PoshBot middlware hook to notify chatty people in a Slack channel to use threaded conversations if they post too many messages in a short time interval

rate_limiting_notice.ps1

<#
.SYNOPSIS
    Suggest Slack threads for talkative users.
.DESCRIPTION
    This middleware tracks how many messages (x) users send per (y) amount of time.
    If a user goes over the threshold, we'll send a message suggesting that Slack threads should be used.
.NOTES
    Based on https://stackoverflow.com/questions/667508/whats-a-good-rate-limiting-algorithm
#>
param(
    $Context,
    $Bot
)

$Bot.LogDebug('Beginning message ratelimit middleware')

# We'll allow (5) messages per user in a 60 second window before suggesting threads
$maxMsgs    = 6
$timePeriod = 60

$userId       = $Context.Message.From
$timePeriodMS = $timePeriod * 1000

# Only measure messages NOT already in a thread
# This middlware hook stage also receives extra messages whenever a user replies in a thread
# We need to ensure we DON'T count these against the rate limiting
$unThreadedMsg = (
    ([string]::IsNullOrWhiteSpace($Context.Message.RawMessage.thread_ts) -and
    ($Context.Message.RawMessage.type -eq 'message' -and $Context.Message.RawMessage.subtype -ne 'message_replied'))
)

if ($unThreadedMsg) {
    # Load the tracker
    $trackerPath = Join-Path $Bot.Configuration.ConfigurationDirectory 'msg_ratelimiting_tracking.clixml'
    if (Test-Path $trackerPath) {
        $tracker = Import-Clixml $trackerPath
    } else {
        $tracker = @{
            $userId = @{
                Allowance   = $maxMsgs
                LastMsgTime = [datetime]::UtcNow
            }
        }
    }

    $now        = [datetime]::UtcNow
    $timePassed = ($now - $tracker[$userId].LastMsgTime).TotalSeconds
    $tracker[$userId].LastMsgTime = $now
    $tracker[$userId].Allowance  += $timePassed * ($maxMsgs / $timePeriodMS)

    if ($tracker[$userId].Allowance -gt $maxMsgs) {
        $tracker[$userId].Allowance = $maxMsgs
    }

    If ($tracker[$userId].Allowance -lt 1.0) {
        $Bot.LogDebug("User [$userId] has breached ratelimit of [$maxMsgs] messages in [$timePeriod)] seconds. Sending thread reminder response")
        $response                 = [Response]::new()
        $response.To              = $Context.Message.To
        $response.MessageFrom     = $Context.Message.From
        $response.OriginalMessage = $Context.Message
        $mentionUser = "<@$($Context.Message.From)>"
        $text = "Hey $mentionUser, we noticed you have a lot to say. Perhaps creating a Slack thread would be useful."
        $response.Data = New-PoshBotTextResponse -Text $text -AsCode
        $Bot.SendMessage($response)

        $Bot.LogDebug('Sending thread reminding response')

        # Reset so we don't send again until they breach the limit again
        $tracker[$userId].Allowance = $maxMsgs
    } else {
        $tracker[$userId].Allowance -= 1.0
    }

    $tracker | Export-Clixml -Path $trackerPath
} else {
    $Bot.LogDebug("Ignoring message. It's already in a threaded conversation.")
}

# Return context back for any subsequent middleware
$Bot.LogDebug('Ending message ratelimit middleware')
$Context