Improved Suggestions

resolves #100

app/src/main/java/xyz/quaver/pupil/util/SavedSet.kt

@@ -0,0 +1,88 @@
+/*
+ *     Pupil, Hitomi.la viewer for Android
+ *     Copyright (C) 2020  tom5079
+ *
+ *     This program is free software: you can redistribute it and/or modify
+ *     it under the terms of the GNU General Public License as published by
+ *     the Free Software Foundation, either version 3 of the License, or
+ *     (at your option) any later version.
+ *
+ *     This program is distributed in the hope that it will be useful,
+ *     but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *     GNU General Public License for more details.
+ *
+ *     You should have received a copy of the GNU General Public License
+ *     along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package xyz.quaver.pupil.util
+
+import kotlinx.serialization.*
+import kotlinx.serialization.builtins.ListSerializer
+import kotlinx.serialization.json.Json
+import java.io.File
+
+class SavedSet <T: Any> (private val file: File, private val any: T, private val set: MutableSet<T> = mutableSetOf()) : MutableSet<T> by set {
+
+    @Suppress("UNCHECKED_CAST")
+    @OptIn(ExperimentalSerializationApi::class)
+    val serializer: KSerializer<List<T>>
+        get() = ListSerializer(serializer(any::class.java) as KSerializer<T>)
+
+    init {
+        if (!file.exists()) {
+            file.parentFile?.mkdirs()
+            save()
+        }
+        load()
+    }
+
+    fun load() {
+        synchronized(this) {
+            set.clear()
+            kotlin.runCatching {
+                Json.decodeFromString(serializer, file.readText())
+            }.onSuccess {
+                set.addAll(it)
+            }
+        }
+    }
+
+    @OptIn(ExperimentalSerializationApi::class)
+    fun save() {
+        synchronized(this) {
+            file.writeText(Json.encodeToString(serializer, set.toList()))
+        }
+    }
+
+    override fun add(element: T): Boolean {
+        load()
+
+        return set.add(element).also {
+            save()
+        }
+    }
+
+    override fun addAll(elements: Collection<T>): Boolean {
+        load()
+
+        return set.addAll(elements).also {
+            save()
+        }
+    }
+
+    override fun remove(element: T): Boolean {
+        load()
+
+        return set.remove(element).also {
+            save()
+        }
+    }
+
+    override fun clear() {
+        set.clear()
+        save()
+    }
+
+}