## Usage
## sp = SlackPost(token=app_token, channel='#random')
## await sp.post_update("Look at this cool graph", ['img1.png', 'img2.png'])
## await sp.post_update("The data has changed!", ['img3.png', 'img4.png'])

class SlackPost():
    def __init__(self, token, channel):
        self.channel = channel
        self.client = client = slack.WebClient(
          token=token,
          run_async=True
          )
        self.ts = None


    async def post_update(self, message, fnames = []):
        attachments=[
            {
                'fallback': 'graph',
                'image_url': await self.upload_image(f)
            } for f in fnames
        ]

        await self.send_message(
            channel=self.channel,
            text=message,
            attachments=attachments
        )

    async def send_message(self, **kwargs):
        if self.ts:
            await (self.client.chat_update(ts=self.ts, **kwargs))
        else:
            response = await (self.client.chat_postMessage(**kwargs))
            self.ts = response.data['ts']
            self.channel = response.data['channel']

    async def upload_image(self, fname):
        img_response = await self.client.files_upload(
          file=fname,
          title="image"
        )

        file_response = await self.client.files_sharedPublicURL(
            file=img_response.data['file']['id'],
        )

        return file_response.data['file']['permalink_public']