add Get-MatrixRoomId (#2)

public/Get-MatrixRoomId.ps1

@@ -0,0 +1,42 @@
+<#
+    .Synopsis
+    Get the Matrix Room ID for the given Room Alias.
+
+    .Description
+    Get the Matrix Room ID for the given Room Alias from _matrix/client/v3/directory/room/{roomAlias}. See https://spec.matrix.org/v1.2/client-server-api/#get_matrixclientv3directoryroomroomalias.
+
+    .Parameter ServerUrl
+    URL for the Matrix server to query, for example "https://matrix.example.com".
+
+    .Parameter RoomAlias
+    The Matrix Room Alias to retrieve the Room ID for (e.g. '#matrix:matrix.org').
+
+    .Example
+    Get-MatrixRoomId -ServerUrl $matrix -RoomAlias "#synapse:matrix.org"
+#>
+function Get-MatrixRoomId {
+    param(
+        [Parameter(Mandatory)]
+        [string]$ServerUrl,
+
+        [Parameter(Mandatory)]
+        [string]$RoomAlias
+    )
+
+    $encodedRoomAlias = $RoomAlias.Replace('#', '%23')
+    $url = New-MatrixUrl -ServerUrl $ServerUrl -ApiPath "_matrix/client/v3/directory/room/$encodedRoomAlias"
+    Write-Debug "URL: $url"
+
+    try {
+        $res = Invoke-RestMethod -Uri $url
+
+        $roomId = [PSCustomObject]@{
+            RoomId = $res.room_id
+            Servers = $res.servers
+        }
+
+        return $roomId
+    } catch {
+        Write-Error $_
+    }
+}