"""Password change for the signed-in user (FR-5, FR-6, FR-7; AD-3, AD-4, AD-8).

The order is fixed: throttle check, policy read, verification of the current password, local
hints, then the directory change, the ended sessions, the audit entry and the queued mail in
one transaction. Passwords live only in local variables here: they are never logged, audited,
stored or put into an exception.
"""

from __future__ import annotations

import logging
import math
from dataclasses import dataclass
from datetime import timedelta
from zoneinfo import ZoneInfo

from django.conf import settings
from django.db import transaction
from django.utils import timezone
from django.utils.translation import gettext as _
from django.utils.translation import ngettext

from portal.accounts import throttle
from portal.accounts.sessions import SessionUser, end_sessions
from portal.adapters.directory import DirectoryUnavailable, PasswordPolicy, PasswordRejected
from portal.adapters.registry import get_directory
from portal.audit import services as audit
from portal.mailer import services as mailer

logger = logging.getLogger(__name__)

ENDPOINT = "password-change"
CHARACTER_GROUPS_REQUIRED = 3  # AD complexity: three of upper, lower, digit, other


class WrongCurrentPassword(Exception):
    def __init__(self, policy: PasswordPolicy | None = None) -> None:
        self.policy = policy
        super().__init__("The current password is not correct")


class PasswordNotAccepted(Exception):
    """The new password breaks a rule. `reasons` holds keys for rules the portal could name."""

    def __init__(self, reasons: list[str], policy: PasswordPolicy | None = None) -> None:
        self.reasons = reasons
        self.policy = policy
        super().__init__("The new password is not accepted")


class OutcomeUnknown(Exception):
    """The directory accepted the new password but the portal could not finish its own part."""


@dataclass(frozen=True)
class Changed:
    mail_queued: bool
    other_sessions_ended: int


# -- the rules, in words ----------------------------------------------------------------------


def describe_policy(policy: PasswordPolicy) -> list[str]:
    """The user's password rules as sentences in the active language."""
    rules = []
    if policy.min_length:
        rules.append(
            ngettext(
                "At least %(n)s character",
                "At least %(n)s characters",
                policy.min_length,
            )
            % {"n": policy.min_length}
        )
    if policy.complexity:
        rules.append(
            _(
                "Characters from at least three of these groups: upper case letters, "
                "lower case letters, digits and special characters"
            )
        )
        rules.append(_("No part of your user name or display name"))
    if policy.history_length:
        rules.append(
            ngettext(
                "Not your last %(n)s password",
                "Not one of your last %(n)s passwords",
                policy.history_length,
            )
            % {"n": policy.history_length}
        )
    if policy.min_age:
        rules.append(_min_age_rule(policy.min_age))
    if policy.max_age:
        days = max(1, round(policy.max_age.total_seconds() / 86400))
        rules.append(
            ngettext(
                "A password is valid for %(n)s day",
                "A password is valid for %(n)s days",
                days,
            )
            % {"n": days}
        )
    return rules


def _min_age_rule(age: timedelta) -> str:
    if age >= timedelta(days=1):
        days = math.ceil(age.total_seconds() / 86400)  # round up: too early is refused
        return ngettext(
            "A new password can be changed again after %(n)s day",
            "A new password can be changed again after %(n)s days",
            days,
        ) % {"n": days}
    hours = max(1, math.ceil(age.total_seconds() / 3600))
    return ngettext(
        "A new password can be changed again after %(n)s hour",
        "A new password can be changed again after %(n)s hours",
        hours,
    ) % {"n": hours}


def _character_groups(password: str) -> int:
    groups = set()
    for char in password:
        if char.isupper():
            groups.add("upper")
        elif char.islower():
            groups.add("lower")
        elif char.isdigit():
            groups.add("digit")
        else:
            groups.add("other")
    return len(groups)


def local_hints(new: str, policy: PasswordPolicy) -> list[str]:
    """Rule keys the portal can check itself; the directory stays the authority.

    Nothing is claimed when a fine-grained policy applies but could not be read: the domain
    values may be stricter or looser than the rules that really apply.
    """
    if policy.fine_grained and not policy.fine_grained_readable:
        return []
    reasons = []
    if len(new) < policy.min_length:
        reasons.append("too_short")
    if policy.complexity and _character_groups(new) < CHARACTER_GROUPS_REQUIRED:
        reasons.append("too_few_groups")
    return reasons


# -- the limit -----------------------------------------


def failure_limit(policy: PasswordPolicy) -> int:
    """Wrong current passwords allowed: below the directory's lockout threshold (FR-6)."""
    threshold = policy.lockout_threshold
    if threshold <= 0:
        return throttle.THROTTLE_MAX_FAILURES
    return max(1, min(throttle.THROTTLE_MAX_FAILURES, threshold - 1))


def pause_seconds(policy: PasswordPolicy) -> int:
    window = int(policy.lockout_window.total_seconds()) if policy.lockout_window else 0
    return max(throttle.THROTTLE_PAUSE_SECONDS, window)


# -- the change -----------------------------------------


def _threshold_note(policy: PasswordPolicy | None) -> dict:
    """Audit note for a lockout threshold of 1, which the portal cannot protect against."""
    if policy is not None and policy.lockout_threshold == 1:
        return {"lockout_protection": "none"}
    return {}


def _record_failure(user: SessionUser, ip: str, reason: str, **detail) -> None:
    audit.record_failure(
        user.key, "password.change_failed", ip=ip, detail={"reason": reason, **detail}
    )


def change_password(
    user: SessionUser, current: str, new: str, *, ip: str, session_key: str | None
) -> Changed:
    """Change the signed-in user's password.

    Raises Throttled, WrongCurrentPassword, PasswordNotAccepted, DirectoryUnavailable or
    OutcomeUnknown. Must be called outside an open transaction.
    """
    try:
        throttle.check(ENDPOINT, user=user.key, ip=ip or None)
    except throttle.Throttled:
        audit.record_failure(user.key, "password.throttled", ip=ip)
        raise

    directory = get_directory()
    try:
        policy = directory.password_policy(user.sam)
        if not directory.verify_password(user.sam, current):
            throttle.hit(
                ENDPOINT,
                user=user.key,
                ip=ip or None,
                max_failures=failure_limit(policy),
                pause_seconds=pause_seconds(policy),
            )
            _record_failure(user, ip, "wrong_current", **_threshold_note(policy))
            raise WrongCurrentPassword(policy)
        account = directory.find_user(user.sam)
    except DirectoryUnavailable:
        _record_failure(user, ip, "unavailable")
        raise

    reasons = local_hints(new, policy)
    if reasons:
        _record_failure(user, ip, "policy", rules=reasons)
        raise PasswordNotAccepted(reasons, policy)

    changed_in_directory = False
    step = "directory"
    try:
        with transaction.atomic():
            directory.change_password(user.sam, current, new)
            changed_in_directory = True
            step = "end_sessions"
            ended = end_sessions(user, except_session_key=session_key)
            step = "queue_mail"
            mail_queued = _queue_mail(account)
            step = "audit"
            audit.record(
                user.key,
                "password.changed",
                ip=ip,
                detail={
                    "other_sessions_ended": ended,
                    "mail": "queued" if mail_queued else "skipped",
                    **_threshold_note(policy),
                },
            )
    except PasswordRejected as exc:
        if exc.reason == "wrong_current":  # the password changed between the check and the change
            throttle.hit(
                ENDPOINT,
                user=user.key,
                ip=ip or None,
                max_failures=failure_limit(policy),
                pause_seconds=pause_seconds(policy),
            )
            _record_failure(user, ip, "wrong_current", **_threshold_note(policy))
            raise WrongCurrentPassword(policy) from exc
        _record_failure(user, ip, "policy")
        raise PasswordNotAccepted([], policy) from exc
    except DirectoryUnavailable:
        _record_failure(user, ip, "unavailable")
        raise
    except Exception as exc:
        if changed_in_directory:
            # AD-4: the directory changed but the portal's part did not commit.
            _after_unclear_outcome(user, ip, session_key, step, exc)
            raise OutcomeUnknown("The password was changed but not recorded") from exc
        raise

    throttle.reset(ENDPOINT, user=user.key)
    return Changed(mail_queued=mail_queued, other_sessions_ended=ended)


def _after_unclear_outcome(
    user: SessionUser, ip: str, session_key: str | None, step: str, exc: Exception
) -> None:
    """The directory has the new password but the portal's part rolled back.

    Log it with the change details (AD-4, never the exception text, which could hold input),
    then do what can still be done: end the other sessions and write a failure entry. The
    database may be the very thing that failed, so each attempt stands alone.
    """
    logger.error(
        "Password changed in the directory but the portal did not record it: "
        "user=%s ip=%s time=%s step=%s error=%s",
        user.key,
        ip,
        timezone.now().isoformat(),
        step,
        type(exc).__name__,
    )
    try:
        end_sessions(user, except_session_key=session_key)
    except Exception:
        logger.error("The other sessions of %s could not be ended", user.key)
    try:
        _record_failure(user, ip, "unclear", step=step)
    except Exception:
        logger.error("The failure entry for %s could not be written", user.key)


def _queue_mail(account) -> bool:
    """Queue the confirmation e-mail inside the caller's transaction; False if there is none."""
    address = (account.mail if account else "") or ""
    if not mailer.is_valid_address(address):
        return False
    name = account.display_name or " ".join(p for p in (account.given_name, account.surname) if p)
    now = timezone.now().astimezone(ZoneInfo(settings.DISPLAY_TIME_ZONE))
    mailer.enqueue(
        "password_changed",
        address,
        {"name": name or account.sam, "changed_at": now, "zone_name": settings.DISPLAY_TIME_ZONE},
    )
    return True