd_header_start = off;
        return imcol(app.viewer.col_highlight, brighten);
      }
    }
  } else {  
    app.viewer.last_seen_zstd_header_start = 0;
  }

  return 0;
}

internal
u32 mem_edit_bg_color_fn(const u8 *data, u64 off, void *user_data)
{
  App_State *app = reinterpret_cast<App_State *>(user_data);
  off += app->base_display_addr;

  f32 brighten = 0;
  if (app->viewer.hovered_range.start <= off && off < app->viewer.hovered_range.end())
    brighten = 0.3;

  u32 col = highlight_zstd_header(data, off, *app, brighten);
  if (app->viewer.last_seen_zstd_header_start)
    return col;

  i64 hilite_cluster = app->viewer.highlight_cluster ? app->viewer.highlighted_cluster : -1;
  Section section = find_section(*app, off, hilite_cluster);
  
  if (section.highlighted) return imcol(app->viewer.col_highlight, brighten);
  if (section.id == Sec_Page && off == section.range.start) return imcol(app->viewer.col_page_start, brighten);
  if (off < section.range.start) return imcol(app->viewer.col_key, brighten);
  if (section.range.end() - section.post_size <= off && off < section.range.end()) return imcol(app->viewer.col_checksum, brighten);
  return imcol(app->viewer.col_section[section.id], brighten);
}

internal
void mem_edit_interact_fn(const u8 *, u64 off, void *user_data)
{
  App_State *app = reinterpret_cast<App_State *>(user_data);
  off += app->base_display_addr;
  app->viewer.hovered_off = off + 1;
}

internal
MemoryEditor make_memory_editor(App_State &app, i32 n_cols)
{
  MemoryEditor mem_edit;
  mem_edit.Cols = n_cols ? n_cols : 32;
  mem_edit.OptShowDataPreview = true;
  // Do nothing on write.
  // Note that we don't use ReadOnly = true because that disables selecting bytes
  mem_edit.WriteFn = [] (ImU8*, size_t, ImU8) {};
  mem_edit.BgColorFn = mem_edit_bg_color_fn;
  mem_edit.BgColorFnUserData = &app;
  mem_edit.InteractFn = mem_edit_interact_fn;
  mem_edit.InteractFnUserData = &app;
  return mem_edit;
}

internal
void make_viewer(App_State &app, u16 n_cols)
{
  Viewer viewer {};
  viewer.mem_edit = make_memory_editor(app, (i32)n_cols);

#define COL(c, r, g, b) viewer.c[0] = r/255.0, viewer.c[1] = g/255.0, viewer.c[2] = b/255.0
  COL(col_key,    0, 100, 50);
  COL(col_page_start, 200, 0, 200);
  COL(col_checksum, 134, 65, 25);
  COL(col_highlight, 190, 190, 190);
#define COL_S(c, r, g, b) viewer.col_section[c][0] = r/255.0, viewer.col_section[c][1] = g/255.0, viewer.col_section[c][2] = b/255.0
  COL_S(Sec_RNTuple_Anchor, 150, 150, 0);
  COL_S(Sec_RNTuple_Header, 150, 0, 50);
  COL_S(Sec_RNTuple_Footer, 50, 0, 150);
  COL_S(Sec_TFile_Header,  90, 90, 90);
  COL_S(Sec_TFile_Object,  120, 120, 120);
  COL_S(Sec_TFile_Info, 95, 76, 76);
  COL_S(Sec_TFile_FreeList, 60, 60, 90);
  COL_S(Sec_Page,   125, 0, 125);
  COL_S(Sec_Page_List, 60, 110, 120);
  COL_S(Sec_TKey_List, 100, 140, 100);
#undef COL
#undef COL_S

  app.viewer = viewer;
}

internal
void viewer_jump_to(App_State &app, u64 addr)
{
  app.viewer.mem_edit.GotoAddr = addr;
}

internal
void viewer_jump_to_page(App_State &app, u64 page_idx)
{
  assert(app.rndata.n_pages > 0);
  page_idx = (page_idx + app.rndata.n_pages) % app.rndata.n_pages;
  
  // @Speed
  Page_Info_Node *page = app.rndata.pages;
  for (u64 i = 0; i < page_idx; ++i) {
    page = page->next;    
    assert(page);
  }

  app.viewer.latest_page_gone_to = page_idx;
  viewer_jump_to(app, page->range.start);
}

internal
void viewer_jump_to_page_list(App_State &app, u64 page_list_idx)
{
  assert(app.rndata.n_cluster_groups > 0);
  page_list_idx = (page_list_idx + app.rndata.n_cluster_groups) % app.rndata.n_cluster_groups;
  
  Cluster_Group_Info &cg_info = app.rndata.cluster_groups[page_list_idx];

  app.viewer.latest_page_list_gone_to = page_list_idx;
  viewer_jump_to(app, cg_info.rng_page_list.start);
}

internal
void viewer_jump_to_cluster(App_State &app, u64 cluster_idx)
{
  assert(app.rndata.n_clusters > 0);
  cluster_idx = (cluster_idx + app.rndata.n_clusters) % app.rndata.n_clusters;
  
  Cluster_Info &cluster = app.rndata.clusters[cluster_idx];
  Page_Info_Node *page = cluster.first_page;
  assert(page);

  app.viewer.highlighted_cluster = cluster_idx;
  app.viewer.latest_page_gone_to = cluster.first_page_idx;
  viewer_jump_to(app, page->range.start);
}

internal
void imgui_render_string_tree(Arena *arena, String8_Node *root, u16 indent = 0)
{
  String8 indent_str;
  if (indent) {
    indent_str = { arena_push_array_nozero<u8>(arena, indent + 1), indent };
    indent_str.str[indent] = 0;
    memset(indent_str.str, ' ', indent);
  } else {
    indent_str = str8("");
  }
  
  for (String8_Node *node = root; node; node = node->next) {
    ImGui::Text("%s%s", indent_str.c(), node->str.c());

    if (node->first_child)
      imgui_render_string_tree(arena, node->first_child, indent + 2);
  }
}

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 = scratch_begin(&arena, 1);
  defer { scratch_end(scratch); };

  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.rndata);
    ImGui::Text("RNTuple '%s' (%s) from file \"%s\"", app.ntpl_name.c(), ntpl_desc.c(), app.inspected_file.name.c());

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

      f32 avg_dt = calc_avg_dt_ms(app.delta_time_accum);

      String8 mem_used = to_pretty_size(scratch.arena, arena->mem_used);
      String8 mem_peak = to_pretty_size(scratch.arena, arena->mem_peak_used);
      String8 stat_txt = push_str8f(scratch.arena, "mem used: %s (peak: %s) | avg dt: %.1f", 
                                    mem_used.c(), mem_peak.c(), 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
    {
      const i64 step_i64 = 1;

      ImGui::BeginTable("Hex View", 2, ImGuiTableFlags_Resizable);

      ImGui::TableNextColumn();

      app.viewer.hovered_off = 0;

      assert(app.base_display_addr < app.inspected_file.size);
      void *content = app.inspected_file.mem + app.base_display_addr;
      u64 content_size = app.inspected_file.size - app.base_display_addr;
      app.last_pinfo = &invalid_pinfo;
      app.viewer.mem_edit.DrawContents(content, content_size, app.base_display_addr);

      ImGui::TableNextColumn();
      ImGuiColorEditFlags flags =  ImGuiColorEditFlags_NoInputs|ImGuiColorEditFlags_NoLabel;

      // Unique sections: just display a button that jumps to the start of it and show their size
      for (u32 i = 0; i < Sec_COUNT; ++i) {
        Byte_Range range = get_section_range(app, static_cast<Section_Id>(i));
        if (!range.len) continue;

        String8 sec_name = section_names[i];
        String8 col_label = push_str8f(scratch.arena, "_%s", sec_name.c());
        ImGui::ColorEdit3(col_label.c(), app.viewer.col_section[i], flags);
        ImGui::SameLine(); 
        if (ImGui::Button(sec_name.c())) 
          viewer_jump_to(app, range.start);
        ImGui::SameLine(); 
        ImGui::Text("%s", to_pretty_size(scratch.arena, range.len).c());
      }

      // Repeated sections: allow jumping to the N-th
      ImGui::ColorEdit3("_TKey Header", app.viewer.col_key, flags);
      ImGui::SameLine(); 
      if (ImGui::Button("TKey Header")) {} // TODO: jump to next key

      ImGui::ColorEdit3("_Page Start", app.viewer.col_page_start, flags);
      ImGui::SameLine(); 
      if (ImGui::Button("Page Start"))
        viewer_jump_to_page(app, 0);

      ImGui::ColorEdit3("_Page", app.viewer.col_section[Sec_Page], flags);
      ImGui::SameLine();
      if (ImGui::Button("Page"))
        viewer_jump_to_page(app, app.viewer.latest_page_gone_to);
      ImGui::SameLine();
      {
        const i64 step_fast_i64 = app.rndata.n_pages / 100;
        i64 page_to_go_to = app.viewer.latest_page_gone_to;
        ImGui::PushItemWidth(100.f);
        if (ImGui::InputScalar("##page_viewed", ImGuiDataType_S64, &page_to_go_to, &step_i64, &step_fast_i64, "%u"))
          viewer_jump_to_page(app, page_to_go_to);
        ImGui::PopItemWidth();
      }
      ImGui::SameLine();
      ImGui::Text("%s", to_pretty_size(scratch.arena, app.rndata.tot_page_size).c());

      ImGui::ColorEdit3("_Checksum", app.viewer.col_checksum, flags);
      ImGui::SameLine(); 
      if (ImGui::Button("Checksum")) {} // TODO jump to next checksum

      ImGui::ColorEdit3("_Page List", app.viewer.col_section[Sec_Page_List], flags);
      ImGui::SameLine(); 
      if (ImGui::Button("Page List"))
        viewer_jump_to_page_list(app, app.viewer.latest_page_list_gone_to);

      ImGui::SameLine();
      {
        i64 page_list_to_go_to = app.viewer.latest_page_list_gone_to;
        ImGui::PushItemWidth(80.f);
        if (ImGui::InputScalar("##page_list_viewed", ImGuiDataType_S64, &page_list_to_go_to, &step_i64, nullptr, "%u"))
          viewer_jump_to_page_list(app, page_list_to_go_to);
        ImGui::PopItemWidth();
      }
      ImGui::SameLine(); 
      ImGui::Text("%s", to_pretty_size(scratch.arena, app.rndata.tot_page_list_size).c());

      // -------------------------------
      ImGui::Separator();
      String8 root_version_str = push_str8f(scratch.arena, "%u.%u.%u", 
                                            app.tfile_data.root_version_major,
                                            app.tfile_data.root_version_minor,
                                            app.tfile_data.root_version_patch);
      ImGui::Text("ROOT version: %s", root_version_str.c());
      ImGui::Text("TFile compression: %u", app.tfile_data.compression);
      ImGui::Text("Num pages: %lu", app.rndata.n_pages);
      ImGui::Text("Num elements: %lu", app.rndata.n_elems);

      {
        const i64 step_fast_i64 = app.rndata.n_clusters / 100;
        i64 cluster_to_highlight = app.viewer.highlighted_cluster;
        ImGui::PushItemWidth(100.f);
        if (ImGui::InputScalar("##highlighted_cluster", ImGuiDataType_S64, &cluster_to_highlight, &step_i64, &step_fast_i64, "%u")) {
          viewer_jump_to_cluster(app, cluster_to_highlight);
        }
        ImGui::PopItemWidth();
        ImGui::SameLine();
        ImGui::Checkbox("Highlight cluster", &app.viewer.highlight_cluster);
      }
      ImGui::Checkbox("Highlight ZSTD headers", &app.viewer.highlight_zstd_headers);

      // ---------------------------------
      ImGui::Separator();

      if (app.viewer.hovered_off)
      {
        Section hovered_section = find_section(app, app.viewer.hovered_off - 1);
        Sec_Hover_Info hover_info = get_section_hover_info(scratch.arena, hovered_section, app.viewer.hovered_off - 1, app.inspected_file.mem);
        imgui_render_string_tree(scratch.arena, hover_info.desc);
        app.viewer.hovered_range = hover_info.rng;
      } else {
        app.viewer.hovered_range = {};
      }

      ImGui::EndTable();
    }

    ImGui::End();
  }
}