# -*- coding: utf-8 -*-
# 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.

import cgi
import datetime
import errno
import fnmatch
import itertools
import logging
import os
import re
import shutil
import sys
import traceback

import six
from six import string_types
from six.moves import urllib_parse as urlparse

from canonicaljson import json

from twisted.internet import defer
from twisted.web.resource import Resource
from twisted.web.server import NOT_DONE_YET

from synapse.api.errors import Codes, SynapseError
from synapse.http.client import SpiderHttpClient
from synapse.http.server import (
    respond_with_json,
    respond_with_json_bytes,
    wrap_json_request_handler,
)
from synapse.http.servlet import parse_integer, parse_string
from synapse.metrics.background_process_metrics import run_as_background_process
from synapse.util.async_helpers import ObservableDeferred
from synapse.util.caches.expiringcache import ExpiringCache
from synapse.util.logcontext import make_deferred_yieldable, run_in_background
from synapse.util.stringutils import is_ascii, random_string

from ._base import FileInfo

logger = logging.getLogger(__name__)


class PreviewUrlResource(Resource):
    isLeaf = True

    def __init__(self, hs, media_repo, media_storage):
        Resource.__init__(self)

        self.auth = hs.get_auth()
        self.clock = hs.get_clock()
        self.filepaths = media_repo.filepaths
        self.max_spider_size = hs.config.max_spider_size
        self.server_name = hs.hostname
        self.store = hs.get_datastore()
        self.client = SpiderHttpClient(hs)
        self.media_repo = media_repo
        self.primary_base_path = media_repo.primary_base_path
        self.media_storage = media_storage

        self.url_preview_url_blacklist = hs.config.url_preview_url_blacklist

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

        self._cleaner_loop = self.clock.looping_call(
            self._start_expire_url_cache_data, 10 * 1000,
        )

    def render_OPTIONS(self, request):
        return respond_with_json(request, 200, {}, send_cors=True)

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

    @wrap_json_request_handler
    @defer.inlineCallbacks
    def _async_render_GET(self, request):

        # 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 = parse_string(request, "url")
        if b"ts" in request.args:
            ts = parse_integer(request, "ts")
        else:
            ts = self.clock.time_msec()

        # XXX: we could move this into _do_preview if we wanted.
        url_tuple = urlparse.urlsplit(url)
        for entry in self.url_preview_url_blacklist:
            match = True
            for attrib in entry:
                pattern = entry[attrib]
                value = getattr(url_tuple, attrib)
                logger.debug((
                    "Matching attrib '%s' with value '%s' against"
                    " pattern '%s'"
                ) % (attrib, value, pattern))

                if value is None:
                    match = False
                    continue

                if pattern.startswith('^'):
                    if not re.match(pattern, getattr(url_tuple, attrib)):
                        match = False
                        continue
                else:
                    if not fnmatch.fnmatch(getattr(url_tuple, attrib), pattern):
                        match = False
                        continue
            if match:
                logger.warn(
                    "URL %s blocked by url_blacklist entry %s", url, entry
                )
                raise SynapseError(
                    403, "URL blocked by url pattern blacklist entry",
                    Codes.UNKNOWN
                )

        # the in-memory cache:
        # * ensures that only one request is active at a time
        # * takes load off the DB for the thundering herds
        # * also caches any failures (unlike the DB) so we don't keep
        #    requesting the same endpoint

        observable = self._cache.get(url)

        if not observable:
            download = run_in_background(
                self._do_preview,
                url, requester.user, ts,
            )
            observable = ObservableDeferred(
                download,
                consumeErrors=True
            )
            self._cache[url] = observable
        else:
            logger.info("Returning cached response")

        og = yield make_deferred_yieldable(observable.observe())
        respond_with_json_bytes(request, 200, og, send_cors=True)

    @defer.inlineCallbacks
    def _do_preview(self, url, user, ts):
        """Check the db, and download the URL and build a preview

        Args:
            url (str):
            user (str):
            ts (int):

        Returns:
            Deferred[str]: json-encoded og data
        """
        # 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["expires_ts"] > ts and
            cache_result["response_code"] / 100 == 2
        ):
            # It may be stored as text in the database, not as bytes (such as
            # PostgreSQL). If so, encode it back before handing it on.
            og = cache_result["og"]
            if isinstance(og, six.text_type):
                og = og.encode('utf8')
            defer.returnValue(og)
            return

        media_info = yield self._download_url(url, user)

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

        if _is_media(media_info['media_type']):
            file_id = media_info['filesystem_id']
            dims = yield self.media_repo._generate_thumbnails(
                None, file_id, file_id, media_info["media_type"],
                url_cache=True,
            )

            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'],
                "matrix:image:size": media_info['media_length'],
            }

            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 _is_html(media_info['media_type']):
            # TODO: somehow stop a big HTML tree from exploding synapse's RAM

            with open(media_info['filename'], 'rb') as file:
                body = file.read()

            # clobber the encoding from the content-type, or default to utf-8
            # XXX: this overrides any <meta/> or XML charset headers in the body
            # which may pose problems, but so far seems to work okay.
            match = re.match(
                r'.*; *charset="?(.*?)"?(;|$)',
                media_info['media_type'],
                re.I
            )
            encoding = match.group(1) if match else "utf-8"

            og = decode_and_calc_og(body, media_info['uri'], encoding)

            # 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 on the master request to speed things up.
            if 'og:image' in og and og['og:image']:
                image_info = yield self._download_url(
                    _rebase_url(og['og:image'], media_info['uri']), user
                )

                if _is_media(image_info['media_type']):
                    # TODO: make sure we don't choke on white-on-transparent images
                    file_id = image_info['filesystem_id']
                    dims = yield self.media_repo._generate_thumbnails(
                        None, file_id, file_id, image_info["media_type"],
                        url_cache=True,
                    )
                    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']
                    og["matrix:image:size"] = image_info['media_length']
                else:
                    del og["og:image"]
        else:
            logger.warn("Failed to find any OG data in %s", url)
            og = {}

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

        jsonog = json.dumps(og).encode('utf8')

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

        defer.returnValue(jsonog)

    @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?

        file_id = datetime.date.today().isoformat() + '_' + random_string(16)

        file_info = FileInfo(
            server_name=None,
            file_id=file_id,
            url_cache=True,
        )

        with self.media_storage.store_into_file(file_info) as (f, fname, finish):
            try:
                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,
                )
            except Exception as e:
                # FIXME: pass through 404s and other error messages nicely
                logger.warn("Error downloading %s: %r", url, e)
                raise SynapseError(
                    500, "Failed to download content: %s" % (
                        traceback.format_exception_only(sys.exc_info()[0], e),
                    ),
                    Codes.UNKNOWN,
                )
            yield finish()

        try:
            if b"Content-Type" in headers:
                media_type = headers[b"Content-Type"][0].decode('ascii')
            else:
                media_type = "application/octet-stream"
            time_now_ms = self.clock.time_msec()

            content_disposition = headers.get(b"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,
                url_cache=url,
            )

        except Exception as e:
            logger.error("Error handling downloaded %s: %r", url, e)
            # TODO: we really ought to delete the downloaded file in this
            # case, since we won't have recorded it in the db, and will
            # therefore not expire it.
            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"][0] if "ETag" in headers else None,
        })

    def _start_expire_url_cache_data(self):
        return run_as_background_process(
            "expire_url_cache_data", self._expire_url_cache_data,
        )

    @defer.inlineCallbacks
    def _expire_url_cache_data(self):
        """Clean up expired url cache content, media and thumbnails.
        """
        # TODO: Delete from backup media store

        now = self.clock.time_msec()

        logger.info("Running url preview cache expiry")

        if not (yield self.store.has_completed_background_updates()):
            logger.info("Still running DB updates; skipping expiry")
            return

        # First we delete expired url cache entries
        media_ids = yield self.store.get_expired_url_cache(now)

        removed_media = []
        for media_id in media_ids:
            fname = self.filepaths.url_cache_filepath(media_id)
            try:
                os.remove(fname)
            except OSError as e:
                # If the path doesn't exist, meh
                if e.errno != errno.ENOENT:
                    logger.warn("Failed to remove media: %r: %s", media_id, e)
                    continue

            removed_media.append(media_id)

            try:
                dirs = self.filepaths.url_cache_filepath_dirs_to_delete(media_id)
                for dir in dirs:
                    os.rmdir(dir)
            except Exception:
                pass

        yield self.store.delete_url_cache(removed_media)

        if removed_media:
            logger.info("Deleted %d entries from url cache", len(removed_media))

        # Now we delete old images associated with the url cache.
        # These may be cached for a bit on the client (i.e., they
        # may have a room open with a preview url thing open).
        # So we wait a couple of days before deleting, just in case.
        expire_before = now - 2 * 24 * 60 * 60 * 1000
        media_ids = yield self.store.get_url_cache_media_before(expire_before)

        removed_media = []
        for media_id in media_ids:
            fname = self.filepaths.url_cache_filepath(media_id)
            try:
                os.remove(fname)
            except OSError as e:
                # If the path doesn't exist, meh
                if e.errno != errno.ENOENT:
                    logger.warn("Failed to remove media: %r: %s", media_id, e)
                    continue

            try:
                dirs = self.filepaths.url_cache_filepath_dirs_to_delete(media_id)
                for dir in dirs:
                    os.rmdir(dir)
            except Exception:
                pass

            thumbnail_dir = self.filepaths.url_cache_thumbnail_directory(media_id)
            try:
                shutil.rmtree(thumbnail_dir)
            except OSError as e:
                # If the path doesn't exist, meh
                if e.errno != errno.ENOENT:
                    logger.warn("Failed to remove media: %r: %s", media_id, e)
                    continue

            removed_media.append(media_id)

            try:
                dirs = self.filepaths.url_cache_thumbnail_dirs_to_delete(media_id)
                for dir in dirs:
                    os.rmdir(dir)
            except Exception:
                pass

        yield self.store.delete_url_cache_media(removed_media)

        logger.info("Deleted %d media from url cache", len(removed_media))


def decode_and_calc_og(body, media_uri, request_encoding=None):
    from lxml import etree

    try:
        parser = etree.HTMLParser(recover=True, encoding=request_encoding)
        tree = etree.fromstring(body, parser)
        og = _calc_og(tree, media_uri)
    except UnicodeDecodeError:
        # blindly try decoding the body as utf-8, which seems to fix
        # the charset mismatches on https://google.com
        parser = etree.HTMLParser(recover=True, encoding=request_encoding)
        tree = etree.fromstring(body.decode('utf-8', 'ignore'), parser)
        og = _calc_og(tree, media_uri)

    return og


def _calc_og(tree, media_uri):
    # 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"         : "video",
    # "og:url"          : "https://www.youtube.com/watch?v=LXDBoHyjmtw",
    # "og:site_name"    : "YouTube",
    # "og:video:type"   : "application/x-shockwave-flash",
    # "og:description"  : "Fun stuff happening here",
    # "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",

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

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

    # "article:publisher" : "https://www.facebook.com/thethudonline" />
    # "article:author" content="https://www.facebook.com/thethudonline" />
    # "article:tag" content="baby" />
    # "article:section" content="Breaking News" />
    # "article:published_time" content="2016-03-31T19:58:24+00:00" />
    # "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]")
        if title and title[0].text is not None:
            og['og:title'] = title[0].text.strip()
        else:
            og['og:title'] = 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'] = _rebase_url(meta_image[0], media_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 * float(i.attrib['width']) * float(i.attrib['height'])
            ))
            if not images:
                images = tree.xpath("//img[@src]")
            if images:
                og['og:image'] = images[0].attrib['src']

    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:
            # grab any text nodes which are inside the <body/> tag...
            # unless they are within an HTML5 semantic markup tag...
            # <header/>, <nav/>, <aside/>, <footer/>
            # ...or if they are within a <script/> or <style/> tag.
            # This is a very very very coarse approximation to a plain text
            # render of the page.

            # We don't just use XPATH here as that is slow on some machines.

            from lxml import etree

            TAGS_TO_REMOVE = (
                "header",
                "nav",
                "aside",
                "footer",
                "script",
                "noscript",
                "style",
                etree.Comment
            )

            # Split all the text nodes into paragraphs (by splitting on new
            # lines)
            text_nodes = (
                re.sub(r'\s+', '\n', el).strip()
                for el in _iterate_over_text(tree.find("body"), *TAGS_TO_REMOVE)
            )
            og['og:description'] = summarize_paragraphs(text_nodes)
    else:
        og['og:description'] = summarize_paragraphs([og['og:description']])

    # TODO: delete the url downloads to stop diskfilling,
    # as we only ever cared about its OG
    return og


def _iterate_over_text(tree, *tags_to_ignore):
    """Iterate over the tree returning text nodes in a depth first fashion,
    skipping text nodes inside certain tags.
    """
    # This is basically a stack that we extend using itertools.chain.
    # This will either consist of an element to iterate over *or* a string
    # to be returned.
    elements = iter([tree])
    while True:
        el = next(elements, None)
        if el is None:
            return

        if isinstance(el, string_types):
            yield el
        elif el.tag not in tags_to_ignore:
            # el.text is the text before the first child, so we can immediately
            # return it if the text exists.
            if el.text:
                yield el.text

            # We add to the stack all the elements children, interspersed with
            # each child's tail text (if it exists). The tail text of a node
            # is text that comes *after* the node, so we always include it even
            # if we ignore the child node.
            elements = itertools.chain(
                itertools.chain.from_iterable(  # Basically a flatmap
                    [child, child.tail] if child.tail else [child]
                    for child in el.iterchildren()
                ),
                elements
            )


def _rebase_url(url, base):
    base = list(urlparse.urlparse(base))
    url = list(urlparse.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 urlparse.urlunparse(url)


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


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


def summarize_paragraphs(text_nodes, min_size=200, max_size=500):
    # Try to get a summary of between 200 and 500 words, respecting
    # first paragraph and then word boundaries.
    # TODO: Respect sentences?

    description = ''

    # Keep adding paragraphs until we get to the MIN_SIZE.
    for text_node in text_nodes:
        if len(description) < min_size:
            text_node = re.sub(r'[\t \r\n]+', ' ', text_node)
            description += text_node + '\n\n'
        else:
            break

    description = description.strip()
    description = re.sub(r'[\t ]+', ' ', description)
    description = re.sub(r'[\t \r\n]*[\r\n]+', '\n\n', description)

    # If the concatenation of paragraphs to get above MIN_SIZE
    # took us over MAX_SIZE, then we need to truncate mid paragraph
    if len(description) > max_size:
        new_desc = ""

        # This splits the paragraph into words, but keeping the
        # (preceeding) whitespace intact so we can easily concat
        # words back together.
        for match in re.finditer(r"\s*\S+", description):
            word = match.group()

            # Keep adding words while the total length is less than
            # MAX_SIZE.
            if len(word) + len(new_desc) < max_size:
                new_desc += word
            else:
                # At this point the next word *will* take us over
                # MAX_SIZE, but we also want to ensure that its not
                # a huge word. If it is add it anyway and we'll
                # truncate later.
                if len(new_desc) < min_size:
                    new_desc += word
                break

        # Double check that we're not over the limit
        if len(new_desc) > max_size:
            new_desc = new_desc[:max_size]

        # We always add an ellipsis because at the very least
        # we chopped mid paragraph.
        description = new_desc.strip() + u"…"
    return description if description else None