"""Authentication business logic: login, register, tokens, MFA."""

from datetime import datetime, timedelta, timezone

from fastapi import HTTPException, status
from sqlalchemy.orm import Session

from app.config import get_settings
from app.core.exceptions import AccountLockedError, InvalidCredentialsError
from app.core.security import (
    create_access_token,
    create_refresh_token,
    generate_mfa_secret,
    get_mfa_uri,
    hash_password,
    hash_token,
    verify_mfa_code,
    verify_password,
)
from app.models.user import AllowedDomain, InvitationLink, RefreshToken, User

settings = get_settings()


# ---------------------------------------------------------------------------
# Login
# ---------------------------------------------------------------------------

def authenticate_user(
    db: Session,
    email: str,
    password: str,
    mfa_code: str | None = None,
) -> User:
    """Authenticate a user by email/password (+ optional MFA).

    Handles:
    * Account-lock detection (locked_until).
    * Failed-attempt counting with auto-lock after 5 failures.
    * TOTP verification when MFA is enabled.
    """
    user = db.query(User).filter(User.email == email).first()

    if not user or not user.is_active:
        raise InvalidCredentialsError()

    # Check whether the account is currently locked.
    if user.locked_until and user.locked_until > datetime.now(timezone.utc):
        raise AccountLockedError(
            detail=f"Account locked until {user.locked_until.isoformat()}"
        )

    # Verify password.
    if not verify_password(password, user.password_hash):
        user.failed_login_attempts += 1
        if user.failed_login_attempts >= 5:
            user.locked_until = datetime.now(timezone.utc) + timedelta(minutes=30)
        db.commit()
        raise InvalidCredentialsError()

    # MFA check (if enabled on this account).
    if user.mfa_enabled:
        if not mfa_code:
            raise InvalidCredentialsError(detail="MFA code required")
        if not verify_mfa_code(user.mfa_secret, mfa_code):
            raise InvalidCredentialsError(detail="Invalid MFA code")

    # Success -- reset counters and record last login.
    user.failed_login_attempts = 0
    user.locked_until = None
    user.last_login = datetime.now(timezone.utc)
    db.commit()
    return user


# ---------------------------------------------------------------------------
# Registration
# ---------------------------------------------------------------------------

def register_user(
    db: Session,
    username: str,
    email: str,
    password: str,
    invitation_token: str | None = None,
) -> User:
    """Register a new user account.

    Either a valid (unexpired, unused) invitation token OR an email whose
    domain is in the ``allowed_domains`` whitelist is required.
    """
    # Uniqueness check.
    existing = (
        db.query(User)
        .filter((User.email == email) | (User.username == username))
        .first()
    )
    if existing:
        raise HTTPException(
            status_code=status.HTTP_409_CONFLICT,
            detail="User already exists",
        )

    role = "dak_mitarbeiter"

    if invitation_token:
        invite = (
            db.query(InvitationLink)
            .filter(
                InvitationLink.token == invitation_token,
                InvitationLink.is_active == True,  # noqa: E712
                InvitationLink.used_at == None,  # noqa: E711
                InvitationLink.expires_at > datetime.now(timezone.utc),
            )
            .first()
        )
        if not invite:
            raise HTTPException(
                status_code=status.HTTP_400_BAD_REQUEST,
                detail="Invalid or expired invitation",
            )
        if invite.email and invite.email.lower() != email.lower():
            raise HTTPException(
                status_code=status.HTTP_400_BAD_REQUEST,
                detail="Email does not match invitation",
            )
        role = invite.role
    else:
        # Domain whitelist.
        domain = email.split("@")[1].lower()
        allowed = (
            db.query(AllowedDomain)
            .filter(
                AllowedDomain.domain == domain,
                AllowedDomain.is_active == True,  # noqa: E712
            )
            .first()
        )
        if not allowed:
            raise HTTPException(
                status_code=status.HTTP_403_FORBIDDEN,
                detail="Email domain not allowed for registration",
            )
        role = allowed.role

    user = User(
        username=username,
        email=email,
        password_hash=hash_password(password),
        role=role,
    )
    db.add(user)
    db.commit()
    db.refresh(user)

    # Mark invitation as consumed.
    if invitation_token:
        invite.used_at = datetime.now(timezone.utc)
        invite.used_by = user.id
        invite.is_active = False
        db.commit()

    return user


# ---------------------------------------------------------------------------
# Token management
# ---------------------------------------------------------------------------

def create_tokens(db: Session, user: User) -> tuple[str, str]:
    """Create an access/refresh token pair and persist the refresh hash."""
    access = create_access_token(user.id, user.role)
    refresh = create_refresh_token()

    rt = RefreshToken(
        user_id=user.id,
        token_hash=hash_token(refresh),
        expires_at=datetime.now(timezone.utc)
        + timedelta(days=settings.REFRESH_TOKEN_EXPIRE_DAYS),
    )
    db.add(rt)
    db.commit()
    return access, refresh


def refresh_access_token(db: Session, refresh_token: str) -> tuple[str, User]:
    """Validate a refresh token and return a fresh access token + user."""
    token_hash = hash_token(refresh_token)
    rt = (
        db.query(RefreshToken)
        .filter(
            RefreshToken.token_hash == token_hash,
            RefreshToken.revoked == False,  # noqa: E712
            RefreshToken.expires_at > datetime.now(timezone.utc),
        )
        .first()
    )
    if not rt:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="Invalid or expired refresh token",
        )

    user = (
        db.query(User)
        .filter(User.id == rt.user_id, User.is_active == True)  # noqa: E712
        .first()
    )
    if not user:
        raise HTTPException(
            status_code=status.HTTP_401_UNAUTHORIZED,
            detail="User not found or inactive",
        )

    access = create_access_token(user.id, user.role)
    return access, user


def revoke_refresh_token(db: Session, refresh_token: str) -> None:
    """Revoke a refresh token (used on logout)."""
    token_hash = hash_token(refresh_token)
    rt = (
        db.query(RefreshToken)
        .filter(RefreshToken.token_hash == token_hash)
        .first()
    )
    if rt:
        rt.revoked = True
        db.commit()


# ---------------------------------------------------------------------------
# MFA helpers
# ---------------------------------------------------------------------------

def setup_mfa(user: User) -> tuple[str, str]:
    """Generate a fresh MFA secret and provisioning URI for *user*.

    Does NOT persist the secret -- the caller must save it after the user
    confirms activation via ``activate_mfa``.
    """
    secret = generate_mfa_secret()
    uri = get_mfa_uri(secret, user.email)
    return secret, uri


def activate_mfa(db: Session, user: User, secret: str, code: str) -> None:
    """Verify the TOTP *code* against *secret* and enable MFA on *user*."""
    if not verify_mfa_code(secret, code):
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail="Invalid MFA code",
        )
    user.mfa_secret = secret
    user.mfa_enabled = True
    db.commit()


# ---------------------------------------------------------------------------
# Password change
# ---------------------------------------------------------------------------

def change_password(
    db: Session,
    user: User,
    old_password: str,
    new_password: str,
) -> None:
    """Change the authenticated user's password after verifying the old one."""
    if not verify_password(old_password, user.password_hash):
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail="Current password is incorrect",
        )
    user.password_hash = hash_password(new_password)
    user.must_change_password = False
    db.commit()


# ---------------------------------------------------------------------------
# Profile update
# ---------------------------------------------------------------------------

def update_profile(
    db: Session,
    user: User,
    username: str | None = None,
    email: str | None = None,
    first_name: str | None = None,
    last_name: str | None = None,
    display_name: str | None = None,
) -> User:
    """Update the authenticated user's own profile fields."""
    if username and username != user.username:
        existing = db.query(User).filter(User.username == username, User.id != user.id).first()
        if existing:
            raise HTTPException(
                status_code=status.HTTP_409_CONFLICT,
                detail="Username already taken",
            )
        user.username = username

    if email and email != user.email:
        existing = db.query(User).filter(User.email == email, User.id != user.id).first()
        if existing:
            raise HTTPException(
                status_code=status.HTTP_409_CONFLICT,
                detail="Email already taken",
            )
        user.email = email

    if first_name is not None:
        user.first_name = first_name
    if last_name is not None:
        user.last_name = last_name
    if display_name is not None:
        user.display_name = display_name

    db.commit()
    db.refresh(user)
    return user


# ---------------------------------------------------------------------------
# MFA disable
# ---------------------------------------------------------------------------

def disable_mfa(db: Session, user: User, password: str) -> None:
    """Disable MFA on the user's account after verifying their password."""
    if not verify_password(password, user.password_hash):
        raise HTTPException(
            status_code=status.HTTP_400_BAD_REQUEST,
            detail="Incorrect password",
        )
    user.mfa_secret = None
    user.mfa_enabled = False
    db.commit()