아빠는 어디까지 들었을까?

import math
import re

HEARD_CHARS_PER_SECOND = 6    # cautious: guessing the take long makes the claim small


def heard_chars(unit_range: tuple[int, int], current_time: float, duration: float,
                buffered_seconds: float = 0.0) -> int:
    """Map a playback position inside one unit back to characters of the reply."""
    start, end = unit_range
    length = end - start
    if not current_time > 0 or length <= 0:
        return start
    if duration > 0 and math.isfinite(duration):
        total = duration
    else:                                      # a streamed take: length not known yet
        total = max(buffered_seconds, length / HEARD_CHARS_PER_SECOND)
    return start + math.floor(length * min(1.0, current_time / total))


SENTENCE_END = re.compile(r"(?:[.!?。！？…]+[\"'”’)\]]*)(?=\s|$)|\n")


def snap_heard(content: str, heard_until: int) -> int:
    """Back to the last sentence end at or before the cut: a half-heard sentence counts as unheard."""
    limit = max(0, min(heard_until, len(content)))
    if limit >= len(content.rstrip()):
        return len(content)
    snapped = 0
    for match in SENTENCE_END.finditer(content):   # the whole reply, so '$' means its real end
        if match.end() > limit:
            break
        snapped = match.end()
    return snapped


english = "x" * 151                           # a 151-character unit, 9.5 s when finished
old_rule = 0                                   # 'duration unknown -> the unit's start'
print("old rule:", old_rule, "| cautious rule:",
      heard_chars((0, 151), current_time=4.0, duration=float("inf")))

reply = "내일은 비가 와. 우산 챙겨. 오후엔 그친대\n저녁엔 쌀쌀하니까 겉옷도 가져가."
cut = reply.index("그친대") + 2              # he cut in mid-sentence
print(repr(reply[: snap_heard(reply, cut)]))

decimal = "It took 3.5 seconds. Then it stopped."
cut = decimal.index("3.") + 2                  # cut right after "3."
print(snap_heard(decimal, cut), "| searching only up to the cut would say",
      max((m.end() for m in SENTENCE_END.finditer(decimal, 0, cut)), default=0))