from contextlib import contextmanager
import sys
import warnings
import re
import functools
import os

__all__ = ['all_warnings', 'expected_warnings', 'warn']


# A version of `warnings.warn` with a default stacklevel of 2.
# functool is used so as not to increase the call stack accidentally
warn = functools.partial(warnings.warn, stacklevel=2)


@contextmanager
def all_warnings():
    """
    Context for use in testing to ensure that all warnings are raised.

    Examples
    --------
    >>> import warnings
    >>> def foo():
    ...     warnings.warn(RuntimeWarning("bar"), stacklevel=2)

    We raise the warning once, while the warning filter is set to "once".
    Hereafter, the warning is invisible, even with custom filters:

    >>> with warnings.catch_warnings():
    ...     warnings.simplefilter('once')
    ...     foo()                         # doctest: +SKIP

    We can now run ``foo()`` without a warning being raised:

    >>> from numpy.testing import assert_warns
    >>> foo()                             # doctest: +SKIP

    To catch the warning, we call in the help of ``all_warnings``:

    >>> with all_warnings():
    ...     assert_warns(RuntimeWarning, foo)
    """
    # _warnings.py is on the critical import path.
    # Since this is a testing only function, we lazy import inspect.
    import inspect
    # Whenever a warning is triggered, Python adds a __warningregistry__
    # member to the *calling* module.  The exercize here is to find
    # and eradicate all those breadcrumbs that were left lying around.
    #
    # We proceed by first searching all parent calling frames and explicitly
    # clearing their warning registries (necessary for the doctests above to
    # pass).  Then, we search for all submodules of skimage and clear theirs
    # as well (necessary for the skimage test suite to pass).

    frame = inspect.currentframe()
    if frame:
        for f in inspect.getouterframes(frame):
            f[0].f_locals['__warningregistry__'] = {}
    del frame

    for mod_name, mod in list(sys.modules.items()):
        try:
            mod.__warningregistry__.clear()
        except AttributeError:
            pass

    with warnings.catch_warnings(record=True) as w:
        warnings.simplefilter("always")
        yield w


@contextmanager
def expected_warnings(matching):
    r"""Context for use in testing to catch known warnings matching regexes

    Parameters
    ----------
    matching : None or a list of strings or compiled regexes
        Regexes for the desired warning to catch
        If matching is None, this behaves as a no-op.

    Examples
    --------
    >>> import numpy as np
    >>> image = np.random.randint(0, 2**16, size=(100, 100), dtype=np.uint16)
    >>> # rank filters are slow when bit-depth exceeds 10 bits
    >>> from skimage import filters
    >>> with expected_warnings(['Bad rank filter performance']):
    ...     median_filtered = filters.rank.median(image)

    Notes
    -----
    Uses `all_warnings` to ensure all warnings are raised.
    Upon exiting, it checks the recorded warnings for the desired matching
    pattern(s).
    Raises a ValueError if any match was not found or an unexpected
    warning was raised.
    Allows for three types of behaviors: `and`, `or`, and `optional` matches.
    This is done to accommodate different build environments or loop conditions
    that may produce different warnings.  The behaviors can be combined.
    If you pass multiple patterns, you get an orderless `and`, where all of the
    warnings must be raised.
    If you use the `|` operator in a pattern, you can catch one of several
    warnings.
    Finally, you can use `|\A\Z` in a pattern to signify it as optional.

    """
    if isinstance(matching, str):
        raise ValueError('``matching`` should be a list of strings and not '
                         'a string itself.')

    # Special case for disabling the context manager
    if matching is None:
        yield None
        return

    strict_warnings = os.environ.get('SKIMAGE_TEST_STRICT_WARNINGS', '1')
    if strict_warnings.lower() == 'true':
        strict_warnings = True
    elif strict_warnings.lower() == 'false':
        strict_warnings = False
    else:
        strict_warnings = bool(int(strict_warnings))

    with all_warnings() as w:
        # enter context
        yield w
        # exited user context, check the recorded warnings
        # Allow users to provide None
        while None in matching:
            matching.remove(None)
        remaining = [m for m in matching if r'\A\Z' not in m.split('|')]
        for warn in w:
            found = False
            for match in matching:
                if re.search(match, str(warn.message)) is not None:
                    found = True
                    if match in remaining:
                        remaining.remove(match)
            if strict_warnings and not found:
                raise ValueError('Unexpected warning: %s' % str(warn.message))
        if strict_warnings and (len(remaining) > 0):
            msg = 'No warning raised matching:\n%s' % '\n'.join(remaining)
            raise ValueError(msg)
