--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/piecrust/admin/views/mentions.py	Sun Feb 18 20:37:54 2018 -0800
@@ -0,0 +1,130 @@
+import os
+import os.path
+import json
+import time
+import logging
+import requests
+from bs4 import BeautifulSoup
+from flask import current_app, g, request, make_response, abort
+from ..blueprint import foodtruck_bp
+from piecrust.app import PieCrustFactory
+from piecrust.serving.util import get_requested_page
+
+
+logger = logging.getLogger(__name__)
+
+
+@foodtruck_bp.route('/webmention', methods=['POST'])
+def post_webmention():
+    # Basic validation of source/target.
+    src_url = request.form.get('source')
+    tgt_url = request.form.get('target')
+    if not src_url or not tgt_url:
+        logger.error("No source or target specified.")
+        abort(400)
+    if src_url.lower().rstrip('/') == tgt_url.lower().rstrip('/'):
+        logger.error("Source and target are the same.")
+        abort(400)
+
+    # See if we need to do this synchronously or asynchronously, and other
+    # things we should know up-front.
+    wmcfg = g.site.piecrust_app.config.get('webmention')
+    if wmcfg.get('use_task_queue') is True:
+        tasks_dir = os.path.join(g.site.piecrust_app.root_dir, '_tasks')
+        _ensure_dir(tasks_dir)
+        task_data = {
+            'type': 'webmention',
+            'data': {'source': src_url, 'target': tgt_url}}
+        task_path = os.path.join(tasks_dir, '%s.json' % int(time.time()))
+        with open(task_path, 'w', encoding='utf8') as fp:
+            json.dump(task_data, fp)
+        return make_response("Webmention queued.", 202, [])
+
+    # Find if we have a page at the target URL.
+    # To do that we need to spin up a PieCrust app that knows how the website
+    # works. Because the website might have been baked with custom settings
+    # (usually the site root URL) there's a good chance we need to apply
+    # some variants, which the user can specify in the config.
+    pcappfac = PieCrustFactory(
+        current_app.config['FOODTRUCK_ROOT_DIR'],
+        cache_key='webmention')
+    if wmcfg.get('config_variant'):
+        pcappfac.config_variants = [wmcfg.get('config_variant')]
+    if wmcfg.get('config_variants'):
+        pcappfac.config_variants = list(wmcfg.get('config_variants'))
+    if wmcfg.get('config_values'):
+        pcappfac.config_values = list(wmcfg.get('config_values').items())
+    pcapp = pcappfac.create()
+    try:
+        req_page = get_requested_page(pcapp, tgt_url)
+        if req_page.page is None:
+            abort(404)
+    except Exception as ex:
+        logger.error("Can't check webmention target page: %s" % tgt_url)
+        logger.exception(ex)
+        abort(404)
+
+    # Grab the source URL's contents and see if anything references the
+    # target (ours) URL.
+    src_t = requests.get(src_url)
+    src_html = BeautifulSoup(src_t.text, 'html.parser')
+    for link in src_html.find_all('a'):
+        href = link.get('href')
+        if href == tgt_url:
+            break
+    else:
+        logger.error("Source '%s' doesn't link to target: %s" %
+                     (src_url, tgt_url))
+        abort(400)
+
+    # Find something to quote for this webmention. We find an `h-entry`
+    # to get a title, excerpt, and/or text.
+    blurb = None
+    hentry = src_html.find(class_='h-entry')
+    if hentry:
+        try:
+            pname = hentry.find(class_='p-name')
+            pauthor = hentry.find(class_='p-author')
+            blurb = {
+                'pname': _bs4_contents_str(pname),
+                'pauthor': _bs4_contents_str(pauthor)}
+        except:  # NOQA
+            logger.error("Couldn't get h-entry info.")
+
+    dirname, _ = os.path.splitext(req_page.page.content_spec)
+    dirname += '-assets'
+    _ensure_dir(dirname)
+    mention_path = os.path.join(dirname, 'mentions.json')
+    try:
+        with open(mention_path, 'r', encoding='utf-8') as fp:
+            mention = json.load(fp)
+    except IOError:
+        mention = {'mentions': []}
+
+    for m in mention['mentions']:
+        if m['source'] == src_url:
+            return
+
+    new_mention = {'source': src_url}
+    if blurb:
+        new_mention.update(blurb)
+
+    mention['mentions'].append(new_mention)
+
+    with open(mention_path, 'w', encoding='utf-8') as fp:
+        json.dump(mention, fp)
+    logger.info("Received webmention from: %s" % src_url)
+
+    return make_response(("Webmention received.", 202, []))
+
+
+def _bs4_contents_str(node):
+    return ''.join([str(c).strip() for c in node.contents])
+
+
+def _ensure_dir(path, mode=0o775):
+    try:
+        os.makedirs(path, mode=mode, exist_ok=True)
+    except OSError:
+        pass
+