From 19c197e0205e2605a3d6dbdbfdaf43e50f11a4b2 Mon Sep 17 00:00:00 2001
From: jpirnay <jens@pirnay.com>
Date: Sat, 28 Feb 2026 16:19:45 +0100
Subject: [PATCH] Establish LUT cache

---
 lib/Epub/Epub/Section.cpp | 53 +++++++++++++++++++++++++--------------
 lib/Epub/Epub/Section.h   |  4 ++-
 2 files changed, 37 insertions(+), 20 deletions(-)

diff --git a/lib/Epub/Epub/Section.cpp b/lib/Epub/Epub/Section.cpp
index 814f5029..e85ece26 100644
--- a/lib/Epub/Epub/Section.cpp
+++ b/lib/Epub/Epub/Section.cpp
@@ -71,9 +71,8 @@ bool Section::loadSectionFile(const int fontId, const float lineCompression, con
     uint8_t version;
     serialization::readPod(file, version);
     if (version != SECTION_FILE_VERSION) {
-      file.close();
       LOG_ERR("SCT", "Deserialization failed: Unknown version %u", version);
-      clearCache();
+      clearCache();  // closes file before removal
       return false;
     }
 
@@ -97,21 +96,30 @@ bool Section::loadSectionFile(const int fontId, const float lineCompression, con
         extraParagraphSpacing != fileExtraParagraphSpacing || paragraphAlignment != fileParagraphAlignment ||
         viewportWidth != fileViewportWidth || viewportHeight != fileViewportHeight ||
         hyphenationEnabled != fileHyphenationEnabled || embeddedStyle != fileEmbeddedStyle) {
-      file.close();
       LOG_ERR("SCT", "Deserialization failed: Parameters do not match");
-      clearCache();
+      clearCache();  // closes file before removal
       return false;
     }
   }
 
   serialization::readPod(file, pageCount);
-  file.close();
-  LOG_DBG("SCT", "Deserialization succeeded: %d pages", pageCount);
+
+  // Load LUT into memory (file is now positioned at the lutOffset field)
+  uint32_t lutOffset;
+  serialization::readPod(file, lutOffset);
+  lut.resize(pageCount);
+  file.seek(lutOffset);
+  for (uint32_t& pos : lut) {
+    serialization::readPod(file, pos);
+  }
+  // File is intentionally left open; subsequent loadPageFromSectionFile() calls
+  // seek within this handle instead of re-opening the file each time.
+  LOG_DBG("SCT", "Deserialization succeeded: %d pages, LUT cached", pageCount);
   return true;
 }
 
-// Your updated class method (assuming you are using the 'SD' object, which is a wrapper for a specific filesystem)
-bool Section::clearCache() const {
+bool Section::clearCache() {
+  file.close();  // Must be closed before removal on FAT32
   if (!Storage.exists(filePath.c_str())) {
     LOG_DBG("SCT", "Cache does not exist, no action needed");
     return true;
@@ -242,23 +250,30 @@ bool Section::createSectionFile(const int fontId, const float lineCompression, c
   if (cssParser) {
     cssParser->clear();
   }
+
+  // Cache the LUT in memory and open the file for reading so that
+  // subsequent loadPageFromSectionFile() calls can seek directly without re-opening.
+  this->lut = std::move(lut);
+  Storage.openFileForRead("SCT", filePath, file);
   return true;
 }
 
 std::unique_ptr<Page> Section::loadPageFromSectionFile() {
-  if (!Storage.openFileForRead("SCT", filePath, file)) {
+  if (currentPage < 0 || currentPage >= static_cast<int>(lut.size())) {
+    LOG_ERR("SCT", "loadPageFromSectionFile: page %d out of LUT range (%u entries)", currentPage,
+            static_cast<uint32_t>(lut.size()));
     return nullptr;
   }
 
-  file.seek(HEADER_SIZE - sizeof(uint32_t));
-  uint32_t lutOffset;
-  serialization::readPod(file, lutOffset);
-  file.seek(lutOffset + sizeof(uint32_t) * currentPage);
-  uint32_t pagePos;
-  serialization::readPod(file, pagePos);
-  file.seek(pagePos);
+  if (!file) {
+    // Safety fallback: file was closed unexpectedly; reopen
+    LOG_ERR("SCT", "loadPageFromSectionFile: file not open, reopening");
+    if (!Storage.openFileForRead("SCT", filePath, file)) {
+      return nullptr;
+    }
+  }
 
-  auto page = Page::deserialize(file);
-  file.close();
-  return page;
+  file.seek(lut[currentPage]);
+  return Page::deserialize(file);
+  // File is intentionally NOT closed; stays open for the next page load
 }
diff --git a/lib/Epub/Epub/Section.h b/lib/Epub/Epub/Section.h
index 42a6d993..90792191 100644
--- a/lib/Epub/Epub/Section.h
+++ b/lib/Epub/Epub/Section.h
@@ -1,6 +1,7 @@
 #pragma once
 #include <functional>
 #include <memory>
+#include <vector>
 
 #include "Epub.h"
 
@@ -13,6 +14,7 @@ class Section {
   GfxRenderer& renderer;
   std::string filePath;
   FsFile file;
+  std::vector<uint32_t> lut;  // Cached page byte-offsets; loaded once, avoids per-page LUT seek
 
   void writeSectionFileHeader(int fontId, float lineCompression, bool extraParagraphSpacing, uint8_t paragraphAlignment,
                               uint16_t viewportWidth, uint16_t viewportHeight, bool hyphenationEnabled,
@@ -31,7 +33,7 @@ class Section {
   ~Section() = default;
   bool loadSectionFile(int fontId, float lineCompression, bool extraParagraphSpacing, uint8_t paragraphAlignment,
                        uint16_t viewportWidth, uint16_t viewportHeight, bool hyphenationEnabled, bool embeddedStyle);
-  bool clearCache() const;
+  bool clearCache();
   bool createSectionFile(int fontId, float lineCompression, bool extraParagraphSpacing, uint8_t paragraphAlignment,
                          uint16_t viewportWidth, uint16_t viewportHeight, bool hyphenationEnabled, bool embeddedStyle,
                          const std::function<void()>& popupFn = nullptr);