Blame for rules/fraction.py

import random
import re

from num2fawords import ordinal_words, words
from num2words import num2words
from persiantools import digits

from rules.base import BaseProcessor
from utils import NO_LETTERS, detect_digit_language


VULGAR_FRACTIONS = {
    "½": (1, 2),
    "⅓": (1, 3),
    "⅔": (2, 3),
    "¼": (1, 4),
    "¾": (3, 4),
    "⅕": (1, 5),
    "⅖": (2, 5),
    "⅗": (3, 5),
    "⅘": (4, 5),
    "⅙": (1, 6),
    "⅚": (5, 6),
    "⅛": (1, 8),
    "⅜": (3, 8),
    "⅝": (5, 8),
    "⅞": (7, 8),
}

VULGAR = "".join(VULGAR_FRACTIONS)

# A whole number, optionally with thousands separators: `12`, `1,000`, `۱٬۰۰۰`.
NUMBER = r"(?:\d{1,3}(?:[,٬]\d{3})+|\d+)"

# The fraction itself: `1/3`, `۱/۳`, `1,000/2`, `2 1/2` (mixed number), `½`, `1½`.
# Shared with `UnitProcessor`, which reads `1/2 kg`.
FRACTION_BODY = rf"""
    (?:
        (?:(?P<whole>{NUMBER})[ ])?(?P<numerator>{NUMBER})/(?P<denominator>{NUMBER})
        |
        (?:(?P<vulgar_whole>{NUMBER})[ ]?)?(?P<vulgar>[{VULGAR}])
    )
"""

# Does not match parts of dates (`1402/05/10`), decimals (`3.1/2`), or fractions
# glued to a word or currency/percent sign (`and/or`, `1/2$`).
FRACTION_PATTERN = re.compile(
    rf"""
    (?<![\w/])(?<!\d[.,٫٬])
    {FRACTION_BODY}
    (?![\w/$€£%°])(?![.,٫٬]\d)
    """,
    re.VERBOSE,
)


class FractionProcessor(BaseProcessor):
    """Converts fractions into spoken text.

    Persian: `۱/۳`   -> `یک سوم`
             `۳/۴`   -> `سه چهارم`
             `۲ ۱/۲` -> `دو و یک دوم`
    English: `1/3`   -> `one third`
             `3/4`   -> `three quarters`
             `2 1/2` -> `two and one half`
             `½`     -> `one half`
             `1,000/2` -> `one thousand halves`

    Works on the whole text (not word by word) because a mixed number such as
    `2 1/2` spans two words. If the text has no letters at all, the digits pick
    the language: Persian digits -> Persian, ASCII digits -> English.

    A fraction followed by a unit (`1/2 kg`) is handled by `UnitProcessor`.
    """

    def __init__(self, epsilon: float = 1.0):
        super(FractionProcessor, self).__init__(epsilon=epsilon)

    def process(self, text: str, language: str = None, *args, **kwargs) -> str:
        if random.random() > self.epsilon:
            return text

        if language in (None, NO_LETTERS):
            language = detect_digit_language(text)
        if language not in ("fa", "en"):
            return text

        return FRACTION_PATTERN.sub(lambda match: self._convert(match, language), text)

    @staticmethod
    def _convert(match: re.Match, language: str) -> str:
        parsed = FractionProcessor.parse(match)
        if parsed is None:
            return match.group(0)
        return FractionProcessor.to_text(*parsed, language=language)

    @staticmethod
    def parse(match: re.Match):
        """Returns (whole, numerator, denominator) from a match of `FRACTION_BODY`.

        `whole` is None when there is no mixed-number part. Returns None for
        `1/0` (not a fraction) and `3/1` (just a ratio), which are left alone.
        """
        if match.group("vulgar"):
            numerator, denominator = VULGAR_FRACTIONS[match.group("vulgar")]
            whole = match.group("vulgar_whole")
        else:
            numerator = FractionProcessor._to_int(match.group("numerator"))
            denominator = FractionProcessor._to_int(match.group("denominator"))
            whole = match.group("whole")

        if denominator in (0, 1):
            return None
        return (
            None if whole is None else FractionProcessor._to_int(whole),
            numerator,
            denominator,
        )

    @staticmethod
    def to_text(whole, numerator: int, denominator: int, language: str) -> str:
        if language == "fa":
            fraction = FractionProcessor._persian_fraction(numerator, denominator)
            joiner, spell = " و ", words
        else:
            fraction = FractionProcessor._english_fraction(numerator, denominator)
            joiner, spell = " and ", num2words

        if whole is None:
            return fraction
        return f"{spell(whole)}{joiner}{fraction}"

    @staticmethod
    def _to_int(number: str) -> int:
        clean = digits.fa_to_en(number).replace(",", "").replace("٬", "")
        return int(clean)

    @staticmethod
    def _persian_fraction(numerator: int, denominator: int) -> str:
        ordinal = ordinal_words(denominator)
        # The library writes 30 as `سیم`; the correct form is `سی‌ام`.
        if ordinal.endswith("سیم"):
            ordinal = ordinal[: -len("سیم")] + "سی‌ام"
        # `یک صدم` / `یک هزارم`, not `یک یکصدم` / `یک یک هزارم`.
        if ordinal == "یکصدم":
            ordinal = "صدم"
        elif ordinal.startswith("یک "):
            ordinal = ordinal[len("یک "):]
        return f"{words(numerator)} {ordinal}"

    @staticmethod
    def _english_fraction(numerator: int, denominator: int) -> str:
        singular = numerator == 1
        if denominator == 2:
            unit = "half" if singular else "halves"
        elif denominator == 4:
            unit = "quarter" if singular else "quarters"
        else:
            ordinal = num2words(denominator, to="ordinal")
            # `one hundredth`, not `one one hundredth`.
            if ordinal.startswith("one "):
                ordinal = ordinal[len("one "):]
            unit = ordinal if singular else f"{ordinal}s"
        return f"{num2words(numerator)} {unit}"