Kotlin conversion: MultiMap

Warning: This commit changes the semantics of MultiMap.put()
put() now replaces values, while plus() adds them.

pgpainless-core/src/main/kotlin/org/pgpainless/util/MultiMap.kt

@@ -0,0 +1,75 @@
+// SPDX-FileCopyrightText: 2023 Paul Schaub <vanitasvitae@fsfe.org>
+//
+// SPDX-License-Identifier: Apache-2.0
+
+package org.pgpainless.util
+
+class MultiMap<K, V> : Iterable<Map.Entry<K, Set<V>>> {
+
+    private val map: Map<K, MutableSet<V>>
+
+    constructor(): this(mutableMapOf())
+    constructor(other: MultiMap<K, V>): this(other.map)
+    constructor(content: Map<K, Set<V>>) {
+        map = mutableMapOf()
+        content.forEach {
+            map[it.key] = it.value.toMutableSet()
+        }
+    }
+
+    override fun iterator(): Iterator<Map.Entry<K, Set<V>>> {
+        return map.iterator()
+    }
+
+    val size: Int
+        get() = map.size
+    fun size() = size
+    val keys: Set<K>
+        get() = map.keys
+    fun keySet() = keys
+    val values: Collection<Set<V>>
+        get() = map.values
+    fun values() = values
+    val entries: Set<Map.Entry<K, Set<V>>>
+        get() = map.entries
+    fun entrySet() = entries
+    fun isEmpty(): Boolean = map.isEmpty()
+    fun containsKey(key: K): Boolean = map.containsKey(key)
+    fun containsValue(value: V): Boolean = map.values.any { it.contains(value) }
+    fun contains(key: K, value: V): Boolean = map[key]?.contains(value) ?: false
+    operator fun get(key: K): Set<V>? = map[key]
+    fun put(key: K, value: V) =
+            (map as MutableMap).put(key, mutableSetOf(value))
+    fun plus(key: K, value: V) =
+            (map as MutableMap).getOrPut(key) { mutableSetOf() }.add(value)
+    fun put(key: K, values: Set<V>) =
+            (map as MutableMap).put(key, values.toMutableSet())
+    fun plus(key: K, values: Set<V>) =
+            (map as MutableMap).getOrPut(key) { mutableSetOf() }.addAll(values)
+    fun putAll(other: MultiMap<K, V>) = other.map.entries.forEach {
+        put(it.key, it.value)
+    }
+    fun plusAll(other: MultiMap<K, V>) = other.map.entries.forEach {
+        plus(it.key, it.value)
+    }
+    fun removeAll(key: K) = (map as MutableMap).remove(key)
+    fun remove(key: K, value: V) = (map as MutableMap)[key]?.remove(value)
+    fun clear() = (map as MutableMap).clear()
+    fun flatten() = map.flatMap { it.value }.toSet()
+
+    override fun equals(other: Any?): Boolean {
+        return if (other == null)
+            false
+        else if (other !is MultiMap<*, *>)
+            false
+        else if (this === other) {
+            true
+        } else {
+            map == other.map
+        }
+    }
+
+    override fun hashCode(): Int {
+        return map.hashCode()
+    }
+}