TeamCity Build Step to determine last successful build Git Commit ID

Determining Last Successful Build Git Commit Hash

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# Retrieves the last successful build of a TeamCity Project
# Finding the Commit Hash
# http://blogs.lessthandot.com/index.php/uncategorized/access-git-commits-during-a-teamcity-build-using-powershell/
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function Get-TeamCityLastSuccessfulRun([string] $TeamCityUrl, [string] $TeamCityBuildTypeId, [string] $TeamCityUsername, [string] $TeamCityPassword)
{
    $Credentials = "$($TeamCityUsername):$($TeamCityPassword)"
    $AuthString = [System.Convert]::ToBase64String([System.Text.Encoding]::UTF8.GetBytes("$Credentials"))
 
    $Url = "$($TeamCityUrl)/app/rest/buildTypes/id:$($TeamCityBuildTypeId)/builds/status:SUCCESS,count:1" 
 
    $Content = Invoke-WebRequest "$Url" -Headers @{"Authorization" = "Basic $AuthString"}
 
    return $Content
}

function Get-LatestSuccessfulRunCommitHash([string] $TeamCityUrl, [string] $TeamCityBuildTypeId, [string] $TeamCityUsername, [string] $TeamCityPassword)
{
    $Run = Get-TeamCityLastSuccessfulRun -TeamCityUrl "$TeamCityUrl" -TeamCityBuildTypeId "$TeamCityBuildTypeId" -TeamCityUsername "$TeamCityUsername" -TeamCityPassword "$TeamCityPassword"
    Write-Host "$Run"
    $LatestCommitFromRun = (Select-Xml -Content "$Run" -Xpath "/build/revisions/revision/@version").Node.Value
 
    return $LatestCommitFromRun
}

$LastGitCommitId = "%env.LastSuccessfulRunGitCommitId%"

# Only try to process if the Last Git Commit Id is not passed in as a run-time parameter
if (!$LastGitCommitId)
{
   $LastGitCommitId = Get-LatestSuccessfulRunCommitHash -TeamCityUrl "%teamcity.serverUrl%" -TeamCityBuildTypeId "%system.teamcity.buildType.id%" -TeamCityUsername "%system.teamcity.auth.userId%" -TeamCityPassword "%system.teamcity.auth.password%"
   
   # Set the TeamCity variable
   Write-Host "##teamcity[setParameter name='env.LastSuccessfulRunGitCommitId' value='$LastGitCommitId']"
}