#!/usr/bin/python
#
# Copyright Istio Authors
#
#   Licensed under the Apache License, Version 2.0 (the "License");
#   you may not use this file except in compliance with the License.
#   You may obtain a copy of the License at
#
#       http://www.apache.org/licenses/LICENSE-2.0
#
#   Unless required by applicable law or agreed to in writing, software
#   distributed under the License is distributed on an "AS IS" BASIS,
#   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
#   See the License for the specific language governing permissions and
#   limitations under the License.


from __future__ import print_function
from flask_bootstrap import Bootstrap
from flask import Flask, request, session, render_template, redirect, url_for
from flask import _request_ctx_stack as stack
from jaeger_client import Tracer, ConstSampler
from jaeger_client.reporter import NullReporter
from jaeger_client.codecs import B3Codec
from opentracing.ext import tags
from opentracing.propagation import Format
from opentracing_instrumentation.request_context import get_current_span, span_in_context
import simplejson as json
import requests
import sys
from json2html import *
import logging
import requests
import os
import asyncio

# These two lines enable debugging at httplib level (requests->urllib3->http.client)
# You will see the REQUEST, including HEADERS and DATA, and RESPONSE with HEADERS but without DATA.
# The only thing missing will be the response.body which is not logged.
try:
    import http.client as http_client
except ImportError:
    # Python 2
    import httplib as http_client
http_client.HTTPConnection.debuglevel = 1

app = Flask(__name__)
logging.basicConfig(stream=sys.stdout, level=logging.DEBUG)
requests_log = logging.getLogger("requests.packages.urllib3")
requests_log.setLevel(logging.DEBUG)
requests_log.propagate = True
app.logger.addHandler(logging.StreamHandler(sys.stdout))
app.logger.setLevel(logging.DEBUG)

# Set the secret key to some random bytes. Keep this really secret!
app.secret_key = b'_5#y2L"F4Q8z\n\xec]/'

Bootstrap(app)

servicesDomain = "" if (os.environ.get("SERVICES_DOMAIN") is None) else "." + os.environ.get("SERVICES_DOMAIN")
detailsHostname = "details" if (os.environ.get("DETAILS_HOSTNAME") is None) else os.environ.get("DETAILS_HOSTNAME")
ratingsHostname = "ratings" if (os.environ.get("RATINGS_HOSTNAME") is None) else os.environ.get("RATINGS_HOSTNAME")
reviewsHostname = "reviews" if (os.environ.get("REVIEWS_HOSTNAME") is None) else os.environ.get("REVIEWS_HOSTNAME")

flood_factor = 0 if (os.environ.get("FLOOD_FACTOR") is None) else int(os.environ.get("FLOOD_FACTOR"))

details = {
    "name": "http://{0}{1}:9080".format(detailsHostname, servicesDomain),
    "endpoint": "details",
    "children": []
}

ratings = {
    "name": "http://{0}{1}:9080".format(ratingsHostname, servicesDomain),
    "endpoint": "ratings",
    "children": []
}

reviews = {
    "name": "http://{0}{1}:9080".format(reviewsHostname, servicesDomain),
    "endpoint": "reviews",
    "children": [ratings]
}

productpage = {
    "name": "http://{0}{1}:9080".format(detailsHostname, servicesDomain),
    "endpoint": "details",
    "children": [details, reviews]
}

service_dict = {
    "productpage": productpage,
    "details": details,
    "reviews": reviews,
}

# A note on distributed tracing:
#
# Although Istio proxies are able to automatically send spans, they need some
# hints to tie together the entire trace. Applications need to propagate the
# appropriate HTTP headers so that when the proxies send span information, the
# spans can be correlated correctly into a single trace.
#
# To do this, an application needs to collect and propagate headers from the
# incoming request to any outgoing requests. The choice of headers to propagate
# is determined by the trace configuration used. See getForwardHeaders for
# the different header options.
#
# This example code uses OpenTracing (http://opentracing.io/) to propagate
# the 'b3' (zipkin) headers. Using OpenTracing for this is not a requirement.
# Using OpenTracing allows you to add application-specific tracing later on,
# but you can just manually forward the headers if you prefer.
#
# The OpenTracing example here is very basic. It only forwards headers. It is
# intended as a reference to help people get started, eg how to create spans,
# extract/inject context, etc.

# A very basic OpenTracing tracer (with null reporter)
tracer = Tracer(
    one_span_per_rpc=True,
    service_name='productpage',
    reporter=NullReporter(),
    sampler=ConstSampler(decision=True),
    extra_codecs={Format.HTTP_HEADERS: B3Codec()}
)


def trace():
    '''
    Function decorator that creates opentracing span from incoming b3 headers
    '''
    def decorator(f):
        def wrapper(*args, **kwargs):
            request = stack.top.request
            try:
                # Create a new span context, reading in values (traceid,
                # spanid, etc) from the incoming x-b3-*** headers.
                span_ctx = tracer.extract(
                    Format.HTTP_HEADERS,
                    dict(request.headers)
                )
                # Note: this tag means that the span will *not* be
                # a child span. It will use the incoming traceid and
                # spanid. We do this to propagate the headers verbatim.
                rpc_tag = {tags.SPAN_KIND: tags.SPAN_KIND_RPC_SERVER}
                span = tracer.start_span(
                    operation_name='op', child_of=span_ctx, tags=rpc_tag
                )
            except Exception as e:
                # We failed to create a context, possibly due to no
                # incoming x-b3-*** headers. Start a fresh span.
                # Note: This is a fallback only, and will create fresh headers,
                # not propagate headers.
                span = tracer.start_span('op')
            with span_in_context(span):
                r = f(*args, **kwargs)
                return r
        wrapper.__name__ = f.__name__
        return wrapper
    return decorator


def getForwardHeaders(request):
    headers = {}

    # x-b3-*** headers can be populated using the opentracing span
    span = get_current_span()
    carrier = {}
    tracer.inject(
        span_context=span.context,
        format=Format.HTTP_HEADERS,
        carrier=carrier)

    headers.update(carrier)

    # We handle other (non x-b3-***) headers manually
    if 'user' in session:
        headers['end-user'] = session['user']

    # Keep this in sync with the headers in details and reviews.
    incoming_headers = [
        # All applications should propagate x-request-id. This header is
        # included in access log statements and is used for consistent trace
        # sampling and log sampling decisions in Istio.
        'x-request-id',

        # Lightstep tracing header. Propagate this if you use lightstep tracing
        # in Istio (see
        # https://istio.io/latest/docs/tasks/observability/distributed-tracing/lightstep/)
        # Note: this should probably be changed to use B3 or W3C TRACE_CONTEXT.
        # Lightstep recommends using B3 or TRACE_CONTEXT and most application
        # libraries from lightstep do not support x-ot-span-context.
        'x-ot-span-context',

        # Datadog tracing header. Propagate these headers if you use Datadog
        # tracing.
        'x-datadog-trace-id',
        'x-datadog-parent-id',
        'x-datadog-sampling-priority',

        # W3C Trace Context. Compatible with OpenCensusAgent and Stackdriver Istio
        # configurations.
        'traceparent',
        'tracestate',

        # Cloud trace context. Compatible with OpenCensusAgent and Stackdriver Istio
        # configurations.
        'x-cloud-trace-context',

        # Grpc binary trace context. Compatible with OpenCensusAgent nad
        # Stackdriver Istio configurations.
        'grpc-trace-bin',

        # b3 trace headers. Compatible with Zipkin, OpenCensusAgent, and
        # Stackdriver Istio configurations. Commented out since they are
        # propagated by the OpenTracing tracer above.
        # 'x-b3-traceid',
        # 'x-b3-spanid',
        # 'x-b3-parentspanid',
        # 'x-b3-sampled',
        # 'x-b3-flags',

        # Application-specific headers to forward.
        'user-agent',
    ]
    # For Zipkin, always propagate b3 headers.
    # For Lightstep, always propagate the x-ot-span-context header.
    # For Datadog, propagate the corresponding datadog headers.
    # For OpenCensusAgent and Stackdriver configurations, you can choose any
    # set of compatible headers to propagate within your application. For
    # example, you can propagate b3 headers or W3C trace context headers with
    # the same result. This can also allow you to translate between context
    # propagation mechanisms between different applications.

    for ihdr in incoming_headers:
        val = request.headers.get(ihdr)
        if val is not None:
            headers[ihdr] = val

    return headers


# The UI:
@app.route('/')
@app.route('/index.html')
def index():
    """ Display productpage with normal user and test user buttons"""
    global productpage

    table = json2html.convert(json=json.dumps(productpage),
                              table_attributes="class=\"table table-condensed table-bordered table-hover\"")

    return render_template('index.html', serviceTable=table)


@app.route('/health')
def health():
    return 'Product page is healthy'


@app.route('/login', methods=['POST'])
def login():
    user = request.values.get('username')
    response = app.make_response(redirect(request.referrer))
    session['user'] = user
    return response


@app.route('/logout', methods=['GET'])
def logout():
    response = app.make_response(redirect(request.referrer))
    session.pop('user', None)
    return response

# a helper function for asyncio.gather, does not return a value


async def getProductReviewsIgnoreResponse(product_id, headers):
    getProductReviews(product_id, headers)

# flood reviews with unnecessary requests to demonstrate Istio rate limiting, asynchoronously


async def floodReviewsAsynchronously(product_id, headers):
    # the response is disregarded
    await asyncio.gather(*(getProductReviewsIgnoreResponse(product_id, headers) for _ in range(flood_factor)))

# flood reviews with unnecessary requests to demonstrate Istio rate limiting


def floodReviews(product_id, headers):
    loop = asyncio.new_event_loop()
    loop.run_until_complete(floodReviewsAsynchronously(product_id, headers))
    loop.close()


@app.route('/productpage')
@trace()
def front():
    product_id = 0  # TODO: replace default value
    headers = getForwardHeaders(request)
    user = session.get('user', '')
    product = getProduct(product_id)
    detailsStatus, details = getProductDetails(product_id, headers)

    if flood_factor > 0:
        floodReviews(product_id, headers)

    reviewsStatus, reviews = getProductReviews(product_id, headers)
    return render_template(
        'productpage.html',
        detailsStatus=detailsStatus,
        reviewsStatus=reviewsStatus,
        product=product,
        details=details,
        reviews=reviews,
        user=user)


# The API:
@app.route('/api/v1/products')
def productsRoute():
    return json.dumps(getProducts()), 200, {'Content-Type': 'application/json'}


@app.route('/api/v1/products/<product_id>')
@trace()
def productRoute(product_id):
    headers = getForwardHeaders(request)
    status, details = getProductDetails(product_id, headers)
    return json.dumps(details), status, {'Content-Type': 'application/json'}


@app.route('/api/v1/products/<product_id>/reviews')
@trace()
def reviewsRoute(product_id):
    headers = getForwardHeaders(request)
    status, reviews = getProductReviews(product_id, headers)
    return json.dumps(reviews), status, {'Content-Type': 'application/json'}


@app.route('/api/v1/products/<product_id>/ratings')
@trace()
def ratingsRoute(product_id):
    headers = getForwardHeaders(request)
    status, ratings = getProductRatings(product_id, headers)
    return json.dumps(ratings), status, {'Content-Type': 'application/json'}


# Data providers:
def getProducts():
    return [
        {
            'id': 0,
            'title': 'The Comedy of Errors',
            'descriptionHtml': '<a href="https://en.wikipedia.org/wiki/The_Comedy_of_Errors">Wikipedia Summary</a>: The Comedy of Errors is one of <b>William Shakespeare\'s</b> early plays. It is his shortest and one of his most farcical comedies, with a major part of the humour coming from slapstick and mistaken identity, in addition to puns and word play.'
        }
    ]


def getProduct(product_id):
    products = getProducts()
    if product_id + 1 > len(products):
        return None
    else:
        return products[product_id]


def getProductDetails(product_id, headers):
    try:
        url = details['name'] + "/" + details['endpoint'] + "/" + str(product_id)
        res = requests.get(url, headers=headers, timeout=3.0)
    except BaseException:
        res = None
    if res and res.status_code == 200:
        return 200, res.json()
    else:
        status = res.status_code if res is not None and res.status_code else 500
        return status, {'error': 'Sorry, product details are currently unavailable for this book.'}


def getProductReviews(product_id, headers):
    # Do not remove. Bug introduced explicitly for illustration in fault injection task
    # TODO: Figure out how to achieve the same effect using Envoy retries/timeouts
    for _ in range(2):
        try:
            url = reviews['name'] + "/" + reviews['endpoint'] + "/" + str(product_id)
            res = requests.get(url, headers=headers, timeout=3.0)
        except BaseException:
            res = None
        if res and res.status_code == 200:
            return 200, res.json()
    status = res.status_code if res is not None and res.status_code else 500
    return status, {'error': 'Sorry, product reviews are currently unavailable for this book.'}


def getProductRatings(product_id, headers):
    try:
        url = ratings['name'] + "/" + ratings['endpoint'] + "/" + str(product_id)
        res = requests.get(url, headers=headers, timeout=3.0)
    except BaseException:
        res = None
    if res and res.status_code == 200:
        return 200, res.json()
    else:
        status = res.status_code if res is not None and res.status_code else 500
        return status, {'error': 'Sorry, product ratings are currently unavailable for this book.'}


class Writer(object):
    def __init__(self, filename):
        self.file = open(filename, 'w')

    def write(self, data):
        self.file.write(data)

    def flush(self):
        self.file.flush()


if __name__ == '__main__':
    if len(sys.argv) < 2:
        logging.error("usage: %s port" % (sys.argv[0]))
        sys.exit(-1)

    p = int(sys.argv[1])
    logging.info("start at port %s" % (p))
    # Python does not work on an IPv6 only host
    # https://bugs.python.org/issue10414
    app.run(host='0.0.0.0', port=p, debug=True, threaded=True)