import re
import shutil
import subprocess

from datetime import datetime, timezone

HASHTAG_PATTERN = re.compile(r'(?<!\w)(#\w+)\b')


def parse_datetime(value):
    """Returns an aware datetime in local timezone"""

    # In Python < 3.7, `%z` does not match `Z` offset
    # https://docs.python.org/3.7/library/datetime.html#strftime-and-strptime-behavior
    if value.endswith("Z"):
        dttm = datetime.strptime(value, "%Y-%m-%dT%H:%M:%S.%fZ").replace(tzinfo=timezone.utc)
    else:
        dttm = datetime.strptime(value, "%Y-%m-%dT%H:%M:%S.%f%z")

    return dttm.astimezone()


def highlight_keys(text, high_attr, low_attr=""):
    """
    Takes a string and adds high_attr attribute to parts in square brackets,
    and optionally low_attr attribute to parts outside square brackets.

    The result can be rendered using a urwid.Text widget.

    For example:

    >>> highlight_keys("[P]rint [V]iew", "blue")
    >>> [('blue', 'P'), 'rint ', ('blue', 'V'), 'iew']
    """
    def _gen():
        highlighted = False
        for part in re.split("\\[|\\]", text):
            if part:
                if highlighted:
                    yield (high_attr, part) if high_attr else part
                else:
                    yield (low_attr, part) if low_attr else part
            highlighted = not highlighted
    return list(_gen())


def highlight_hashtags(line, attr="hashtag"):
    return [
        (attr, p) if p.startswith("#") else p
        for p in re.split(HASHTAG_PATTERN, line)
    ]


def show_media(paths):
    """
    Attempt to open an image viewer to show given media files.

    FIXME: This is not very thought out, but works for me.
    Once settings are implemented, add an option for the user to configure their
    prefered media viewer.
    """
    viewer = None
    potential_viewers = [
        "feh",
        "eog",
        "display"
    ]
    for v in potential_viewers:
        viewer = shutil.which(v)
        if viewer:
            break

    if not viewer:
        raise Exception("Cannot find an image viewer")

    subprocess.run([viewer] + paths)