Exclude more reserved file name characters

src/main/kotlin/nl/avisi/structurizr/site/generatr/StringUtilities.kt

@@ -1,3 +1,21 @@
 package nl.avisi.structurizr.site.generatr
 
-fun String.normalize(): String = lowercase().replace("\\s+".toRegex(), "-")
+// based on https://stackoverflow.com/questions/1976007/what-characters-are-forbidden-in-windows-and-linux-directory-names
+private const val reservedChars = "|\\?*<\":>+[]/'"
+private val reservedNames = setOf(
+    "CON", "PRN", "AUX", "NUL",
+    "COM1", "COM2", "COM3", "COM4", "COM5", "COM6", "COM7", "COM8", "COM9",
+    "LPT1", "LPT2", "LPT3", "LPT4", "LPT5", "LPT6", "LPT7", "LPT8", "LPT9"
+)
+
+fun String.normalize(): String =
+    lowercase()
+        .replace("\\s+".toRegex(), "-")
+        .filterNot { reservedChars.contains(it) }
+        .trim()
+        .let {
+            if (reservedNames.contains(it.uppercase()))
+                "${it}-"
+            else
+                it
+        }

src/test/kotlin/nl/avisi/structurizr/site/generatr/site/StringUtilitiesTest.kt

@@ -0,0 +1,23 @@
+package nl.avisi.structurizr.site.generatr.site
+
+import assertk.assertThat
+import assertk.assertions.isEqualTo
+import nl.avisi.structurizr.site.generatr.normalize
+import org.junit.jupiter.api.DynamicTest
+import org.junit.jupiter.api.TestFactory
+
+class StringUtilitiesTest {
+
+    @TestFactory
+    fun `normalize strips invalid chars`() = listOf(
+        listOf("doc", "doc"),
+        listOf("d c", "d-c"),
+        listOf("doc:", "doc"),
+        listOf(" doc ", "-doc-"),
+        listOf("aux", "aux-"),
+    ).map { (actual, expected) ->
+        DynamicTest.dynamicTest("normalize replaces $actual with $expected") {
+            assertThat(actual.normalize()).isEqualTo(expected)
+        }
+    }
+}