"""Registration/login/refresh/logout/verify-email/password-reset business
logic.

Kept independent of FastAPI so it's reachable from tests and (later) from
Celery tasks or an admin script without pulling in the HTTP layer.
"""

from __future__ import annotations

import uuid
from datetime import UTC, datetime, timedelta

from sqlalchemy.ext.asyncio import AsyncSession

from app.core.config import Settings
from app.core.errors import (
    AuthenticationError,
    ConflictError,
    NotFoundError,
    ThrottledError,
    ValidationAppError,
)
from app.core.security import (
    InvalidTokenError,
    TokenType,
    create_access_token,
    create_refresh_token,
    decode_token,
    generate_email_code,
    hash_email_code,
    hash_password,
    hash_token_identifier,
    verify_password,
)
from app.db.base import ensure_aware_utc
from app.models.enums import EmailCodePurpose, SecurityEventType, ThrottleAction
from app.models.user import LOCAL_DEV_USER_EMAIL, LOCAL_DEV_USER_ID, User
from app.models.user_security_event import UserSecurityEvent
from app.repositories.email_code_repository import EmailCodeRepository
from app.repositories.password_history_repository import PasswordHistoryRepository
from app.repositories.refresh_token_repository import RefreshTokenRepository
from app.repositories.user_known_ip_repository import UserKnownIpRepository
from app.repositories.user_repository import UserRepository
from app.repositories.user_security_event_repository import UserSecurityEventRepository
from app.schemas.auth import (
    ChangePasswordRequest,
    ConfirmPasswordResetRequest,
    LoginRequest,
    RegisterRequest,
    RequestPasswordResetRequest,
    ResendVerificationRequest,
    TokenResponse,
    VerifyEmailRequest,
)
from app.services import ip_throttle_service, security_email_service

EMAIL_CODE_VALID_HOURS = 36

# The local-dev bypass (AUTH_MODE=local + loopback, see
# app/auth/dependencies.py) has no real login step - get_or_create_local_user
# runs on every authenticated request. Logging a login_success event on every
# single request would flood Account activity, so a fresh one is only
# recorded once per this cooldown window, treated as a proxy for "a new
# session" rather than every request within one.
LOCAL_DEV_LOGIN_LOG_COOLDOWN_MINUTES = 30


async def get_or_create_local_user(db: AsyncSession, client_ip: str) -> User:
    repo = UserRepository(db)
    user = await repo.get_by_id(LOCAL_DEV_USER_ID)
    if user is None:
        user = await repo.create(
            email=LOCAL_DEV_USER_EMAIL,
            password_hash=None,
            display_name="Local Developer",
            timezone="America/New_York",
            user_id=LOCAL_DEV_USER_ID,
            is_admin=True,
            email_verified=True,
        )
        await db.commit()

    event_repo = UserSecurityEventRepository(db)
    last_login = await event_repo.most_recent_of_type(user.id, SecurityEventType.LOGIN_SUCCESS)
    cutoff = datetime.now(UTC) - timedelta(minutes=LOCAL_DEV_LOGIN_LOG_COOLDOWN_MINUTES)
    if last_login is None or ensure_aware_utc(last_login.created_at) < cutoff:
        await event_repo.create(
            user_id=user.id, event_type=SecurityEventType.LOGIN_SUCCESS, ip_address=client_ip
        )
        await UserKnownIpRepository(db).record_login(user.id, client_ip, datetime.now(UTC))
        await db.commit()
    return user


async def _issue_and_send_email_code(
    db: AsyncSession, settings: Settings, user: User, purpose: EmailCodePurpose
) -> None:
    code = generate_email_code()
    code_repo = EmailCodeRepository(db)
    # A fresh code must fully supersede every prior unused one for this
    # purpose - otherwise an old code (e.g. still sitting in an earlier
    # email) stays valid until it naturally expires, even after the user
    # explicitly asked for a new one.
    await code_repo.invalidate_unused(user.id, purpose)
    await code_repo.create(
        user_id=user.id,
        purpose=purpose,
        code_hash=hash_email_code(code),
        expires_at=datetime.now(UTC) + timedelta(hours=EMAIL_CODE_VALID_HOURS),
    )
    if purpose == EmailCodePurpose.VERIFY_EMAIL:
        await security_email_service.send_verification_code_email(settings, user.email, code)
    else:
        await security_email_service.send_password_reset_email(settings, user.email, code)


async def register(
    db: AsyncSession, settings: Settings, client_ip: str, payload: RegisterRequest
) -> User:
    if await ip_throttle_service.is_banned(db, client_ip):
        raise ThrottledError("This IP address has been temporarily blocked.")

    repo = UserRepository(db)
    existing = await repo.get_by_email(payload.email)
    if existing is not None:
        raise ConflictError("An account with this email already exists")

    # Bootstraps admin access on a fresh deployment - otherwise the only way
    # to ever get an admin account is direct DB access, which is a real
    # chicken-and-egg problem for anyone self-hosting from a clean clone.
    # Checked by admin *count*, not total user count, so this also
    # self-heals if the last admin ever deletes their own account (Settings
    # -> Delete account) - the next registration becomes admin again rather
    # than leaving the deployment permanently admin-less. A benign race is
    # possible if two people register in the same instant on a brand-new,
    # zero-admin deployment (both could become admin) - acceptable for a
    # bootstrapping check that only ever matters once, before any real
    # traffic exists.
    is_first_admin = await repo.count_admins() == 0

    user = await repo.create(
        email=payload.email,
        password_hash=hash_password(payload.password),
        display_name=payload.display_name,
        timezone=payload.timezone,
        is_admin=is_first_admin,
        # Test suite has no inbox to read a real code from - same
        # app_env == "test" precedent already used to disable rate limiting
        # (app/core/rate_limit.py). The code-generation/sending/throttle
        # path below still runs unconditionally either way, so it's still
        # exercised by every test that registers a user, not skipped.
        email_verified=settings.app_env == "test",
    )
    await _issue_and_send_email_code(db, settings, user, EmailCodePurpose.VERIFY_EMAIL)
    # Deliberately does NOT call ip_throttle_service.record_attempt here -
    # this is per-IP, not per-account (see ip_throttle_service's docstring),
    # so unconditionally charging every new registration against it would
    # let unrelated people sharing an IP (an office, a NAT'd network) drive
    # each other toward a shared ban purely through legitimate signups. The
    # escalation ladder starts from the first *manual* resend click instead
    # (resend_verification endpoint) - "first resend allowed in 30s" is a
    # frontend-only initial cooldown after registration, not a backend-
    # enforced one; the backend ladder governs resend #2 onward.
    await UserSecurityEventRepository(db).create(
        user_id=user.id, event_type=SecurityEventType.EMAIL_VERIFICATION_SENT, ip_address=client_ip
    )
    await db.commit()
    return user


async def verify_email(db: AsyncSession, client_ip: str, payload: VerifyEmailRequest) -> None:
    """Generic failure for both 'no such account' and 'wrong/expired code' -
    never distinguishes the two to the caller. Guessing the code itself is
    IP-throttled the same way a login password guess is - a 6-digit code
    has only 1M possible values, so without this an attacker could
    brute-force it well within its 36-hour validity window."""
    throttle = await ip_throttle_service.peek_throttle(
        db, client_ip, ThrottleAction.VERIFY_EMAIL_CODE
    )
    if not throttle.allowed:
        _raise_throttled(throttle)

    user_repo = UserRepository(db)
    code_repo = EmailCodeRepository(db)
    user = await user_repo.get_by_email(payload.email)
    record = (
        await code_repo.get_latest_valid(
            user.id, EmailCodePurpose.VERIFY_EMAIL, hash_email_code(payload.code)
        )
        if user is not None
        else None
    )
    if record is None:
        await ip_throttle_service.record_attempt(
            db,
            client_ip,
            ThrottleAction.VERIFY_EMAIL_CODE,
            ip_throttle_service.LOGIN_BACKOFF_SECONDS,
        )
        await db.commit()
        raise AuthenticationError("Invalid or expired verification code")

    await code_repo.mark_used(record)
    user.email_verified = True
    await ip_throttle_service.reset_on_success(db, client_ip, ThrottleAction.VERIFY_EMAIL_CODE)
    await UserSecurityEventRepository(db).create(
        user_id=user.id, event_type=SecurityEventType.EMAIL_VERIFIED, ip_address=client_ip
    )
    await db.commit()


async def resend_verification(
    db: AsyncSession, settings: Settings, client_ip: str, payload: ResendVerificationRequest
) -> None:
    throttle = await ip_throttle_service.peek_throttle(
        db, client_ip, ThrottleAction.RESEND_VERIFICATION
    )
    if not throttle.allowed:
        _raise_throttled(throttle)

    user_repo = UserRepository(db)
    user = await user_repo.get_by_email(payload.email)
    # Always record the attempt, whether or not the account exists, so the
    # throttle behavior itself can never leak account existence.
    await ip_throttle_service.record_attempt(
        db,
        client_ip,
        ThrottleAction.RESEND_VERIFICATION,
        ip_throttle_service.RESEND_BACKOFF_SECONDS,
    )
    if user is not None and not user.email_verified:
        await _issue_and_send_email_code(db, settings, user, EmailCodePurpose.VERIFY_EMAIL)
        await UserSecurityEventRepository(db).create(
            user_id=user.id,
            event_type=SecurityEventType.EMAIL_VERIFICATION_SENT,
            ip_address=client_ip,
        )
    await db.commit()


async def request_password_reset(
    db: AsyncSession, settings: Settings, client_ip: str, payload: RequestPasswordResetRequest
) -> None:
    throttle = await ip_throttle_service.peek_throttle(db, client_ip, ThrottleAction.RESEND_RESET)
    if not throttle.allowed:
        _raise_throttled(throttle)

    user_repo = UserRepository(db)
    user = await user_repo.get_by_email(payload.email)
    await ip_throttle_service.record_attempt(
        db, client_ip, ThrottleAction.RESEND_RESET, ip_throttle_service.RESEND_BACKOFF_SECONDS
    )
    if user is not None:
        await _issue_and_send_email_code(db, settings, user, EmailCodePurpose.PASSWORD_RESET)
        await UserSecurityEventRepository(db).create(
            user_id=user.id,
            event_type=SecurityEventType.PASSWORD_RESET_REQUESTED,
            ip_address=client_ip,
        )
    # Always a generic success, regardless of whether the account exists -
    # the classic enumeration-safe pattern.
    await db.commit()


async def confirm_password_reset(
    db: AsyncSession, client_ip: str, payload: ConfirmPasswordResetRequest
) -> None:
    """Same code-guess throttling rationale as verify_email - a reset code
    is just as brute-forceable if left unthrottled."""
    throttle = await ip_throttle_service.peek_throttle(
        db, client_ip, ThrottleAction.CONFIRM_RESET_CODE
    )
    if not throttle.allowed:
        _raise_throttled(throttle)

    user_repo = UserRepository(db)
    code_repo = EmailCodeRepository(db)
    user = await user_repo.get_by_email(payload.email)
    record = (
        await code_repo.get_latest_valid(
            user.id, EmailCodePurpose.PASSWORD_RESET, hash_email_code(payload.code)
        )
        if user is not None
        else None
    )
    if record is None:
        await ip_throttle_service.record_attempt(
            db,
            client_ip,
            ThrottleAction.CONFIRM_RESET_CODE,
            ip_throttle_service.LOGIN_BACKOFF_SECONDS,
        )
        await db.commit()
        raise AuthenticationError("Invalid or expired reset code")

    # Checked before consuming the code, and before recording any throttle
    # attempt, so a rejected-for-reuse password never burns the (correctly
    # entered) code - the user can immediately retry with a different one.
    history_repo = PasswordHistoryRepository(db)
    previous_hashes = await history_repo.list_hashes_for_user(user.id)
    if user.password_hash is not None:
        previous_hashes.append(user.password_hash)
    if any(verify_password(payload.new_password, h) for h in previous_hashes):
        raise ValidationAppError("You've used this password before. Choose a different one.")

    await code_repo.mark_used(record)
    if user.password_hash is not None:
        await history_repo.add(user_id=user.id, password_hash=user.password_hash)
    user.password_hash = hash_password(payload.new_password)
    # This is the documented unlock mechanism - a successful reset always
    # clears any prior lockout, regardless of how it got there.
    user.locked_at = None
    user.failed_login_count = 0

    await ip_throttle_service.reset_on_success(db, client_ip, ThrottleAction.CONFIRM_RESET_CODE)
    await RefreshTokenRepository(db).revoke_all_for_user(user.id)
    await UserSecurityEventRepository(db).create(
        user_id=user.id, event_type=SecurityEventType.PASSWORD_RESET_COMPLETED, ip_address=client_ip
    )
    await db.commit()


def _raise_throttled(throttle: ip_throttle_service.ThrottleResult) -> None:
    if throttle.banned:
        raise ThrottledError("This IP address has been temporarily blocked.")
    raise ThrottledError(
        f"Too many attempts. Try again in {throttle.retry_after_seconds} seconds.",
        retry_after_seconds=throttle.retry_after_seconds,
    )


async def _issue_token_pair(db: AsyncSession, settings: Settings, user: User) -> TokenResponse:
    access_token = create_access_token(user.id, settings)
    refresh_jwt, jti, expires_at = create_refresh_token(user.id, settings)

    token_repo = RefreshTokenRepository(db)
    await token_repo.create(
        user_id=user.id, token_hash=hash_token_identifier(jti), expires_at=expires_at
    )
    await db.commit()

    return TokenResponse(
        access_token=access_token,
        refresh_token=refresh_jwt,
        expires_in_minutes=settings.jwt_access_token_minutes,
    )


# 5 free instant retries, then 5s/15s/30s/60s/2min/5min/15min - the 12th
# failure (index past the end of LOGIN_BACKOFF_SECONDS) is also where the
# account itself locks, in lockstep with the IP throttle's own escalation.
LOGIN_LOCKOUT_THRESHOLD = len(ip_throttle_service.LOGIN_BACKOFF_SECONDS) + 1


async def login(
    db: AsyncSession, settings: Settings, client_ip: str, payload: LoginRequest
) -> TokenResponse:
    # Enforced *before* password verification - a correct password during a
    # penalty window must still be rejected, or the delay is meaningless.
    throttle = await ip_throttle_service.peek_throttle(db, client_ip, ThrottleAction.FAILED_LOGIN)
    if not throttle.allowed:
        _raise_throttled(throttle)

    repo = UserRepository(db)
    user = await repo.get_by_email(payload.email)

    if user is not None and user.locked_at is not None:
        # Generic message either way - never confirms the account exists.
        raise AuthenticationError("Account locked. Reset your password to unlock it.")

    password_ok = (
        user is not None
        and user.password_hash is not None
        and verify_password(payload.password, user.password_hash)
    )

    if not password_ok:
        await ip_throttle_service.record_attempt(
            db, client_ip, ThrottleAction.FAILED_LOGIN, ip_throttle_service.LOGIN_BACKOFF_SECONDS
        )
        if user is not None:
            user.failed_login_count += 1
            await UserSecurityEventRepository(db).create(
                user_id=user.id, event_type=SecurityEventType.LOGIN_FAILED, ip_address=client_ip
            )
            if user.failed_login_count >= LOGIN_LOCKOUT_THRESHOLD:
                user.locked_at = datetime.now(UTC)
                await UserSecurityEventRepository(db).create(
                    user_id=user.id,
                    event_type=SecurityEventType.ACCOUNT_LOCKED,
                    ip_address=client_ip,
                )
                await security_email_service.send_account_locked_email(settings, user.email)
        await db.commit()
        raise AuthenticationError("Invalid email or password")

    assert user is not None  # password_ok implies this
    if not user.is_active:
        raise AuthenticationError("This account has been deactivated")
    if not user.email_verified:
        raise AuthenticationError("Verify your email before signing in.")

    user.failed_login_count = 0
    await ip_throttle_service.reset_on_success(db, client_ip, ThrottleAction.FAILED_LOGIN)
    await UserSecurityEventRepository(db).create(
        user_id=user.id, event_type=SecurityEventType.LOGIN_SUCCESS, ip_address=client_ip
    )
    await UserKnownIpRepository(db).record_login(user.id, client_ip, datetime.now(UTC))
    return await _issue_token_pair(db, settings, user)


async def refresh(db: AsyncSession, settings: Settings, raw_refresh_token: str) -> TokenResponse:
    try:
        decoded = decode_token(raw_refresh_token, settings, TokenType.REFRESH)
    except InvalidTokenError as exc:
        raise AuthenticationError("Invalid or expired refresh token") from exc

    token_repo = RefreshTokenRepository(db)
    stored = await token_repo.get_valid_by_hash(hash_token_identifier(decoded.jti))
    if stored is None:
        raise AuthenticationError("Invalid or expired refresh token")

    user_repo = UserRepository(db)
    user = await user_repo.get_by_id(decoded.user_id)
    if user is None or not user.is_active:
        raise AuthenticationError("Invalid or expired refresh token")

    # Rotate: revoke the token just used before issuing a new pair.
    await token_repo.revoke(stored)
    return await _issue_token_pair(db, settings, user)


async def logout(db: AsyncSession, settings: Settings, raw_refresh_token: str) -> None:
    try:
        decoded = decode_token(raw_refresh_token, settings, TokenType.REFRESH)
    except InvalidTokenError:
        return  # Already unusable; logout is idempotent.

    token_repo = RefreshTokenRepository(db)
    stored = await token_repo.get_valid_by_hash(hash_token_identifier(decoded.jti))
    if stored is not None:
        await token_repo.revoke(stored)
    await db.commit()


async def list_security_events(db: AsyncSession, user_id: uuid.UUID) -> list[UserSecurityEvent]:
    """The calling user's own security activity - the user-facing
    counterpart to the admin-only app-wide log feed (core/logging.py)."""
    return await UserSecurityEventRepository(db).list_for_user(user_id)


async def delete_account(db: AsyncSession, user: User, password: str) -> None:
    """Permanently deletes the account and, via ON DELETE CASCADE foreign
    keys (see migrations), everything it owns - companies and everything
    under them, refresh tokens, security events, API keys, etc. There is no
    soft-delete or recovery path. Rejected for accounts with no
    password_hash (the fixed AUTH_MODE=local user) - there's nothing to
    verify the caller's identity against."""
    if user.password_hash is None:
        raise ValidationAppError("Account deletion isn't available for this account.")
    if not verify_password(password, user.password_hash):
        raise AuthenticationError("Incorrect password")
    await UserRepository(db).delete(user)
    await db.commit()


async def change_password(
    db: AsyncSession,
    settings: Settings,
    client_ip: str,
    user: User,
    payload: ChangePasswordRequest,
) -> TokenResponse:
    """Authenticated in-app password change - distinct from
    confirm_password_reset (which is the emailed-code flow for someone who
    can't log in at all). Also the only way to clear must_change_password,
    the admin-forced-reset flag (see require_password_change below)."""
    if user.password_hash is None:
        raise ValidationAppError("This account doesn't use password sign-in.")
    if not verify_password(payload.current_password, user.password_hash):
        raise AuthenticationError("Incorrect current password")

    history_repo = PasswordHistoryRepository(db)
    previous_hashes = await history_repo.list_hashes_for_user(user.id)
    previous_hashes.append(user.password_hash)
    if any(verify_password(payload.new_password, h) for h in previous_hashes):
        raise ValidationAppError("You've used this password before. Choose a different one.")

    await history_repo.add(user_id=user.id, password_hash=user.password_hash)
    user.password_hash = hash_password(payload.new_password)
    user.must_change_password = False

    # Rotate every session, including the one making this request - the
    # fresh token pair returned below replaces it immediately, so the
    # caller keeps working without a forced re-login.
    await RefreshTokenRepository(db).revoke_all_for_user(user.id)
    await UserSecurityEventRepository(db).create(
        user_id=user.id, event_type=SecurityEventType.PASSWORD_CHANGED, ip_address=client_ip
    )
    return await _issue_token_pair(db, settings, user)


async def require_password_change(db: AsyncSession, client_ip: str, email: str) -> User:
    """Admin action: flags an account so its next request is blocked
    everywhere except /auth/me, /auth/change-password, and /auth/logout
    (enforced in app.auth.dependencies.get_current_user) until they set a
    new password. Meant for handing a demo account to someone with a known
    sample password."""
    user = await UserRepository(db).get_by_email(email)
    if user is None:
        raise NotFoundError("No account with that email")
    if user.password_hash is None:
        raise ValidationAppError("This account doesn't use password sign-in.")
    user.must_change_password = True
    await UserSecurityEventRepository(db).create(
        user_id=user.id,
        event_type=SecurityEventType.PASSWORD_CHANGE_REQUIRED,
        ip_address=client_ip,
    )
    await db.commit()
    return user