3. Logger Configuration

For operating this project reliably, I need a robust logging system. So I decided the Loguru library for its simplicity and powerful features. The configuration was customized to meet the following requirements:

Custom Log Formatting Example:

2025-06-26 23:09:24 | INFO     | main                :lifespan       :16   - Starting up the application...

Persistent Log Files
- Save logs using filenames that include the current date.
- Retain logs for 7 days only.
Integration with FastAPI and Uvicorn Logs
- Ensure logs from FastAPI, Uvicorn, and Starlette are captured uniformly

1. Pseudocode Summary

IF LogConfigurator not configured:
    - Create log directory
    - Remove default handlers
    - Add colored console logger
    - Add rotating file logger
    - Setup InterceptHandler for uvicorn/starlette/fastapi loggers
    - Mark as configured

2. How I Configured the Logger

To satisfy the logging requirements mentioned above, I built a singleton LogConfigurator using Loguru, which includes:

2.1 Installing loguru

First, install Loguru using uv:
```
uv pip install loguru
```

2.2 Singleton Pattern

I wanted to ensure that the logger is configured only once, even if multiple modules try to initialize it. The class uses a standard __new__ pattern to maintain a single instance.
```
def __new__(cls, *args, **kwargs):
    if cls._instance is None:
        cls._instance = super().__new__(cls)
    return cls._instance
```

2.3 Log File Management

Each log file is automatically named using the current date and saved under /backend/logs. I use Loguru’s built-in rotation and retention to:

Create a new file every day at midnight
Retain logs only for 7 days
Avoid manual cleanup

logger.add(
    str(self.log_file),
    rotation="00:00",       # Daily rotation
    retention="7 days",     # Keep logs for 7 days
    encoding="utf-8",
    level="INFO",
    ...
)

2.4 Console Output with Colors

Loguru’s colorize=True option lets me apply colors to console logs, improving readability during development.

logger.add(
    sys.stdout,
    level="INFO",
    colorize=True,
    format="<green>{time:YYYY-MM-DD HH:mm:ss}</green> | <level>{level: <8}</level> | <cyan>{name: <20}</cyan>:<cyan>{function: <15}</cyan>:<cyan>{line: <4}</cyan> - <level>{message}</level>",
)

2.5 Intercepting FastAPI/Uvicorn Logs

By default, FastAPI and Uvicorn use the built-in logging module. To unify all logs under Loguru, I wrote a custom InterceptHandler which:
- Captures standard logging logs
- Redirects them to Loguru with correct context (function name, line number, etc.)
```
logging.basicConfig(
    handlers=[InterceptHandler()],
    level=logging.INFO,
    force=True
)
```

I explicitly intercept common loggers:

loggers_to_intercept = [
    "uvicorn", "uvicorn.access", "uvicorn.error",
    "fastapi", "starlette", "starlette.routing",
]

2.6 Execution Outputs

This setup ensures that all logs—whether they come from my own modules or external frameworks—are managed consistently, well-formatted, and stored efficiently.