import base64
import os
from datetime import datetime, timezone

import json

from flask import current_app, session
from webauthn import (
    generate_authentication_options,
    generate_registration_options,
    verify_authentication_response,
    verify_registration_response,
)
from webauthn.helpers.parse_authentication_credential_json import (
    parse_authentication_credential_json,
)
from webauthn.helpers.parse_registration_credential_json import (
    parse_registration_credential_json,
)
from webauthn.helpers.structs import (
    AuthenticatorSelectionCriteria,
    PublicKeyCredentialDescriptor,
    ResidentKeyRequirement,
    UserVerificationRequirement,
)

from app import db
from app.models import UserPasskey


def _rp_id():
    return os.getenv("WEBAUTHN_RP_ID", "localhost")


def _rp_name():
    return os.getenv("WEBAUTHN_RP_NAME", "PhotoHost")


def _origin():
    return os.getenv("WEBAUTHN_ORIGIN", "http://localhost:8080")


def _b64url_encode(data):
    return base64.urlsafe_b64encode(data).rstrip(b"=").decode("utf-8")


def _b64url_decode(data):
    padding = "=" * (-len(data) % 4)
    return base64.urlsafe_b64decode(data + padding)


def registration_options(user):
    existing = UserPasskey.query.filter_by(user_id=user.id).all()
    exclude = [
        PublicKeyCredentialDescriptor(id=_b64url_decode(item.credential_id))
        for item in existing
    ]

    options = generate_registration_options(
        rp_id=_rp_id(),
        rp_name=_rp_name(),
        user_id=str(user.id).encode("utf-8"),
        user_name=user.username,
        user_display_name=user.username,
        exclude_credentials=exclude,
        authenticator_selection=AuthenticatorSelectionCriteria(
            resident_key=ResidentKeyRequirement.PREFERRED,
            user_verification=UserVerificationRequirement.PREFERRED,
        ),
    )
    session["passkey_reg_challenge"] = _b64url_encode(options.challenge)
    return options


def verify_registration(user, credential_json, name):
    challenge = session.pop("passkey_reg_challenge", None)
    if not challenge:
        raise ValueError("Сессия регистрации passkey истекла")

    verification = verify_registration_response(
        credential=parse_registration_credential_json(json.dumps(credential_json)),
        expected_challenge=_b64url_decode(challenge),
        expected_rp_id=_rp_id(),
        expected_origin=_origin(),
    )

    passkey = UserPasskey(
        user_id=user.id,
        credential_id=credential_json.get("id") or _b64url_encode(verification.credential_id),
        public_key=_b64url_encode(verification.credential_public_key),
        sign_count=verification.sign_count,
        name=(name or "Passkey").strip()[:120] or "Passkey",
    )
    db.session.add(passkey)
    db.session.commit()
    return passkey


def authentication_options(user):
    passkeys = UserPasskey.query.filter_by(user_id=user.id).all()
    if not passkeys:
        raise ValueError("Passkey не настроен")

    allow = [
        PublicKeyCredentialDescriptor(id=_b64url_decode(item.credential_id))
        for item in passkeys
    ]
    options = generate_authentication_options(
        rp_id=_rp_id(),
        allow_credentials=allow,
        user_verification=UserVerificationRequirement.PREFERRED,
    )
    session["passkey_auth_challenge"] = _b64url_encode(options.challenge)
    session["passkey_auth_user_id"] = user.id
    return options


def verify_authentication(credential_json):
    challenge = session.pop("passkey_auth_challenge", None)
    user_id = session.pop("passkey_auth_user_id", None)
    if not challenge or not user_id:
        raise ValueError("Сессия входа passkey истекла")

    credential_id = credential_json.get("id") or credential_json.get("rawId")
    if isinstance(credential_id, dict):
        credential_id = credential_id.get("id")
    if not credential_id:
        raise ValueError("Некорректные данные passkey")

    passkey = UserPasskey.query.filter_by(
        user_id=user_id, credential_id=credential_id
    ).first()
    if not passkey:
        passkey = UserPasskey.query.filter_by(credential_id=credential_id).first()
    if not passkey:
        raise ValueError("Passkey не найден")

    verification = verify_authentication_response(
        credential=parse_authentication_credential_json(json.dumps(credential_json)),
        expected_challenge=_b64url_decode(challenge),
        expected_rp_id=_rp_id(),
        expected_origin=_origin(),
        credential_public_key=_b64url_decode(passkey.public_key),
        credential_current_sign_count=passkey.sign_count,
    )

    passkey.sign_count = verification.new_sign_count
    passkey.last_used_at = datetime.now(timezone.utc)
    db.session.commit()
    return passkey.user


def delete_passkey(user, passkey_id):
    passkey = UserPasskey.query.filter_by(id=passkey_id, user_id=user.id).first()
    if not passkey:
        return False
    db.session.delete(passkey)
    db.session.commit()
    return True