feat: Add central logging pragma (#843)

## Summary

* Definition and use of a central LOG function, that can later be
extended or completely be removed (for public use where debugging
information may not be required) to save flash by suppressing the
-DENABLE_SERIAL_LOG like in the slim branch

* **What changes are included?**

## Additional Context
* By using the central logger the usual:
```
#include <HardwareSerial.h>
...
  Serial.printf("[%lu] [WCS] Obfuscating/deobfuscating %zu bytes\n", millis(), data.size());
```
would then become
```
#include <Logging.h>
...
  LOG_DBG("WCS", "Obfuscating/deobfuscating %zu bytes", data.size());
```
You do have ``LOG_DBG`` for debug messages, ``LOG_ERR`` for error
messages and ``LOG_INF`` for informational messages. Depending on the
verbosity level defined (see below) soe of these message types will be
suppressed/not-compiled.

* The normal compilation (default) will create a firmware.elf file of
42.194.356 bytes, the same code via slim will create 42.024.048 bytes -
170.308 bytes less
* Firmware.bin : 6.469.984 bytes for default, 6.418.672 bytes for slim -
51.312 bytes less


### AI Usage

While CrossPoint doesn't have restrictions on AI tools in contributing,
please be transparent about their usage as it
helps set the right context for reviewers.

Did you use AI tools to help write this code? _NO_

---------

Co-authored-by: Xuan Son Nguyen <son@huggingface.co>

src/activities/reader/EpubReaderActivity.cpp

@@ -4,6 +4,7 @@
 #include <FsHelpers.h>
 #include <GfxRenderer.h>
 #include <HalStorage.h>
+#include <Logging.h>
 
 #include "CrossPointSettings.h"
 #include "CrossPointState.h"
@@ -84,7 +85,7 @@ void EpubReaderActivity::onEnter() {
       currentSpineIndex = data[0] + (data[1] << 8);
       nextPageNumber = data[2] + (data[3] << 8);
       cachedSpineIndex = currentSpineIndex;
-      Serial.printf("[%lu] [ERS] Loaded cache: %d, %d\n", millis(), currentSpineIndex, nextPageNumber);
+      LOG_DBG("ERS", "Loaded cache: %d, %d", currentSpineIndex, nextPageNumber);
     }
     if (dataSize == 6) {
       cachedChapterTotalPageCount = data[4] + (data[5] << 8);
@@ -97,8 +98,7 @@ void EpubReaderActivity::onEnter() {
     int textSpineIndex = epub->getSpineIndexForTextReference();
     if (textSpineIndex != 0) {
       currentSpineIndex = textSpineIndex;
-      Serial.printf("[%lu] [ERS] Opened for first time, navigating to text reference at index %d\n", millis(),
-                    textSpineIndex);
+      LOG_DBG("ERS", "Opened for first time, navigating to text reference at index %d", textSpineIndex);
     }
   }
 
@@ -567,7 +567,7 @@ void EpubReaderActivity::renderScreen() {
 
   if (!section) {
     const auto filepath = epub->getSpineItem(currentSpineIndex).href;
-    Serial.printf("[%lu] [ERS] Loading file: %s, index: %d\n", millis(), filepath.c_str(), currentSpineIndex);
+    LOG_DBG("ERS", "Loading file: %s, index: %d", filepath.c_str(), currentSpineIndex);
     section = std::unique_ptr<Section>(new Section(epub, currentSpineIndex, renderer));
 
     const uint16_t viewportWidth = renderer.getScreenWidth() - orientedMarginLeft - orientedMarginRight;
@@ -576,19 +576,19 @@ void EpubReaderActivity::renderScreen() {
     if (!section->loadSectionFile(SETTINGS.getReaderFontId(), SETTINGS.getReaderLineCompression(),
                                   SETTINGS.extraParagraphSpacing, SETTINGS.paragraphAlignment, viewportWidth,
                                   viewportHeight, SETTINGS.hyphenationEnabled, SETTINGS.embeddedStyle)) {
-      Serial.printf("[%lu] [ERS] Cache not found, building...\n", millis());
+      LOG_DBG("ERS", "Cache not found, building...");
 
       const auto popupFn = [this]() { GUI.drawPopup(renderer, "Indexing..."); };
 
       if (!section->createSectionFile(SETTINGS.getReaderFontId(), SETTINGS.getReaderLineCompression(),
                                       SETTINGS.extraParagraphSpacing, SETTINGS.paragraphAlignment, viewportWidth,
                                       viewportHeight, SETTINGS.hyphenationEnabled, SETTINGS.embeddedStyle, popupFn)) {
-        Serial.printf("[%lu] [ERS] Failed to persist page data to SD\n", millis());
+        LOG_ERR("ERS", "Failed to persist page data to SD");
         section.reset();
         return;
       }
     } else {
-      Serial.printf("[%lu] [ERS] Cache found, skipping build...\n", millis());
+      LOG_DBG("ERS", "Cache found, skipping build...");
     }
 
     if (nextPageNumber == UINT16_MAX) {
@@ -622,7 +622,7 @@ void EpubReaderActivity::renderScreen() {
   renderer.clearScreen();
 
   if (section->pageCount == 0) {
-    Serial.printf("[%lu] [ERS] No pages to render\n", millis());
+    LOG_DBG("ERS", "No pages to render");
     renderer.drawCenteredText(UI_12_FONT_ID, 300, "Empty chapter", true, EpdFontFamily::BOLD);
     renderStatusBar(orientedMarginRight, orientedMarginBottom, orientedMarginLeft);
     renderer.displayBuffer();
@@ -630,7 +630,7 @@ void EpubReaderActivity::renderScreen() {
   }
 
   if (section->currentPage < 0 || section->currentPage >= section->pageCount) {
-    Serial.printf("[%lu] [ERS] Page out of bounds: %d (max %d)\n", millis(), section->currentPage, section->pageCount);
+    LOG_DBG("ERS", "Page out of bounds: %d (max %d)", section->currentPage, section->pageCount);
     renderer.drawCenteredText(UI_12_FONT_ID, 300, "Out of bounds", true, EpdFontFamily::BOLD);
     renderStatusBar(orientedMarginRight, orientedMarginBottom, orientedMarginLeft);
     renderer.displayBuffer();
@@ -640,14 +640,14 @@ void EpubReaderActivity::renderScreen() {
   {
     auto p = section->loadPageFromSectionFile();
     if (!p) {
-      Serial.printf("[%lu] [ERS] Failed to load page from SD - clearing section cache\n", millis());
+      LOG_ERR("ERS", "Failed to load page from SD - clearing section cache");
       section->clearCache();
       section.reset();
       return renderScreen();
     }
     const auto start = millis();
     renderContents(std::move(p), orientedMarginTop, orientedMarginRight, orientedMarginBottom, orientedMarginLeft);
-    Serial.printf("[%lu] [ERS] Rendered page in %dms\n", millis(), millis() - start);
+    LOG_DBG("ERS", "Rendered page in %dms", millis() - start);
   }
   saveProgress(currentSpineIndex, section->currentPage, section->pageCount);
 }
@@ -664,9 +664,9 @@ void EpubReaderActivity::saveProgress(int spineIndex, int currentPage, int pageC
     data[5] = (pageCount >> 8) & 0xFF;
     f.write(data, 6);
     f.close();
-    Serial.printf("[%lu] [ERS] Progress saved: Chapter %d, Page %d\n", millis(), spineIndex, currentPage);
+    LOG_DBG("ERS", "Progress saved: Chapter %d, Page %d", spineIndex, currentPage);
   } else {
-    Serial.printf("[%lu] [ERS] Could not save progress!\n", millis());
+    LOG_ERR("ERS", "Could not save progress!");
   }
 }
 void EpubReaderActivity::renderContents(std::unique_ptr<Page> page, const int orientedMarginTop,

src/activities/reader/KOReaderSyncActivity.cpp

@@ -1,6 +1,7 @@
 #include "KOReaderSyncActivity.h"
 
 #include <GfxRenderer.h>
+#include <Logging.h>
 #include <WiFi.h>
 #include <esp_sntp.h>
 
@@ -32,9 +33,9 @@ void syncTimeWithNTP() {
   }
 
   if (retry < maxRetries) {
-    Serial.printf("[%lu] [KOSync] NTP time synced\n", millis());
+    LOG_DBG("KOSync", "NTP time synced");
   } else {
-    Serial.printf("[%lu] [KOSync] NTP sync timeout, using fallback\n", millis());
+    LOG_DBG("KOSync", "NTP sync timeout, using fallback");
   }
 }
 }  // namespace
@@ -48,12 +49,12 @@ void KOReaderSyncActivity::onWifiSelectionComplete(const bool success) {
   exitActivity();
 
   if (!success) {
-    Serial.printf("[%lu] [KOSync] WiFi connection failed, exiting\n", millis());
+    LOG_DBG("KOSync", "WiFi connection failed, exiting");
     onCancel();
     return;
   }
 
-  Serial.printf("[%lu] [KOSync] WiFi connected, starting sync\n", millis());
+  LOG_DBG("KOSync", "WiFi connected, starting sync");
 
   xSemaphoreTake(renderingMutex, portMAX_DELAY);
   state = SYNCING;
@@ -88,7 +89,7 @@ void KOReaderSyncActivity::performSync() {
     return;
   }
 
-  Serial.printf("[%lu] [KOSync] Document hash: %s\n", millis(), documentHash.c_str());
+  LOG_DBG("KOSync", "Document hash: %s", documentHash.c_str());
 
   xSemaphoreTake(renderingMutex, portMAX_DELAY);
   statusMessage = "Fetching remote progress...";
@@ -188,12 +189,12 @@ void KOReaderSyncActivity::onEnter() {
   }
 
   // Turn on WiFi
-  Serial.printf("[%lu] [KOSync] Turning on WiFi...\n", millis());
+  LOG_DBG("KOSync", "Turning on WiFi...");
   WiFi.mode(WIFI_STA);
 
   // Check if already connected
   if (WiFi.status() == WL_CONNECTED) {
-    Serial.printf("[%lu] [KOSync] Already connected to WiFi\n", millis());
+    LOG_DBG("KOSync", "Already connected to WiFi");
     state = SYNCING;
     statusMessage = "Syncing time...";
     updateRequired = true;
@@ -216,7 +217,7 @@ void KOReaderSyncActivity::onEnter() {
   }
 
   // Launch WiFi selection subactivity
-  Serial.printf("[%lu] [KOSync] Launching WifiSelectionActivity...\n", millis());
+  LOG_DBG("KOSync", "Launching WifiSelectionActivity...");
   enterNewActivity(new WifiSelectionActivity(renderer, mappedInput,
                                              [this](const bool connected) { onWifiSelectionComplete(connected); }));
 }

src/activities/reader/ReaderActivity.cpp

@@ -30,7 +30,7 @@ bool ReaderActivity::isTxtFile(const std::string& path) {
 
 std::unique_ptr<Epub> ReaderActivity::loadEpub(const std::string& path) {
   if (!Storage.exists(path.c_str())) {
-    Serial.printf("[%lu] [   ] File does not exist: %s\n", millis(), path.c_str());
+    LOG_ERR("READER", "File does not exist: %s", path.c_str());
     return nullptr;
   }
 
@@ -39,13 +39,13 @@ std::unique_ptr<Epub> ReaderActivity::loadEpub(const std::string& path) {
     return epub;
   }
 
-  Serial.printf("[%lu] [   ] Failed to load epub\n", millis());
+  LOG_ERR("READER", "Failed to load epub");
   return nullptr;
 }
 
 std::unique_ptr<Xtc> ReaderActivity::loadXtc(const std::string& path) {
   if (!Storage.exists(path.c_str())) {
-    Serial.printf("[%lu] [   ] File does not exist: %s\n", millis(), path.c_str());
+    LOG_ERR("READER", "File does not exist: %s", path.c_str());
     return nullptr;
   }
 
@@ -54,13 +54,13 @@ std::unique_ptr<Xtc> ReaderActivity::loadXtc(const std::string& path) {
     return xtc;
   }
 
-  Serial.printf("[%lu] [   ] Failed to load XTC\n", millis());
+  LOG_ERR("READER", "Failed to load XTC");
   return nullptr;
 }
 
 std::unique_ptr<Txt> ReaderActivity::loadTxt(const std::string& path) {
   if (!Storage.exists(path.c_str())) {
-    Serial.printf("[%lu] [   ] File does not exist: %s\n", millis(), path.c_str());
+    LOG_ERR("READER", "File does not exist: %s", path.c_str());
     return nullptr;
   }
 
@@ -69,7 +69,7 @@ std::unique_ptr<Txt> ReaderActivity::loadTxt(const std::string& path) {
     return txt;
   }
 
-  Serial.printf("[%lu] [   ] Failed to load TXT\n", millis());
+  LOG_ERR("READER", "Failed to load TXT");
   return nullptr;
 }
 

src/activities/reader/TxtReaderActivity.cpp

@@ -191,8 +191,7 @@ void TxtReaderActivity::initializeReader() {
   linesPerPage = viewportHeight / lineHeight;
   if (linesPerPage < 1) linesPerPage = 1;
 
-  Serial.printf("[%lu] [TRS] Viewport: %dx%d, lines per page: %d\n", millis(), viewportWidth, viewportHeight,
-                linesPerPage);
+  LOG_DBG("TRS", "Viewport: %dx%d, lines per page: %d", viewportWidth, viewportHeight, linesPerPage);
 
   // Try to load cached page index first
   if (!loadPageIndexCache()) {
@@ -215,7 +214,7 @@ void TxtReaderActivity::buildPageIndex() {
   size_t offset = 0;
   const size_t fileSize = txt->getFileSize();
 
-  Serial.printf("[%lu] [TRS] Building page index for %zu bytes...\n", millis(), fileSize);
+  LOG_DBG("TRS", "Building page index for %zu bytes...", fileSize);
 
   GUI.drawPopup(renderer, "Indexing...");
 
@@ -244,7 +243,7 @@ void TxtReaderActivity::buildPageIndex() {
   }
 
   totalPages = pageOffsets.size();
-  Serial.printf("[%lu] [TRS] Built page index: %d pages\n", millis(), totalPages);
+  LOG_DBG("TRS", "Built page index: %d pages", totalPages);
 }
 
 bool TxtReaderActivity::loadPageAtOffset(size_t offset, std::vector<std::string>& outLines, size_t& nextOffset) {
@@ -259,7 +258,7 @@ bool TxtReaderActivity::loadPageAtOffset(size_t offset, std::vector<std::string>
   size_t chunkSize = std::min(CHUNK_SIZE, fileSize - offset);
   auto* buffer = static_cast<uint8_t*>(malloc(chunkSize + 1));
   if (!buffer) {
-    Serial.printf("[%lu] [TRS] Failed to allocate %zu bytes\n", millis(), chunkSize);
+    LOG_ERR("TRS", "Failed to allocate %zu bytes", chunkSize);
     return false;
   }
 
@@ -588,7 +587,7 @@ void TxtReaderActivity::loadProgress() {
       if (currentPage < 0) {
         currentPage = 0;
       }
-      Serial.printf("[%lu] [TRS] Loaded progress: page %d/%d\n", millis(), currentPage, totalPages);
+      LOG_DBG("TRS", "Loaded progress: page %d/%d", currentPage, totalPages);
     }
     f.close();
   }
@@ -610,7 +609,7 @@ bool TxtReaderActivity::loadPageIndexCache() {
   std::string cachePath = txt->getCachePath() + "/index.bin";
   FsFile f;
   if (!Storage.openFileForRead("TRS", cachePath, f)) {
-    Serial.printf("[%lu] [TRS] No page index cache found\n", millis());
+    LOG_DBG("TRS", "No page index cache found");
     return false;
   }
 
@@ -618,7 +617,7 @@ bool TxtReaderActivity::loadPageIndexCache() {
   uint32_t magic;
   serialization::readPod(f, magic);
   if (magic != CACHE_MAGIC) {
-    Serial.printf("[%lu] [TRS] Cache magic mismatch, rebuilding\n", millis());
+    LOG_DBG("TRS", "Cache magic mismatch, rebuilding");
     f.close();
     return false;
   }
@@ -626,7 +625,7 @@ bool TxtReaderActivity::loadPageIndexCache() {
   uint8_t version;
   serialization::readPod(f, version);
   if (version != CACHE_VERSION) {
-    Serial.printf("[%lu] [TRS] Cache version mismatch (%d != %d), rebuilding\n", millis(), version, CACHE_VERSION);
+    LOG_DBG("TRS", "Cache version mismatch (%d != %d), rebuilding", version, CACHE_VERSION);
     f.close();
     return false;
   }
@@ -634,7 +633,7 @@ bool TxtReaderActivity::loadPageIndexCache() {
   uint32_t fileSize;
   serialization::readPod(f, fileSize);
   if (fileSize != txt->getFileSize()) {
-    Serial.printf("[%lu] [TRS] Cache file size mismatch, rebuilding\n", millis());
+    LOG_DBG("TRS", "Cache file size mismatch, rebuilding");
     f.close();
     return false;
   }
@@ -642,7 +641,7 @@ bool TxtReaderActivity::loadPageIndexCache() {
   int32_t cachedWidth;
   serialization::readPod(f, cachedWidth);
   if (cachedWidth != viewportWidth) {
-    Serial.printf("[%lu] [TRS] Cache viewport width mismatch, rebuilding\n", millis());
+    LOG_DBG("TRS", "Cache viewport width mismatch, rebuilding");
     f.close();
     return false;
   }
@@ -650,7 +649,7 @@ bool TxtReaderActivity::loadPageIndexCache() {
   int32_t cachedLines;
   serialization::readPod(f, cachedLines);
   if (cachedLines != linesPerPage) {
-    Serial.printf("[%lu] [TRS] Cache lines per page mismatch, rebuilding\n", millis());
+    LOG_DBG("TRS", "Cache lines per page mismatch, rebuilding");
     f.close();
     return false;
   }
@@ -658,7 +657,7 @@ bool TxtReaderActivity::loadPageIndexCache() {
   int32_t fontId;
   serialization::readPod(f, fontId);
   if (fontId != cachedFontId) {
-    Serial.printf("[%lu] [TRS] Cache font ID mismatch (%d != %d), rebuilding\n", millis(), fontId, cachedFontId);
+    LOG_DBG("TRS", "Cache font ID mismatch (%d != %d), rebuilding", fontId, cachedFontId);
     f.close();
     return false;
   }
@@ -666,7 +665,7 @@ bool TxtReaderActivity::loadPageIndexCache() {
   int32_t margin;
   serialization::readPod(f, margin);
   if (margin != cachedScreenMargin) {
-    Serial.printf("[%lu] [TRS] Cache screen margin mismatch, rebuilding\n", millis());
+    LOG_DBG("TRS", "Cache screen margin mismatch, rebuilding");
     f.close();
     return false;
   }
@@ -674,7 +673,7 @@ bool TxtReaderActivity::loadPageIndexCache() {
   uint8_t alignment;
   serialization::readPod(f, alignment);
   if (alignment != cachedParagraphAlignment) {
-    Serial.printf("[%lu] [TRS] Cache paragraph alignment mismatch, rebuilding\n", millis());
+    LOG_DBG("TRS", "Cache paragraph alignment mismatch, rebuilding");
     f.close();
     return false;
   }
@@ -694,7 +693,7 @@ bool TxtReaderActivity::loadPageIndexCache() {
 
   f.close();
   totalPages = pageOffsets.size();
-  Serial.printf("[%lu] [TRS] Loaded page index cache: %d pages\n", millis(), totalPages);
+  LOG_DBG("TRS", "Loaded page index cache: %d pages", totalPages);
   return true;
 }
 
@@ -702,7 +701,7 @@ void TxtReaderActivity::savePageIndexCache() const {
   std::string cachePath = txt->getCachePath() + "/index.bin";
   FsFile f;
   if (!Storage.openFileForWrite("TRS", cachePath, f)) {
-    Serial.printf("[%lu] [TRS] Failed to save page index cache\n", millis());
+    LOG_ERR("TRS", "Failed to save page index cache");
     return;
   }
 
@@ -723,5 +722,5 @@ void TxtReaderActivity::savePageIndexCache() const {
   }
 
   f.close();
-  Serial.printf("[%lu] [TRS] Saved page index cache: %d pages\n", millis(), totalPages);
+  LOG_DBG("TRS", "Saved page index cache: %d pages", totalPages);
 }

src/activities/reader/XtcReaderActivity.cpp

@@ -206,7 +206,7 @@ void XtcReaderActivity::renderPage() {
   // Allocate page buffer
   uint8_t* pageBuffer = static_cast<uint8_t*>(malloc(pageBufferSize));
   if (!pageBuffer) {
-    Serial.printf("[%lu] [XTR] Failed to allocate page buffer (%lu bytes)\n", millis(), pageBufferSize);
+    LOG_ERR("XTR", "Failed to allocate page buffer (%lu bytes)", pageBufferSize);
     renderer.clearScreen();
     renderer.drawCenteredText(UI_12_FONT_ID, 300, "Memory error", true, EpdFontFamily::BOLD);
     renderer.displayBuffer();
@@ -216,7 +216,7 @@ void XtcReaderActivity::renderPage() {
   // Load page data
   size_t bytesRead = xtc->loadPage(currentPage, pageBuffer, pageBufferSize);
   if (bytesRead == 0) {
-    Serial.printf("[%lu] [XTR] Failed to load page %lu\n", millis(), currentPage);
+    LOG_ERR("XTR", "Failed to load page %lu", currentPage);
     free(pageBuffer);
     renderer.clearScreen();
     renderer.drawCenteredText(UI_12_FONT_ID, 300, "Page load error", true, EpdFontFamily::BOLD);
@@ -265,8 +265,8 @@ void XtcReaderActivity::renderPage() {
         pixelCounts[getPixelValue(x, y)]++;
       }
     }
-    Serial.printf("[%lu] [XTR] Pixel distribution: White=%lu, DarkGrey=%lu, LightGrey=%lu, Black=%lu\n", millis(),
-                  pixelCounts[0], pixelCounts[1], pixelCounts[2], pixelCounts[3]);
+    LOG_DBG("XTR", "Pixel distribution: White=%lu, DarkGrey=%lu, LightGrey=%lu, Black=%lu", pixelCounts[0],
+            pixelCounts[1], pixelCounts[2], pixelCounts[3]);
 
     // Pass 1: BW buffer - draw all non-white pixels as black
     for (uint16_t y = 0; y < pageHeight; y++) {
@@ -329,8 +329,7 @@ void XtcReaderActivity::renderPage() {
 
     free(pageBuffer);
 
-    Serial.printf("[%lu] [XTR] Rendered page %lu/%lu (2-bit grayscale)\n", millis(), currentPage + 1,
-                  xtc->getPageCount());
+    LOG_DBG("XTR", "Rendered page %lu/%lu (2-bit grayscale)", currentPage + 1, xtc->getPageCount());
     return;
   } else {
     // 1-bit mode: 8 pixels per byte, MSB first
@@ -366,8 +365,7 @@ void XtcReaderActivity::renderPage() {
     pagesUntilFullRefresh--;
   }
 
-  Serial.printf("[%lu] [XTR] Rendered page %lu/%lu (%u-bit)\n", millis(), currentPage + 1, xtc->getPageCount(),
-                bitDepth);
+  LOG_DBG("XTR", "Rendered page %lu/%lu (%u-bit)", currentPage + 1, xtc->getPageCount(), bitDepth);
 }
 
 void XtcReaderActivity::saveProgress() const {
@@ -389,7 +387,7 @@ void XtcReaderActivity::loadProgress() {
     uint8_t data[4];
     if (f.read(data, 4) == 4) {
       currentPage = data[0] | (data[1] << 8) | (data[2] << 16) | (data[3] << 24);
-      Serial.printf("[%lu] [XTR] Loaded progress: page %lu\n", millis(), currentPage);
+      LOG_DBG("XTR", "Loaded progress: page %lu", currentPage);
 
       // Validate page number
       if (currentPage >= xtc->getPageCount()) {