"""Small, shared helpers for values returned by ExifTool."""

from __future__ import annotations

import math
import re
from collections.abc import Iterable, Mapping
from datetime import datetime, timedelta, timezone


DATETIME_RE = re.compile(
    r"(?P<Y>\d{4})[:\-]?(?P<M>\d{2})[:\-]?(?P<D>\d{2})"
    r"(?:[ T_])?"
    r"(?P<h>\d{2}):?(?P<m>\d{2}):?(?P<s>\d{2})"
    r"(?:[.,](?P<sub>\d+))?"
    r"(?:\s*(?P<tz>Z|[+-]\d{2}:?\d{2}))?"
)


def first_tag(metadata: Mapping[str, object], tags: Iterable[str]) -> object | None:
    for tag in tags:
        if tag in metadata:
            return metadata[tag]
    return None


def tag_value(metadata: Mapping[str, object], tag: str) -> str | None:
    value = metadata.get(tag)
    return None if value is None else str(value)


def parse_exif_datetime(value: object, assume_utc: bool = False) -> datetime | None:
    if value is None:
        return None
    match = DATETIME_RE.search(str(value).strip())
    if not match:
        return None
    try:
        tz_text = match.group("tz")
        if tz_text == "Z":
            tzinfo = timezone.utc
        elif tz_text:
            sign = 1 if tz_text[0] == "+" else -1
            digits = tz_text[1:].replace(":", "")
            tzinfo = timezone(sign * timedelta(hours=int(digits[:2]), minutes=int(digits[2:])))
        else:
            tzinfo = None
        parsed = datetime(
            int(match.group("Y")),
            int(match.group("M")),
            int(match.group("D")),
            int(match.group("h")),
            int(match.group("m")),
            int(match.group("s")),
            tzinfo=tzinfo,
        )
        return parsed.replace(tzinfo=timezone.utc) if assume_utc and tzinfo is None else parsed
    except ValueError:
        return None


def round_half_up(value: float) -> int:
    return math.floor(value + 0.5)