Add abstract Importer class for data migration

Introduced an extendable `Importer` class to facilitate data migration. Provides methods to import world groups and player data with customizable implementations for reading source data.

Author: NonSwag

src/main/java/net/thenextlvl/perworlds/importer/Importer.java

@@ -0,0 +1,81 @@
+package net.thenextlvl.perworlds.importer;
+
+import net.thenextlvl.perworlds.PerWorldsPlugin;
+import net.thenextlvl.perworlds.WorldGroup;
+import net.thenextlvl.perworlds.data.PlayerData;
+import org.bukkit.generator.WorldInfo;
+import org.jspecify.annotations.NullMarked;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import java.util.UUID;
+
+@NullMarked
+public abstract class Importer {
+    protected final PerWorldsPlugin plugin;
+
+    private final Path dataPath;
+    private final String name;
+
+    protected Importer(PerWorldsPlugin plugin, String name) {
+        this.dataPath = Path.of("plugins", name);
+        this.name = name;
+        this.plugin = plugin;
+    }
+
+    public Path getDataPath() {
+        return dataPath;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void load() {
+        try {
+            var groups = loadGroups();
+            loadPlayers(groups);
+        } catch (IOException e) {
+            plugin.getComponentLogger().error("Failed to import {}", name, e);
+        }
+    }
+
+    public Set<WorldGroup> loadGroups() throws IOException {
+        var read = readGroups();
+        var groups = new HashSet<WorldGroup>(read.size());
+        read.forEach((group, worlds) -> {
+            var worldGroup = plugin.groupProvider().getGroup(group).orElseGet(() ->
+                    plugin.groupProvider().createGroup(group));
+            worlds.stream().map(plugin.getServer()::getWorld)
+                    .filter(Objects::nonNull)
+                    .forEach(worldGroup::addWorld);
+            groups.add(worldGroup);
+        });
+        return groups;
+    }
+
+    public void loadPlayers(Set<WorldGroup> groups) throws IOException {
+        // todo: extract to readPlayer
+        readPlayers().forEach((uuid, name) -> {
+            groups.stream().forEach(group -> group.getWorlds().map(WorldInfo::getName)
+                    .map(this.dataPath.resolve("worlds")::resolve)
+                    .map(path -> path.resolve(name + ".json"))
+                    .filter(Files::isRegularFile)
+                    .findAny().ifPresent(path -> {
+                        // todo: load player data from path into the current group
+                    })
+            );
+        });
+    }
+
+    public abstract Map<String, Set<String>> readGroups() throws IOException;
+
+    public abstract Map<UUID, String> readPlayers() throws IOException;
+
+    public abstract PlayerData readPlayer(UUID uuid, String name, WorldGroup group) throws IOException;
+}