Implement find free time feature

Author: codebreaker64

src/main/java/devin/Devin.java

@@ -53,6 +53,7 @@ public String getResponse(String text) throws DevinException, IOException {
         case "deadline" -> Command.deadlineCommand(list, texts, storage);
         case "event" -> Command.eventCommand(list, texts, storage);
         case "find" -> Command.findCommand(list, texts);
+        case "schedule" -> Command.scheduleCommand(list);
         default -> throw new DevinException("""
                 Unknown command.
                 Please choose one of the following commands:

src/main/java/devin/command/Command.java

@@ -1,6 +1,9 @@
 package devin.command;
 
 import java.io.IOException;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
 
 import devin.Devin;
 import devin.exception.DevinException;
@@ -183,4 +186,14 @@ public static String findCommand(TaskList list, String[] texts) throws DevinExce
         texts[0] = "";
         return list.findTask(String.join(" ", texts));
     }
+
+    /**
+     * A schedule command to find all free time slot and display it to user.
+     * 
+     * @param list of all tasks.
+     * @return a message showing all free time slot.
+     */
+    public static String scheduleCommand(TaskList list) {
+        return list.getTimedTasks();
+    }
 }

src/main/java/devin/task/Deadline.java

@@ -24,6 +24,11 @@ public Deadline(String description, LocalDateTime by, boolean isDone) {
         this.by = by;
     }
 
+    @Override
+    public LocalDateTime getEndTime() {
+        return by; 
+    }
+
     @Override
     public String toFileString() {
         return "D | " + super.toFileString() + " | " + by.format(FORMATTER1);

src/main/java/devin/task/Event.java

@@ -27,6 +27,16 @@ public Event(String description, LocalDateTime from, LocalDateTime to, boolean i
         this.to = to;
     }
 
+    @Override
+    public LocalDateTime getStartTime() {
+        return from;
+    }
+
+    @Override
+    public LocalDateTime getEndTime() {
+        return to;
+    }
+
     @Override
     public String toFileString() {
         return "E | " + super.toFileString() + " | " + from.format(FORMATTER1) + " | " + to.format(FORMATTER1);
@@ -36,4 +46,5 @@ public String toFileString() {
     public String toString() {
         return "[E]" + super.toString() + " (from: " + from.format(FORMATTER2) + " to: " + to.format(FORMATTER2) + ")";
     }
+    
 }

src/main/java/devin/task/Task.java

@@ -1,5 +1,7 @@
 package devin.task;
 
+import java.time.LocalDateTime;
+
 /**
  * Representation of a Task.
  */
@@ -49,6 +51,14 @@ public void markTask() {
     public void unmarkTask() {
         this.isDone = false;
     }
+    
+    public LocalDateTime getStartTime() {
+        return null;
+    }
+    
+    public LocalDateTime getEndTime() {
+        return null;
+    }
 
     public String toFileString() {
         return getStatusIcon() + " | " + this.name;
@@ -58,4 +68,6 @@ public String toFileString() {
     public String toString() {
         return "[" + getStatusIcon() + "] " + this.name;
     }
+    
+    
 }

src/main/java/devin/task/TaskList.java

@@ -1,7 +1,12 @@
 package devin.task;
 
 import java.io.IOException;
+import java.time.Duration;
+import java.time.LocalDateTime;
+import java.time.format.DateTimeFormatter;
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
 import java.util.stream.Collectors;
@@ -128,4 +133,41 @@ public String findTask(String keyword) {
     public ArrayList<Task> getTasks() {
         return tasks;
     }
+
+    /**
+     * Find all the free time slot that the user can schedule.
+     * 
+     * @return a message of all free time slot
+     */
+    public String getTimedTasks() {
+        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("d/M/yyyy HHmm");
+        
+        LocalDateTime now = LocalDateTime.now();
+        
+        ArrayList<Task> timedTasks = tasks.stream()
+                .filter(task -> task.getStartTime() != null && task.getEndTime() != null)
+                .sorted(Comparator.comparing(Task::getStartTime))
+                .collect(Collectors.toCollection(ArrayList::new));
+        
+        StringBuilder freeSlots = new StringBuilder();
+        LocalDateTime previousEndTime = now;
+
+        for (Task task : timedTasks) {
+            if (previousEndTime.isBefore(task.getStartTime())) {
+                freeSlots.append("Free slot from ")
+                        .append(previousEndTime.format(formatter))
+                        .append(" to ")
+                        .append(task.getStartTime().format(formatter))
+                        .append("\n"); // Newline separator
+            }
+            previousEndTime = task.getEndTime();
+        }
+        
+        freeSlots.append("Free slot from ")
+                .append(previousEndTime.format(formatter))
+                .append(" to forever")
+                .append("\n"); 
+
+        return freeSlots.toString().trim();
+    }
 }