Implement generate emails command

src/main/java/seedu/address/logic/commands/GenerateEmailsCommand.java

@@ -0,0 +1,52 @@
+package seedu.address.logic.commands;
+
+import static java.util.Objects.requireNonNull;
+
+import java.util.List;
+import seedu.address.commons.core.Messages;
+import seedu.address.commons.core.index.Index;
+import seedu.address.logic.commands.exceptions.CommandException;
+import seedu.address.model.Model;
+import seedu.address.model.task.Task;
+
+public class GenerateEmailsCommand extends Command {
+
+    public static final String COMMAND_WORD = "gen";
+
+    public static final String MESSAGE_USAGE = COMMAND_WORD
+            + ": Generates all the emails of the people related to the task "
+            +  "identified by the index number in the task list.\n"
+            + "Parameters: INDEX (must be a positive integer)\n"
+            + "Example: " + COMMAND_WORD + " 1";
+
+    public static final String MESSAGE_NO_CONTACTS_ASSIGNED =
+            "Failed: There are no contacts assigned to the task %1$s";
+
+    private static final String MESSAGE_GENERATED_EMAILS = "Here are the emails related to the task %1$s:\n"
+            + "%2$s";
+
+
+    private final Index targetIndex;
+
+    public GenerateEmailsCommand(Index targetIndex) {
+        this.targetIndex = targetIndex;
+    }
+
+    @Override
+    public CommandResult execute(Model model) throws CommandException {
+        requireNonNull(model);
+        List<Task> shownTaskList = model.getFilteredTaskList();
+
+        if (targetIndex.getZeroBased() >= shownTaskList.size()) {
+            throw new CommandException(Messages.MESSAGE_INVALID_TASK_DISPLAYED_INDEX);
+        }
+
+        Task task = shownTaskList.get(targetIndex.getZeroBased());
+
+        if (task.getNoOfPeople() == 0) {
+            return new CommandResult(String.format(MESSAGE_NO_CONTACTS_ASSIGNED, task));
+        }
+
+        return new CommandResult(String.format(MESSAGE_GENERATED_EMAILS, task, task.getEmails()));
+    }
+}

src/main/java/seedu/address/logic/parser/AddressBookParser.java

@@ -18,6 +18,7 @@
 import seedu.address.logic.commands.ExitCommand;
 import seedu.address.logic.commands.FilterCommand;
 import seedu.address.logic.commands.FindCommand;
+import seedu.address.logic.commands.GenerateEmailsCommand;
 import seedu.address.logic.commands.HelpCommand;
 import seedu.address.logic.commands.ListCommand;
 import seedu.address.logic.commands.UnassignCommand;
@@ -96,6 +97,9 @@ public Command parseCommand(String userInput) throws ParseException {
         case EditTaskCommand.COMMAND_WORD:
             return new EditTaskCommandParser().parse(arguments);
 
+        case GenerateEmailsCommand.COMMAND_WORD:
+            return new GenerateEmailsCommandParser().parse(arguments);
+
         default:
             throw new ParseException(MESSAGE_UNKNOWN_COMMAND);
         }

src/main/java/seedu/address/logic/parser/GenerateEmailsCommandParser.java

@@ -0,0 +1,21 @@
+package seedu.address.logic.parser;
+
+import static seedu.address.commons.core.Messages.MESSAGE_INVALID_COMMAND_FORMAT;
+
+import seedu.address.commons.core.index.Index;
+import seedu.address.logic.commands.GenerateEmailsCommand;
+import seedu.address.logic.parser.exceptions.ParseException;
+
+public class GenerateEmailsCommandParser implements Parser<GenerateEmailsCommand> {
+
+    @Override
+    public GenerateEmailsCommand parse(String args) throws ParseException {
+        try {
+            Index index = ParserUtil.parseIndex(args);
+            return new GenerateEmailsCommand(index);
+        } catch (ParseException pe) {
+            throw new ParseException(
+                    String.format(MESSAGE_INVALID_COMMAND_FORMAT, GenerateEmailsCommand.MESSAGE_USAGE), pe);
+        }
+    }
+}

src/main/java/seedu/address/model/task/Task.java

@@ -140,6 +140,16 @@ public int getNoOfPeople() {
         return this.people.size();
     }
 
+    /**
+     * Returns a copy-paste friendly string containing all the emails related to this task.
+     *
+     * @return The generated email string
+     */
+    public String getEmails() {
+        String[] emails = this.people.stream().map(p -> p.getEmail().toString()).toArray(String[]::new);
+        return String.join(", ", emails);
+    }
+
     @Override
     public boolean equals(Object other) {
         if (other == this) {