from __future__ import annotations

import base64
import hashlib
import hmac
import secrets
import time
from collections.abc import Mapping
from dataclasses import dataclass
from datetime import UTC, datetime
from ipaddress import ip_address, ip_network

from fastapi import HTTPException, Request

from .settings import DdnsSettings

DASHBOARD_UNLOCK_COOKIE = "ddns_dashboard_unlock"
DASHBOARD_UNLOCK_DEFAULT_SECONDS = 24 * 60 * 60
DASHBOARD_UNLOCK_STAY_SIGNED_IN_SECONDS = 30 * 24 * 60 * 60
BEARER_SECRET_PREFIX = "karl_"
PRIVATE_PROXY_NETWORKS = tuple(
    ip_network(network)
    for network in (
        "10.0.0.0/8",
        "172.16.0.0/12",
        "192.168.0.0/16",
        "127.0.0.0/8",
        "169.254.0.0/16",
        "::1/128",
        "fc00::/7",
        "fe80::/10",
    )
)


@dataclass(frozen=True, slots=True)
class _DashboardUnlockCookieParts:
    timestamp: int
    max_age_seconds: int
    signature: str


@dataclass(frozen=True, slots=True)
class DashboardUnlockIdentity:
    hostname: str
    management_slug: str
    password_hash: str

    def payload(self, timestamp: int, max_age_seconds: int) -> bytes:
        return f"{self.hostname}\0{self.management_slug}\0{self.password_hash}\0{timestamp}\0{max_age_seconds}".encode()


def credentials_from_basic_auth(header: str) -> tuple[str | None, str | None]:
    try:
        raw = base64.b64decode(header.split(" ", 1)[1]).decode("utf-8")
    except Exception:
        return None, None
    if ":" not in raw:
        return None, None
    username, password = raw.split(":", 1)
    return username, password


def hash_secret(token: str) -> str:
    salt = secrets.token_hex(16)
    digest = hashlib.pbkdf2_hmac("sha256", token.encode("utf-8"), salt.encode("ascii"), 200_000)
    return f"pbkdf2_sha256${salt}${digest.hex()}"


def verify_secret(token: str, stored: str) -> bool:
    try:
        algorithm, salt, expected = stored.split("$", 2)
    except ValueError:
        return False
    if algorithm != "pbkdf2_sha256":
        return False
    digest = hashlib.pbkdf2_hmac("sha256", token.encode("utf-8"), salt.encode("ascii"), 200_000)
    return hmac.compare_digest(digest.hex(), expected)


def hash_lookup_token(token: str) -> str:
    return hashlib.sha256(token.encode("utf-8")).hexdigest()


def new_bearer_secret() -> str:
    return f"{BEARER_SECRET_PREFIX}{secrets.token_urlsafe(32)}"


def sign_dashboard_unlock_cookie(
    identity: DashboardUnlockIdentity,
    signing_secret: str,
    max_age_seconds: int,
    now: int | None = None,
) -> str:
    timestamp = int(time.time() if now is None else now)
    bounded_max_age = _bounded_dashboard_unlock_seconds(max_age_seconds)
    signature = _dashboard_unlock_signature(
        identity,
        signing_secret,
        timestamp,
        bounded_max_age,
    )
    return f"v3:{timestamp}:{bounded_max_age}:{signature}"


def verify_dashboard_unlock_cookie(
    hostname: str,
    management_slug: str,
    password_hash: str | None,
    signing_secret: str,
    cookie_value: str | None,
) -> bool:
    identity = _dashboard_unlock_identity(hostname, management_slug, password_hash)
    parts = _active_dashboard_unlock_cookie_parts(cookie_value)
    if identity is None or not signing_secret or parts is None:
        return False
    expected = _dashboard_unlock_signature(
        identity,
        signing_secret,
        parts.timestamp,
        parts.max_age_seconds,
    )
    return hmac.compare_digest(parts.signature, expected)


def _dashboard_unlock_identity(
    hostname: str,
    management_slug: str,
    password_hash: str | None,
) -> DashboardUnlockIdentity | None:
    if not password_hash:
        return None
    return DashboardUnlockIdentity(hostname, management_slug, password_hash)


def _active_dashboard_unlock_cookie_parts(cookie_value: str | None) -> _DashboardUnlockCookieParts | None:
    if cookie_value is None:
        return None
    parts = _dashboard_unlock_cookie_parts(cookie_value)
    if parts is None:
        return None
    if _dashboard_unlock_cookie_expired(parts, int(time.time())):
        return None
    return parts


def _dashboard_unlock_cookie_parts(cookie_value: str) -> _DashboardUnlockCookieParts | None:
    try:
        version, raw_timestamp, raw_max_age, signature = cookie_value.split(":", 3)
        timestamp = int(raw_timestamp)
        max_age_seconds = _bounded_dashboard_unlock_seconds(int(raw_max_age))
    except ValueError:
        return None
    if version != "v3":
        return None
    return _DashboardUnlockCookieParts(timestamp, max_age_seconds, signature)


def _dashboard_unlock_cookie_expired(parts: _DashboardUnlockCookieParts, now: int) -> bool:
    return parts.timestamp > now + 60 or now - parts.timestamp > parts.max_age_seconds


def _dashboard_unlock_signature(
    identity: DashboardUnlockIdentity,
    signing_secret: str,
    timestamp: int,
    max_age_seconds: int,
) -> str:
    return hmac.new(signing_secret.encode(), identity.payload(timestamp, max_age_seconds), hashlib.sha256).hexdigest()


def dashboard_cookie_signing_secret(settings: DdnsSettings) -> str:
    return settings.dashboard_cookie_secret or settings.admin_password


def dashboard_csrf_token(management_slug: str, account: Mapping[str, object]) -> str:
    hostname = str(account["hostname"])
    password_hash = str(account.get("dashboard_password_hash") or "")
    day = datetime.now(UTC).strftime("%Y-%m-%d")
    key = f"{management_slug}\0{password_hash}".encode()
    return hmac.new(key, f"dashboard:{hostname}:{day}".encode(), hashlib.sha256).hexdigest()


def require_dashboard_csrf(management_slug: str, account: Mapping[str, object], supplied: str) -> None:
    if not supplied or not hmac.compare_digest(supplied, dashboard_csrf_token(management_slug, account)):
        raise HTTPException(status_code=403, detail="invalid csrf token")


def _bounded_dashboard_unlock_seconds(max_age_seconds: int) -> int:
    return max(60, min(max_age_seconds, DASHBOARD_UNLOCK_STAY_SIGNED_IN_SECONDS))


def admin_csrf_token(settings: DdnsSettings) -> str:
    day = datetime.now(UTC).strftime("%Y-%m-%d")
    return hmac.new(settings.admin_password.encode("utf-8"), f"admin:{day}".encode(), hashlib.sha256).hexdigest()


def require_admin_csrf(settings: DdnsSettings, supplied: str) -> None:
    if not supplied or not hmac.compare_digest(supplied, admin_csrf_token(settings)):
        raise HTTPException(status_code=403, detail="invalid csrf token")


def client_ip(request: Request, settings: DdnsSettings | None = None) -> str:
    peer = request.client.host if request.client else "unknown"
    if _should_trust_proxy_headers(peer, settings):
        forwarded_ip = _client_ip_from_headers(request)
        if forwarded_ip:
            return forwarded_ip
    return peer


def is_rate_limited_path(path: str) -> bool:
    return path == "/" or path.startswith(("/m/", "/api/v1/hostnames", "/api/v1/router/"))


def rate_limit_bucket(path: str) -> str:
    for prefix in ("/m/", "/api/v1/hostnames", "/api/v1/router/"):
        if path.startswith(prefix):
            return prefix.rstrip("/")
    return path


def _trusted_proxy(peer: str, trusted: set[str]) -> bool:
    if not trusted:
        return False
    return any(_trusted_proxy_candidate(peer, candidate) for candidate in trusted)


def _trusted_proxy_candidate(peer: str, candidate: str) -> bool:
    try:
        peer_ip = ip_address(peer)
    except ValueError:
        return False
    try:
        if "/" in candidate:
            return peer_ip in ip_network(candidate, strict=False)
        return peer_ip == ip_address(candidate)
    except ValueError:
        return False


def _should_trust_proxy_headers(peer: str, settings: DdnsSettings | None) -> bool:
    if settings and _trusted_proxy(peer, settings.trusted_proxy_ips):
        return True
    if settings and settings.trust_private_proxy_headers:
        return _private_proxy_peer(peer)
    return False


def _private_proxy_peer(peer: str) -> bool:
    try:
        peer_ip = ip_address(peer)
    except ValueError:
        return False
    return any(peer_ip in network for network in PRIVATE_PROXY_NETWORKS)


def _client_ip_from_headers(request: Request) -> str | None:
    for header_name in ("cf-connecting-ip", "true-client-ip", "x-real-ip"):
        candidate = _valid_header_ip(request.headers.get(header_name, ""))
        if candidate:
            return candidate
    for candidate in request.headers.get("x-forwarded-for", "").split(","):
        parsed = _valid_header_ip(candidate)
        if parsed:
            return parsed
    return _client_ip_from_forwarded(request.headers.get("forwarded", ""))


def _client_ip_from_forwarded(value: str) -> str | None:
    for forwarded_pair in value.split(";"):
        key, separator, candidate = forwarded_pair.strip().partition("=")
        if separator and key.lower() == "for":
            parsed = _valid_header_ip(candidate)
            if parsed:
                return parsed
    return None


def _valid_header_ip(value: str) -> str | None:
    cleaned = _strip_header_ip(value)
    if not cleaned:
        return None
    try:
        return str(ip_address(cleaned))
    except ValueError:
        return None


def _strip_header_ip(value: str) -> str:
    cleaned = _strip_header_ip_quotes(value)
    if _empty_header_ip(cleaned):
        return ""
    return _strip_bracketed_ip(cleaned) or _strip_host_port(cleaned) or cleaned


def _strip_header_ip_quotes(value: str) -> str:
    return value.strip().strip('"').strip("'")


def _empty_header_ip(value: str) -> bool:
    return not value or value.lower() == "unknown"


def _strip_bracketed_ip(value: str) -> str:
    if value.startswith("[") and "]" in value:
        return value[1 : value.index("]")]
    return ""


def _strip_host_port(value: str) -> str:
    if value.count(":") != 1:
        return ""
    host, port = value.rsplit(":", 1)
    return host if port.isdigit() else ""