Calculate the progress in the book by file sizes of each chapter. (#38)

## Summary

Addresses #35.

Maybe it could be wise to do some caching of the spine sizes (but
performance isn't too bad).

lib/Epub/Epub.cpp

@@ -148,6 +148,18 @@ bool Epub::load() {
     return false;
   }
 
+  // determine size of spine items
+  size_t spineItemsCount = getSpineItemsCount();
+  size_t spineItemsSize = 0;
+  for (size_t i = 0; i < spineItemsCount; i++) {
+    std::string spineItem = getSpineItem(i);
+    size_t s = 0;
+    getItemSize(spineItem, &s);
+    spineItemsSize += s;
+    cumulativeSpineItemSize.emplace_back(spineItemsSize);
+  }
+  Serial.printf("[%lu] [EBP] Book size: %u\n", millis(), spineItemsSize);
+
   Serial.printf("[%lu] [EBP] Loaded ePub: %s\n", millis(), filepath.c_str());
 
   return true;
@@ -255,6 +267,8 @@ bool Epub::getItemSize(const std::string& itemHref, size_t* size) const {
 
 int Epub::getSpineItemsCount() const { return spine.size(); }
 
+size_t Epub::getCumulativeSpineItemSize(const int spineIndex) const { return cumulativeSpineItemSize.at(spineIndex); }
+
 std::string& Epub::getSpineItem(const int spineIndex) {
   if (spineIndex < 0 || spineIndex >= spine.size()) {
     Serial.printf("[%lu] [EBP] getSpineItem index:%d is out of range\n", millis(), spineIndex);
@@ -302,3 +316,14 @@ int Epub::getTocIndexForSpineIndex(const int spineIndex) const {
   Serial.printf("[%lu] [EBP] TOC item not found\n", millis());
   return -1;
 }
+
+size_t Epub::getBookSize() const { return getCumulativeSpineItemSize(getSpineItemsCount() - 1); }
+
+// Calculate progress in book
+uint8_t Epub::calculateProgress(const int currentSpineIndex, const float currentSpineRead) {
+  size_t prevChapterSize = getCumulativeSpineItemSize(currentSpineIndex - 1);
+  size_t curChapterSize = getCumulativeSpineItemSize(currentSpineIndex) - prevChapterSize;
+  size_t bookSize = getBookSize();
+  size_t sectionProgSize = currentSpineRead * curChapterSize;
+  return round(static_cast<float>(prevChapterSize + sectionProgSize) / bookSize * 100.0);
+}

lib/Epub/Epub.h

@@ -20,6 +20,8 @@ class Epub {
   std::string filepath;
   // the spine of the EPUB file
   std::vector<std::pair<std::string, std::string>> spine;
+  // the file size of the spine items (proxy to book progress)
+  std::vector<size_t> cumulativeSpineItemSize;
   // the toc of the EPUB file
   std::vector<EpubTocEntry> toc;
   // the base path for items in the EPUB file
@@ -51,8 +53,12 @@ class Epub {
   bool getItemSize(const std::string& itemHref, size_t* size) const;
   std::string& getSpineItem(int spineIndex);
   int getSpineItemsCount() const;
-  EpubTocEntry& getTocItem(int tocTndex);
+  size_t getCumulativeSpineItemSize(const int spineIndex) const;
+  EpubTocEntry& getTocItem(int tocIndex);
   int getTocItemsCount() const;
   int getSpineIndexForTocIndex(int tocIndex) const;
   int getTocIndexForSpineIndex(int spineIndex) const;
+
+  size_t getBookSize() const;
+  uint8_t calculateProgress(const int currentSpineIndex, const float currentSpineRead);
 };

src/screens/EpubReaderScreen.cpp

@@ -324,8 +324,14 @@ void EpubReaderScreen::renderContents(std::unique_ptr<Page> page) {
 
 void EpubReaderScreen::renderStatusBar() const {
   constexpr auto textY = 776;
+
+  // Calculate progress in book
+  float sectionChapterProg = static_cast<float>(section->currentPage) / section->pageCount;
+  uint8_t bookProgress = epub->calculateProgress(currentSpineIndex, sectionChapterProg);
+
   // Right aligned text for progress counter
-  const std::string progress = std::to_string(section->currentPage + 1) + " / " + std::to_string(section->pageCount);
+  const std::string progress = std::to_string(section->currentPage + 1) + "/" + std::to_string(section->pageCount) +
+                               "  " + std::to_string(bookProgress) + "%";
   const auto progressTextWidth = renderer.getTextWidth(SMALL_FONT_ID, progress.c_str());
   renderer.drawText(SMALL_FONT_ID, GfxRenderer::getScreenWidth() - marginRight - progressTextWidth, textY,
                     progress.c_str());