feat(ui): add progress bar for chapter indexing

- Add progressFn callback to ChapterHtmlSlimParser for file-based progress
- Update progress every 10% to avoid excessive e-ink refreshes
- Display 200px progress bar below "Indexing..." text
- Use FAST_REFRESH for responsive progress updates

lib/Epub/Epub/Section.cpp

@@ -115,7 +115,7 @@ bool Section::clearCache() const {
 
 bool Section::persistPageDataToSD(const int fontId, const float lineCompression, const int marginTop,
                                   const int marginRight, const int marginBottom, const int marginLeft,
-                                  const bool extraParagraphSpacing) {
+                                  const bool extraParagraphSpacing, const std::function<void(int)>& progressFn) {
   const auto localPath = epub->getSpineItem(spineIndex).href;
   const auto tmpHtmlPath = epub->getCachePath() + "/.tmp_" + std::to_string(spineIndex) + ".html";
 
@@ -144,7 +144,8 @@ bool Section::persistPageDataToSD(const int fontId, const float lineCompression,
 
   ChapterHtmlSlimParser visitor(tmpHtmlPath, renderer, fontId, lineCompression, marginTop, marginRight, marginBottom,
                                 marginLeft, extraParagraphSpacing,
-                                [this](std::unique_ptr<Page> page) { this->onPageComplete(std::move(page)); });
+                                [this](std::unique_ptr<Page> page) { this->onPageComplete(std::move(page)); },
+                                progressFn);
   success = visitor.parseAndBuildPages();
 
   SD.remove(tmpHtmlPath.c_str());

lib/Epub/Epub/Section.h

@@ -1,4 +1,5 @@
 #pragma once
+#include <functional>
 #include <memory>
 
 #include "Epub.h"
@@ -31,6 +32,7 @@ class Section {
   void setupCacheDir() const;
   bool clearCache() const;
   bool persistPageDataToSD(int fontId, float lineCompression, int marginTop, int marginRight, int marginBottom,
-                           int marginLeft, bool extraParagraphSpacing);
+                           int marginLeft, bool extraParagraphSpacing,
+                           const std::function<void(int)>& progressFn = nullptr);
   std::unique_ptr<Page> loadPageFromSD() const;
 };

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp

@@ -221,6 +221,11 @@ bool ChapterHtmlSlimParser::parseAndBuildPages() {
     return false;
   }
 
+  // Get file size for progress calculation
+  const size_t totalSize = file.size();
+  size_t bytesRead = 0;
+  int lastProgress = -1;
+
   XML_SetUserData(parser, this);
   XML_SetElementHandler(parser, startElement, endElement);
   XML_SetCharacterDataHandler(parser, characterData);
@@ -249,6 +254,16 @@ bool ChapterHtmlSlimParser::parseAndBuildPages() {
       return false;
     }
 
+    // Update progress (call every 10% change to avoid too frequent updates)
+    bytesRead += len;
+    if (progressFn && totalSize > 0) {
+      const int progress = static_cast<int>((bytesRead * 100) / totalSize);
+      if (progress != lastProgress && progress % 10 == 0) {
+        lastProgress = progress;
+        progressFn(progress);
+      }
+    }
+
     done = file.available() == 0;
 
     if (XML_ParseBuffer(parser, static_cast<int>(len), done) == XML_STATUS_ERROR) {

lib/Epub/Epub/parsers/ChapterHtmlSlimParser.h

@@ -18,6 +18,7 @@ class ChapterHtmlSlimParser {
   const std::string& filepath;
   GfxRenderer& renderer;
   std::function<void(std::unique_ptr<Page>)> completePageFn;
+  std::function<void(int)> progressFn;  // Progress callback (0-100)
   int depth = 0;
   int skipUntilDepth = INT_MAX;
   int boldUntilDepth = INT_MAX;
@@ -48,7 +49,8 @@ class ChapterHtmlSlimParser {
   explicit ChapterHtmlSlimParser(const std::string& filepath, GfxRenderer& renderer, const int fontId,
                                  const float lineCompression, const int marginTop, const int marginRight,
                                  const int marginBottom, const int marginLeft, const bool extraParagraphSpacing,
-                                 const std::function<void(std::unique_ptr<Page>)>& completePageFn)
+                                 const std::function<void(std::unique_ptr<Page>)>& completePageFn,
+                                 const std::function<void(int)>& progressFn = nullptr)
       : filepath(filepath),
         renderer(renderer),
         fontId(fontId),
@@ -58,7 +60,8 @@ class ChapterHtmlSlimParser {
         marginBottom(marginBottom),
         marginLeft(marginLeft),
         extraParagraphSpacing(extraParagraphSpacing),
-        completePageFn(completePageFn) {}
+        completePageFn(completePageFn),
+        progressFn(progressFn) {}
   ~ChapterHtmlSlimParser() = default;
   bool parseAndBuildPages();
   void addLineToPage(std::shared_ptr<TextBlock> line);

src/activities/reader/EpubReaderActivity.cpp

@@ -219,23 +219,40 @@ void EpubReaderActivity::renderScreen() {
                                     SETTINGS.extraParagraphSpacing)) {
       Serial.printf("[%lu] [ERS] Cache not found, building...\n", millis());
 
+      // Progress bar dimensions
+      constexpr int barWidth = 200;
+      constexpr int barHeight = 10;
+      constexpr int boxMargin = 20;
+      const int textWidth = renderer.getTextWidth(READER_FONT_ID, "Indexing...");
+      const int boxWidth = (barWidth > textWidth ? barWidth : textWidth) + boxMargin * 2;
+      const int boxHeight = renderer.getLineHeight(READER_FONT_ID) + barHeight + boxMargin * 3;
+      const int boxX = (GfxRenderer::getScreenWidth() - boxWidth) / 2;
+      constexpr int boxY = 50;
+      const int barX = boxX + (boxWidth - barWidth) / 2;
+      const int barY = boxY + renderer.getLineHeight(READER_FONT_ID) + boxMargin * 2;
+
+      // Draw initial indexing box with 0% progress
       {
-        const int textWidth = renderer.getTextWidth(READER_FONT_ID, "Indexing...");
+        renderer.fillRect(boxX, boxY, boxWidth, boxHeight, false);
-        constexpr int margin = 20;
+        renderer.drawText(READER_FONT_ID, boxX + boxMargin, boxY + boxMargin, "Indexing...");
-        const int x = (GfxRenderer::getScreenWidth() - textWidth - margin * 2) / 2;
+        renderer.drawRect(boxX + 5, boxY + 5, boxWidth - 10, boxHeight - 10);
-        constexpr int y = 50;
+        // Draw empty progress bar outline
-        const int w = textWidth + margin * 2;
+        renderer.drawRect(barX, barY, barWidth, barHeight);
-        const int h = renderer.getLineHeight(READER_FONT_ID) + margin * 2;
-        renderer.fillRect(x, y, w, h, false);
-        renderer.drawText(READER_FONT_ID, x + margin, y + margin, "Indexing...");
-        renderer.drawRect(x + 5, y + 5, w - 10, h - 10);
         renderer.displayBuffer();
         pagesUntilFullRefresh = 0;
       }
 
       section->setupCacheDir();
+
+      // Progress callback to update progress bar
+      auto progressCallback = [this, barX, barY, barWidth, barHeight](int progress) {
+        const int fillWidth = (barWidth - 2) * progress / 100;
+        renderer.fillRect(barX + 1, barY + 1, fillWidth, barHeight - 2, true);
+        renderer.displayBuffer(EInkDisplay::FAST_REFRESH);
+      };
+
       if (!section->persistPageDataToSD(READER_FONT_ID, lineCompression, marginTop, marginRight, marginBottom,
-                                        marginLeft, SETTINGS.extraParagraphSpacing)) {
+                                        marginLeft, SETTINGS.extraParagraphSpacing, progressCallback)) {
         Serial.printf("[%lu] [ERS] Failed to persist page data to SD\n", millis());
         section.reset();
         return;