toFileName tweaks

Author: codeconscious

src/UniqueFileGenerator.Console/StringGeneration.fs

@@ -1,7 +1,6 @@
 namespace UniqueFileGenerator.Console
 
 open System
-open System.Text
 
 module StringGeneration =
     let private charBank =
@@ -18,13 +17,14 @@ module StringGeneration =
     let generateMultiple itemLength count : string array =
         Array.init count (fun _ -> generateSingle itemLength)
 
-    let toFileName prefix extension baseName : string =
-        let ensureValidExtension ext =
-            if String.IsNullOrWhiteSpace ext then String.Empty
-            elif ext.StartsWith '.' then ext.Trim()
-            else $".%s{ext.Trim()}"
+    let toFileName (prefix: string) (extension: string) (baseName: string) : string =
+        let safeExtension =
+            match extension.Trim() with
+            | ext when String.IsNullOrWhiteSpace ext -> String.Empty
+            | ext when ext.StartsWith '.' -> ext
+            | ext -> $".%s{ext}"
 
-        $"%s{prefix}%s{baseName}%s{ensureValidExtension extension}"
+        $"%s{prefix}%s{baseName}%s{safeExtension}"
 
     let generateFileContent sizeInBytes fallback : string =
         sizeInBytes