interactive bots: Create Howdoi bot.

This bot allows users to search technical questions from Stack
Overflow.

contrib_bots/lib/HowdoiBot/docs.md

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+# Howdoi bot
+
+This bot will allow users to get technical answers from
+[StackOverflow](https://stackoverflow.com). It is build on top of the
+python command line tool [howdoi](https://github.com/gleitz/howdoi) by
+Benjamin Gleitzman.
+
+## Usage
+
+Simply prepend your questions with one of the following commands. The
+answer will be formatted differently depending the chosen command.
+
+| Command     | Respond                                                |
+| ----------- | ------------------------------------------------------ |
+| `@howdowe`  | Concise answer to the same stream.                     |
+| `@howdowe!` | Same as `@howdowe` but with full answer and URL of the solutions. |
+| `@howdoi`   | Concise answer replied to sender via private message.  |
+| `@howdoi!`  | Same as `@howdoi` but with full answer and URL of the solutions. |
+
+## Screenshots
+
+#### Example 1
+
+Question -> `@howdowe use supervisor in elixir`
+
+  ![howdowe question](question_howdowe.png)
+
+Answer ->  Howdoi would try to **only** respond with the coding section
+of the answer.
+
+  ![howdowe answer](answer_howdowe.png)
+
+#### Example 2
+
+Question -> `@howdoi! stack vs heap`
+
+  ![howdoi! question](question_howdoi_all.png)
+
+Answer -> Howdoi would return the **full** stackoverflow answer via
+**private message** to the original sender. The URL of the answer can be
+seen at the bottom of the message.
+
+  ![howdoi! answer](answer_howdoi_all.png)
+
+**Note:**
+
+* Line wrapped is enabled with a maximum line length of 85 characters.
+This could be adjusted in the source code (`HowdoiHandler.MAX_LINE_LENGTH`).
+
+* *Howdoi* generally perform better if you ask a question using keywords
+instead of a complete sentences (eg: "How do i make a decorator in Python"
+-> "python decorator").
+
+* __[*Limitation*]__ If a answer contains multiple code blocks, the `@howdoi`
+and `@howdowe` commands would only return the first coding section, use
+`@howdo[we|i]!` in that case.

contrib_bots/lib/howdoi_bot.py

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+"""
+This bot uses the python library `howdoi` which is not a
+dependency of Zulip. To use this module, you will have to
+install it in your local machine. In your terminal, enter
+the following command:
+
+    $ sudo pip install howdoi --upgrade
+
+Note:
+    * You might have to use `pip3` if you are using python 3.
+    * The install command would also download any dependency
+      required by `howdoi`.
+"""
+
+import sys
+import logging
+from textwrap import fill
+try:
+    from howdoi.howdoi import howdoi
+except ImportError:
+    logging.error("Dependency missing!!\n%s" % (__doc__))
+    sys.exit(0)
+
+
+class HowdoiHandler(object):
+    '''
+    This plugin facilitates searching Stack Overflow for
+    techanical answers based on the Python library `howdoi`.
+    To get the best possible answer, only include keywords
+    in your questions.
+
+    There are two possible commands:
+    * @howdowe > This would return the answer to the same
+                 stream that it was called from.
+
+    * @howdoi > The bot would send a private message to the
+                user containing the answer.
+
+    By default, howdoi only returns the coding section of the
+    first search result if possible, to see the full answer
+    from Stack Overflow, append a '!' to the commands.
+    (ie '@howdoi!', '@howdowe!')
+    '''
+
+    MAX_LINE_LENGTH = 85
+
+    def usage(self):
+        return '''
+            This plugin will allow users to get techanical
+            answers from Stackoverflow. Users should preface
+            their questions with one of the following:
+
+                * @howdowe > Answer to the same stream
+                * @howdoi > Answer via private message
+
+                * @howdowe! OR @howdoi! > Full answer from SO
+            '''
+
+    def triage_message(self, message):
+        cmd_list = ['@howdowe', '@howdoi', '@howdowe!', '@howdoi!']
+        question = message['content']
+
+        # This next line of code is defensive, as we never want
+        # to get into an infinite loop of searching answers
+        # from Stackoverflow!
+        if message['sender_email'].startswith('howdoi'):
+            return False
+
+        is_howdoi = any([question.startswith(cmd) for cmd in cmd_list])
+
+        return is_howdoi
+
+    def line_wrap(self, string, length):
+        lines = string.split("\n")
+
+        wrapped = [(fill(line) if len(line) > length else line)
+                   for line in lines]
+
+        return "\n".join(wrapped).strip()
+
+    def get_answer(self, command, query):
+        question = query[len(command):].strip()
+        result = howdoi(dict(
+            query=question,
+            num_answers=1,
+            pos=1,
+            all=command[-1] == '!',
+            color=False
+        ))
+        _answer = self.line_wrap(result, HowdoiHandler.MAX_LINE_LENGTH)
+
+        answer = "Answer to '%s':\n```\n%s\n```" % (question, _answer)
+
+        return answer
+
+    def handle_message(self, message, client, state_handler):
+        question = message['content']
+
+        if question.startswith('@howdowe!'):
+            client.send_message(dict(
+                type='stream',
+                to=message['display_recipient'],
+                subject=message['subject'],
+                content=self.get_answer('@howdowe!', question)
+            ))
+
+        elif question.startswith('@howdoi!'):
+            client.send_message(dict(
+                type='private',
+                to=message['sender_email'],
+                content=self.get_answer('@howdoi!', question)
+            ))
+
+        elif question.startswith('@howdowe'):
+            client.send_message(dict(
+                type='stream',
+                to=message['display_recipient'],
+                subject=message['subject'],
+                content=self.get_answer('@howdowe', question)
+            ))
+
+        elif question.startswith('@howdoi'):
+            client.send_message(dict(
+                type='private',
+                to=message['sender_email'],
+                content=self.get_answer('@howdoi', question)
+            ))
+
+
+handler_class = HowdoiHandler