Normalizes hashtag transformations for filters.

quartz/src/main/java/com/vitorpamplona/quartz/nip01Core/tags/hashtags/MipMapHashTags.kt

@@ -0,0 +1,37 @@
+/**
+ * Copyright (c) 2024 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.quartz.nip01Core.tags.hashtags
+
+import java.util.Locale
+
+fun hashtagAlts(tag: String): Set<String> =
+    setOf(
+        tag,
+        tag.lowercase(),
+        tag.uppercase(),
+        tag.replaceFirstChar {
+            if (it.isLowerCase()) it.titlecase(Locale.ROOT) else it.toString()
+        },
+    )
+
+fun hashtagAlts(tags: List<String>): Set<String> = tags.map { hashtagAlts(it) }.flatten().toSet()
+
+fun hashtagAlts(tags: Set<String>): Set<String> = tags.map { hashtagAlts(it) }.flatten().toSet()