import json
import secrets
import webauthn
from app.config import URL as SITE_URL
from urllib.parse import urlparse

from flask import request, render_template, redirect, url_for, flash, session
from flask_login import login_user
from flask_wtf import FlaskForm
from wtforms import HiddenField, validators

from app.auth.base import auth_bp
from app.config import MFA_USER_ID
from app.log import LOG
from app.models import User
from app.extensions import db


class FidoTokenForm(FlaskForm):
    sk_assertion = HiddenField("sk_assertion", validators=[validators.DataRequired()])


@auth_bp.route("/fido", methods=["GET", "POST"])
def fido():
    # passed from login page
    user_id = session.get(MFA_USER_ID)

    # user access this page directly without passing by login page
    if not user_id:
        flash("Unknown error, redirect back to main page", "warning")
        return redirect(url_for("auth.login"))

    user = User.get(user_id)

    if not (user and (user.fido_uuid is not None)):
        flash("Only user with security key linked should go to this page", "warning")
        return redirect(url_for("auth.login"))

    fido_token_form = FidoTokenForm()

    next_url = request.args.get("next")

    RP_ID = urlparse(SITE_URL).hostname

    webauthn_user = webauthn.WebAuthnUser(
            user.fido_uuid, user.email, user.name, False,
            user.fido_credential_id, user.fido_pk, user.fido_sign_count, RP_ID)

    # Handling POST requests
    if fido_token_form.validate_on_submit():
        try:
            sk_assertion = json.loads(fido_token_form.sk_assertion.data)
        except Exception as e:
            flash('Key verification failed. Error: Invalid Payload', "warning")
            return redirect(url_for("auth.login"))
                    
        challenge = session['fido_challenge']
        credential_id = sk_assertion['id']

        webauthn_assertion_response = webauthn.WebAuthnAssertionResponse(
            webauthn_user,
            sk_assertion,
            challenge,
            SITE_URL,
            uv_required=False
        )

        is_webauthn_verified = False
        try:
            new_sign_count = webauthn_assertion_response.verify()
            is_webauthn_verified = True
        except Exception as e:
            flash('Key verification failed. Error: {}'.format(e), "warning")

        if is_webauthn_verified:
            user.fido_sign_count = new_sign_count
            db.session.commit()
            del session[MFA_USER_ID]

            login_user(user)
            flash(f"Welcome back {user.name}!", "success")

            # User comes to login page from another page
            if next_url:
                LOG.debug("redirect user to %s", next_url)
                return redirect(next_url)
            else:
                LOG.debug("redirect user to dashboard")
                return redirect(url_for("dashboard.index"))
        else:
            # Verification failed, put else here to make structure clear
            pass
    
    # Prepare information for key registration process
    session.pop('challenge', None)
    challenge = secrets.token_urlsafe(32)
    
    session['fido_challenge'] = challenge.rstrip('=')

    webauthn_assertion_options = webauthn.WebAuthnAssertionOptions(
        webauthn_user, challenge)
    webauthn_assertion_options = webauthn_assertion_options.assertion_dict

    return render_template("auth/fido.html", fido_token_form=fido_token_form, 
                        webauthn_assertion_options=webauthn_assertion_options,
                        enable_otp=user.enable_otp)