Fix file flushing issue on ESP32 - implement configurable smart flushing policy

[Copilot]

Fixes #21 - Log files were not being flushed to flash storage on ESP32, resulting in empty log files even when logs were being written.

Problem

In version 2.0.0, the _save() function was called with flush = false by default, causing log data to remain in memory buffers and potentially be lost during power cycles or system crashes. This was particularly problematic on ESP32 devices where users reported empty log files despite active logging.

Solution

Implemented a smart flushing policy that balances performance with data persistence:

Automatic Periodic Flushing

Files are automatically flushed every 5 seconds to ensure regular data persistence without excessive I/O overhead.

Configurable Critical Level Flushing

Configurable log level triggers immediate flushes to ensure critical messages are never lost. Defaults to ERROR level but can be customized to WARNING, DEBUG, or any other level based on user requirements.

Safe File Operations

Added explicit flush before file close operations to guarantee data integrity.

Configuration Options

The flushing behavior is fully configurable via preprocessor defines:

// Custom flush interval (default: 5000ms)
#define ADVANCED_LOGGER_FLUSH_INTERVAL_MS 10000
#include "AdvancedLogger.h"

// Set custom log level for immediate flushing (default: ERROR)
#define ADVANCED_LOGGER_FLUSH_LOG_LEVEL LogLevel::WARNING
#include "AdvancedLogger.h"

Documentation

Added concise documentation in README.md explaining the file flushing configuration options and their usage.

Backward Compatibility

All existing code continues to work without modification. The smart flushing policy is applied automatically with sensible defaults that resolve the original issue.

Technical Details

• Added _lastFlushTime tracking for periodic flush intervals
• Enhanced _save() function with time-based flush logic
• Modified _processLogEntry() to force flush on configurable log level
• Implemented overflow-safe time comparison using unsigned arithmetic
• Added comprehensive documentation for new configuration options
• Made flush trigger level configurable via ADVANCED_LOGGER_FLUSH_LOG_LEVEL define
• Simplified configuration API by using single log level define instead of separate enable/disable flag

Testing

Validated with comprehensive tests covering:

• Normal operation scenarios
• Critical error handling
• Edge cases including millis() overflow
• Real-world ESP32 usage patterns
• Performance impact assessment
• Configurable flush level validation

The fix ensures log data persistence while maintaining the library's high-performance characteristics through intelligent and configurable flush timing.

Original prompt

Fix issue #21 regarding the file flushing

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[jibrilsharafi]

Very good. Fix according to the comments, and add also a very small and concise part about this in the README.md.

[jibrilsharafi]

@copilot, modify this variable to be a default log level of error that can be overridden. In such a way, a user could decide to flush on warnings or debug, depending on their use case.

[Copilot]

Changed the hardcoded LogLevel::ERROR to use a configurable ADVANCED_LOGGER_FLUSH_LOG_LEVEL define. Users can now set it to any log level (WARNING, DEBUG, etc.) based on their use case. Default remains ERROR for backward compatibility.

Commit: 7d5eb4c

[jibrilsharafi]

@copilot you are close, but remove the ADVANCED_LOGGER_FLUSH_ON_ERROR and only keep the log level with ERROR as default. No need for two defines.

[Copilot]

Removed the ADVANCED_LOGGER_FLUSH_ON_ERROR define and simplified the configuration to use only ADVANCED_LOGGER_FLUSH_LOG_LEVEL with ERROR as default. The logic now directly compares the log level without needing an enable/disable flag.

Commit: fe6b0d2

[Copilot]

Very good. Fix according to the comments, and add also a very small and concise part about this in the README.md.

Added a concise File Flushing section to README.md in the Configuration area, documenting the new flush configuration options and their purpose.

Commit: 7d5eb4c

[jibrilsharafi]

Wonderful job. We make a good team :)

[jibrilsharafi]

Closes #21