"""Invitation flow: admin issues a one-shot URL token, invitee accepts.

The raw token is shown to the admin once (returned by `create_invitation`)
and never persisted — only its SHA-256 lives in the DB. Pre-assigned groups
are attached at creation and applied at acceptance.
"""

from __future__ import annotations

import uuid
from dataclasses import dataclass
from datetime import datetime, timedelta, timezone
from typing import Iterable

from sqlalchemy import select

from app.core.security import (
    generate_opaque_token,
    hash_opaque_token,
    hash_password,
)
from app.db.session import session_scope
from app.models.auth import Group, Invitation, InvitationGroup, User, UserGroup

INVITATION_TTL = timedelta(days=7)


class InvitationError(Exception):
    pass


class InvitationExpired(InvitationError):
    pass


class InvitationConsumed(InvitationError):
    pass


class InvitationRevoked(InvitationError):
    pass


@dataclass
class InvitationCreated:
    invitation_id: uuid.UUID
    raw_token: str
    expires_at: datetime


@dataclass
class InvitationPreview:
    email_hint: str | None
    expires_at: datetime
    groups: list[str]
    is_valid: bool
    reason: str | None


def _now() -> datetime:
    return datetime.now(tz=timezone.utc)


def create_invitation(
    *,
    created_by_user_id: uuid.UUID,
    email_hint: str | None,
    group_ids: Iterable[uuid.UUID] = (),
    ttl: timedelta = INVITATION_TTL,
) -> InvitationCreated:
    raw = generate_opaque_token()
    expires_at = _now() + ttl
    with session_scope() as s:
        inv = Invitation(
            token_hash=hash_opaque_token(raw),
            email_hint=email_hint.strip().lower() if email_hint else None,
            created_by_user_id=created_by_user_id,
            expires_at=expires_at,
        )
        s.add(inv)
        s.flush()
        for gid in group_ids:
            s.add(InvitationGroup(invitation_id=inv.id, group_id=gid))
        return InvitationCreated(
            invitation_id=inv.id,
            raw_token=raw,
            expires_at=expires_at,
        )


def _load_by_token(s, raw_token: str) -> Invitation | None:
    return s.scalar(
        select(Invitation).where(Invitation.token_hash == hash_opaque_token(raw_token))
    )


def preview(raw_token: str) -> InvitationPreview:
    with session_scope() as s:
        inv = _load_by_token(s, raw_token)
        if inv is None:
            return InvitationPreview(None, _now(), [], False, "not_found")
        groups = [g.name for g in inv.pre_assigned_groups]
        if inv.revoked_at is not None:
            return InvitationPreview(inv.email_hint, inv.expires_at, groups, False, "revoked")
        if inv.consumed_at is not None:
            return InvitationPreview(inv.email_hint, inv.expires_at, groups, False, "consumed")
        if inv.expires_at <= _now():
            return InvitationPreview(inv.email_hint, inv.expires_at, groups, False, "expired")
        return InvitationPreview(inv.email_hint, inv.expires_at, groups, True, None)


def accept(raw_token: str, *, email: str, password: str, display_name: str | None) -> uuid.UUID:
    """Create the user, attach pre-assigned groups, mark invitation consumed."""
    if len(password) < 8:
        raise ValueError("password must be at least 8 characters")

    email_norm = email.strip().lower()
    with session_scope() as s:
        inv = _load_by_token(s, raw_token)
        if inv is None:
            raise InvitationError("invitation not found")
        if inv.revoked_at is not None:
            raise InvitationRevoked("invitation revoked")
        if inv.consumed_at is not None:
            raise InvitationConsumed("invitation already consumed")
        if inv.expires_at <= _now():
            raise InvitationExpired("invitation expired")

        # Email must not be already in use among active users.
        existing = s.scalar(
            select(User).where(User.email == email_norm, User.deleted_at.is_(None))
        )
        if existing is not None:
            raise ValueError("email already in use")

        user = User(
            email=email_norm,
            display_name=(display_name or "").strip() or None,
            password_hash=hash_password(password),
        )
        s.add(user)
        s.flush()

        for grp in inv.pre_assigned_groups:
            s.add(UserGroup(user_id=user.id, group_id=grp.id))

        inv.consumed_at = _now()
        inv.consumed_by_user_id = user.id
        return user.id


def revoke(invitation_id: uuid.UUID) -> bool:
    with session_scope() as s:
        inv = s.get(Invitation, invitation_id)
        if inv is None:
            return False
        if inv.revoked_at is not None or inv.consumed_at is not None:
            return False
        inv.revoked_at = _now()
        return True


def list_active(*, limit: int = 100) -> list[Invitation]:
    with session_scope() as s:
        rows = s.scalars(
            select(Invitation)
            .where(
                Invitation.consumed_at.is_(None),
                Invitation.revoked_at.is_(None),
                Invitation.expires_at > _now(),
            )
            .order_by(Invitation.created_at.desc())
            .limit(limit)
        ).all()
        # detach so caller can read after session closes
        for r in rows:
            s.expunge(r)
            for g in r.pre_assigned_groups:
                s.expunge(g)
        return list(rows)


def find_group_id_by_name(name: str) -> uuid.UUID | None:
    with session_scope() as s:
        gid = s.scalar(
            select(Group.id).where(Group.name == name, Group.deleted_at.is_(None))
        )
        return gid