--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/name/blackcap/exifwasher/Whitelist.kt	Wed Apr 01 14:23:54 2020 -0700
@@ -0,0 +1,48 @@
+/*
+ * An exif key whitelist. Supports both prefixes and entire strings.
+ */
+package name.blackcap.exifwasher
+
+import java.util.regex.Pattern
+import kotlin.collections.mutableSetOf
+import kotlin.collections.mutableListOf
+
+class Whitelist {
+    private val entire = mutableSetOf<String>()
+    private val prefixes = mutableListOf<String>()
+
+    fun addEntire(s: String) = entire.add(s)
+
+    fun addPrefix(s: String) = prefixes.add(s)
+
+    private fun autoOp(s: String, pfx: (String) -> Boolean, ent: (String) -> Boolean): Boolean {
+        return if (s.endsWith('*')) { pfx(s.dropLast(1)) } else { ent(s) }
+    }
+
+    fun add(s: String) = autoOp(s, ::addPrefix, ::addEntire)
+
+    fun removeEntire(s: String) = entire.remove(s)
+
+    fun removePrefix(s: String) = prefixes.remove(s)
+
+    fun remove(s: String) = autoOp(s, ::removePrefix, ::removeEntire)
+
+    fun contains(s: String) = entire.contains(s) || prefixes.find { s.startsWith(it) } != null
+
+    fun toList(): List<String> = mutableListOf<String>().also {
+        it.addAll(entire)
+        it.addAll(prefixes)
+        it.sort()
+    }
+
+    override fun toString(): String = toList().joinToString(",")
+
+    companion object {
+        private val SPLITTER = Pattern.compile(",\\s*")
+        fun parse(raw: String) = Whitelist().also { 
+            for (s in raw.split(SPLITTER)) {
+                it.add(s)
+            }
+        }
+    }
+}