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import re

from datetime import datetime, timedelta

from difflib import SequenceMatcher

class ParseError(ValueError):

pass

TIME_UNITS = dict(

seconds="seconds",

minutes="minutes",

hours="hours",

days="days",

weeks="weeks",

months="months",

years="years",

# Shortcuts

s="seconds",

min="minutes",

h="hours",

d="days",

w="weeks",

mon="months",

y="years",

)

EXTRAPOLATED = {"months": (30, "days"), "years": (365, "days")}

assert set(EXTRAPOLATED) <= set(TIME_UNITS)

TIME_RE = re.compile(r"(\d+)([a-z]+)")

UNITS_STR = ", ".join(sorted(TIME_UNITS.keys()))

def string_similarity(a, b):

return SequenceMatcher(None, a, b).ratio()

def parse_time_atom(count, unit):

count = int(count)

try:

unit = TIME_UNITS[unit]

except KeyError:

most_similar = max(TIME_UNITS, key=lambda k: string_similarity(k, unit))

raise ParseError(

f"'{unit}' is not a recognized time unit. Did you mean '{most_similar}'?" f"\nSupported units: {UNITS_STR}"

)

if unit in EXTRAPOLATED:

mul, unit = EXTRAPOLATED[unit]

count *= mul

return count, unit

def parse_time_delta(t: str):

time_dict = {}

while t:

m = TIME_RE.match(t)

if not m:

raise ParseError(f"Cannot parse '{t}': Not a recognized time delta")

count, unit = parse_time_atom(*m.groups())

if unit in time_dict:

raise ParseError(f"Time unit {unit} specified more than once")

time_dict[unit] = count

t = t[m.end() :]

if not time_dict:

raise ParseError("No time difference specified")

return timedelta(**time_dict)

def parse_time_before_now(t: str):

return datetime.now() - parse_time_delta(t)