add `Get-MatrixRoomId` (#2)

PSMatrix.psd1

@@ -73,7 +73,8 @@ FunctionsToExport = @(
     'New-MatrixAccessToken',
     'Remove-MatrixAccessToken',
     'Get-MatrixJoinedRooms',
-    'Get-MatrixJoinedMembers'
+    'Get-MatrixJoinedMembers',
+    'Get-MatrixRoomId'
 )
 
 # Cmdlets to export from this module, for best performance, do not use wildcards and do not delete the entry, use an empty array if there are no cmdlets to export.

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 $_
+    }
+}