Update Dart manifest for Scoop

updateDartManifestForScoop.ps1

# TODO(guillermooo): add dartium manifest

function getManifest {
    param($url)
    invoke-restmethod $url
}

function getLatestVersion {
    param($manifest)
    invoke-restmethod $manifest.checkver.url | select -expandproperty version
}

function getCheckSum {
    param($manifest, $arch)
    $type = "$($arch)bit"
    [void] ((invoke-restmethod "$($manifest.architecture.$type.url).sha256sum") -match "^(.+?)\s")
    $matches.1
}

function buildUrl {
	param($manifest, $arch, $latestVersion)
	$url = [System.Uri] $manifest.architecture."$($arch)bit".url
	$segments = $url.segments
	$segments[5] = "$latestVersion/"
	[System.UriBuilder]::new($url.scheme, $url.host, -1, $($segments -join '')).ToString()
}

function updateManifest {
    param($url)
    $manifest = getManifest $url
    $latestVersion = getLatestVersion $manifest
    if ($latestVersion -eq $manifest.version) {
        return
    }
    $manifest.version = $latestVersion
    $manifest.architecture."64bit".url = buildUrl $manifest 64 $latestVersion
    $manifest.architecture."32bit".url = buildUrl $manifest 32 $latestVersion
    $manifest.architecture."64bit".hash = getCheckSum $manifest 64
    $manifest.architecture."32bit".hash = getCheckSum $manifest 32
    $manifest
}

function writeManifest {
    param($manifest, $fileName)
    if ($manifest -eq $null) {
        write-output "Dart manifest is up to date: $fileName."
        return
    }
    $manifest | convertto-json | out-file $fileName -encoding ascii
    write-output "Updated manifest: $fileName."
}

$stableManifest = "https://raw.githubusercontent.com/lukesampson/scoop/master/bucket/dart.json"
$devManifest = "https://raw.githubusercontent.com/lukesampson/scoop-extras/master/dart-dev.json"

writeManifest (updateManifest $stableManifest) "dart.json"
writeManifest (updateManifest $devManifest) "dart-dev.json"