implemented battle handler

~ 1.5h work

src/at/nanopenguin/mtcg/Pair.java

@@ -1,4 +1,18 @@
 package at.nanopenguin.mtcg;
 
-public record Pair<T, U>(T left, U right) {
+import lombok.Setter;
+
+public class Pair<T, U> {
+    @Setter
+    private T left;
+    @Setter
+    private U right;
+
+    public Pair (T left, U right) {
+        this.left = left;
+        this.right = right;
+    }
+
+    public T left() { return this.left; };
+    public U right() { return this.right; };
 }

src/at/nanopenguin/mtcg/application/Battle.java

@@ -0,0 +1,27 @@
+package at.nanopenguin.mtcg.application;
+
+import at.nanopenguin.mtcg.Pair;
+import lombok.Getter;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class Battle {
+    private Pair<Combatant, Combatant> combatants;
+    @Getter
+    private volatile List<String> log = new ArrayList<>();
+    @Getter
+    private boolean waiting = true;
+
+    public Battle(Combatant combatant) {
+        this.combatants = new Pair<>(combatant, null);
+    }
+
+    public void addCombatant(Combatant combatant) {
+        this.combatants.setRight(combatant);
+    }
+
+    public void start() {
+
+    }
+}

src/at/nanopenguin/mtcg/application/BattleHandler.java

@@ -0,0 +1,53 @@
+package at.nanopenguin.mtcg.application;
+
+import java.sql.SQLException;
+import java.util.UUID;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+public class BattleHandler {
+    private static BattleHandler INSTANCE;
+    private Lock lock = new ReentrantLock();
+    private Battle waiting = null;
+    private BattleHandler() {
+
+    }
+
+    public static BattleHandler getInstance() {
+        if (INSTANCE == null) {
+            INSTANCE = new BattleHandler();
+        }
+
+        return INSTANCE;
+    }
+
+    public String[] startBattle(UUID userUuid) throws SQLException {
+        Battle battle;
+
+        this.lock.lock();
+        if ((battle = this.waiting) == null) {
+            battle = (this.waiting = new Battle(new Combatant(userUuid)));
+        }
+
+        synchronized (battle) {
+            this.lock.unlock();
+
+            if (battle.isWaiting()) {
+                try {
+                    battle.wait();
+                } catch (InterruptedException e) {
+                    e.printStackTrace();
+                    throw new RuntimeException(e);
+                }
+
+                return battle.getLog().toArray(new String[0]);
+            }
+
+            battle.addCombatant(new Combatant(userUuid));
+            battle.start();
+        }
+
+        battle.notify();
+        return battle.getLog().toArray(new String[0]);
+    }
+}

src/at/nanopenguin/mtcg/application/Combatant.java

@@ -0,0 +1,19 @@
+package at.nanopenguin.mtcg.application;
+
+import at.nanopenguin.mtcg.application.service.schemas.Card;
+
+import java.sql.SQLException;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.UUID;
+
+public class Combatant {
+    private UUID userUuid;
+    private List<Card> deck = new ArrayList<Card>();
+
+    public Combatant(UUID userUuid) throws SQLException {
+        this.userUuid = userUuid;
+        this.deck = Arrays.asList(UserCards.get(userUuid, true));
+    }
+}