Fix file flushing issue on ESP32 - implement configurable smart flushing policy (#22)

README.md

@@ -91,6 +91,18 @@ build_flags =
     -DADVANCED_LOGGER_MAX_MESSAGE_LENGTH=512
 ```
 
+### File Flushing
+Configure when log files are flushed to ensure data persistence:
+
+```cpp
+#define ADVANCED_LOGGER_FLUSH_INTERVAL_MS 5000        // Flush every 5 seconds (default)
+#define ADVANCED_LOGGER_FLUSH_LOG_LEVEL LogLevel::ERROR // Log level that triggers immediate flush (default)
+
+#include "AdvancedLogger.h"
+```
+
+The library automatically flushes files periodically and on the specified log level to prevent data loss during power cycles or crashes.
+
 ### Callbacks
 Register a function to handle log entries:
 

src/AdvancedLogger.cpp

@@ -38,6 +38,9 @@ namespace AdvancedLogger
     static TaskHandle_t _logTaskHandle = nullptr;
     static bool _queueInitialized = false;
 
+    // File flushing control
+    static unsigned long _lastFlushTime = 0;
+
     // Forward declarations of private functions
     static void _log(const char *message, const char *file, const char *function, int line, LogLevel logLevel);
     static void _internalLog(const char* level, const char* format, ...);
@@ -142,6 +145,9 @@ namespace AdvancedLogger
 
         _logLines = getLogLines();
 
+        // Initialize flush timestamp
+        _lastFlushTime = millis();
+
         _initLogQueue();
 
         _internalLog("DEBUG", "AdvancedLogger initialized");
@@ -331,7 +337,11 @@ namespace AdvancedLogger
 #endif
 
 #ifndef ADVANCED_LOGGER_DISABLE_FILE_LOGGING
-        if (entry.level >= _saveLevel) _save(messageFormatted);
+        if (entry.level >= _saveLevel) {
+            // Determine if immediate flush is needed based on log level
+            bool forceFlush = (entry.level >= ADVANCED_LOGGER_FLUSH_LOG_LEVEL);
+            _save(messageFormatted, forceFlush);
+        }
 #endif
     }
 
@@ -657,7 +667,21 @@ namespace AdvancedLogger
         if (!_checkAndOpenLogFile(FileMode::APPEND)) return;
 
         _logFile.println(messageFormatted);
-        if (flush) _logFile.flush();
+
+        // Smart flushing logic
+        unsigned long currentTime = millis();
+        bool shouldFlush = flush;
+
+        // Check if periodic flush interval has elapsed
+        if (!shouldFlush && (currentTime - _lastFlushTime >= ADVANCED_LOGGER_FLUSH_INTERVAL_MS)) {
+            shouldFlush = true;
+        }
+
+        if (shouldFlush) {
+            _logFile.flush();
+            _lastFlushTime = currentTime;
+        }
+
         _logLines++;
 
         if (_logLines >= _maxLogLines) {
@@ -830,6 +854,7 @@ namespace AdvancedLogger
     void _closeLogFile() 
     {
         if (_logFile) {
+            _logFile.flush(); // Ensure all data is written before closing
             _logFile.close();
             _currentFileMode = FileMode::APPEND; // Reset to default
         }

src/AdvancedLogger.h

@@ -33,6 +33,8 @@
  * - ADVANCED_LOGGER_TASK_PRIORITY: Priority for the log processing task.
  * - ADVANCED_LOGGER_TASK_CORE: Core ID for the log processing task.
  * - ADVANCED_LOGGER_MAX_MESSAGE_LENGTH: Maximum length of log messages.
+ * - ADVANCED_LOGGER_FLUSH_INTERVAL_MS: Interval in milliseconds for periodic file flushing (default: 5000ms).
+ * - ADVANCED_LOGGER_FLUSH_LOG_LEVEL: Log level that triggers immediate flush (default: ERROR).
  *
  * Usage:
  * In platformio.ini: build_flags = -DADVANCED_LOGGER_ALLOCABLE_HEAP_SIZE=10240
@@ -63,6 +65,14 @@
     #define ADVANCED_LOGGER_MAX_MESSAGE_LENGTH 512
 #endif
 
+#ifndef ADVANCED_LOGGER_FLUSH_INTERVAL_MS
+    #define ADVANCED_LOGGER_FLUSH_INTERVAL_MS 5000  // Flush every 5 seconds
+#endif
+
+#ifndef ADVANCED_LOGGER_FLUSH_LOG_LEVEL
+    #define ADVANCED_LOGGER_FLUSH_LOG_LEVEL LogLevel::ERROR  // Default to ERROR level
+#endif
+
 
 /*
  * Compilation flags to conditionally disable logging: