feat: create libretime_shared package (#1349)

* feat: create libretime_shared package

- We don't use pydantic.BaseSettings because of some
  incompatble loading behavior.

* fix: whitelist pydantic in pylintrc

* docs: update to new BaseConfig behavior

* docs: change confusing config filepath

shared/libretime_shared/logging.py

@@ -0,0 +1,117 @@
+import sys
+from copy import deepcopy
+from pathlib import Path
+from typing import TYPE_CHECKING, NamedTuple, Optional
+
+from loguru import logger
+
+if TYPE_CHECKING:
+    from loguru import Logger
+
+logger.remove()
+
+
+class LogLevel(NamedTuple):
+    name: str
+    no: int
+
+    def is_debug(self) -> bool:
+        return self.no <= 10
+
+
+# See https://loguru.readthedocs.io/en/stable/api/logger.html#levels
+ERROR = LogLevel(name="error", no=40)
+WARNING = LogLevel(name="warning", no=30)
+INFO = LogLevel(name="info", no=20)
+DEBUG = LogLevel(name="debug", no=10)
+TRACE = LogLevel(name="trace", no=5)
+
+
+def level_from_verbosity(verbosity: int) -> LogLevel:
+    """
+    Find logging level, depending on the verbosity requested.
+
+    -q         -1   =>  ERROR
+    default     0   =>  WARNING
+    -v          1   =>  INFO
+    -vv         2   =>  DEBUG
+    -vvv        3   =>  TRACE
+
+    :param verbosity: verbosity (between -1 and 3) of the logger
+    :returns: log level guessed from the verbosity
+    """
+    if verbosity < 0:
+        return ERROR
+    return [WARNING, INFO, DEBUG, TRACE][min(3, verbosity)]
+
+
+def setup_logger(
+    verbosity: int,
+    filepath: Optional[Path] = None,
+    serialize: bool = False,
+) -> LogLevel:
+    """
+    Configure the logger and return the computed log level.
+
+    See https://loguru.readthedocs.io/en/stable/overview.html
+
+    :param verbosity: verbosity (between -1 and 3) of the logger
+    :param filepath: write logs to filepath
+    :param serialize: generate JSON formatted log records
+    :returns: log level guessed from the verbosity
+    """
+    level = level_from_verbosity(verbosity)
+
+    handlers = [dict(sink=sys.stderr, level=level.no, serialize=serialize)]
+
+    if filepath is not None:
+        handlers.append(
+            dict(
+                sink=filepath,
+                enqueue=True,
+                level=level.no,
+                serialize=serialize,
+                rotation="12:00",
+                retention="7 days",
+            )
+        )
+
+    logger.configure(handlers=handlers)
+
+    return level
+
+
+_empty_logger = deepcopy(logger)
+
+
+def create_task_logger(
+    verbosity: int,
+    filepath: Path,
+    serialize: bool = False,
+) -> "Logger":
+    """
+    Create and configure an independent logger for a task, return the new logger.
+
+    See #creating-independent-loggers-with-separate-set-of-handlers in
+    https://loguru.readthedocs.io/en/stable/resources/recipes.html
+
+    :returns: new logger
+    """
+    task_logger = deepcopy(_empty_logger)
+
+    level = level_from_verbosity(verbosity)
+
+    task_logger.configure(
+        handlers=[
+            dict(
+                sink=filepath,
+                enqueue=True,
+                level=level.no,
+                serialize=serialize,
+                rotation="12:00",
+                retention="7 days",
+            )
+        ],
+    )
+
+    return task_logger