badge.txt

caches:

    user_unread
    # tracks total unread count for each user
    key
    user_id -> count

    receipt_users
    # tracks which users are at a given read receipt
    # used to know when we can stop tracking the count for a receipt
    set
    receipt_id -> users

    channel_receipt
    # tracks unread count for a given read receipt
    # used to provide quick decr when a user updates a rooms read receipt
    hash
    channel_id, receipt_id -> count

    channel_read
    # tracks which read receipt a user is at, 
    # used to quickly locate a user's previous read receipt
    hash
    channel_id, user_id -> (receipt_id, command_id)

    channel_command
    # the stream for a channel
    # note for receipt commands only the most recent from a user is kept
    scored set
    channel_id, command_id -> command_type, commands

flows:

    message new ->
        channel_command append new
        for receipt in channel_receipt:
            channel_receipt incr receipt count
        # :(
        for user in room:
            user_unread incr user

    message read ->
        channel_command append new
        last = channel_read get user
        channel_read put user new
        channel_command remove last

        receipt_users smove last new user

        if receipt_users scard last == 0:
            receipt_users remove last
            channel_receipt remove last

        if receipt_users scard new == 1: 
            channel_receipt put new (count channel_command of type message > new)

        user_unread decr user (channel_receipt last - channel_receipt new)