"""Blocking policy.

The backend decides *whether* blocking should be on right now and *what* is on
the list; the desktop app is the thing that actually enforces it (it is the only
piece running on your machine with the privileges to rewrite `/etc/hosts` or
kill a process). Keeping the policy here means the web UI can edit the rules,
and a second machine running the desktop app obeys the same list.
"""

from __future__ import annotations

import re
from dataclasses import dataclass, field
from datetime import date, datetime
from fnmatch import fnmatch
from typing import Any

from sqlalchemy import func, select
from sqlalchemy.orm import Session

from app.models import BlockEvent
from app.services import pomodoro
from app.settings_schema import AppSettings
from app.timeutil import ensure_utc, in_window, local_date, local_time

# One label of a hostname: what may legally sit in front of `.example.com`.
_LABEL_RE = re.compile(r"^[a-z0-9]([a-z0-9-]{0,61}[a-z0-9])?$")


@dataclass(frozen=True)
class Expansion:
    """What `subdomain_expansions` asked for, split three ways.

    * `labels` — real DNS labels, usable as hostnames (`web`, `m`).
    * `wildcard` — a bare `*` was in the list, meaning *every* subdomain. That is
      the entry people type when they mean "all of them", and it is now supported
      rather than refused: a hosts file still cannot express it (that is what
      [expand_entry] reports as unexpandable), but the desktop app routes the
      suffix through a local resolver stub and the phone matches the mask in the
      URL bar, so it works on both.
    * `rejected` — anything that is neither a label nor `*` (`not a label`, `..`),
      reported so the UI can say why it was ignored.
    """

    labels: list[str] = field(default_factory=list)
    wildcard: bool = False
    rejected: list[str] = field(default_factory=list)


def parse_expansions(raw: list[str]) -> Expansion:
    """Split `subdomain_expansions` into labels, the `*` flag, and rejects.

    The trap this replaced is worth stating plainly: `*` used to slip through as a
    subdomain label, so `*.telegram.org` expanded to the literal `*.telegram.org` —
    not a hostname, which the desktop app's own filter dropped without a word. The
    mask looked configured, `unexpandable` stayed empty, and `web.telegram.org` was
    never blocked. Silent, and exactly the shape of "the blocker does not work".
    """
    labels: list[str] = []
    rejected: list[str] = []
    wildcard = False
    for entry in raw:
        label = entry.strip().lower()
        if not label:
            continue
        if label == "*":
            wildcard = True
            continue
        if _LABEL_RE.match(label):
            if label not in labels:
                labels.append(label)
        elif label not in rejected:
            rejected.append(label)
    return Expansion(labels=labels, wildcard=wildcard, rejected=rejected)


#: What makes an entry a mask rather than a name, `fnmatch`'s own metacharacters.
_WILDCARDS = "*?["


def is_mask(entry: str) -> bool:
    return any(char in entry for char in _WILDCARDS)


def is_allowed(host: str, allow_masks: list[str]) -> bool:
    """Whether an allow-list entry (plain or masked) covers this hostname.

    A plain entry covers itself *and its subdomains*, which is the same rule a
    plain entry follows on the block side — `youtube.com` blocked catches
    `music.youtube.com`. It did not used to: an exception was glob-matched, so a
    plain one meant exactly one hostname while a plain block meant a subtree, and
    the two halves of one list read the same and behaved differently.

    A masked entry is glob-matched as it always was, so `docs.*` and
    `*.docs.google.com` are unchanged — and still the way to allow something
    *narrower* than a subtree.
    """
    for mask in allow_masks:
        if is_mask(mask):
            if fnmatch(host, mask):
                return True
        elif host == mask or host.endswith(f".{mask}"):
            return True
    return False


def expand_entry(raw: str, expansion: Expansion) -> tuple[list[str], str | None]:
    """Turn one blocklist entry into concrete hostnames.

    A hosts file has no wildcards, so a mask has to be expanded into real names:

    * `youtube.com`    → `youtube.com`, `www.youtube.com`, `m.youtube.com`
    * `*.youtube.com`  → the bare domain plus every configured subdomain
    * `*gram*`         → nothing expandable; returned as a leftover pattern so the
                         clients that *can* match masks (the phone's URL bar, and
                         the desktop's resolver stub) know to enforce it

    With `*` in `subdomain_expansions`, `*.youtube.com` means *every* subdomain.
    The concrete names are still expanded — they block without any resolver help —
    and the pattern comes back alongside them for the stub to catch the rest.

    Returns `(hostnames, unexpandable_pattern)`.
    """
    entry = raw.strip().lower().lstrip(".")
    if not entry:
        return [], None

    if entry.startswith("*."):
        base = entry[2:]
        if not base or "*" in base:
            return [], entry
        hosts = [base, *[f"{label}.{base}" for label in expansion.labels]]
        return hosts, (entry if expansion.wildcard else None)

    if "*" in entry:
        return [], entry

    return [entry, f"www.{entry}", f"m.{entry}"], None


def expand_domains(settings: AppSettings) -> list[str]:
    """Every hostname the desktop app should point at the redirect IP.

    `youtube.com` means "that site", so `www.` and `m.` come along; masks are
    expanded as described above; and anything the allow list covers — itself
    maskable — is taken back out, which is how `*.google.com` blocked plus
    `*.docs.google.com` allowed works.
    """
    blocker = settings.blocker
    allow_masks = [
        entry.strip().lower().lstrip(".") for entry in blocker.allowed_domains if entry.strip()
    ]
    expansion = parse_expansions(blocker.subdomain_expansions)

    hosts: list[str] = []
    for raw in blocker.blocked_domains:
        expanded, _ = expand_entry(raw, expansion)
        for host in expanded:
            if host not in hosts and not is_allowed(host, allow_masks):
                hosts.append(host)
    return hosts


def unexpandable_masks(settings: AppSettings) -> list[str]:
    """Blocklist entries a hosts file cannot express.

    These are what the desktop app's local resolver stub is handed: patterns with
    a domain anchor (`*.youtube.com`, `*gram.com`) it can answer at DNS level, and
    `*gram*`-style patterns it has to report as unenforceable on this machine
    because no zone can be routed for them.
    """
    expansion = parse_expansions(settings.blocker.subdomain_expansions)
    leftovers: list[str] = []
    for raw in settings.blocker.blocked_domains:
        _, pattern = expand_entry(raw, expansion)
        if pattern and pattern not in leftovers:
            leftovers.append(pattern)
    return leftovers


def schedule_active(settings: AppSettings, moment: datetime | None = None) -> bool:
    now_time = local_time(settings.timezone, moment)
    weekday = (moment or datetime.now()).weekday()
    for window in settings.blocker.schedule:
        if weekday in window.days and in_window(now_time, window.start, window.end):
            return True
    return False


def policy(session: Session, settings: AppSettings) -> dict[str, Any]:
    """What the desktop app polls: should I block, and what."""
    blocker = settings.blocker
    current = pomodoro.current_session(session)
    active = False
    reason = "disabled"

    if blocker.enabled:
        if blocker.mode == "always":
            active, reason = True, "always on"
        elif blocker.mode == "scheduled":
            active = schedule_active(settings)
            reason = "inside a blocking window" if active else "outside every window"
        else:  # during_work
            if current is not None and current.kind == "work" and current.status in ("running", "paused"):
                active, reason = True, "a work interval is running"
            elif (
                current is not None
                and current.kind != "work"
                and blocker.block_during_breaks
                and current.status in ("running", "paused")
            ):
                active, reason = True, "blocking stays on through breaks"
            else:
                reason = "no work interval is running"

    return {
        "active": active,
        "reason": reason,
        "mode": blocker.mode,
        "enabled": blocker.enabled,
        "strict": blocker.strict,
        "redirect_ip": blocker.redirect_ip,
        "domains": expand_domains(settings) if active else [],
        "apps": [app.strip() for app in blocker.blocked_apps if app.strip()] if active else [],
        "unexpandable": unexpandable_masks(settings),
        "invalid_expansions": parse_expansions(blocker.subdomain_expansions).rejected,
        "allowed": [
            entry.strip().lower().lstrip(".")
            for entry in blocker.allowed_domains
            if entry.strip()
        ],
        "kill_apps": blocker.kill_blocked_apps,
        "notify_on_block": blocker.notify_on_block,
        "poll_seconds": blocker.app_poll_seconds,
        "session_id": current.id if current else None,
        "all_domains": expand_domains(settings),
        "all_apps": [app.strip() for app in blocker.blocked_apps if app.strip()],
    }


def record_event(
    session: Session,
    settings: AppSettings,
    *,
    kind: str,
    target: str,
    action: str = "blocked",
    details: str | None = None,
) -> BlockEvent:
    current = pomodoro.current_session(session)
    event = BlockEvent(
        kind=kind,
        target=target.strip().lower(),
        action=action,
        details=details,
        local_date=local_date(settings.timezone),
        session_id=current.id if current else None,
    )
    session.add(event)
    session.commit()
    return event


def events_for_day(session: Session, settings: AppSettings, day: date | None = None) -> dict[str, Any]:
    day = day or local_date(settings.timezone)
    rows = list(session.scalars(select(BlockEvent).where(BlockEvent.local_date == day)))
    by_target = dict(
        session.execute(
            select(BlockEvent.target, func.count(BlockEvent.id))
            .where(BlockEvent.local_date == day)
            .group_by(BlockEvent.target)
            .order_by(func.count(BlockEvent.id).desc())
        ).all()
    )
    return {
        "date": day.isoformat(),
        "total": len(rows),
        "by_target": [{"target": target, "count": count} for target, count in by_target.items()],
        "events": [
            {
                "id": row.id,
                "kind": row.kind,
                "target": row.target,
                "action": row.action,
                "at": ensure_utc(row.at).isoformat(),
                "details": row.details,
            }
            for row in sorted(rows, key=lambda row: ensure_utc(row.at), reverse=True)[:100]
        ],
    }


DEFAULT_DOMAINS = [
    "*.youtube.com",
    "twitter.com",
    "x.com",
    "*.instagram.com",
    "tiktok.com",
    "reddit.com",
    "facebook.com",
    "vk.com",
    "twitch.tv",
    "netflix.com",
    "9gag.com",
    "pikabu.ru",
]

DEFAULT_APPS = ["steam*", "discord", "telegram-desktop", "spotify"]