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"""A common configuration-storage class with a .diag() method.

This module provides four classes that may be used as base classes for
storing program runtime configuration with a `verbose` boolean field.
The classes provide a `.diag(msg)` method that decides whether to
output the provided message based on the value of the object's
`verbose` field.

The `ConfigDiagUnfrozen` and `ConfigDiagUnfrozenStdOut` classes are
normal dataclasses, while the `ConfigDiag` and `ConfigDiagStdOut` ones
are frozen.

The `ConfigDiag` and `ConfigDiagUnfrozen` classes will output any
diagnostic messages to the standard error stream, while
the `ConfigDiagStdOut` and `ConfigDiagUnfrozenStdOut` ones will output
the diagnostic messages to the standard output stream.

Example:

Subclass the frozen `ConfigDiag` class, add a program-specific field:

    @dataclasses.dataclass(frozen=True)
    class Config(cfg_diag.ConfigDiag):
        '''Runtime configuration for the fribble program.'''
        path: pathlib.Path

Initialize this class from an argument parser object:

    return Config(path=args.path, verbose=args.verbose)

Output a diagnostic message if requested:

    cfg.diag("This will either appear or it will not")
"""


import dataclasses
import sys


VERSION = "0.1.1"


class ConfigDiagBase:
    """Output diagnostic messages if requested.

    Child classes MUST define a boolean-like `verbose` attribute!"""

    # pylint: disable=too-few-public-methods

    _config_diag_to_stderr = True

    def diag(self, msg: str) -> None:
        """Output a diagnostic message if requested."""
        if self.verbose:  # type: ignore  # pylint: disable=no-member
            print(
                msg,
                file=sys.stderr if self._config_diag_to_stderr else sys.stdout,
            )


@dataclasses.dataclass
class ConfigDiagUnfrozen(ConfigDiagBase):
    """A base class for configuration storage."""

    verbose: bool


@dataclasses.dataclass(frozen=True)
class ConfigDiag(ConfigDiagBase):
    """A frozen base class for configuration storage."""

    verbose: bool


@dataclasses.dataclass
class ConfigDiagUnfrozenStdOut(ConfigDiagUnfrozen):
    """A base class that outputs diagnostic messages to stdout."""

    def __post_init__(self) -> None:
        """Redirect the output to the standard output stream."""
        self._config_diag_to_stderr = False


@dataclasses.dataclass(frozen=True)
class ConfigDiagStdOut(ConfigDiag):
    """A frozen base class with diagnostic messages output to stdout."""

    def __post_init__(self) -> None:
        """Redirect the output to the standard output stream."""
        object.__setattr__(self, "_config_diag_to_stderr", False)
