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

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 = "blog"
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))

##
# "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:
    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(BACKEND_URL, "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):
    if not order_id:
        return flask.jsonify(
            dict(error="Aborting refund: article not payed")
        ), 401
    session_id = flask.session.get("session_id", "")
    pay_params = dict(order_id=order_id, session_id=session_id)
    pay_status = backend_get(BACKEND_URL, "check-payment", pay_params)
    if not pay_status.get("paid"):
        err_abort(
            402,
            message="You did not pay for this article (nice try!)",
            json=pay_status
        )
    article_name = pay_status["contract_terms"]["extra"]["article_name"]
    refund_spec = dict(
        order_id=order_id,
        reason="Demo reimbursement",
        refund=ARTICLE_AMOUNT
    )
    resp = backend_post(BACKEND_URL, "refund", refund_spec)
    try:
        # delete from paid article cache
        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(BACKEND_URL, "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=dict(t_ms=1000*int(time.time() + 10 * 30)),
            wire_transfer_deadline=dict(t_ms=1000*int(time.time() + 15 * 30)),
        )
        order_resp = backend_post(BACKEND_URL, "private/orders", 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(BACKEND_URL, "private/orders/{}".format(order_id), params=dict())
    if pay_status.get("paid"):
        # Checks to do:
        #
        # - check that the paid article is actually the one
        #   mentioned in the requested URI.
        #
        # - check if the article was refunded before, and act
        #   accordingly.
        #

        # FLOW HERE == ARTICLE PAID AND CAN BE SHOWN.

        # 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)

    if 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")
            )
        )

    ##
    # 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