From 6420570aaa0adbef6a30d28ba7ee681a5bfe2409 Mon Sep 17 00:00:00 2001
From: Zach Nelson <zach@zdnelson.com>
Date: Wed, 15 Jul 2026 18:27:38 -0500
Subject: [PATCH] fix: Unify book-progress percent across reader screens

---
 lib/Epub/Epub.cpp                            | 12 +++++++++
 lib/Epub/Epub.h                              |  9 +++++++
 src/activities/reader/EpubReaderActivity.cpp | 26 +++++++++-----------
 3 files changed, 32 insertions(+), 15 deletions(-)

diff --git a/lib/Epub/Epub.cpp b/lib/Epub/Epub.cpp
index 3dd7400319..c68c716e99 100644
--- a/lib/Epub/Epub.cpp
+++ b/lib/Epub/Epub.cpp
@@ -967,6 +967,18 @@ float Epub::calculateProgress(const uint16_t currentSpineIndex, const float curr
   return totalProgress / static_cast<float>(bookSize);
 }
 
+float Epub::calculateProgressForPage(const uint16_t spineIndex, const uint16_t pageInSpine,
+                                     const uint16_t spinePageCount) const {
+  if (spinePageCount == 0) {
+    return calculateProgress(spineIndex, 0.0f);
+  }
+  float intra = static_cast<float>(pageInSpine + 1) / static_cast<float>(spinePageCount);
+  if (intra > 1.0f) {
+    intra = 1.0f;
+  }
+  return calculateProgress(spineIndex, intra);
+}
+
 std::optional<uint16_t> Epub::resolveHrefToSpineIndex(const std::string& href) const {
   if (!bookMetadataCache || !bookMetadataCache->isLoaded()) return std::nullopt;
 
diff --git a/lib/Epub/Epub.h b/lib/Epub/Epub.h
index 5f1f546e15..934b832d86 100644
--- a/lib/Epub/Epub.h
+++ b/lib/Epub/Epub.h
@@ -82,7 +82,16 @@ class Epub {
   uint16_t getSpineIndexForTextReference() const;
 
   size_t getBookSize() const;
+
+  // Byte-weighted primitive: maps a [0,1] fraction through a spine to book
+  // progress. Page-based callers use calculateProgressForPage (public) instead.
   float calculateProgress(uint16_t currentSpineIndex, float currentSpineRead) const;
+
+  // Book progress (0.0-1.0) for a 0-based page within a spine. The 1-based
+  // fraction ((pageInSpine + 1) / spinePageCount) makes the final page read as
+  // a full 1.0. Shared by all progress readouts so the convention can't drift.
+  float calculateProgressForPage(uint16_t spineIndex, uint16_t pageInSpine, uint16_t spinePageCount) const;
+
   CssParser* getCssParser() const { return cssParser.get(); }
   std::optional<uint16_t> resolveHrefToSpineIndex(const std::string& href) const;
 };
diff --git a/src/activities/reader/EpubReaderActivity.cpp b/src/activities/reader/EpubReaderActivity.cpp
index 3e282dbaf1..c8166f203c 100644
--- a/src/activities/reader/EpubReaderActivity.cpp
+++ b/src/activities/reader/EpubReaderActivity.cpp
@@ -250,9 +250,9 @@ void EpubReaderActivity::loop() {
       const int totalPages = getChapterTotalPages();
       float bookProgress = 0.0f;
       if (epub->getBookSize() > 0 && spineItem && spineItem->getPageCount() > 0) {
-        const float chapterProgress =
-            static_cast<float>(spineItem->currentPage) / static_cast<float>(spineItem->getPageCount());
-        bookProgress = epub->calculateProgress(currentSpineIndex, chapterProgress) * 100.0f;
+        bookProgress =
+            epub->calculateProgressForPage(currentSpineIndex, spineItem->currentPage, spineItem->getPageCount()) *
+            100.0f;
       }
       const int bookProgressPercent = clampPercent(static_cast<int>(bookProgress + 0.5f));
       startActivityForResult(std::make_unique<EpubReaderMenuActivity>(renderer, mappedInput, epub->getTitle(),
@@ -543,9 +543,9 @@ void EpubReaderActivity::onReaderMenuConfirm(EpubReaderMenuActivity::MenuAction
     case EpubReaderMenuActivity::MenuAction::GO_TO_PERCENT: {
       float bookProgress = 0.0f;
       if (epub && epub->getBookSize() > 0 && spineItem && spineItem->getPageCount() > 0) {
-        const float chapterProgress =
-            static_cast<float>(spineItem->currentPage) / static_cast<float>(spineItem->getPageCount());
-        bookProgress = epub->calculateProgress(currentSpineIndex, chapterProgress) * 100.0f;
+        bookProgress =
+            epub->calculateProgressForPage(currentSpineIndex, spineItem->currentPage, spineItem->getPageCount()) *
+            100.0f;
       }
       const int initialPercent = clampPercent(static_cast<int>(bookProgress + 0.5f));
       startActivityForResult(std::make_unique<ReaderPercentSelectionActivity>(renderer, mappedInput, initialPercent),
@@ -999,10 +999,8 @@ void EpubReaderActivity::renderContents(std::unique_ptr<Page> page, const uint16
 
 void EpubReaderActivity::renderStatusBar() const {
   // Calculate progress in book
-  const int currentPage = spineItem->currentPage + 1;
-  const float pageCount = spineItem->getPageCount();
-  const float sectionChapterProg = (pageCount > 0) ? (static_cast<float>(currentPage) / pageCount) : 0;
-  const float bookProgress = epub->calculateProgress(currentSpineIndex, sectionChapterProg) * 100;
+  const float bookProgress =
+      epub->calculateProgressForPage(currentSpineIndex, spineItem->currentPage, spineItem->getPageCount()) * 100;
 
   // Use chapter-relative page counts when available
   const int chapterPage = getChapterRelativePage() + 1;
@@ -1253,11 +1251,9 @@ ScreenshotInfo EpubReaderActivity::getScreenshotInfo() const {
     info.currentPage = spineItem->currentPage + 1;
     info.totalPages = spineItem->getPageCount();
     if (epub && epub->getBookSize() > 0 && info.totalPages > 0) {
-      const float chapterProgress = static_cast<float>(spineItem->currentPage) / static_cast<float>(info.totalPages);
-      int pct = static_cast<int>(epub->calculateProgress(currentSpineIndex, chapterProgress) * 100.0f + 0.5f);
-      if (pct < 0) pct = 0;
-      if (pct > 100) pct = 100;
-      info.progressPercent = pct;
+      const int pct = static_cast<int>(
+          epub->calculateProgressForPage(currentSpineIndex, spineItem->currentPage, info.totalPages) * 100.0f + 0.5f);
+      info.progressPercent = clampPercent(pct);
     }
   }
   return info;