from __future__ import annotations

from collections.abc import Sequence
from dataclasses import dataclass
from datetime import UTC, datetime, timedelta
import secrets

from app.extensions import db
from app.models import ShareLink

DEFAULT_SHARE_LINK_EXPIRE_DAYS = 30
MIN_SHARE_LINK_EXPIRE_DAYS = 1
MAX_SHARE_LINK_EXPIRE_DAYS = 365
SHARE_LINK_TOKEN_BYTES = 16
SHARE_EDITABLE_FIELDS = (
    "phone",
    "attendance_status",
    "actual_attendee_count",
    "child_count",
    "red_packet_child_count",
    "total_gift_amount",
    "gift_method_option_id",
    "gift_scene_option_id",
    "favor_status",
    "candy_status",
    "child_red_packet_status",
    "note",
)


@dataclass(frozen=True)
class ShareTokenCheckResult:
    ok: bool
    reason: str
    link: ShareLink | None = None


def list_share_links() -> Sequence[ShareLink]:
    result = db.session.execute(
        db.select(ShareLink).order_by(ShareLink.created_at.desc(), ShareLink.id.desc()),
    )
    return result.scalars().all()


def get_share_link_by_token(token: str) -> ShareLink | None:
    normalized = token.strip()
    if not normalized:
        return None
    result = db.session.execute(db.select(ShareLink).where(ShareLink.token == normalized).limit(1))
    return result.scalar_one_or_none()


def get_share_link_or_none(link_id: int) -> ShareLink | None:
    return db.session.get(ShareLink, link_id)


def normalize_expire_days(raw_days: int) -> int:
    if raw_days < MIN_SHARE_LINK_EXPIRE_DAYS:
        return MIN_SHARE_LINK_EXPIRE_DAYS
    if raw_days > MAX_SHARE_LINK_EXPIRE_DAYS:
        return MAX_SHARE_LINK_EXPIRE_DAYS
    return raw_days


def parse_share_link_create_form(form: dict[str, str]) -> tuple[dict[str, object], list[str]]:
    errors: list[str] = []
    label = form.get("label", "").strip() or None
    raw_expire_days = form.get("expire_days", "").strip() or str(DEFAULT_SHARE_LINK_EXPIRE_DAYS)

    try:
        expire_days = int(raw_expire_days)
    except ValueError:
        return {}, ["有效期天数必须是整数。"]

    if expire_days < MIN_SHARE_LINK_EXPIRE_DAYS or expire_days > MAX_SHARE_LINK_EXPIRE_DAYS:
        errors.append(f"有效期天数必须在 {MIN_SHARE_LINK_EXPIRE_DAYS}-{MAX_SHARE_LINK_EXPIRE_DAYS} 之间。")

    if errors:
        return {}, errors

    return {"label": label, "expire_days": expire_days}, []


def create_share_link(*, created_by: int | None, label: str | None, expire_days: int) -> ShareLink:
    normalized_days = normalize_expire_days(expire_days)
    token = _generate_unique_share_token()
    link = ShareLink(
        token=token,
        label=(label or "").strip() or None,
        expires_at=_build_expire_at(normalized_days),
        revoked_at=None,
        created_by=created_by,
    )
    db.session.add(link)
    db.session.flush()
    return link


def revoke_share_link(link: ShareLink, *, now: datetime | None = None) -> bool:
    if link.revoked_at is not None:
        return False

    link.revoked_at = (now or datetime.now(UTC)).replace(tzinfo=None)
    return True


def check_share_token(token: str, *, now: datetime | None = None) -> ShareTokenCheckResult:
    link = get_share_link_by_token(token)
    if link is None:
        return ShareTokenCheckResult(ok=False, reason="not_found")

    current = (now or datetime.now(UTC)).replace(tzinfo=None)
    if link.revoked_at is not None:
        return ShareTokenCheckResult(ok=False, reason="revoked", link=link)
    if link.expires_at <= current:
        return ShareTokenCheckResult(ok=False, reason="expired", link=link)
    return ShareTokenCheckResult(ok=True, reason="ok", link=link)


def build_share_link_url(token: str) -> str:
    return f"/s/{token}"


def _build_expire_at(expire_days: int) -> datetime:
    return (datetime.now(UTC) + timedelta(days=expire_days)).replace(tzinfo=None)


def _generate_share_token() -> str:
    return secrets.token_urlsafe(SHARE_LINK_TOKEN_BYTES)


def _generate_unique_share_token() -> str:
    while True:
        token = _generate_share_token()
        exists = db.session.execute(db.select(ShareLink.id).where(ShareLink.token == token).limit(1)).scalar_one_or_none()
        if exists is None:
            return token