ps/Modules/Alkami.DevOps.Common/Public/Publish-MessageToSlack.ps1

function Publish-MessageToSlack {
<#
.SYNOPSIS
    Posts a message to Slack.

.DESCRIPTION
    Posts a message to Slack.

.PARAMETER Channels
    Array of channels to post to, such as @("@username","#some-channel-name")

.PARAMETER SlackHookUrl
    Slack webhook url

.PARAMETER SlackParameters
    Hashtable of "messagebody" parameters. Cannot be used in conjunction with
    MessageText, UserName and IconEmoji. This is used when the caller wants to
    build their own message body JSON.

.PARAMETER SlackAttachments
    Hashtable of Slack message attachments to be added to the "messagebody"

.PARAMETER MessageText
    String of simple message text. If this is populated, MessageBody must be
    left empty or MessageBody will be used instead. This is used in combination
    with UserName and IconEmoji to construct a simple message JSON object. Caller
    does not have to build JSON object to send a simple message.

.EXAMPLE
    $chan = @("@trowton","#eng-sre-ci-cd-alerts")
    $buildlog = "http://duckduckgo.com"
    $fallback = "View the Build: $buildLog"
    $actions = @(
        @{
            "type" = "button"
            "text" = "Build Log"
            "url"  = $buildLog
        }
    )
    $attachments = @{
        fallback = $fallback
        color    = "#009EFF"
        actions  = $actions
    }
    $params = @{
        "username"="someuser";"icon_emoji"=":teamcity:";"text"="Text [with square brackets] and a period."
    }

    Publish-MessageToSlack -Channels $chan -SlackHookUrl $slackHookUrl -MessageBody $params -SlackAttachments $attachments

    Publish-MessageToSlack -Channels $chan -SlackHookUrl $slackHookUrl -MessageText "sampletext" -IconEmoji ":smiley:" -Username "TC job" -SlackAttachments $attachments

.LINK
    https://api.slack.com/methods/chat.postMessage

.NOTES
    Either MessageBody or MessageText must be populated to send a message. If MessageBody
    is populated, it will take precedence over MessageText.
#>
    [CmdletBinding()]
    [OutputType([void])]
    param(
        [Parameter(Mandatory = $True)]
        [array]$Channels,
        [Parameter(Mandatory = $True)]
        [string]$SlackHookUrl,
        [Parameter(Mandatory = $False)]
        [Alias ("MessageBody")]
        [hashtable]$SlackParameters,
        [Parameter(Mandatory = $False)]
        [hashtable]$SlackAttachments,
        [Parameter(Mandatory = $False)]
        [string] $MessageText,
        [Parameter(Mandatory = $False)]
        [string] $Username = "Publish Message",
        [Parameter(Mandatory = $False)]
        [string] $IconEmoji = ":slack:"
    )

    $loglead = (Get-LogLeadName)

    # Test if either MessageBody and MessageText are populated. One must be populated.
    if($null -eq $SlackParameters -and [string]::IsNullOrWhiteSpace($MessageText)) {
        throw "SlackParameters or MessageText must be populated to send a message!"
    }

    # Test if both MessageBody and MessageText are populated.
    if($null -ne $SlackParameters -and !([string]::IsNullOrWhiteSpace($MessageText))) {
        Write-Host "$loglead Both SlackParameters and MessageText parameters are not null. Choosing SlackParameters as message body."
    }

    # If MessageText is populated and SlackParameters is null, build a body.
    if($null -eq $SlackParameters) {
        Write-Verbose "$loglead SlackParameters is null, using MessageText [$MessageText], UserName [$UserName] and Icon [$IconEmoji] to send message."
        $messageBody = @{
            "username"    = "$Username";
            "text"        = "$MessageText";
            "icon_emoji"  = "$IconEmoji";
        }
    } else {
        # Parameters are a direct mapping to the message body.
        $messageBody = $SlackParameters
    }

    # Add attachments to message body, if they're provided.
    if ($null -ne $SlackAttachments) {
        $messageBody["attachments"] = @($SlackAttachments)
    }

    # Test for required keys in attachments.
    if($messageBody["attachments"].Count -gt 0) {
        $hasFallback = $false
        foreach ($attachment in $messageBody["attachments"]) {
            foreach ($aKey in $attachment.Keys) {
                if ($aKey -eq "fallback") {
                    $hasFallback = $true
                }
            }
        }

        if ($hasFallback -eq $false) {
            throw "Missing required parameter key 'fallback' on 'SlackAttachments'."
        }
    }

    # Test for 'text' key in MessageBody.
    $hasText = $false
    foreach ($param in $messageBody) {
        foreach ($key in $param.Keys) {
            if ($key -eq "text") {
                $hasText = $true
            }
        }
    }

    if ($hasText -eq $false) {
        throw "Missing required parameter key 'text' on 'SlackParameters'."
    }

    # Check $channels for commas to split on.
    if ($Channels[0].Contains(",")) {
        Write-Host "$loglead : Channels was supplied as a comma delimited string, not an array. Splitting..."
        $sanitizedChannels = $Channels[0].Split(",")
    } else {
        $sanitizedChannels = $Channels
    }

    # Send message to each specified channel(s).
    foreach ($channel in $sanitizedChannels) {
        $messageBody["channel"] = $channel;
        $messageJson = ($messageBody | ConvertTo-Json -Depth 100).Replace('\\r\\n', '\r\n')
        Write-Verbose "$loglead : Posting JSON:"
        Write-Verbose $messageJson

        try {
            (Invoke-RestMethod -Uri $SlackHookUrl -Method POST -Body $messageJson -ContentType "application/json") | Out-Null
        } catch {
            $errorMessage = $_.Exception.Message
            Write-Warning "$logLead : Could not post message to Slack.`nError message is: $errorMessage"
            # TODO: Metric this so we know that errors occurred.
        }
    }
}