like two-thirds of the requirements met; interface remaining

exams/2023m-gacha/solution/app/build.gradle.kts

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+/*
+ * This file was generated by the Gradle 'init' task.
+ *
+ * This generated file contains a sample Java application project to get you started.
+ * For more details on building Java & JVM projects, please refer to https://docs.gradle.org/8.14.3/userguide/building_java_projects.html in the Gradle documentation.
+ */
+
+plugins {
+    // Apply the application plugin to add support for building a CLI application in Java.
+    application
+}
+
+repositories {
+    // Use Maven Central for resolving dependencies.
+    mavenCentral()
+}
+
+dependencies {
+    // Use JUnit Jupiter for testing.
+    testImplementation(libs.junit.jupiter)
+
+    testRuntimeOnly("org.junit.platform:junit-platform-launcher")
+
+    // This dependency is used by the application.
+    implementation(libs.guava)
+}
+
+// Apply a specific Java toolchain to ease working on different environments.
+java {
+    toolchain {
+        languageVersion = JavaLanguageVersion.of(21)
+    }
+}
+
+application {
+    // Define the main class for the application.
+    mainClass = "org.example.App"
+}
+
+tasks.withType<Jar> {
+    manifest {
+        attributes["Main-Class"] = "org.example.App"
+    }
+}
+
+tasks.named<Test>("test") {
+    // Use JUnit Platform for unit tests.
+    useJUnitPlatform()
+}

exams/2023m-gacha/solution/app/src/main/java/org/example/App.java

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+/*
+ * This source file was generated by the Gradle 'init' task
+ */
+package org.example;
+
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.InputStream;
+import java.io.OutputStream;
+import java.lang.reflect.Array;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Optional;
+import java.util.Random;
+import java.util.Scanner;
+
+enum PrizeLevel {
+    NORMAL,
+    RARE,
+    EPIC,
+    LEGENDARY,
+    EMPTY,
+}
+
+class Ball extends Object {
+    String name;
+    String colour;
+    String description;
+    String prize = null;
+
+    String formatPrize() {
+        return prize == null ? "... nothing" : " " + prize;
+    }
+
+    @Override
+    public String toString() {
+
+        return String.format("%s (%s), it contains %s.", name, colour, formatPrize());
+    }
+
+    public String toDescriptionString() {
+        return String.format("%s (%s), it contains %s\n%s", name, colour, formatPrize(), description);
+    }
+
+    public Ball(PrizeLevel level, String colour, String desc, String prize) {
+        switch (level) {
+            case NORMAL:
+                this.name = "Normal Prize Ball";
+                break;
+            case RARE:
+                this.name = "Rare Prize Ball";
+                break;
+            case EPIC:
+                this.name = "Epic Prize Ball";
+                break;
+            case LEGENDARY:
+                this.name = "Legendary Prize Ball";
+                break;
+            default:
+                this.name = "Empty Ball";
+                break;
+        }
+        this.colour = colour;
+        this.description = desc;
+        this.prize = prize;
+    }
+}
+
+class BallFactory {
+    PrizeLevel level;
+    String colour;
+    String description;
+    HashMap<String, Integer> prizes;
+    int numBalls;
+
+    public BallFactory(PrizeLevel level, String colour, String description, String[] prizes, int number) {
+        this.level = level;
+        this.colour = colour;
+        this.description = description;
+        int each = number / prizes.length;
+        int error = number % prizes.length;
+        System.out.println("each: " + each + " error: " + error);
+        HashMap<String, Integer> myPrizes = new HashMap<>();
+        for (String prize : prizes) {
+            myPrizes.put(prize, each);
+        }
+        for (int i = 0; i < error; i++) {
+            String randKey = prizes[new Random().nextInt(prizes.length)];
+            myPrizes.put(randKey, myPrizes.get(randKey) + 1);
+        }
+        this.prizes = myPrizes;
+        System.out.println(this.prizes);
+        this.numBalls = number;
+
+    }
+
+    public Ball[] makePrizeBalls() {
+        Ball[] balls = new Ball[numBalls];
+        Random r = new Random();
+        for (int i = 0; i < balls.length; i++) {
+            ArrayList<String> available = new ArrayList<String>(prizes.keySet());
+            System.out.println(this.prizes);
+            int sel = r.nextInt(available.size());
+            System.out.println(available.get(sel));
+            balls[i] = new Ball(level, colour, description, available.get(sel));
+            System.out.println("a ball has been made: " + balls[i]);
+            prizes.put(available.get(sel), prizes.get(available.get(sel)) - 1);
+            prizes.entrySet().removeIf(entry -> entry.getValue() <= 0); // NOTE: Here I had to use AI because
+                                                                        // `ConcurrentModificationException` keeps being
+                                                                        // thrown.
+        }
+        return balls;
+
+    }
+
+    class BallMachine extends Object {
+        Ball[] balls;
+
+        public void showBalls() {
+            for (Ball ball : balls) {
+                System.out.println(ball);
+            }
+        }
+    }
+}
+
+public class App {
+    public static void main(String[] args) {
+        String filename;
+        if (args.length < 1) {
+            System.out.println("A file name was not specified when starting the application. Provide it here: ");
+            Scanner sc = new Scanner(System.in);
+            filename = sc.nextLine();
+            sc.close();
+        } else {
+            filename = args[0];
+        }
+        File file = new File(filename);
+        try {
+            Scanner fileReader = new Scanner(file);
+            ArrayList<String> lines = new ArrayList<>();
+            ArrayList<Ball> balls = new ArrayList<>();
+            while (fileReader.hasNext()) {
+                lines.add(fileReader.nextLine());
+            }
+            for (int i = 0; i < lines.size(); i++) {
+                System.out.println("parsing " + lines.get(i));
+                if (lines.get(i).matches("[A-Z]* [A-Z]* BALL \\[[\\d]*\\]")) {
+                    // A ball collection starts
+                    String[] ballNameParts = lines.get(i).split(" ");
+                    PrizeLevel level = PrizeLevel.valueOf(ballNameParts[0]);
+                    int numBalls = Integer.parseInt(ballNameParts[3].replace("[", "").replace("]", ""));
+                    String colour = lines.get(i + 1);
+                    System.out.println("colour: " + colour);
+                    String desc = lines.get(i + 2);
+                    String prize = null;
+                    if (!(level.equals(PrizeLevel.EMPTY))) {
+                        // ball has prize
+                        prize = lines.get(i + 3);
+                    }
+
+                    BallFactory factory = new BallFactory(level, colour, desc,
+                            prize.replace("{", "").replace("}", "").split(", "), numBalls);
+                    balls.addAll(Arrays.asList(factory.makePrizeBalls()));
+                }
+            }
+            for (Ball b : balls) {
+                System.out.println("ball: " + b.toDescriptionString());
+            }
+            fileReader.close();
+        } catch (FileNotFoundException e) {
+            // TODO: handle exception
+            e.printStackTrace();
+        }
+    }
+}

exams/2023m-gacha/solution/app/src/test/java/org/example/AppTest.java

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+/*
+ * This source file was generated by the Gradle 'init' task
+ */
+package org.example;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class AppTest {
+    @Test void appHasAGreeting() {
+        App classUnderTest = new App();
+        assertNotNull(classUnderTest.getGreeting(), "app should have a greeting");
+    }
+}