persisted interaction workflow state (redux sessions)

[andycmaj]

Summary

use a redux-like state-persistence and updating mechanism.
hydrate and dehydrate state before and after each action runs.

so an HTTP request ~= a redux action.

Idea

Here's an interaction message sent from Slack and handled by a lambda:

{
  "type": "block_actions",
  "team": { ... },
  "user": { ... },
  "api_app_id": "API_APP_ID",
  "token": "MESSAGE_TOKEN",
  "container": {
    "type": "message",
    "message_ts": "1561776627.000500",
    "channel_id": "CHANNEL_ID",
    "is_ephemeral": false
  },
  "trigger_id": "679602909028.575391407056.10172fae809593326ff92c15c4db964d",
  "channel": { ... },
  "message": {
    "type": "message",
    "subtype": "bot_message",
    "text": "This+content+can't+be+displayed.",
    "ts": "1561776627.000500",
    "bot_id": "BOT_ID",
    "blocks": [
      {
        "type": "section",
        "block_id": "P4NT",
        "text": {
          "type": "mrkdwn",
          "text": "Progress:+\u2593\u2593\u2591\u2591\u2591",
          "verbatim": false
        },
        "accessory": {
          "type": "button",
          "action_id": "doAThing",
          "text": { "type": "plain_text", "text": "Go!", "emoji": true }
        }
      }
    ]
  },
  "response_url": "RESPONSE_URL",
  "actions": [
    {
      "action_id": "doAThing",
      "block_id": "P4NT",
      "text": { "type": "plain_text", "text": "Go!", "emoji": true },
      "type": "button",
      "action_ts": "1561776635.121684"
    }
  ]
}

• slack do interaction
• handle request
• hydrate state into store
  • look up current state in distributed cache using previous message's identifiers. block_id
• dispatch action action_id + block_id or some combination of things from actions payload
• run reducers to compute new state
• persist new state with block_id
  • use trigger_id as new block_id
• render message with new block_id