"""Authentication Backends for the People core app."""

from django.conf import settings
from django.contrib.auth import get_user_model
from django.core.exceptions import SuspiciousOperation
from django.utils.translation import gettext_lazy as _

import requests
from mozilla_django_oidc.auth import (
    OIDCAuthenticationBackend as MozillaOIDCAuthenticationBackend,
)

User = get_user_model()


class OIDCAuthenticationBackend(MozillaOIDCAuthenticationBackend):
    """Custom OpenID Connect (OIDC) Authentication Backend.

    This class overrides the default OIDC Authentication Backend to accommodate differences
    in the User model, and handles signed and/or encrypted UserInfo response.
    """

    def get_userinfo(self, access_token, id_token, payload):
        """Return user details dictionary.

        Parameters:
        - access_token (str): The access token.
        - id_token (str): The id token (unused).
        - payload (dict): The token payload (unused).

        Note: The id_token and payload parameters are unused in this implementation,
        but were kept to preserve base method signature.

        Note: It handles signed and/or encrypted UserInfo Response. It is required by
        Agent Connect, which follows the OIDC standard. It forces us to override the
        base method, which deal with 'application/json' response.

        Returns:
        - dict: User details dictionary obtained from the OpenID Connect user endpoint.
        """

        user_response = requests.get(
            self.OIDC_OP_USER_ENDPOINT,
            headers={"Authorization": f"Bearer {access_token}"},
            verify=self.get_settings("OIDC_VERIFY_SSL", True),
            timeout=self.get_settings("OIDC_TIMEOUT", None),
            proxies=self.get_settings("OIDC_PROXY", None),
        )
        user_response.raise_for_status()
        userinfo = self.verify_token(user_response.text)
        return userinfo

    def get_or_create_user(self, access_token, id_token, payload):
        """Return a User based on userinfo. Create a new user if no match is found.

        Parameters:
        - access_token (str): The access token.
        - id_token (str): The ID token.
        - payload (dict): The user payload.

        Returns:
        - User: An existing or newly created User instance.

        Raises:
        - Exception: Raised when user creation is not allowed and no existing user is found.
        """

        user_info = self.get_userinfo(access_token, id_token, payload)

        # Get user's full name from OIDC fields defined in settings
        full_name = self.compute_full_name(user_info)
        email = user_info.get("email")

        claims = {
            "email": email,
            "name": full_name,
        }

        sub = user_info.get("sub")
        if not sub:
            raise SuspiciousOperation(
                _("User info contained no recognizable user identification")
            )

        # if sub is absent, try matching on email
        user = self.get_existing_user(sub, email)
        if user:
            self.update_user_if_needed(user, claims)
        elif self.get_settings("OIDC_CREATE_USER", True):
            user = User.objects.create(sub=sub, password="!", **claims)  # noqa: S106

        return user

    def create_user(self, claims):
        """Return a newly created User instance."""
        sub = claims.get("sub")
        if sub is None:
            raise SuspiciousOperation(
                _("Claims contained no recognizable user identification")
            )

        return self.UserModel.objects.create(
            password="!",  # noqa: S106
            sub=sub,
            email=claims.get("email"),
            name=claims.get("name"),
        )

    def compute_full_name(self, user_info):
        """Compute user's full name based on OIDC fields in settings."""
        name_fields = settings.USER_OIDC_FIELDS_TO_NAME
        full_name = " ".join(
            user_info[field] for field in name_fields if user_info.get(field)
        )
        return full_name or None

    def get_existing_user(self, sub, email):
        """Fetch existing user by sub or email."""
        try:
            return User.objects.get(sub=sub, is_active=True)
        except User.DoesNotExist:
            if email and settings.OIDC_FALLBACK_TO_EMAIL_FOR_IDENTIFICATION:
                try:
                    return User.objects.get(email=email, is_active=True)
                except User.DoesNotExist:
                    pass
        return None

    def update_user_if_needed(self, user, claims):
        """Update user claims if they have changed."""
        has_changed = any(
            value and value != getattr(user, key) for key, value in claims.items()
        )
        if has_changed:
            updated_claims = {key: value for key, value in claims.items() if value}
            self.UserModel.objects.filter(sub=user.sub).update(**updated_claims)