Use Java streams to handle matching strings and refactor code

src/main/java/duke/Parser.java

@@ -1,14 +1,16 @@
 package duke;
 
 import java.time.LocalDate;
-import java.util.Arrays;
+import java.util.Set;
+import java.util.stream.Stream;
 
 /**
  * Processes the information from the user. Based upon the user's commands, calls upon and relays the necessary
  * information accordingly.
  */
 public class Parser {
-
+    private static final Set<String> VALID_COMMANDS = Set.of("list", "mark", "unmark", "todo", "event", "deadline",
+            "delete");
     private String inputString;
 
     public Parser(String inputString) {
@@ -33,14 +35,17 @@ public String getString() {
      */
     public void process(TaskList tasks, Ui ui) throws EmptyTaskException, InvalidCommandException,
             EmptyCommandException, TaskListOutOfBoundsException {
-        String command = inputString.split(" ", 2)[0];
-        if (command.equals("list")) {
+        String[] parts = inputString.split(" ", 2);
+        String instruction = parts[0];
+        String remainingInput = parts.length > 1 ? parts[1] : "";
+        throwInvalidInputExceptions();
+
+        if (instruction.equals("list")) {
             ui.display(tasks);
             return;
         }
         throwInvalidInputExceptions();
-        String remainingInput = inputString.split(" ", 2)[1];
-        System.out.println(performCommandAndGetParseResponse(tasks, ui, command, remainingInput));
+        System.out.println(performCommandAndGetParseResponse(tasks, ui, instruction, remainingInput));
     }
 
     /**
@@ -49,84 +54,96 @@ public void process(TaskList tasks, Ui ui) throws EmptyTaskException, InvalidCom
      * @param tasks This contains the user's tasks listed thus far.
      * @param ui The instance holding the current's user's interface for the programme.
      * @return Returns the appropriate response to match the user's instruction.
-     * @throws EmptyTaskException
-     * @throws InvalidCommandException
-     * @throws EmptyCommandException
+     * @throws EmptyTaskException If a task without description is provided, an exception will be thrown.
+     * @throws InvalidCommandException If an invalid command is given, an exception will be thrown.
+     * @throws EmptyCommandException If an empty command is given, an exception will be thrown.
      */
     public String stringProcess(TaskList tasks, Ui ui) throws EmptyTaskException, InvalidCommandException,
             EmptyCommandException, TaskListOutOfBoundsException {
-        String command = inputString.split(" ", 2)[0];
-        if (command.equals("list")) {
+        String[] parts = inputString.split(" ", 2);
+        String instruction = parts[0];
+        String remainingInput = parts.length > 1 ? parts[1] : "";
+
+        throwInvalidInputExceptions();
+
+        if (instruction.equals("list")) {
             return ui.guiDisplay(tasks);
         }
+
         throwInvalidInputExceptions();
-        String remainingInput = inputString.split(" ", 2)[1];
-        return performCommandAndGetParseResponse(tasks, ui, command, remainingInput);
+        return performCommandAndGetParseResponse(tasks, ui, instruction, remainingInput);
     }
 
-    private void throwInvalidInputExceptions() throws EmptyCommandException, InvalidCommandException {
-        if (inputString.split(" ", 2).length == 0) {
-            throw new EmptyCommandException();
-        }
-        boolean flag1 = !(Arrays.asList("list", "mark", "unmark", "todo", "event", "deadline", "delete")
-                .contains(inputString.split(" ", 2)[0]));
-        if (inputString.split(" ", 2).length == 1 && flag1) {
-            throw new InvalidCommandException();
-        }
-        boolean flag2 = Arrays.asList("todo", "event", "deadline", "delete").contains(inputString.split(" ", 2)[0]);
-        if (inputString.split(" ", 2).length == 1 && flag2) {
-            throw new EmptyTaskException();
-        }
-    }
+
+
 
     private static String performCommandAndGetParseResponse(
-            TaskList tasks, Ui ui, String command, String remainingInput)
+            TaskList tasks, Ui ui, String instruction, String remainingInput)
             throws InvalidCommandException, TaskListOutOfBoundsException {
-        switch (command) {
-        case "mark" -> {
-            int idx = Integer.parseInt(remainingInput) - 1;
-            tasks.set(idx, true);
-            return "Nice! I've marked this task as done:\n" + tasks.get(idx);
-        }
-        case "unmark" -> {
+        switch (instruction) {
+        case "mark":
+        case "unmark": {
             int idx = Integer.parseInt(remainingInput) - 1;
-            tasks.set(idx, false);
-            return "OK, I've marked this task as not done yet:\n" + tasks.get(idx);
+            tasks.set(idx, instruction.equals("mark"));
+            return (instruction.equals("mark") ? "Nice! " : "OK, ")
+                    + "I've marked this task as " + (instruction.equals("mark") ? "done" : "not done yet") + ":\n"
+                    + tasks.get(idx);
         }
-        case "todo" -> {
+        case "todo": {
             Todo task = new Todo(remainingInput);
             tasks.add(task);
             return ui.guiTaskAddOrDeleteDisplay(task, "add", tasks);
         }
-        case "deadline" -> {
-            String name = remainingInput.split(" /by ", 2)[0];
-            LocalDate endDate = LocalDate.parse(remainingInput.split(" /by ", 2)[1]);
+        case "deadline": {
+            String[] deadlineParts = remainingInput.split(" /by ", 2);
+            String name = deadlineParts[0];
+            LocalDate endDate = LocalDate.parse(deadlineParts[1]);
             Deadline task = new Deadline(name, endDate);
             tasks.add(task);
             return ui.guiTaskAddOrDeleteDisplay(task, "add", tasks);
         }
-        case "event" -> {
-            String name = remainingInput.split(" /from ", 2)[0];
-            remainingInput = remainingInput.split(" /from ", 2)[1];
-            String start = remainingInput.split(" /to ", 2)[0];
-            String end = remainingInput.split(" /to ", 2)[1];
+        case "event": {
+            String[] eventParts = remainingInput.split(" /from ", 2);
+            String name = eventParts[0];
+            String[] timeParts = eventParts[1].split(" /to ", 2);
+            String start = timeParts[0];
+            String end = timeParts[1];
             Event task = new Event(name, start, end);
             tasks.add(task);
             return ui.guiTaskAddOrDeleteDisplay(task, "add", tasks);
         }
-        case "delete" -> {
+        case "delete": {
             int idx = Integer.parseInt(remainingInput) - 1;
             Task taskToBeDeleted = tasks.get(idx);
             assert (tasks.size() > idx);
             tasks.delete(idx);
             return ui.guiTaskAddOrDeleteDisplay(taskToBeDeleted, "delet", tasks);
         }
-        case "find" -> {
+        case "find": {
             TaskList matchingTasks = tasks.findAll(remainingInput);
             return ui.guiDisplaySearch(matchingTasks);
 
         }
-        default -> throw new InvalidCommandException();
+        default: {
+            throw new InvalidCommandException();
+        }
         }
     }
+    private void throwInvalidInputExceptions() throws EmptyCommandException, InvalidCommandException {
+        String[] parts = inputString.split(" ", 2);
+        String instruction = parts[0];
+        String remainingInput = parts.length > 1 ? parts[1] : "";
+
+        if (!VALID_COMMANDS.contains(instruction)) {
+            throw new InvalidCommandException();
+        }
+        if (remainingInput.isEmpty()) {
+            if (Stream.of("todo", "event", "deadline", "delete").anyMatch(instruction::equals)) {
+                throw new EmptyTaskException();
+            } else {
+                throw new EmptyCommandException();
+            }
+        }
+    }
+
 }