Introduce toc caching

lib/Epub/Epub.cpp

@@ -868,35 +868,10 @@ bool Epub::hasReliableToc() const {
     return false;
   }
 
-  const int spineCount = bookMetadataCache->getSpineCount();
+  // Reliability is computed once at indexing time and persisted in book.bin's header.
-  const int tocCount = bookMetadataCache->getTocCount();
+  // This avoids the O(tocCount) seek-heavy scan that previously fired on first page load
-
+  // for every book — a large web-novel TOC (~3000 entries) added several seconds of latency.
-  if (spineCount <= 0 || tocCount <= 0) {
+  const bool reliable = bookMetadataCache->isTocReliable();
-    tocReliabilityState = 0;
-    return false;
-  }
-
-  // If a larger book only exposes one TOC entry, treat TOC as unusable for chapter UX.
-  if (spineCount >= 8 && tocCount <= 1) {
-    tocReliabilityState = 0;
-    return false;
-  }
-
-  std::vector<bool> spineReferenced(static_cast<size_t>(spineCount), false);
-  int distinctSpinesReferenced = 0;
-  for (int i = 0; i < tocCount; i++) {
-    const auto toc = bookMetadataCache->getTocEntry(i);
-    if (toc.spineIndex >= 0 && toc.spineIndex < spineCount) {
-      const size_t idx = static_cast<size_t>(toc.spineIndex);
-      if (!spineReferenced[idx]) {
-        spineReferenced[idx] = true;
-        distinctSpinesReferenced++;
-      }
-    }
-  }
-
-  // Require at least 25% spine coverage from TOC references.
-  const bool reliable = (distinctSpinesReferenced * 4 >= spineCount);
   tocReliabilityState = reliable ? 1 : 0;
   return reliable;
 }

lib/Epub/Epub/BookMetadataCache.cpp

@@ -9,7 +9,7 @@
 #include "FsHelpers.h"
 
 namespace {
-constexpr uint8_t BOOK_CACHE_VERSION = 6;
+constexpr uint8_t BOOK_CACHE_VERSION = 7;
 constexpr char bookBinFile[] = "/book.bin";
 constexpr char tmpSpineBinFile[] = "/spine.bin.tmp";
 constexpr char tmpTocBinFile[] = "/toc.bin.tmp";
@@ -113,8 +113,8 @@ bool BookMetadataCache::buildBookBin(const std::string& epubPath, const BookMeta
     return false;
   }
 
-  constexpr uint32_t headerASize =
+  constexpr uint32_t headerASize = sizeof(BOOK_CACHE_VERSION) + /* LUT Offset */ sizeof(uint32_t) + sizeof(spineCount) +
-      sizeof(BOOK_CACHE_VERSION) + /* LUT Offset */ sizeof(uint32_t) + sizeof(spineCount) + sizeof(tocCount);
+                                   sizeof(tocCount) + sizeof(uint8_t) /* tocReliable */;
   const uint32_t metadataSize = metadata.title.size() + metadata.author.size() + metadata.language.size() +
                                 metadata.coverItemHref.size() + metadata.textReferenceHref.size() +
                                 metadata.series.size() + metadata.seriesIndex.size() + metadata.description.size() +
@@ -122,11 +122,14 @@ bool BookMetadataCache::buildBookBin(const std::string& epubPath, const BookMeta
   const uint32_t lutSize = sizeof(uint32_t) * spineCount + sizeof(uint32_t) * tocCount;
   const uint32_t lutOffset = headerASize + metadataSize;
 
-  // Header A
+  // Header A. tocReliable is patched at the end once the TOC scan below has computed it.
+  const uint32_t tocReliableHeaderPos =
+      sizeof(BOOK_CACHE_VERSION) + sizeof(uint32_t) /* lutOffset */ + sizeof(spineCount) + sizeof(tocCount);
   serialization::writePod(bookFile, BOOK_CACHE_VERSION);
   serialization::writePod(bookFile, lutOffset);
   serialization::writePod(bookFile, spineCount);
   serialization::writePod(bookFile, tocCount);
+  serialization::writePod(bookFile, static_cast<uint8_t>(0));  // placeholder for tocReliable
   // Metadata
   serialization::writeString(bookFile, metadata.title);
   serialization::writeString(bookFile, metadata.author);
@@ -156,18 +159,31 @@ bool BookMetadataCache::buildBookBin(const std::string& epubPath, const BookMeta
   // LUTs complete
   // Loop through spines from spine file matching up TOC indexes, calculating cumulative size and writing to book.bin
 
-  // Build spineIndex->tocIndex mapping in one pass (O(n) instead of O(n*m))
+  // Build spineIndex->tocIndex mapping in one pass (O(n) instead of O(n*m)).
+  // Also count distinct spines referenced by the TOC so tocReliable can be persisted in the
+  // header below — without this, every first-page load on a large book pays an O(tocCount)
+  // seek-heavy scan in Epub::hasReliableToc().
   std::deque<int16_t> spineToTocIndex(spineCount, -1);
+  int distinctSpinesReferenced = 0;
   tocFile.seek(0);
   for (int j = 0; j < tocCount; j++) {
     auto tocEntry = readTocEntry(tocFile);
     if (tocEntry.spineIndex >= 0 && tocEntry.spineIndex < spineCount) {
       if (spineToTocIndex[tocEntry.spineIndex] == -1) {
         spineToTocIndex[tocEntry.spineIndex] = static_cast<int16_t>(j);
+        distinctSpinesReferenced++;
       }
     }
   }
 
+  // Mirrors the heuristic in Epub::hasReliableToc(): require >=25% distinct spine coverage,
+  // with short-circuits for edge cases (no entries, or large book with a single TOC entry).
+  if (spineCount > 0 && tocCount > 0 && !(spineCount >= 8 && tocCount <= 1)) {
+    tocReliable = (distinctSpinesReferenced * 4 >= spineCount);
+  } else {
+    tocReliable = false;
+  }
+
   ZipFile zip(epubPath);
   // Pre-open zip file to speed up size calculations
   if (!zip.open()) {
@@ -269,6 +285,10 @@ bool BookMetadataCache::buildBookBin(const std::string& epubPath, const BookMeta
     writeTocEntry(bookFile, tocEntry);
   }
 
+  // Patch tocReliable placeholder in header A
+  bookFile.seek(tocReliableHeaderPos);
+  serialization::writePod(bookFile, static_cast<uint8_t>(tocReliable ? 1 : 0));
+
   bookFile.close();
   spineFile.close();
   tocFile.close();
@@ -384,6 +404,9 @@ bool BookMetadataCache::load() {
   serialization::readPod(bookFile, lutOffset);
   serialization::readPod(bookFile, spineCount);
   serialization::readPod(bookFile, tocCount);
+  uint8_t tocReliableByte;
+  serialization::readPod(bookFile, tocReliableByte);
+  tocReliable = (tocReliableByte != 0);
 
   serialization::readString(bookFile, coreMetadata.title);
   serialization::readString(bookFile, coreMetadata.author);

lib/Epub/Epub/BookMetadataCache.h

@@ -50,6 +50,7 @@ class BookMetadataCache {
   size_t lutOffset;
   uint16_t spineCount;
   uint16_t tocCount;
+  bool tocReliable;
   bool loaded;
   bool buildMode;
 
@@ -88,7 +89,13 @@ class BookMetadataCache {
   BookMetadata coreMetadata;
 
   explicit BookMetadataCache(std::string cachePath)
-      : cachePath(std::move(cachePath)), lutOffset(0), spineCount(0), tocCount(0), loaded(false), buildMode(false) {}
+      : cachePath(std::move(cachePath)),
+        lutOffset(0),
+        spineCount(0),
+        tocCount(0),
+        tocReliable(false),
+        loaded(false),
+        buildMode(false) {}
   ~BookMetadataCache() = default;
 
   // Building phase (stream to disk immediately)
@@ -111,5 +118,6 @@ class BookMetadataCache {
   TocEntry getTocEntry(int index);
   int getSpineCount() const { return spineCount; }
   int getTocCount() const { return tocCount; }
+  bool isTocReliable() const { return tocReliable; }
   bool isLoaded() const { return loaded; }
 };