Task Scheduler

This assignment is a PHP-based task management system where users can add tasks to a common list and subscribe to receive hourly email reminders for pending tasks.

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🚀 Your Task

Your objective is to implement the functionality in the src/ directory while following these rules:

✅ DO NOT change function names or modify the file structure.
✅ DO NOT modify anything outside the src/ folder. You can add additional files if required inside src folder. ✅ DO NOT use a database; use text files for storage.
✅ Implement all required functions in functions.php.
✅ Implement the main interface in index.php.
✅ Implement email verification and unsubscribe functionality.

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📝 Submission Steps [ Non adherence to this will cause disqualification ]

1. Clone the repository to your local machine.
2. Create a new branch from the main branch. Do not push code directly to main.
3. Implement the required features inside the src/ directory.
4. Push your code to your branch (not main).
5. Raise a Pull Request (PR) only once against the main branch when all your code is finalized.
   • Do not raise multiple PRs.
   • Do not add multiple commits to a PR after submission.
6. Failure to follow these instructions will result in disqualification.
7. Wait for your submission to be reviewed. Do not merge the PR.

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⚠️ Important Notes

All form elements should always be visible on the page and should not be conditionally rendered. This ensures the assignment can be tested properly at the appropriate steps.

Please ensure that if the base repository shows the original template repo, update it so that your repo's main branch is set as the base branch.

Recommended PHP version: 8.3

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📌 Features to Implement

1️⃣ Task Management

• Add new tasks to the common list
• Duplicate tasks should not be added.
• Mark tasks as complete/incomplete
• Delete tasks
• Store tasks in tasks.txt

2️⃣ Email Subscription System

• Users can subscribe with their email
• Email verification process:
  • System generates a unique 6-digit verification code
  • Sends verification email with activation link
  • Link contains email and verification code
  • User clicks link to verify subscription
  • System moves email from pending to verified subscribers
• Store subscribers in subscribers.txt
• Store pending verifications in pending_subscriptions.txt

3️⃣ Reminder System

• CRON job runs every hour
• Sends emails to verified subscribers
• Only includes pending tasks in reminders
• Includes unsubscribe link in emails
• Unsubscribe process:
  • Every email includes an unsubscribe link
  • Link contains encoded email address
  • One-click unsubscribe removes email from subscribers

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📜 File Details & Function Stubs

You must implement the following functions in functions.php:

function addTask($task_name) {
    // Add a new task to the list
}

function getAllTasks() {
    // Get all tasks from tasks.txt
}

function markTaskAsCompleted($task_id, $is_completed) {
    // Mark/unmark a task as complete
}

function deleteTask($task_id) {
    // Delete a task from the list
}

function generateVerificationCode() {
    // Generate a 6-digit verification code
}

function subscribeEmail($email) {
    // Add email to pending subscriptions and send verification
}

function verifySubscription($email, $code) {
    // Verify email subscription
}

function unsubscribeEmail($email) {
    // Remove email from subscribers list
}

function sendTaskReminders() {
    // Sends task reminders to all subscribers
 	// Internally calls  sendTaskEmail() for each subscriber
}

function sendTaskEmail( $email, $pending_tasks ) {
	// Sends a task reminder email to a subscriber with pending tasks.
}

📁 File Structure

• functions.php (Core functions)
• index.php (Main interface)
• verify.php (Email verification handler)
• unsubscribe.php (Unsubscribe handler)
• cron.php (Reminder sender)
• setup_cron.sh (CRON job setup)
• tasks.txt (Task storage)
• subscribers.txt (Verified subscribers)
• pending_subscriptions.txt (Pending verifications)

🔄 CRON Job Implementation

📌 You must implement a CRON job that runs cron.php every 1 hour.
📌 Do not just write instructions—provide an actual setup_cron.sh script inside src/.
📌 Your script should automatically configure the CRON job on execution.

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🛠 Required Files

• setup_cron.sh (Must configure the CRON job)
• cron.php (Must handle sending GitHub updates via email)

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🚀 How It Should Work

• The setup_cron.sh script should register a CRON job that executes cron.php every 1 hour.
• The CRON job must be automatically added when the script runs.
• The cron.php file should actually fetch pending tasks and send emails to subscribed users.

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📩 Email Handling

✅ The email content must be in HTML format (not JSON).
✅ Use PHP's mail() function for sending emails.
✅ Each email should include an unsubscribe link.
✅ Store subscribers email in subscribers.txt (Do not use a database). ✅ Store pending verifications in pending_subscriptions.txt (Do not use a database). ✅ Each email should include an unsubscribe link.

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❌ Disqualification Criteria

🚫 Hardcoding verification codes.
🚫 Using a database (use subscribers.txt).
🚫 Modifying anything outside the src/ directory.
🚫 Changing function names.
🚫 Not implementing a working CRON job.
🚫 Not formatting emails as HTML. 🚫 Using 3rd party libraries, only pure PHP is allowed.

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📌 Input & Button Formatting Guidelines

📝 Task Management Inputs & Button:

• Add task input must have name="task-name" and id="task-name"
• Add task button must have id="add-task"

✅ Example:

<input type="text" name="task-name" id="task-name" placeholder="Enter new task" required>
<button type="submit" id="add-task">Add Task</button>

• Task list must have class="task-list".
• Task item in that list must have class="task-item
• Task item must have have a checkbox <input type="checkbox" class="task-status" > so user can mark it done.
• Once task item is completed add class completed. <li class="task-item completed">
• Task item should have a delete action with class="delete-task".

✅ Example:

<ul class="tasks-list">
	<li class="task-item">
		<input type="checkbox" class="task-status">
		<button class="delete-task">Delete</button>
	</li>	
</ul>

📧 Email Input & Submission Button:

• The email input field must have name="email".
• The submit button must have id="submit-email".

✅ Example:

<input type="email" name="email" required />
<button id="submit-email">Submit</button>

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📩 Email Content Guidelines

✅ Verification Email:

• Subject: Verify subscription to Task Planner
• Body Format:

<p>Click the link below to verify your subscription to Task Planner:</p>
';
<p><a id="verification-link" href="{verification_link}">Verify Subscription</a></p>

• Sender: no-reply@example.com

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📩 Email Content Guidelines

⚠️ Note: The Subject and Body of the email must strictly follow the formats below, including the exact HTML structure.

✅ Task Reminder Email:

• Subject: Task Planner - Pending Tasks Reminder
• Body Format:

<h2>Pending Tasks Reminder</h2>
<p>Here are the current pending tasks:</p>
<ul>
	<li>Task 1</li>
	<li>Task 2</li>
</ul>
<p><a id="unsubscribe-link" href="{unsubscribe_link}">Unsubscribe from notifications</a></p>

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📊 Data Storage Format

All data must be stored in JSON format in the text files.

Tasks Format (tasks.txt):

Tasks must be stored as a JSON array of objects with the following schema:

[
	{
		"id": "unique_task_id",
		"name": "Task Name",
		"completed": false
	},
	{
		"id": "another_task_id",
		"name": "Another Task",
		"completed": true
	}
]

Subscribers Format (subscribers.txt):

Subscribers must be stored as a JSON array of email addresses:

["user1@example.com", "user2@example.com"]

Pending Subscriptions Format (pending_subscriptions.txt):

Pending subscriptions must be stored as a JSON object with emails as keys:

{
	"user1@example.com": {
		"code": "123456",
		"timestamp": 1717694230
	},
	"user2@example.com": {
		"code": "654321",
		"timestamp": 1717694245
	}
}

⚠️ Important: Ensuring your data follows these exact JSON schemas is critical for proper validation.