# When running this script locally, provide it with your own PAT.
$token = ""
$headers = @{}

if (-not $token) {
    # This block is using the Azure DevOps variables available in the pipeline
    $headers["Authorization"] = "Bearer $($env:SYSTEM_ACCESSTOKEN)"
    $adoReleaseManagerOrgEndpoint = "$($env:SYSTEM_COLLECTIONURI)"
    $projectName = "$($env:BUILD_PROJECTNAME)"
    $releaseDefinitionId = $($env:RELEASE_DEFINITIONID)
    $currentReleasedId = $($env:RELEASE_RELEASEID)
} else {
    # This block is used for local testing.
    # The $releaseDefinitionId and $currentReleasedId might need to be changed, depending on what you want to do.
    $encodedToken = [System.Convert]::ToBase64String([System.Text.Encoding]::ASCII.GetBytes(":$($token)"))
    $headers["Authorization"] = "Basic $encodedToken"

    $adoReleaseManagerOrgEndpoint = "https://vsrm.dev.azure.com/myOrganization/"   # SYSTEM_COLLECTIONURI
    $projectName = "myProject"                                                     # BUILD_PROJECTNAME
    $releaseDefinitionId = 123                                                     # RELEASE_DEFINITIONID
    $currentReleasedId = 45678                                                     # RELEASE_RELEASEID
}

# The Azure DevOps endpoint to retrieve all releases for a given release definition.
# https://learn.microsoft.com/en-us/rest/api/azure/devops/release/releases/list
$latestReleasesEndpoint = "$($adoReleaseManagerOrgEndpoint)$($projectName)/_apis/release/releases?api-version=6.0&`$expand=environments&definitionId=$($releaseDefinitionId)"
Write-Host "Invoking: $latestReleasesEndpoint"
$releasesResponse = Invoke-RestMethod -Uri $latestReleasesEndpoint -Headers $headers -Method Get
Write-Host "Found $($releasesResponse.count) releases."

# Filtering the releases to only include the ones that have a `MySpecificStage` environment and that have succeeded.
$filteredReleases = $releasesResponse.value | Where-Object {
    $_.environments -ne $null -and 
    ($_.environments | Where-Object {
        $_.name -eq "MySpecificStage" -and
        $_.status -eq "succeeded"
    })
}

Write-Host "Found $($filteredReleases.count) releases with a MySpecificStage environment that succeeded."
Write-Host "Current release - ID: $($currentReleasedId)"
$previousSuccesfulReleaseId = ""

# Take the identifier from the previous release.
$filteredReleases | Select-Object -First 1 -Skip 1 | ForEach-Object {
    $previousSuccesfulReleaseId = $_.id
    $name = $_.name
    Write-Host "Previous succeeded release - ID: $previousSuccesfulReleaseId, Name: $name"
}

# The Azure DevOps endpoint to retrieve all changes between two releases.
# This endpoint for releases specifically IS NOT documented, but the documentation for the builds endpoint is very similar.
# For Builds: https://learn.microsoft.com/en-us/rest/api/azure/devops/build/builds/get-changes-between-builds
$changesBetweenReleaseEndpoint = "$($adoReleaseManagerOrgEndpoint)$($projectName)/_apis/Release/releases/$($currentReleasedId)/changes?baseReleaseId=$($previousSuccesfulReleaseId)"
Write-Host "Invoking: $changesBetweenReleaseEndpoint"
$changesResponse = Invoke-RestMethod -Uri $changesBetweenReleaseEndpoint -Headers $headers -Method Get

Write-Host "Found $($changesResponse.count) changes."
$output = ""
# Retrieve all the titles from the changes
$changesResponse.value | ForEach-Object {
    $output += $_.message + " | "
    Write-Host $_.message
}

Write-Host "##vso[task.setvariable variable=changesBetweenReleases;]$output"

Function GetChangesWhenRepositoryArtifactIsUsed {
    $nameOfRepositoryArtifact = "_MyRepositoryArtifactName"
    $remoteName = "origin"
    $branchToGetChangesFrom = "main"

    # Get the Source Version of the release run
    $detailsForCurrentReleaseEndpoint = "$($adoReleaseManagerOrgEndpoint)$($projectName)/_apis/Release/releases/$($currentReleasedId)"
    Write-Host "Invoking: $detailsForCurrentReleaseEndpoint"
    $detailsForCurrentRelease = Invoke-RestMethod -Uri $detailsForCurrentReleaseEndpoint -Headers $headers -Method Get

    $sourceArtifactForCurrentRelease = $detailsForCurrentRelease.artifacts | Where-Object { $_ -and $_.alias -and $_.alias -eq $nameOfRepositoryArtifact } | Select-Object -First 1
    $sourceVersionForCurrentRelease = $sourceArtifactForCurrentRelease.definitionReference.version.id

    # Get the Source Version of the previous release run ($previousSuccesfulReleaseId)
    $detailsForPreviousSuccessfulReleaseEndpoint = "$($adoReleaseManagerOrgEndpoint)$($projectName)/_apis/Release/releases/$($previousSuccesfulReleaseId)"
    Write-Host "Invoking: $detailsForPreviousSuccessfulReleaseEndpoint"
    $detailsForPreviousSuccessfulRelease = Invoke-RestMethod -Uri $detailsForPreviousSuccessfulReleaseEndpoint -Headers $headers -Method Get

    $sourceArtifactForPreviousRelease = $detailsForPreviousSuccessfulRelease.artifacts | Where-Object { $_ -and $_.alias -and $_.alias -eq $nameOfRepositoryArtifact } | Select-Object -First 1
    $sourceVersionForPreviousRelease = $sourceArtifactForPreviousRelease.definitionReference.version.id
    
    # If the Git repository is not found in the artifacts, search for the Build with a matching name, it also contains a source version.
    if(-not $sourceVersionForPreviousRelease) {
        $nameOfBuild = "_MyReleaseBuild"
        $sourceArtifactForPreviousRelease = $detailsForPreviousSuccessfulRelease.artifacts | Where-Object { $_ -and $_.alias -and $_.alias -eq $nameOfBuild } | Select-Object -First 1
        $sourceVersionForPreviousRelease = $sourceArtifactForPreviousRelease.definitionReference.sourceVersion.id    
    }

    # Get the changes between the two source versions
    Write-Host "Searching for the changes between commit '$sourceVersionForPreviousRelease' and '$sourceVersionForCurrentRelease'."

    # Need to create a Git repository, before the git commands can be invoked over here.
    git init
    # The $repositoryUrl can be retrieved from an environment variable. The name of this variable differs on how you named the artifact.
    git -c http.extraheader="AUTHORIZATION: Bearer $($env:SYSTEM_ACCESSTOKEN)" remote add $remoteName $repositoryUrl
    # Use the `--filter` over here, so files aren't downloaded. This makes the call much more efficient (https://github.blog/2020-12-21-get-up-to-speed-with-partial-clone-and-shallow-clone/#user-content-partial-clone)
    git -c http.extraheader="AUTHORIZATION: Bearer $($env:SYSTEM_ACCESSTOKEN)" fetch --filter=blob:none
    $output = git log "$remoteName/$branchToGetChangesFrom" --pretty=oneline "$sourceVersionForPreviousRelease..$sourceVersionForCurrentRelease"

    Write-Host "Changes between releases: $output"
    Write-Host "##vso[task.setvariable variable=changesBetweenReleases;]$output"
}