Implement configuration files migration

src/main/java/com/tomff/beesplus/BeesPlus.java

@@ -1,12 +1,15 @@
 package com.tomff.beesplus;
 
-import com.tomff.beesplus.handlers.DamageHandler;
-import com.tomff.beesplus.handlers.RightClickHandler;
-import com.tomff.beesplus.items.*;
 import com.tomff.beesplus.core.UpdateChecker;
 import com.tomff.beesplus.core.gui.GuiHandler;
 import com.tomff.beesplus.core.gui.GuiViewTracker;
 import com.tomff.beesplus.core.items.CustomItemManager;
+import com.tomff.beesplus.core.migrations.AddField;
+import com.tomff.beesplus.core.migrations.Migration;
+import com.tomff.beesplus.core.migrations.MigrationsExecutor;
+import com.tomff.beesplus.handlers.DamageHandler;
+import com.tomff.beesplus.handlers.RightClickHandler;
+import com.tomff.beesplus.items.*;
 import com.tomff.beesplus.localization.Localization;
 import com.tomff.beesplus.localization.LocalizationWrapper;
 import org.bstats.bukkit.Metrics;
@@ -26,6 +29,7 @@ public class BeesPlus extends JavaPlugin {
 
     @Override
     public void onEnable() {
+        performMigrations();
         saveDefaultConfig();
 
         guiViewTracker = new GuiViewTracker();
@@ -76,6 +80,16 @@ public class BeesPlus extends JavaPlugin {
         return true;
     }
 
+    private void performMigrations() {
+        MigrationsExecutor migrationsExecutor = new MigrationsExecutor(this);
+
+        migrationsExecutor.addMigration(1, new Migration()
+                .add(new AddField("config.yml", "beehiveupgrade.maximumpopulation", 9))
+        );
+
+        migrationsExecutor.migrate();
+    }
+
     private void registerItems() {
         BeeHiveUpgrade beeHiveUpgrade = new BeeHiveUpgrade(this);
 

src/main/java/com/tomff/beesplus/core/migrations/AddField.java

@@ -0,0 +1,35 @@
+package com.tomff.beesplus.core.migrations;
+
+import org.bukkit.configuration.InvalidConfigurationException;
+import org.bukkit.configuration.file.YamlConfiguration;
+
+import java.io.File;
+import java.io.IOException;
+
+public class AddField implements Operation {
+    private File file;
+
+    private String fieldPath;
+    private Object fieldValue;
+
+    public AddField(String filePath, String fieldPath, Object fieldValue) {
+        file = new File(BASE_PATH, filePath);
+
+        this.fieldPath = fieldPath;
+        this.fieldValue = fieldValue;
+    }
+
+    @Override
+    public void execute() throws IOException {
+        YamlConfiguration config = new YamlConfiguration();
+
+        try {
+            config.load(file);
+        } catch (IOException | InvalidConfigurationException e) {
+            e.printStackTrace();
+        }
+
+        config.set(fieldPath, fieldValue);
+        config.save(file);
+    }
+}

src/main/java/com/tomff/beesplus/core/migrations/Migration.java

@@ -0,0 +1,21 @@
+package com.tomff.beesplus.core.migrations;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Migration {
+    private List<Operation> operations;
+
+    public Migration() {
+        this.operations = new ArrayList<>();
+    }
+
+    public Migration add(Operation operation) {
+        operations.add(operation);
+        return this;
+    }
+
+    public List<Operation> getOperations() {
+        return operations;
+    }
+}

src/main/java/com/tomff/beesplus/core/migrations/MigrationsExecutor.java

@@ -0,0 +1,121 @@
+package com.tomff.beesplus.core.migrations;
+
+import com.tomff.beesplus.BeesPlus;
+import org.bukkit.configuration.InvalidConfigurationException;
+import org.bukkit.configuration.file.YamlConfiguration;
+
+import java.io.File;
+import java.io.IOException;
+import java.util.HashMap;
+import java.util.Map;
+
+public class MigrationsExecutor {
+    private int latestVersion;
+
+    private Map<Integer, Migration> migrations;
+    private File migrationFileRegistry;
+    private YamlConfiguration yaml;
+
+    private BeesPlus beesPlus;
+
+    public MigrationsExecutor(BeesPlus beesPlus) {
+        this.beesPlus = beesPlus;
+        this.migrations = new HashMap<>();
+        this.yaml = new YamlConfiguration();
+        this.migrationFileRegistry = new File(beesPlus.getDataFolder(), "migration.yml");
+        this.latestVersion = 0;
+    }
+
+    public void addMigration(int version, Migration migration) {
+        migrations.put(version, migration);
+
+        if (version > latestVersion) {
+            this.latestVersion = version;
+        }
+    }
+
+    public void migrate() {
+        if (hasConfig() && !hasMigrationRegistry()) {
+            loadRegistry();
+
+            migrateFrom(0);
+            return;
+        }
+
+        if (!loadRegistry()) return;
+
+        int version = yaml.getInt("migration", 0);
+        if (version == latestVersion) return;
+
+        migrateFrom(version);
+    }
+
+    private void migrateFrom(int version) {
+        beesPlus.getLogger().info("Old files detected. Migrating files to migration v" + latestVersion);
+
+        for (int nextVersion = version + 1; nextVersion <= latestVersion; nextVersion++) {
+            performMigration(migrations.get(nextVersion));
+        }
+
+        setCurrentMigration(latestVersion);
+    }
+
+    public void setCurrentMigration(int version) {
+        yaml.set("migration", version);
+        try {
+            yaml.save(migrationFileRegistry);
+        } catch (IOException e) {
+            beesPlus.getLogger().severe("An error occurred while trying to update the migration version");
+            e.printStackTrace();
+        }
+    }
+
+    private void createIfNotExist() {
+        if (!hasMigrationRegistry()) {
+            yaml.set("migration", latestVersion);
+
+            try {
+                yaml.save(migrationFileRegistry);
+            } catch (IOException e) {
+                e.printStackTrace();
+                beesPlus.getLogger().severe("An error occurred while trying to create the migration registry file!");
+            }
+        }
+    }
+
+    private boolean loadRegistry() {
+        createIfNotExist();
+
+        try {
+            yaml.load(migrationFileRegistry);
+        } catch (IOException | InvalidConfigurationException e) {
+            beesPlus.getLogger().severe("An error occurred while opening the migration registry file.");
+            beesPlus.getLogger().severe("Suggested action: please delete the BeesPlus plugin folder and restart.");
+            e.printStackTrace();
+
+            return false;
+        }
+
+        return true;
+    }
+
+    private void performMigration(Migration migration) {
+        for(Operation operation : migration.getOperations()) {
+            try {
+                operation.execute();
+            } catch (IOException e) {
+                e.printStackTrace();
+                beesPlus.getLogger().severe("An error occurred while migrating a file");
+            }
+        }
+    }
+
+    private boolean hasMigrationRegistry() {
+        return migrationFileRegistry.exists();
+    }
+
+    private boolean hasConfig() {
+        return new File(beesPlus.getDataFolder(), "config.yml").exists();
+    }
+
+}

src/main/java/com/tomff/beesplus/core/migrations/Operation.java

@@ -0,0 +1,13 @@
+package com.tomff.beesplus.core.migrations;
+
+import com.tomff.beesplus.BeesPlus;
+import org.bukkit.plugin.java.JavaPlugin;
+
+import java.io.File;
+import java.io.IOException;
+
+public interface Operation {
+    File BASE_PATH = JavaPlugin.getPlugin(BeesPlus.class).getDataFolder();
+
+    void execute() throws IOException;
+}