import hashlib
import logging
from icalendar import Calendar

logger = logging.getLogger(__name__)


def _stable_event_key(component) -> str:
    event_bytes = component.to_ical()
    text = event_bytes.decode("utf-8", errors="replace")
    stable_lines = []
    for line in text.split("\r\n"):
        key = line.split(":")[0].upper() if ":" in line else ""
        if key in ("DTSTAMP", "LAST-MODIFIED"):
            continue
        stable_lines.append(line)
    stable_text = "\r\n".join(stable_lines)
    return hashlib.sha256(stable_text.encode("utf-8")).hexdigest()


def parse_ics_events(ics_text: str) -> dict[str, str]:
    cal = Calendar.from_ical(ics_text.encode() if isinstance(ics_text, str) else ics_text)
    result = {}
    for component in cal.walk():
        if component.name != "VEVENT":
            continue
        uid = component.get("UID")
        if uid is None:
            logger.warning("Skipping event with no UID")
            continue
        uid_str = str(uid)
        try:
            result[uid_str] = _stable_event_key(component)
        except Exception as e:
            logger.warning("Failed to process event %s: %s", uid_str, e)
    return result


def compute_diff(ics_uids: dict[str, str], known_uids: dict[str, str]) -> dict:
    to_add = []
    to_update = []
    to_delete = []

    for uid, file_hash in ics_uids.items():
        if uid not in known_uids:
            to_add.append((uid, file_hash))
        elif known_uids[uid] != file_hash:
            to_update.append((uid, file_hash))

    for uid in known_uids:
        if uid not in ics_uids:
            to_delete.append(uid)

    return {
        "to_add": to_add,
        "to_update": to_update,
        "to_delete": to_delete,
    }


def parse_ics_events_with_data(ics_text: str) -> dict[str, bytes]:
    cal = Calendar.from_ical(ics_text.encode() if isinstance(ics_text, str) else ics_text)
    result = {}
    for component in cal.walk():
        if component.name != "VEVENT":
            continue
        uid = component.get("UID")
        if uid is None:
            logger.warning("Skipping event with no UID")
            continue
        uid_str = str(uid)
        try:
            result[uid_str] = component.to_ical()
        except Exception as e:
            logger.warning("Failed to process event %s: %s", uid_str, e)
    return result