from flask import jsonify, redirect, request
from flask_login import LoginManager


def init_login_manager(app, login_url_builder, load_user, api_prefixes=("/api/",)):
    login_manager = LoginManager()
    login_manager.init_app(app)
    login_manager.user_loader(load_user)

    @login_manager.unauthorized_handler
    def unauthorized():
        # API clients get JSON instead of a redirect to the login page.
        if request.path.startswith(tuple(api_prefixes)):
            return jsonify({"error": "authentication required"}), 401
        return redirect(login_url_builder(request))

    return login_manager