# Copyright 2016 OpenMarket Ltd
#
# 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 .base_resource import BaseMediaResource
from synapse.api.errors import Codes
from twisted.web.resource import Resource
from twisted.web.server import NOT_DONE_YET
from twisted.internet import defer
from lxml import html
from urlparse import urlparse, urlunparse
from synapse.util.stringutils import random_string
from synapse.util.caches.expiringcache import ExpiringCache
from synapse.http.client import SpiderHttpClient
from synapse.http.server import request_handler, respond_with_json, respond_with_json_bytes
from synapse.util.async import ObservableDeferred

import os
import re
import ujson as json

import logging
logger = logging.getLogger(__name__)

class PreviewUrlResource(BaseMediaResource):
    isLeaf = True

    def __init__(self, hs, filepaths):
        BaseMediaResource.__init__(self, hs, filepaths)
        self.client = SpiderHttpClient(hs)

        # simple memory cache mapping urls to OG metadata
        self.cache = ExpiringCache(
            cache_name = "url_previews",
            clock = self.clock,
            expiry_ms = 60*60*1000, # don't spider URLs more often than once an hour
        )
        self.cache.start()

        self.downloads = {}

    def render_GET(self, request):
        self._async_render_GET(request)
        return NOT_DONE_YET

    @request_handler
    @defer.inlineCallbacks
    def _async_render_GET(self, request):
        
        try:
            # XXX: if get_user_by_req fails, what should we do in an async render?
            requester = yield self.auth.get_user_by_req(request)
            url = request.args.get("url")[0]
            ts = request.args.get("ts")[0] if "ts" in request.args else self.clock.time_msec()

            # first check the memory cache - good to handle all the clients on this
            # HS thundering away to preview the same URL at the same time.
            try:
                og = self.cache[url]
                respond_with_json_bytes(request, 200, json.dumps(og), send_cors=True)
                return
            except:
                pass

            # then check the URL cache in the DB (which will also provide us with
            # historical previews, if we have any)
            cache_result = yield self.store.get_url_cache(url, ts)
            if (
                cache_result and
                cache_result["download_ts"] + cache_result["expires"] > ts and
                cache_result["response_code"] / 100 == 2
            ):
                respond_with_json_bytes(
                    request, 200, cache_result["og"].encode('utf-8'),
                    send_cors=True
                )
                return

            # Ensure only one download for a given URL is active at a time
            download = self.downloads.get(url)
            if download is None:
                download = self._download_url(url, requester.user)
                download = ObservableDeferred(
                    download,
                    consumeErrors=True
                )
                self.downloads[url] = download

                @download.addBoth
                def callback(media_info):
                    del self.downloads[key]
                    return media_info
            media_info = yield download.observe()

            # FIXME: we should probably update our cache now anyway, so that
            # even if the OG calculation raises, we don't keep hammering on the
            # remote server.  For now, leave it uncached to aid debugging OG
            # calculation problems

            logger.debug("got media_info of '%s'" % media_info)

            if self._is_media(media_info['media_type']):
                dims = yield self._generate_local_thumbnails(
                        media_info['filesystem_id'], media_info
                      )

                og = {
                    "og:description" : media_info['download_name'],
                    "og:image" : "mxc://%s/%s" % (self.server_name, media_info['filesystem_id']),
                    "og:image:type" : media_info['media_type'],
                }

                if dims:
                    og["og:image:width"] = dims['width']
                    og["og:image:height"] = dims['height']
                else:
                    logger.warn("Couldn't get dims for %s" % url)

                # define our OG response for this media
            elif self._is_html(media_info['media_type']):
                # TODO: somehow stop a big HTML tree from exploding synapse's RAM

                try:
                    tree = html.parse(media_info['filename'])
                    og = yield self._calc_og(tree, media_info, requester)
                except UnicodeDecodeError:
                    # XXX: evil evil bodge
                    file = open(media_info['filename'])
                    body = file.read()
                    file.close()
                    tree = html.fromstring(body.decode('utf-8','ignore'))
                    og = yield self._calc_og(tree, media_info, requester)

            else:
                logger.warn("Failed to find any OG data in %s", url)
                og = {}

            logger.debug("Calculated OG for %s as %s" % (url, og));

            # store OG in ephemeral in-memory cache
            self.cache[url] = og

            # store OG in history-aware DB cache
            yield self.store.store_url_cache(
                url,
                media_info["response_code"],
                media_info["etag"],
                media_info["expires"],
                json.dumps(og),
                media_info["filesystem_id"],
                media_info["created_ts"],
            )

            respond_with_json_bytes(request, 200, json.dumps(og), send_cors=True)
        except:
            # XXX: if we don't explicitly respond here, the request never returns.
            # isn't this what server.py's wrapper is meant to be doing for us?
            respond_with_json(
                request,
                500,
                {
                    "error": "Internal server error",
                    "errcode": Codes.UNKNOWN,
                },
                send_cors=True
            )
            raise

    @defer.inlineCallbacks
    def _calc_og(self, tree, media_info, requester):
        # suck our tree into lxml and define our OG response.

        # if we see any image URLs in the OG response, then spider them
        # (although the client could choose to do this by asking for previews of those URLs to avoid DoSing the server)

        # "og:type"        : "article"
        # "og:url"         : "https://twitter.com/matrixdotorg/status/684074366691356672"
        # "og:title"       : "Matrix on Twitter"
        # "og:image"       : "https://pbs.twimg.com/profile_images/500400952029888512/yI0qtFi7_400x400.png"
        # "og:description" : "Synapse 0.12 is out! Lots of polishing, performance & bugfixes: /sync API, /r0 prefix, fulltext search, 3PID invites https://t.co/5alhXLLEGP"
        # "og:site_name"   : "Twitter"
        
        # or:

        # "og:type"         : "video",
        # "og:url"          : "https://www.youtube.com/watch?v=LXDBoHyjmtw",
        # "og:site_name"    : "YouTube",
        # "og:video:type"   : "application/x-shockwave-flash",
        # "og:description"  : " ",
        # "og:title"        : "RemoteJam - Matrix team hack for Disrupt Europe Hackathon",
        # "og:image"        : "https://i.ytimg.com/vi/LXDBoHyjmtw/maxresdefault.jpg",
        # "og:video:url"    : "http://www.youtube.com/v/LXDBoHyjmtw?version=3&autohide=1",
        # "og:video:width"  : "1280"
        # "og:video:height" : "720",
        # "og:video:secure_url": "https://www.youtube.com/v/LXDBoHyjmtw?version=3&autohide=1",

        og = {}
        for tag in tree.xpath("//*/meta[starts-with(@property, 'og:')]"):
            og[tag.attrib['property']] = tag.attrib['content']

        # TODO: grab article: meta tags too, e.g.:

        # <meta property="article:publisher" content="https://www.facebook.com/thethudonline" />
        # <meta property="article:author" content="https://www.facebook.com/thethudonline" />
        # <meta property="article:tag" content="baby" />
        # <meta property="article:section" content="Breaking News" />
        # <meta property="article:published_time" content="2016-03-31T19:58:24+00:00" />
        # <meta property="article:modified_time" content="2016-04-01T18:31:53+00:00" />

        if 'og:title' not in og:
            # do some basic spidering of the HTML
            title = tree.xpath("(//title)[1] | (//h1)[1] | (//h2)[1] | (//h3)[1]")
            og['og:title'] = title[0].text.strip() if title else None


        if 'og:image' not in og:
            # TODO: extract a favicon failing all else
            meta_image = tree.xpath("//*/meta[translate(@itemprop, 'IMAGE', 'image')='image']/@content");
            if meta_image:
                og['og:image'] = self._rebase_url(meta_image[0], media_info['uri'])
            else:
                # TODO: consider inlined CSS styles as well as width & height attribs
                images = tree.xpath("//img[@src][number(@width)>10][number(@height)>10]")
                images = sorted(images, key=lambda i: (-1 * int(i.attrib['width']) * int(i.attrib['height'])))
                if not images:
                    images = tree.xpath("//img[@src]")
                if images:
                    og['og:image'] = images[0].attrib['src']

        # pre-cache the image for posterity
        # FIXME: it might be cleaner to use the same flow as the main /preview_url request itself
        # and benefit from the same caching etc.  But for now we just rely on the caching
        # of the master request to speed things up.
        if 'og:image' in og and og['og:image']:
            image_info = yield self._download_url(self._rebase_url(og['og:image'], media_info['uri']), requester.user)

            if self._is_media(image_info['media_type']):
                # TODO: make sure we don't choke on white-on-transparent images
                dims = yield self._generate_local_thumbnails(
                        image_info['filesystem_id'], image_info
                      )
                if dims:
                    og["og:image:width"] = dims['width']
                    og["og:image:height"] = dims['height']
                else:
                    logger.warn("Couldn't get dims for %s" % og["og:image"])

                og["og:image"] = "mxc://%s/%s" % (self.server_name, image_info['filesystem_id'])
                og["og:image:type"] = image_info['media_type']
            else:
                del og["og:image"]

        if 'og:description' not in og:
            meta_description = tree.xpath("//*/meta[translate(@name, 'DESCRIPTION', 'description')='description']/@content");
            if meta_description:
                og['og:description'] = meta_description[0]
            else:
                # text_nodes = tree.xpath("//h1/text() | //h2/text() | //h3/text() | //p/text() | //div/text() | //span/text() | //a/text()")                
                text_nodes = tree.xpath("//text()[not(ancestor::header | ancestor::nav | ancestor::aside | " +
                                        "ancestor::footer | ancestor::script | ancestor::style)]" +
                                        "[ancestor::body]")
                text = ''
                for text_node in text_nodes:
                    if len(text) < 500:
                        text += text_node + ' '
                    else:
                        break
                text = re.sub(r'[\t ]+', ' ', text)
                text = re.sub(r'[\t \r\n]*[\r\n]+', '\n', text)
                text = text.strip()[:500]
                og['og:description'] = text if text else None

        # TODO: delete the url downloads to stop diskfilling, as we only ever cared about its OG
        defer.returnValue(og);

    def _rebase_url(self, url, base):
        base = list(urlparse(base))
        url = list(urlparse(url))
        if not url[0]: # fix up schema
            url[0] = base[0] or "http"
        if not url[1]: # fix up hostname
            url[1] = base[1]
            if not url[2].startswith('/'):
                url[2] = re.sub(r'/[^/]+$', '/', base[2]) + url[2]
        return urlunparse(url)

    @defer.inlineCallbacks
    def _download_url(self, url, user):
        # TODO: we should probably honour robots.txt... except in practice
        # we're most likely being explicitly triggered by a human rather than a
        # bot, so are we really a robot?

        # XXX: horrible duplication with base_resource's _download_remote_file()
        file_id = random_string(24)

        fname = self.filepaths.local_media_filepath(file_id)
        self._makedirs(fname)

        try:
            with open(fname, "wb") as f:
                logger.debug("Trying to get url '%s'" % url)
                length, headers, uri, code = yield self.client.get_file(
                    url, output_stream=f, max_size=self.max_spider_size,
                )
                # FIXME: pass through 404s and other error messages nicely

            media_type = headers["Content-Type"][0]
            time_now_ms = self.clock.time_msec()

            content_disposition = headers.get("Content-Disposition", None)
            if content_disposition:
                _, params = cgi.parse_header(content_disposition[0],)
                download_name = None

                # First check if there is a valid UTF-8 filename
                download_name_utf8 = params.get("filename*", None)
                if download_name_utf8:
                    if download_name_utf8.lower().startswith("utf-8''"):
                        download_name = download_name_utf8[7:]

                # If there isn't check for an ascii name.
                if not download_name:
                    download_name_ascii = params.get("filename", None)
                    if download_name_ascii and is_ascii(download_name_ascii):
                        download_name = download_name_ascii

                if download_name:
                    download_name = urlparse.unquote(download_name)
                    try:
                        download_name = download_name.decode("utf-8")
                    except UnicodeDecodeError:
                        download_name = None
            else:
                download_name = None

            yield self.store.store_local_media(
                media_id=file_id,
                media_type=media_type,
                time_now_ms=self.clock.time_msec(),
                upload_name=download_name,
                media_length=length,
                user_id=user,
            )

        except:
            os.remove(fname)
            raise

        defer.returnValue({
            "media_type": media_type,
            "media_length": length,
            "download_name": download_name,
            "created_ts": time_now_ms,
            "filesystem_id": file_id,
            "filename": fname,
            "uri": uri,
            "response_code": code,
            # FIXME: we should calculate a proper expiration based on the
            # Cache-Control and Expire headers.  But for now, assume 1 hour.
            "expires": 60 * 60 * 1000,
            "etag": headers["ETag"] if "ETag" in headers else None,
        })

    def _is_media(self, content_type):
        if content_type.lower().startswith("image/"):
            return True

    def _is_html(self, content_type):
        content_type = content_type.lower()
        if (content_type.startswith("text/html") or
            content_type.startswith("application/xhtml")):
            return True