logger.py

import logging
import json
import uuid
import sys
from contextvars import ContextVar

request_id_var: ContextVar[str] = ContextVar("request_id", default="-")


class JSONFormatter(logging.Formatter):
    """Outputs each log record as a single JSON line."""

    def format(self, record):
        log_entry = {
            "timestamp": self.formatTime(record, self.datefmt),
            "level": record.levelname,
            "logger": record.name,
            "request_id": request_id_var.get("-"),
            "message": record.getMessage(),
        }
        if record.exc_info and record.exc_info[0]:
            log_entry["exception"] = self.formatException(record.exc_info)
        return json.dumps(log_entry)


def get_logger(name: str) -> logging.Logger:
    """Return a logger configured with JSON output and request-id injection."""
    logger = logging.getLogger(name)
    if not logger.handlers:
        handler = logging.StreamHandler(sys.stdout)
        handler.setFormatter(JSONFormatter())
        logger.addHandler(handler)
        logger.setLevel(logging.INFO)
        logger.propagate = False
    return logger


def new_request_id() -> str:
    """Generate a short, readable request ID."""
    return uuid.uuid4().hex[:12]