import ipaddress
from types import SimpleNamespace

from fastapi import HTTPException
from sqlalchemy import func, select
from sqlalchemy.exc import IntegrityError
from sqlalchemy.orm import Session

from app.request_context import request_meta
from app.models import Address, AuditLog, Base

MAX_CAPACITY = 2**53 - 1


SYSTEM = SimpleNamespace(username="system")
ANONYMOUS = SimpleNamespace(username="anonymous")
_NOUNS = {
    "organization": ("Организация", "f"), "vrf": ("VRF", "m"), "prefix": ("Префикс", "m"), "address": ("Адрес", "m"),
    "device": ("Устройство", "n"), "device_type": ("Тип устройства", "m"), "isp": ("Оператор", "m"),
}
_VERBS = {
    "created": ("создан", "создана", "создано"), "updated": ("изменён", "изменена", "изменено"),
    "deleted": ("удалён", "удалена", "удалено"), "assigned": ("назначен", "назначена", "назначено"),
}


def make_message(entity_type: str, action: str, label: str, diff: dict | None = None) -> str:
    noun, gender = _NOUNS.get(entity_type, (entity_type, "m"))
    verb = _VERBS.get(action, (action,) * 3)["mfn".index(gender)]
    text = f"{noun} {label} {verb}"
    if action == "updated" and diff:
        text += ": " + ", ".join(diff)
    return text


def actor_of(username: str) -> str:
    """Актор для журнала: служебные — как есть, пользователи UI — с префиксом ui:."""
    return username if username in ("system", "anonymous") else f"ui:{username}"


def audit(db: Session, user, entity_type: str, entity, action: str, label: str, diff: dict | None = None, message: str | None = None):
    ctx = None if user is SYSTEM else request_meta.get()  # системные события (ротация) — без IP, даже если запущены из запроса
    db.add(AuditLog(
        username=user.username, entity_type=entity_type, entity_id=getattr(entity, "id", None),
        entity_label=label, action=action, diff=diff,
        message=message or make_message(entity_type, action, label, diff),
        client_ip=ctx["client_ip"] if ctx else None, meta=ctx["meta"] if ctx else None,
    ))


def commit(db: Session, conflict_msg: str = "Запись с такими значениями уже существует"):
    try:
        db.commit()
    except IntegrityError:
        db.rollback()
        raise HTTPException(409, conflict_msg)


def flush(db: Session, conflict_msg: str = "Запись с такими значениями уже существует"):
    """flush с тем же переводом нарушений уникальности в 409, что и commit."""
    try:
        db.flush()
    except IntegrityError:
        db.rollback()
        raise HTTPException(409, conflict_msg)


def get_or_404(db: Session, model: type[Base], id_: int, what: str = "Объект"):
    obj = db.get(model, id_)
    if obj is None:
        raise HTTPException(404, f"{what} не найден")
    return obj


def capacity(prefix: str) -> int:
    net = ipaddress.ip_network(prefix)
    n = net.num_addresses
    if net.version == 4 and net.prefixlen <= 30:
        n -= 2  # сеть и broadcast
    return min(n, MAX_CAPACITY)


def utilization(used: int, cap: int) -> int:
    return round(used * 100 / cap) if cap else 0


def apply_update(obj, data: dict) -> dict:
    changed = {}
    for k, v in data.items():
        if getattr(obj, k) != v:
            changed[k] = v
            setattr(obj, k, v)
    return changed


def count(db: Session, stmt) -> int:
    return db.scalar(select(func.count()).select_from(stmt.subquery())) or 0


def next_free(db: Session, prefix_id: int, prefix: str) -> str | None:
    net = ipaddress.ip_network(prefix)
    used = {ipaddress.ip_address(a) for a in db.scalars(select(Address.address).where(Address.prefix_id == prefix_id))}
    hosts = net.hosts() if net.version == 4 and net.prefixlen <= 30 else iter(net)
    for ip in hosts:
        if ip not in used:
            return str(ip)
    return None