Prevent duplicated meta entries in database (#1517)

fixes #1513

server/src/main/kotlin/suwayomi/tachidesk/server/database/migration/M0049_FixDuplicatedMetas.kt

@@ -0,0 +1,39 @@
+package suwayomi.tachidesk.server.database.migration
+
+/*
+ * Copyright (C) Contributors to the Suwayomi project
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+import de.neonew.exposed.migrations.helpers.SQLMigration
+
+@Suppress("ClassName", "unused")
+class M0049_FixDuplicatedMetas : SQLMigration() {
+    private fun createMigrationForTable(
+        table: String,
+        refColumn: String? = null,
+    ): String {
+        val groupBy = listOfNotNull(refColumn, "KEY").joinToString(", ")
+
+        return """
+            DELETE FROM $table
+            WHERE ID NOT IN (
+                SELECT MIN(ID)
+                FROM $table
+                GROUP BY $groupBy
+            );
+
+            ALTER TABLE $table
+                ADD CONSTRAINT UC_$table UNIQUE ($groupBy);
+            """.trimIndent()
+    }
+
+    override val sql: String =
+        createMigrationForTable("CATEGORYMETA", "CATEGORY_REF") +
+            createMigrationForTable("CHAPTERMETA", "CHAPTER_REF") +
+            createMigrationForTable("GLOBALMETA") +
+            createMigrationForTable("MANGAMETA", "MANGA_REF") +
+            createMigrationForTable("SOURCEMETA", "SOURCE_REF")
+}