visibility.py

import re
from fractions import Fraction

from aviation_weather.components import Component
from aviation_weather.exceptions import VisibilityDecodeError


class Visibility(Component):

    def __init__(self, raw):
        """Parse `raw` to create a new Visibility object.

        Args:
            raw (str): The visibility to be parsed.

        Raises:
            VisibilityDecodeError: If `raw` could not be parsed.
        """
        m = re.search(
            r"\b(?:(?P<lt_gt>[MP])?(?P<distance1>\d[ \d/]{,4})(?P<unit>SM)|(?P=lt_gt)?(?P<distance2>\d{4})|(?P<cavok>CAVOK))\b",
            raw
        )
        if not m:
            raise VisibilityDecodeError("Visibility(%r) could not be parsed" % raw)
        if m.group("cavok"):
            self.cavok = True
            self.distance = None
            self.greater_than = False
            self.less_than = False
            self.unit = None
        else:
            self.cavok = None
            self.less_than = m.group("lt_gt") == "M"
            self.greater_than = m.group("lt_gt") == "P"
            distance = m.group("distance1") or m.group("distance2")
            self.unit = m.group("unit") or "m"

            if "/" in distance:
                parts = distance.split(" ", 1)
                if len(parts) == 1:
                    self.distance = float(Fraction(parts[0]))
                else:
                    self.distance = int(parts[0]) + float(Fraction(parts[1]))
            else:
                self.distance = int(distance)

    @property
    def raw(self):
        if self.cavok:
            return "CAVOK"
        else:
            if self.less_than:
                raw = "M"
            elif self.greater_than:
                raw = "P"
            else:
                raw = ""

            whole = self.distance // 1
            fraction = Fraction(self.distance % 1)
            if whole and fraction:
                raw += "%d %s" % (whole, fraction)
            elif whole:
                raw += str(whole)
            elif fraction:
                raw += str(fraction)
            else:
                raw += "0"

            if self.unit != "m":
                raw += self.unit
            return raw