from __future__ import annotations

from datetime import UTC, datetime, time, timedelta

from ..models import TaskInstance, User


def _ics_escape(value: str | None) -> str:
    text = (value or "").replace("\\", "\\\\")
    text = text.replace(";", "\\;").replace(",", "\\,")
    text = text.replace("\r\n", "\\n").replace("\n", "\\n").replace("\r", "\\n")
    return text


def _format_date(value) -> str:
    return value.strftime("%Y%m%d")


def _format_timestamp(value: datetime | None) -> str:
    timestamp = value or datetime.now(UTC).replace(tzinfo=None)
    return timestamp.strftime("%Y%m%dT%H%M%SZ")


def build_calendar_feed(user: User, base_url: str) -> str:
    tasks = (
        TaskInstance.query.filter_by(assigned_user_id=user.id)
        .order_by(TaskInstance.due_date.asc(), TaskInstance.id.asc())
        .all()
    )

    lines = [
        "BEGIN:VCALENDAR",
        "VERSION:2.0",
        "PRODID:-//hnz.io//Putzliga//DE",
        "CALSCALE:GREGORIAN",
        "METHOD:PUBLISH",
        f"X-WR-CALNAME:{_ics_escape(f'Putzliga - {user.name}')}",
        f"X-WR-CALDESC:{_ics_escape('Persoenlicher Aufgabenfeed aus Putzliga')}",
    ]

    for task in tasks:
        due_end = task.due_date + timedelta(days=1)
        description = _ics_escape(task.description)
        lines.extend(
            [
                "BEGIN:VEVENT",
                f"UID:taskinstance-{task.id}@putzliga",
                f"DTSTAMP:{_format_timestamp(task.updated_at)}",
                f"LAST-MODIFIED:{_format_timestamp(task.updated_at)}",
                f"SUMMARY:{_ics_escape(task.title)}",
                f"DESCRIPTION:{description}",
                f"DTSTART;VALUE=DATE:{_format_date(task.due_date)}",
                f"DTEND;VALUE=DATE:{_format_date(due_end)}",
                f"URL:{_ics_escape(base_url)}",
                "END:VEVENT",
            ]
        )

    lines.append("END:VCALENDAR")
    return "\r\n".join(lines) + "\r\n"