timing/backend/exif_parser.py

"""
Parse og normaliser EXIF-metadata fra bilder.
Returnerer et strukturert dict eller kaster ExifError ved manglende/ugyldig data.
"""

import re
from dataclasses import dataclass
from datetime import datetime, timezone
from pathlib import Path
from typing import Optional

import piexif
from PIL import Image


class ExifError(ValueError):
    pass


@dataclass
class ImageMetadata:
    timestamp_utc: datetime
    gps_lat: float
    gps_lon: float
    gps_alt: Optional[float]
    station: Optional[str]  # fra ImageDescription eller CameraLabel


def _rational_to_float(rational) -> float:
    """Konverter EXIF rational (teller, nevner) til float."""
    if isinstance(rational, tuple):
        num, den = rational
        if den == 0:
            return 0.0
        return num / den
    return float(rational)


def _parse_gps_coord(dms_rationals, ref: str) -> float:
    """Konverter GPS DMS rationals + referanse til desimalgrader."""
    deg = _rational_to_float(dms_rationals[0])
    min_ = _rational_to_float(dms_rationals[1])
    sec = _rational_to_float(dms_rationals[2])
    value = deg + min_ / 60.0 + sec / 3600.0
    if ref in ("S", "W"):
        value = -value
    return value


def _parse_timestamp(exif_dict: dict) -> datetime:
    """
    Hent tidsstempel fra DateTimeOriginal + SubSecTimeOriginal.
    Returnerer datetime i UTC. Kaster ExifError hvis manglende.
    """
    ifd0 = exif_dict.get("Exif", {})

    raw_dt = ifd0.get(piexif.ExifIFD.DateTimeOriginal)
    if not raw_dt:
        raise ExifError("Mangler DateTimeOriginal i EXIF")

    if isinstance(raw_dt, bytes):
        raw_dt = raw_dt.decode("ascii", errors="replace")

    # Format: "2024:06:15 10:23:45"
    try:
        dt = datetime.strptime(raw_dt.strip(), "%Y:%m:%d %H:%M:%S")
    except ValueError as e:
        raise ExifError(f"Ugyldig DateTimeOriginal-format: {raw_dt!r}") from e

    # Sub-sekunder
    raw_sub = ifd0.get(piexif.ExifIFD.SubSecTimeOriginal)
    microseconds = 0
    if raw_sub:
        if isinstance(raw_sub, bytes):
            raw_sub = raw_sub.decode("ascii", errors="replace")
        sub_str = raw_sub.strip()
        if sub_str.isdigit():
            # Pad/truncate til 6 siffer (mikrosekunder)
            sub_str = (sub_str + "000000")[:6]
            microseconds = int(sub_str)

    dt = dt.replace(microsecond=microseconds, tzinfo=timezone.utc)
    return dt


def _parse_gps(exif_dict: dict) -> tuple[float, float, Optional[float]]:
    """
    Hent GPS-koordinater. Kaster ExifError hvis lat/lon mangler.
    """
    gps = exif_dict.get("GPS", {})

    lat_dms = gps.get(piexif.GPSIFD.GPSLatitude)
    lat_ref = gps.get(piexif.GPSIFD.GPSLatitudeRef)
    lon_dms = gps.get(piexif.GPSIFD.GPSLongitude)
    lon_ref = gps.get(piexif.GPSIFD.GPSLongitudeRef)

    if not (lat_dms and lat_ref and lon_dms and lon_ref):
        raise ExifError("Mangler GPS-koordinater (lat/lon) i EXIF")

    if isinstance(lat_ref, bytes):
        lat_ref = lat_ref.decode("ascii")
    if isinstance(lon_ref, bytes):
        lon_ref = lon_ref.decode("ascii")

    lat = _parse_gps_coord(lat_dms, lat_ref)
    lon = _parse_gps_coord(lon_dms, lon_ref)

    alt = None
    alt_raw = gps.get(piexif.GPSIFD.GPSAltitude)
    if alt_raw:
        alt = _rational_to_float(alt_raw)
        alt_ref = gps.get(piexif.GPSIFD.GPSAltitudeRef, 0)
        if alt_ref == 1:
            alt = -alt

    return lat, lon, alt


def _parse_station(exif_dict: dict) -> Optional[str]:
    """Hent stasjonsnavn fra ImageDescription."""
    ifd0 = exif_dict.get("0th", {})
    desc = ifd0.get(piexif.ImageIFD.ImageDescription)
    if desc:
        if isinstance(desc, bytes):
            desc = desc.decode("utf-8", errors="replace")
        return desc.strip() or None
    return None


def parse_image(path: Path) -> ImageMetadata:
    """
    Les EXIF fra bildefil og returner ImageMetadata.
    Kaster ExifError hvis påkrevde felt mangler.
    """
    try:
        img = Image.open(path)
        raw_exif = img.info.get("exif")
        if not raw_exif:
            raise ExifError("Bildet har ingen EXIF-data")
        exif_dict = piexif.load(raw_exif)
    except ExifError:
        raise
    except Exception as e:
        raise ExifError(f"Kunne ikke lese EXIF: {e}") from e

    timestamp = _parse_timestamp(exif_dict)
    lat, lon, alt = _parse_gps(exif_dict)
    station = _parse_station(exif_dict)

    return ImageMetadata(
        timestamp_utc=timestamp,
        gps_lat=lat,
        gps_lon=lon,
        gps_alt=alt,
        station=station,
    )