slack_reformat.py

# Module to consolidate logic around reformatting messages that originate on
# slack before they are forwarded.

import datetime
import logging
import re
import sys
import requests
import traceback

from io import BytesIO

_LOGGER = logging.getLogger(__name__)

# These are module-private regular expressions used by the reformatter
_SLACK_USER_MATCH = re.compile("<@([A-Z0-9]+)>")
_SLACK_NOTIF_MATCH = re.compile("<!([a-zA-Z0-9]+)>")
_SLACK_CHANNEL_MATCH = re.compile("<#[a-zA-Z0-9]+\\|([a-zA-Z0-9]+)>")
_SLACK_LINK_BARE_URL_MATCH = re.compile("<([a-zA-Z0-9]+:[^|>]+)(\\|\\1){0,1}>")
_SLACK_LINK_MATCH = re.compile("<([a-zA-Z0-9]+:[^|>]+)(?:\\|([^>]+)){0,1}>")

async def reformat_slack_text(user_formatter, input_text):
    '''This helper method, given a SlackUserFormatter, will format the input_text
       for transmission from Slack to other services.  Using it ensures that any dependencies
       between the individual reformatters is obeyed. '''
    input_text = await user_formatter.format_user(input_text)
    input_text = await format_notifications(input_text)
    input_text = await format_channels(input_text)
    input_text = await format_markdown_links(input_text)

    return input_text


async def _do_transform(input_text,
                        match_pattern, replace_func):
    '''This method provides the basic work of finding parts of a slack message to replace with
       alternate markdown, and then getting them replaced.  Private to this module.

       Searches input_text for regex_search (compiled regex object)
       Strips < > and prefix if specified.
           Ex. "<@U###>" becomes U###, "<!here>" becomes "here"
       Passes the regex match object to (async) replace_func, which returns what to replace it with.
           Ex. for channels which match "<@C##|general>" replace_func would return '**#general**'

       Returns the result of the transform.'''
    transform_shift = 0
    for m in match_pattern.finditer(input_text):
        match = m.group()

        old_text = input_text
        start = m.start() + transform_shift

        input_text = old_text[:start]
        input_text += await replace_func(m)
        input_text += old_text[start + len(match):]

        transform_shift = len(input_text) - len(old_text) + transform_shift
    return input_text


class SlackUserFormatter:
    def __init__(self, user_lookup_function, log_on_error=True):
        '''Constructor.  user_lookup_function should return a couroutine that resolves to
            the display name of the passed in user identifier. It may throw an exception on failure.'''
        self._get_slack_user = user_lookup_function
        self._log_on_error = log_on_error

    async def format_user(self, input_text):
        '''Handles reformatting of slack markdown user references in a string of text. '''

        async def user_reformat(m):
            '''User reformat helper function for _do_transform. '''
            match = m.group()
            at_user_id = match[2:-1]

            try:
                at_user = await self._get_slack_user(at_user_id)

                if at_user:
                    return '**@%s**' % at_user
                else:
                    _LOGGER.info("couldn't find get @ user %s:",
                                 at_user_id)
            except:
                e = sys.exc_info()
                exc_type, exc_value, exc_traceback = e
                trace = repr(traceback.format_exception(exc_type,
                                                        exc_value,
                                                        exc_traceback))
                if (self._log_on_error):
                    _LOGGER.warning("couldn't find get @ user %s: %s",
                                    at_user_id, trace)

            # in failure cases, just return the original text
            return match

        return await _do_transform(input_text,
                                   _SLACK_USER_MATCH,
                                   user_reformat)


async def format_notifications(input_text):
    '''Handles reformatting of things like @here.  Note that this assumes that
       any groups have already been filtered out, as they use a similar format
       but would need the ID to be looked up.'''
    async def notification_reformat(m):
        return ('**@%s**' % m.group(1))

    return await _do_transform(input_text,
                               _SLACK_NOTIF_MATCH,
                               notification_reformat)


async def format_channels(input_text):
    '''Finds anything that looks like a slack channel in the text, and replaces
       it with a bolded version.  Returns the new text.'''
    async def channel_reformat(m):
        return ('**#%s**' % m.group(1))

    return await _do_transform(input_text,
                               _SLACK_CHANNEL_MATCH,
                               channel_reformat)


async def format_markdown_links(input_text):
    '''Finds anything that looks like a markdown link in the text.

       If the display text is identical to the URL, we just remove all the markdown
       and leave a bare URL.  If there is replacement text, we change it to zulip
       markdown.

       NOTE: This later case results in brokenness for groupme, but presumably
       the URL will still be at least visible.

       NOTE: We currently will leave the carets in place for a URL of the form
       <http://foo.com>

       Returns the new text.'''
    async def replace_markdown_link(m):
        match = m.group()
        bare_url_match = _SLACK_LINK_BARE_URL_MATCH.match(match)

        if bare_url_match:
            replacement = bare_url_match.group(1)
        else:
            replacement_url = m.group(1)
            replacement_displaytext = m.group(2)
            replacement = '[%s](%s)' % (replacement_displaytext, replacement_url)

        return replacement

    return await _do_transform(input_text,
                               _SLACK_LINK_MATCH,
                               replace_markdown_link)


def format_files_from_slack(files, needs_leading_newline,
                            slack_bearer_token=None, zulip_client=None):
    '''Given a list of files from the slack API, return both a markdown and plaintext
       string representation of those files.

       Assuming a bearer token and zulip client are provided, the files are mirrored to zulip
       and those links are included in the markdown result.

       This method only uses the passed in message text to determine how to format its output
       caller must append as appropriate.'''
    if files == None:
        files = []

    # TODO: This function should ideally interface with a CDN and actually move the files to a
    # public location.  For now, we just avoid hiding the presense of a file in the message.
    output = { 'markdown': '',
               'plaintext': '' }

    first_file = True
    for file in files:
        if not first_file or needs_leading_newline:
            output['markdown'] += '\n'
            output['plaintext'] += '\n'
        else:
            first_file = False

        if 'name' in file and file['name']:
            rendered_markdown_name = file['name']
            if slack_bearer_token and zulip_client and 'url_private' in file and file['url_private']:
                file_private_url = file['url_private']
                r = requests.get(file_private_url,
                                 headers={"Authorization": f"Bearer {slack_bearer_token}"})
                if r.status_code == 200:
                    if file_private_url != r.url:
                        # we were redirected!
                        _LOGGER.info(
                            f'Apparent slack redirect from {file_private_url} to {r.url} when bridging file.  Skipping.')
                    else:
                        uploadable_file = BytesIO(r.content)
                        uploadable_file.name = file['name']

                        response = zulip_client.upload_file(uploadable_file)
                        if 'uri' in response and response['uri']:
                            rendered_markdown_name = f"[{file['name']}]({response['uri']})"
                        else:
                            _LOGGER.info('Got bad response when uploading to zulip: {}'.format(response))
                else:
                    _LOGGER.info(f"Got code {r.status_code} when fetching {file_private_url} from slack.")

            output['markdown'] += f"*(Bridged Message included file: {rendered_markdown_name}"
            output['plaintext'] += f"(Bridged Message included file: {file['name']}"
            if 'title' in file and file['title'] and file['name'] != file['title']:
                output['markdown'] += f": '{file['title']}'"
                output['plaintext'] += f": '{file['title']}'"
            output['markdown'] += ")*"
            output['plaintext'] += ")"

    return output


async def format_attachments_from_slack(message_text, attachments, edit_or_delete, user_formatter):
    '''Translate a slack-style attachments list into text to be appended to a zulip message
       returning the result in both plaintext and markdown form.
       
       This method only uses the passed in message text to determine how to format its output
       caller must append as appropriate.'''
    output = { 'markdown': '',
               'plaintext': '' }

    if len(attachments) > 0:
        if edit_or_delete or len(message_text) > 0:
            output['markdown'] += '\n\n'
            output['plaintext'] += '\n\n'
        for attach_i in range(len(attachments)):
            if attach_i > 0:
                output['markdown'] += '\n\n'
                output['plaintext'] += '\n\n'
            attachment = attachments[attach_i]
            if 'pretext' in attachment:
                output['markdown'] += attachment['pretext'] + '\n'
                output['plaintext'] += attachment['pretext'] + '\n'
            if ('text' in attachment or
                    'title' in attachment or
                    'author_name' in attachment):
                if (not edit_or_delete and not len(message_text) > 0
                    and 'pretext' not in attachment):
                    output['markdown'] += '\n'
                    output['plaintext'] += '\n'
                output['markdown'] += '```quote\n'
                # no need to extend output['plaintext'] in a similar way
                if 'author_link' in attachment:
                    output['markdown'] += f"[{attachment['author_name']}]({attachment['author_link']})\n"
                    output['plaintext'] += f"{attachment['author_name']}: {attachment['author_link']}\n"
                elif 'author_name' in attachment:
                    output['markdown'] += f"{attachment['author_name']}\n"
                    output['plaintext'] += f"{attachment['author_name']}\n"
                if 'title_link' in attachment:
                    output['markdown'] += f"**[{attachment['title']}]({attachment['title_link']})**\n"
                    output['plaintext'] += f"{attachment['title']}: {attachment['title_link']}\n"
                elif 'title' in attachment:
                    output['markdown'] += f"**{attachment['title']}**\n"
                    output['plaintext'] += f"{attachment['title']}\n"
                if 'text' in attachment:
                    text_formatted = \
                        await reformat_slack_text(user_formatter, attachment['text'])
                    output['markdown'] += f"{text_formatted}\n"
                    output['plaintext'] += f"{text_formatted}\n"
                if 'image_url' in attachment:
                    output['markdown'] += f"[Image]({attachment['image_url']})\n"
                    output['plaintext'] += f"(Image: {attachment['image_url']})\n"
                if 'fields' in attachment:
                    for field in attachment['fields']:
                        if 'title' in field:
                            output['markdown'] += f"**{field['title']}**\n"
                            output['plaintext'] += f"{field['title']}\n"
                        if 'value' in field:
                            field_value_formatted = \
                                await reformat_slack_text(user_formatter, field['value'])
                            output['markdown'] += f"{field_value_formatted}\n"
                            output['plaintext'] += f"{field_value_formatted}\n"
                if 'footer' in attachment:
                    footer_formatted = \
                        await reformat_slack_text(user_formatter, attachment['footer'])
                    output['markdown'] += f"*{footer_formatted}*"
                    output['plaintext'] += f"{footer_formatted}"
                if 'footer' in attachment and 'ts' in attachment:
                    output['markdown'] += " | "
                    output['plaintext'] += " | "
                if 'ts' in attachment:
                    out_time = datetime.datetime.fromtimestamp(attachment['ts']).strftime('%c')
                    output['markdown'] += f"*{out_time}*"
                    output['plaintext'] += f"{out_time}"
                if 'footer' in attachment or 'ts' in attachment:
                    output['markdown'] += "\n"
                    output['plaintext'] += "\n"
                output['markdown'] += '```'
                # no need to extend output['plaintext'] in a similar way

    return output