Add slack-digest script which generates per channel digest emails to …

…be emailed to the respective mailing lists.

Original script by merlimat from his [private repo](https://github.com/merlimat/slack-email-digest).
Copied to BK repo for use with the BookKeeper project.

Reviewers: Enrico Olivelli <eolivelli@gmail.com>

This closes #2367 from Ghatage/slack-digest-jenkins

.test-infra/scripts/slack-email-digest/.gitignore

@@ -0,0 +1 @@
+configuration.yaml

.test-infra/scripts/slack-email-digest/README.md

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+# Slack to email digest bot
+
+This script is responsible for generating daily per channel digests and emailing them to certail mailing lists.
+

.test-infra/scripts/slack-email-digest/configuration-example.yaml

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+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+#
+
+slack:
+    token: xoxp-xxxxxxxxxxxxxx
+
+mail:
+    fromAddress: '"My Slack" <my.slack@gmail.com>'
+    smtp: smtp.gmail.com:587
+    useTLS: true
+    username: my.slack@gmail.com
+    password: xxxxxxxxx
+
+channels:
+    # Maps channels to a particular email address
+    general: users@my.project.org
+    dev: dev@my.project.org
+    random: users@my.project.org

.test-infra/scripts/slack-email-digest/requirements.txt

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+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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.
+#
+slacker
+PyYAML

.test-infra/scripts/slack-email-digest/slack_email_digest.py

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+#!/usr/bin/env python
+#
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you 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 slacker
+import yaml
+import time
+import re
+import datetime
+import smtplib
+from email.mime.text import MIMEText
+
+
+conf = yaml.load(open('configuration.yaml'))
+
+
+def send_digest(channel, address, digest):
+    msg = MIMEText(digest, _charset='utf-8')
+    msg['From'] = conf['mail']['fromAddress']
+    msg['To'] = address
+    msg['Subject'] = 'Slack digest for #%s - %s' % (
+        channel, datetime.datetime.now().strftime('%Y-%m-%d'))
+    server = smtplib.SMTP(conf['mail']['smtp'])
+    if conf['mail']['useTLS']:
+        server.starttls()
+    if 'username' in conf['mail']:
+        server.login(conf['mail']['username'], conf['mail']['password'])
+
+    server.sendmail(conf['mail']['fromAddress'], address, msg.as_string())
+    server.quit()
+
+
+slack = slacker.Slacker(conf['slack']['token'])
+
+channels = slack.channels.list().body['channels']
+
+# Get a mapping between Slack internal user ids and real names
+users = {}
+for user in slack.users.list().body['members']:
+    real_name = user.get('real_name', user.get('name'))
+    users[user['id']] = real_name
+
+last_day_timestamp = time.time() - (24 * 3600)
+
+for channel in channels:
+    id = channel['id']
+    name = channel['name']
+    topic = channel['topic']['value']
+
+    if name not in conf['channels']:
+        print('Ignoring channel: #%s' % name)
+        continue
+
+    toAddress = conf['channels'][name]
+    print('Getting digest of #%s --> %s' % (name, toAddress))
+
+    messages = slack.channels.history(channel=id,
+                                      oldest=last_day_timestamp,
+                                      count=1000)
+    digest = ''
+    for m in reversed(messages.body['messages']):
+        if not m['type'] == 'message':
+            continue
+
+        user = m.get('user')
+        if not user:
+            user = m['comment']['user']
+        sender = users.get(user, '')
+
+        date = datetime.datetime.utcfromtimestamp(float(m['ts'])).strftime('%Y-%m-%d %H:%M:%S UTC')
+        # Replace users id mentions with real names
+        text = re.sub(r'<@(\w+)>', lambda m: '@' + users[m.group(1)], m['text'])
+
+        digest += '%s - %s: %s\n' % (date, sender, text)
+        for reaction in m.get('reactions', []):
+            digest += '%s : %s\n' % (reaction['name'], ', '.join(map(users.get, reaction['users'])))
+        digest += '----\n'
+
+    if digest:
+        send_digest(name, toAddress, digest)