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path: root/talerblog/blog/blog.py
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##
# This file is part of GNU TALER.
# Copyright (C) 2014-2017 INRIA
#
# TALER is free software; you can redistribute it and/or modify it under the
# terms of the GNU Lesser General Public License as published by the Free Software
# Foundation; either version 2.1, or (at your option) any later version.
#
# TALER is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License along with
# GNU TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
#
# @author Florian Dold
# @author Marcello Stanisci
# @brief Implementation of a Taler-compatible blog.

import urllib.parse
from urllib.parse import urljoin, quote, urlencode
import logging
import os
import traceback
import uuid
import qrcode
import qrcode.image.svg
import base64
import requests
import flask
import lxml.etree
import time
from cachelib import UWSGICache, SimpleCache
from taler.util.talerconfig import TalerConfig
from ..blog.content import ARTICLES, get_article_file, get_image_file

BASE_DIR = os.path.dirname(os.path.abspath(__file__))
app = flask.Flask(__name__, template_folder=BASE_DIR)
app.secret_key = base64.b64encode(os.urandom(64)).decode('utf-8')

LOGGER = logging.getLogger(__name__)
TC = TalerConfig.from_env()
BACKEND_BASE_URL = TC["frontends"]["backend"].value_string(required=True)
CURRENCY = TC["taler"]["currency"].value_string(required=True)
APIKEY = TC["frontends"]["backend_apikey"].value_string(required=True)
INSTANCE = TC["blog"]["instance"].value_string(required=True)
ARTICLE_AMOUNT = CURRENCY + ":0.5"
BACKEND_URL = urljoin(BACKEND_BASE_URL, f"instances/{INSTANCE}/")

app.config.from_object(__name__)


##
# Extends the templating language with a function (@c env)
# that fetches values from the environment.
#
# @return a @a dict containing the extension.
@app.context_processor
def utility_processor():
    # These helpers will be available in templates
    def env(name, default=None):
        return os.environ.get(name, default)

    return dict(env=env)


##
# Return a error response to the client.
#
# @param abort_status_code status code to return along the response.
# @param params _kw_ arguments to passed verbatim to the templating engine.
def err_abort(abort_status_code, **params):
    t = flask.render_template("templates/error.html", **params)
    flask.abort(flask.make_response(t, abort_status_code))


##
# Issue a GET request to the backend.
#
# @param endpoint the backend endpoint where to issue the request.
# @param params (dict type of) URL parameters to append to the request.
# @return the JSON response from the backend, or a error response
#         if something unexpected happens.
def backend_get(endpoint, params):
    headers = {"Authorization": "ApiKey " + APIKEY}
    try:
        resp = requests.get(
            urljoin(BACKEND_URL, endpoint), params=params, headers=headers
        )
    except requests.ConnectionError:
        err_abort(500, message="Could not establish connection to backend")
    try:
        response_json = resp.json()
    except ValueError:
        err_abort(500, message="Could not parse response from backend")
    if resp.status_code != 200:
        err_abort(
            500,
            message="Backend returned error status",
            json=response_json,
            status_code=resp.status_code
        )
    return response_json


##
# POST a request to the backend, and return a error
# response if any error occurs.
#
# @param endpoint the backend endpoint where to POST
#        this request.
# @param json the POST's body.
# @return the backend response (JSON format).
def backend_post(endpoint, json):
    headers = {"Authorization": "ApiKey " + APIKEY}
    try:
        resp = requests.post(
            urljoin(BACKEND_URL, endpoint), json=json, headers=headers
        )
    except requests.ConnectionError:
        err_abort(500, message="Could not establish connection to backend")
    try:
        response_json = resp.json()
    except ValueError:
        err_abort(
            500,
            message="Could not parse response from backend",
            status_code=resp.status_code
        )
    if resp.status_code != 200:
        err_abort(
            500,
            message="Backend returned error status",
            json=response_json,
            status_code=resp.status_code
        )
    return response_json


##
# "Fallback" exception handler to capture all the unmanaged errors.
#
# @param e the Exception object, currently unused.
# @return flask-native response object carrying the error message
#         (and execution stack!).
@app.errorhandler(Exception)
def internal_error(e):
    return flask.render_template(
        "templates/error.html",
        message="Internal error",
        stack=traceback.format_exc()
    )


##
# Serve the main index page.
#
# @return response object of the index page.
@app.route("/")
def index():
    return flask.render_template(
        "templates/index.html",
        merchant_currency=CURRENCY,
        articles=ARTICLES.values()
    )


##
# @brief Cache for paid articles (in the form <session_id>-<article_name>),
#        so we don't always have to ask the backend / DB, and so we don't
#        have to store variable-size cookies on the client.
try:
    import uwsgi
    paid_articles_cache = UWSGICache(0, "paid_articles")
except ImportError:
    paid_articles_cache = SimpleCache()


@app.route("/confirm-refund/<order_id>", methods=["GET"])
def confirm_refund(order_id):
    # Here we don't care about the session ID
    pay_params = dict(order_id=order_id)
    pay_status = backend_get("check-payment", pay_params)
    if not pay_status.get("paid"):
        err_abort(
            400,
            message="can't refund unpaid article",
        )
    article_name = pay_status["contract_terms"]["extra"]["article_name"]
    return flask.render_template(
        "templates/confirm_refund.html",
        article_name=article_name,
        order_id=order_id)


##
# Triggers the refund by serving /refund/test?order_id=XY.
# Will be triggered by a "refund button".
#
# @param order_id the order ID of the transaction to refund.
# @return the following errors (named by HTTP response code):
#         - 400: no article was asked to be refunded!
#         - 401: the refund was asked on a non-payed article.
#         - 500: the backend was unable to give response.
#         Or, in the successful case, a redirection to the
#         "refund URL" is returned; then the wallet will run
#         the refund protocol in a transparent way.
@app.route("/refund/<order_id>", methods=["POST"])
def refund(order_id):
    article_name = flask.request.form.get("article_name")
    if not article_name:
        return flask.jsonify(dict(error="No article_name found in form")), 400
    LOGGER.info("Looking for %s to refund" % article_name)
    if not order_id:
        return flask.jsonify(
            dict(error="Aborting refund: article not payed")
        ), 401
    refund_spec = dict(
        order_id=order_id,
        reason="Demo reimbursement",
        refund=ARTICLE_AMOUNT
    )
    resp = backend_post("refund", refund_spec)
    try:
        # delete from paid article cache
        article_name = resp["contract_terms"]["extra"]["article_name"]
        session_id = flask.session.get("session_id", "")
        paid_articles_cache.delete(session_id + "-" + article_name)
        taler_refund_uri = resp["taler_refund_uri"]
        qrcode_svg = get_qrcode_svg(taler_refund_uri)
        content = flask.render_template(
            "templates/show_refund.html",
            article_name=article_name,
            taler_refund_uri=taler_refund_uri,
            qrcode_svg=qrcode_svg,
        )
        headers = {"Taler": taler_refund_uri}
        return flask.Response(content, status=402, headers=headers)
    except KeyError:
        err_abort(
            500,
            message="Response from backend incomplete",
            json=resp,
            stack=traceback.format_exc()
        )


##
# Render the article after a successful purchase.
#
# @param article_name _slugged_ (= spaces converted to underscores) article title.
# @param data image filename to return along the article.
# @param order_id the ID of the order where this article got purchased.
#        (Will be put in the refund-request form action, since any article
#         will also have a "refund button" aside.)
# @return the following errors (named by HTTP return code):
#         - 500: file for article not found.
#         - 404: supplemental @a data not found.
#         In the successful case, a response object carrying the
#         article in it will be returned.
def render_article(article_name, data, order_id):
    article_info = ARTICLES.get(article_name)
    if article_info is None:
        m = "Internal error: Files for article ({}) not found.".format(
            article_name
        )
        err_abort(500, message=m)
    if data is not None:
        if data in article_info.extra_files:
            return flask.send_file(get_image_file(data))
        m = "Supplemental file ({}) for article ({}) not found.".format(
            data, article_name
        )
        err_abort(404, message=m)
    # the order_id is needed for refunds
    return flask.render_template(
        "templates/article_frame.html",
        article_file=get_article_file(article_info),
        article_name=article_name,
        order_id=order_id
    )


def get_qrcode_svg(data):
    factory = qrcode.image.svg.SvgImage
    img = qrcode.make(data, image_factory=factory)
    return lxml.etree.tostring(img.get_image()).decode("utf-8")


##
# This endpoint is used by the payment request page
# to check if the payment has been completed via the QR code.
@app.route("/check-status/<order_id>/<session_id>")
def check_status(order_id, session_id):
    pay_params = dict(order_id=order_id, session_id=session_id)
    pay_status = backend_get("check-payment", pay_params)
    return flask.jsonify(paid=pay_status["paid"])


##
# Trigger a article purchase.  The logic follows the main steps:
#
# 1. Always check if the article was paid already, via the
#    "/check-payment" API from the backend.
# 2. If so, return the article.
# 3. If not, redirect the browser to a page where the
#    wallet will initiate the payment protocol.
#
# @param article_name (slugged) article title.
# @param data filename of a supplement data (image/sound/..)
# @return the following errors might occur (named by HTTP response code):
#         - 402: @a article_name does not correspond to the @a order_id
#                of a PAYED article.
#         - 500: neither the article was paid, nor a payment was triggered.
#         - 400: a invalid order_id was passed along the GET parameters.
#         In the successful case, either the article is returned, or
#         the browser gets redirected to a page where the wallet can
#         send the payment.
@app.route("/essay/<article_name>")
@app.route("/essay/<article_name>/data/<data>")
def article(article_name, data=None):

    # We use an explicit session ID so that each payment (or payment replay) is
    # bound to a browser.  This forces re-play and prevents sharing the article
    # by just sharing the URL.
    session_id = flask.session.get("session_id")
    order_id = flask.request.args.get("order_id")

    if not session_id:
        session_id = flask.session["session_id"] = str(uuid.uuid4())

    cached_order_id = paid_articles_cache.get(session_id + "-" + article_name)
    if cached_order_id:
        return render_article(article_name, data, cached_order_id)

    ##
    # First-timer; generate order first.
    if not order_id:
        order = dict(
            amount=ARTICLE_AMOUNT,
            extra=dict(article_name=article_name),
            fulfillment_url=flask.request.base_url,
            summary="Essay: " + article_name.replace("_", " "),
            # 10 minutes time for a refund
            refund_deadline=f"/Date({int(time.time()) + 10 * 30})/",
            wire_transfer_deadline=f"/Date({int(time.time()) + 15 * 30})/",
        )
        order_resp = backend_post("order", dict(order=order))
        order_id = order_resp["order_id"]
        return flask.redirect(
            flask.url_for(
                "article", article_name=article_name, order_id=order_id
            )
        )

    ##
    # Prepare data for the upcoming payment check.
    pay_params = dict(order_id=order_id, session_id=session_id)

    pay_status = backend_get("check-payment", pay_params)

    if pay_status.get("paid"):

        ##
        # Somehow, a session with a payed article which _differs_ from
        # the article requested in the URL existed; trigger the pay protocol!
        if pay_status["contract_terms"]["extra"]["article_name"] != article_name:
            err_abort(
                402,
                message="You did not pay for this article (nice try!)",
                json=pay_status
            )

        ##
        # Show a "article refunded" page, in that case.
        if pay_status.get("refunded"):
            return flask.render_template(
                "templates/article_refunded.html", article_name=article_name
            )
        ##
        # Put the article in the cache.
        paid_articles_cache.set(session_id + "-" + article_name, order_id)

        ##
        # Finally return the article.
        return render_article(article_name, data, order_id)
    elif pay_status.get("already_paid_order_id") is not None:
        return flask.redirect(
            flask.url_for(
                "article",
                article_name=article_name,
                order_id=pay_status.get("already_paid_order_id")
            )
        )
    else:
        ##
        # Redirect the browser to a page where the wallet can
        # run the payment protocol.
        taler_pay_uri = pay_status["taler_pay_uri"]
        qrcode_svg = get_qrcode_svg(taler_pay_uri)
        check_status_url_enc = urllib.parse.quote(
            flask.url_for(
                "check_status", order_id=order_id, session_id=session_id
            )
        )
        content = flask.render_template(
            "templates/request_payment.html",
            article_name=article_name,
            taler_pay_uri=taler_pay_uri,
            qrcode_svg=qrcode_svg,
            check_status_url_enc=check_status_url_enc
        )
        headers = {"Taler": taler_pay_uri}
        resp = flask.Response(content, status=402, headers=headers)
        return resp

    # no pay_redirect but article not paid, this should never happen!
    err_abort(500, message="Internal error, invariant failed", json=pay_status)