# Product Requirements Document: Todo Task Management Application

## 1. Overview

The Todo Task Management Application is a comprehensive task organization system that enables users to create, manage, and track their personal and professional tasks efficiently. The application provides a centralized platform for users to organize their work, set priorities, track progress, and collaborate on tasks with others. This system aims to improve productivity by offering intuitive task management features including categorization, due dates, priority levels, and status tracking.

## 2. User Roles

### Guest
- View public landing page
- Register for a new account
- Login to existing account

### Registered User (Standard)
- Create, read, update, and delete their own tasks
- Organize tasks into custom lists/categories
- Set task priorities, due dates, and status
- Mark tasks as complete/incomplete
- Search and filter their own tasks
- Share tasks with other users
- Comment on tasks they own or have been shared with
- Attach files/notes to tasks
- View dashboard with task statistics
- Manage their profile and preferences
- Receive notifications about task updates

### Admin
- All Registered User permissions
- View all users in the system
- Deactivate/activate user accounts
- View system-wide task statistics
- Access audit logs
- Manage system settings and configurations
- View and manage all tasks across all users (read-only for oversight)

## 3. Core Entities

### User
Represents a person who uses the application. Contains authentication credentials, profile information, preferences, and account status.

### Task
The primary entity representing a todo item. Contains title, description, priority, status, due date, creation date, completion date, and associated metadata.

### List
A collection or category for organizing related tasks. Users can create custom lists to group tasks by project, context, or any other organizational scheme.

### Tag
A label that can be applied to tasks for flexible categorization and filtering. Tags are user-defined and reusable across multiple tasks.

### Comment
A text-based note or discussion entry attached to a specific task. Enables collaboration and tracking of task-related conversations.

### Attachment
A file or document associated with a task. Stores file metadata including filename, size, type, and storage location.

### Share
Represents the sharing relationship between a task owner and other users. Defines permission levels for shared access.

### Notification
An alert or message sent to users about task-related events (due dates, assignments, comments, etc.).

### Activity Log
A record of actions performed on tasks, tracking who did what and when for audit and history purposes.

### Subtask
A smaller, component task that is part of a larger parent task. Enables breaking down complex tasks into manageable steps.

## 4. Entity Relationships

### User Relationships
- **User → Task**: One-to-Many (one user owns many tasks)
- **User → List**: One-to-Many (one user creates many lists)
- **User → Comment**: One-to-Many (one user authors many comments)
- **User → Notification**: One-to-Many (one user receives many notifications)
- **User → Tag**: One-to-Many (one user creates many tags)

### Task Relationships
- **Task → User**: Many-to-One (many tasks belong to one owner)
- **Task → List**: Many-to-One (many tasks belong to one list; a task can optionally belong to one list)
- **Task → Tag**: Many-to-Many (tasks can have multiple tags; tags can be applied to multiple tasks)
- **Task → Comment**: One-to-Many (one task has many comments)
- **Task → Attachment**: One-to-Many (one task has many attachments)
- **Task → Share**: One-to-Many (one task can be shared with many users)
- **Task → Subtask**: One-to-Many (one task can have many subtasks)
- **Task → Activity Log**: One-to-Many (one task has many activity log entries)
- **Task → Notification**: One-to-Many (one task generates many notifications)

### List Relationships
- **List → User**: Many-to-One (many lists belong to one user)
- **List → Task**: One-to-Many (one list contains many tasks)

### Other Relationships
- **Comment → User**: Many-to-One (many comments authored by one user)
- **Comment → Task**: Many-to-One (many comments belong to one task)
- **Subtask → Task**: Many-to-One (many subtasks belong to one parent task)
- **Share → Task**: Many-to-One (many shares reference one task)
- **Share → User**: Many-to-One (many shares involve one user as recipient)

## 5. Key Workflows

### User Registration & Onboarding
1. Guest visits application landing page
2. Guest clicks "Sign Up" button
3. System displays registration form
4. Guest enters email, password, and full name
5. System validates input (email format, password strength)
6. System creates new user account
7. System sends verification email
8. User clicks verification link in email
9. System activates account
10. User is redirected to dashboard with welcome tutorial

### Task Creation Workflow
1. User clicks "New Task" button
2. System displays task creation form
3. User enters task title (required)
4. User optionally enters description, due date, priority, and selects a list
5. User optionally adds tags
6. User clicks "Create Task"
7. System validates input
8. System creates task with status "Not Started"
9. System logs activity in Activity Log
10. System displays success message and shows task in appropriate view
11. If task has due date, system schedules notification

### Task Update Workflow
1. User selects a task from their task list
2. System displays task detail view
3. User modifies any editable fields (title, description, status, priority, due date, list, tags)
4. User clicks "Save"
5. System validates changes
6. System updates task with timestamp
7. System logs changes in Activity Log
8. If task is shared, system creates notifications for shared users
9. System displays success message
10. System updates task in all relevant views

### Task Completion Workflow
1. User views task in list or detail view
2. User clicks checkbox or "Mark Complete" button
3. System updates task status to "Completed"
4. System records completion timestamp
5. System logs completion in Activity Log
6. System updates completion statistics
7. System visually indicates completion (strikethrough, moved to completed section)
8. If task has subtasks, system checks if all subtasks are complete
9. System cancels any pending due date notifications

### Task Sharing Workflow
1. User opens task detail view
2. User clicks "Share" button
3. System displays share dialog
4. User enters email or username of recipient
5. User selects permission level (View Only or Can Edit)
6. User optionally adds a message
7. User clicks "Share"
8. System validates recipient exists
9. System creates Share record
10. System creates notification for recipient
11. System sends email notification to recipient
12. Recipient sees shared task in their "Shared with Me" view
13. System logs sharing action in Activity Log

### List Management Workflow
1. User clicks "New List" or "Manage Lists"
2. System displays list management interface
3. User enters list name and optional description/color
4. User clicks "Create List"
5. System validates list name is unique for user
6. System creates list
7. System displays list in sidebar navigation
8. User can drag-and-drop tasks into list
9. User can rename, reorder, or delete lists
10. When deleting list, system prompts for action on contained tasks (move to default or delete)

### Search & Filter Workflow
1. User enters search query in search bar or opens filter panel
2. User optionally selects filter criteria (status, priority, due date range, list, tags)
3. User clicks "Search" or filters auto-apply
4. System queries tasks matching criteria
5. System displays filtered results
6. User can save filter as a custom view
7. User can clear filters to return to default view

### Notification Workflow
1. System monitors for notification triggers (due date approaching, task shared, comment added, task assigned)
2. When trigger occurs, system creates Notification record
3. System determines user notification preferences
4. System sends in-app notification
5. If user has email notifications enabled, system sends email
6. User sees notification badge/count in application
7. User clicks notification to view details
8. System marks notification as read
9. User can dismiss or take action on notification

## 6. Features & Requirements

### 6.1 Authentication & User Management

#### F-AUTH-001: User Registration
- System must provide registration form with email, password, and full name fields
- System must validate email format and uniqueness
- System must enforce password requirements (minimum 8 characters, at least one uppercase, one lowercase, one number)
- System must send verification email upon registration
- System must prevent login until email is verified

#### F-AUTH-002: User Login
- System must provide login form with email and password
- System must authenticate credentials against stored hash
- System must generate and return JWT token upon successful authentication
- System must implement "Remember Me" functionality
- System must lock account after 5 failed login attempts

#### F-AUTH-003: Password Reset
- System must provide "Forgot Password" functionality
- System must send password reset link via email
- Reset link must expire after 24 hours
- System must allow user to set new password via reset link

#### F-AUTH-004: User Profile Management
- Users must be able to update their profile information (name, email, avatar)
- Users must be able to change their password
- Users must be able to set notification preferences
- Users must be able to set timezone and date format preferences
- Users must be able to delete their account (with confirmation)

### 6.2 Task Management

#### F-TASK-001: Create Task
- Users must be able to create tasks with title (required)
- Users must be able to add optional description (rich text supported)
- Users must be able to set due date and time
- Users must be able to set priority (Low, Medium, High, Critical)
- Users must be able to assign task to a list
- Users must be able to add tags during creation
- System must set default status to "Not Started"
- System must record creation timestamp and creator

#### F-TASK-002: View Tasks
- Users must be able to view all their tasks in list view
- Users must be able to view task details in expanded view
- Users must be able to view tasks in different layouts (list, board, calendar)
- Users must be able to see task count by status
- System must display overdue tasks prominently
- System must show task progress (subtasks completed)

#### F-TASK-003: Update Task
- Users must be able to edit all task fields
- Users must be able to change task status (Not Started, In Progress, Completed, Blocked)
- Users must be able to update priority
- Users must be able to move task to different list
- Users must be able to add/remove tags
- System must track modification history
- System must show last modified timestamp

#### F-TASK-004: Delete Task
- Users must be able to delete their own tasks
- System must require confirmation before deletion
- System must soft-delete tasks (mark as deleted, not permanently remove)
- System must allow recovery of deleted tasks within 30 days
- System must permanently delete tasks after 30 days
- Deleting parent task must handle subtasks (cascade or orphan)

#### F-TASK-005: Task Status Management
- Users must be able to mark tasks as complete/incomplete
- System must support status transitions: Not Started → In Progress → Completed
- System must allow setting status to "Blocked" with reason
- System must record completion timestamp
- System must calculate time to completion
- Completing parent task must check subtask completion

#### F-TASK-006: Task Priority
- System must support four priority levels: Low, Medium, High, Critical
- Users must be able to set and change priority
- System must visually distinguish priorities (colors/icons)
- System must allow sorting by priority
- System must highlight critical priority tasks

### 6.3 Subtask Management

#### F-SUBTASK-001: Create Subtask
- Users must be able to add subtasks to any task
- Subtasks must have title (required) and status
- Subtasks must inherit parent task's list and tags by default
- System must support unlimited nesting depth (or specify limit)
- System must display subtask count on parent task

#### F-SUBTASK-002: Manage Subtasks
- Users must be able to reorder subtasks
- Users must be able to mark subtasks complete independently
- Users must be able to convert subtask to standalone task
- Users must be able to delete subtasks
- System must update parent task progress based on subtask completion

### 6.4 List & Organization

#### F-LIST-001: Create List
- Users must be able to create custom lists
- Lists must have unique names per user
- Users must be able to set list color/icon
- Users must be able to add description to list
- System must provide default "Inbox" list for all users

#### F-LIST-002: Manage Lists
- Users must be able to rename lists
- Users must be able to reorder lists in sidebar
- Users must be able to archive lists
- Users must be able to delete lists
- System must prompt for task handling when deleting list (move or delete)
- Users must be able to set default list for new tasks

#### F-LIST-003: List Views
- Users must be able to view all tasks in a list
- System must show task count per list
- System must show overdue task count per list
- Users must be able to filter tasks within a list
- Users must be able to sort tasks within a list

### 6.5 Tags

#### F-TAG-001: Create & Manage Tags
- Users must be able to create custom tags
- Tags must have name and optional color
- System must suggest existing tags during task creation
- Users must be able to rename tags
- Users must be able to delete tags
- Deleting tag must remove it from all associated tasks

#### F-TAG-002: Tag Application
- Users must be able to add multiple tags to a task
- Users must be able to remove tags from tasks
- System must support tag autocomplete
- System must show tag count on tasks
- Users must be able to filter tasks by tag

#### F-TAG-003: Tag Views
- Users must be able to view all tasks with specific tag
- System must show task count per tag
- Users must be able to view all their tags
- System must show most used tags

### 6.6 Search & Filter

#### F-SEARCH-001: Search Functionality
- Users must be able to search tasks by title and description
- System must support partial text matching
- System must highlight search terms in results
- Search must be case-insensitive
- System must return results in real-time (as user types)
- Search must include tasks in all lists

#### F-FILTER-001: Filter Tasks
- Users must be able to filter by status
- Users must be able to filter by priority
- Users must be able to filter by due date (overdue, today, this week, this month, no date)
- Users must be able to filter by list
- Users must be able to filter by tag
- Users must be able to apply multiple filters simultaneously
- Users must be able to save filter combinations as custom views

#### F-FILTER-002: Sort Tasks
- Users must be able to sort by due date
- Users must be able to sort by priority
- Users must be able to sort by creation date
- Users must be able to sort by title (alphabetically)
- Users must be able to sort by completion status
- System must remember user's sort preference

### 6.7 Collaboration

#### F-COLLAB-001: Share Tasks
- Users must be able to share tasks with other users by email/username
- System must support two permission levels: View Only and Can Edit
- Users must be able to add message when sharing
- System must notify recipient when task is shared
- Users must be able to view list of users task is shared with
- Users must be able to revoke sharing access

#### F-COLLAB-002: Shared Task Access
- Shared users must see shared tasks in "Shared with Me" section
- Shared users with View Only can see all task details but cannot edit
- Shared users with Can Edit can modify task (except delete or change owner)
- System must indicate shared status on tasks
- System must show who shared the task

#### F-COLLAB-003: Comments
- Users must be able to add comments to tasks they own or have access to
- Comments must support text formatting
- Comments must show author and timestamp
- Users must be able to edit their own comments
- Users must be able to delete their own comments
- System must notify task owner and shared users of new comments
- System must display comment count on task

### 6.8 Attachments

#### F-ATTACH-001: File Upload
- Users must be able to attach files to tasks
- System must support common file types (PDF, DOC, XLS, images, etc.)
- System must enforce maximum file size (e.g., 10MB per file)
- System must scan files for viruses
- System must store files securely
- Users must be able to attach multiple files to one task

#### F-ATTACH-002: File Management
- Users must be able to view list of attachments on task
- Users must be able to download attachments
- Users must be able to preview images inline
- Users must be able to delete attachments
- System must show file name, size, and upload date
- System must show who uploaded the file

### 6.9 Notifications

#### F-NOTIF-001: Notification Types
- System must notify users when task is due today
- System must notify users 1 day before task due date
- System must notify users when task is shared with them
- System must notify users when comment is added to their task
- System must notify users when shared task is updated
- System must notify users when they are mentioned in comments

#### F-NOTIF-002: Notification Delivery
- System must show in-app notifications with badge count
- System must send email notifications based on user preferences
- Users must be able to mark notifications as read
- Users must be able to dismiss notifications
- Users must be able to click notification to view related task
- System must group similar notifications

#### F-NOTIF-003: Notification Preferences
- Users must be able to enable/disable email notifications
- Users must be able to set notification frequency (real-time, daily digest)
- Users must be able to choose which events trigger notifications
- Users must be able to set quiet hours for notifications

### 6.10 Dashboard & Analytics

#### F-DASH-001: Dashboard Overview
- System must display total task count
- System must display tasks by status (breakdown)
- System must display overdue tasks count
- System must display tasks due today
- System must display tasks due this week
- System must show completion rate
- System must show recently completed tasks
- System must show recently created tasks

#### F-DASH-002: Task Views
- System must provide "My Day" view (tasks due today)
- System must provide "Upcoming" view (tasks due soon)
- System must provide "All Tasks" view
- System must provide "Completed" view
- System must provide "Shared with Me" view
- Users must be able to set default view on login

#### F-DASH-003: Calendar View
- System must display tasks on calendar by due date
- Users must be able to navigate months
- Users must be able to click date to see tasks due that day
- Users must be able to drag tasks to change due date
- System must highlight today's date
- System must show overdue tasks indicator

### 6.11 Admin Features

#### F-ADMIN-001: User Management
- Admins must be able to view all users
- Admins must be able to search users
- Admins must be able to deactivate user accounts
- Admins must be able to reactivate user accounts
- Admins must be able to reset user passwords
- Admins must be able to view user activity logs

#### F-ADMIN-002: System Monitoring
- Admins must be able to view system-wide statistics
- Admins must be able to view total users, tasks, lists
- Admins must be able to view active users (last 30 days)
- Admins must be able to view storage usage
- Admins must be able to view error logs
- Admins must be able to export system data

#### F-ADMIN-003: System Configuration
- Admins must be able to configure system settings
- Admins must be able to set maximum file upload size
- Admins must be able to configure email templates
- Admins must be able to set data retention policies
- Admins must be able to configure security settings

## 7. Business Rules

### BR-001: Task Ownership
- Every task must have exactly one owner (the creator)
- Only the task owner can delete the task
- Only the task owner can change sharing permissions
- Task ownership cannot be transferred

### BR-002: Task Validation
- Task title is required and must be between 1-500 characters
- Task description is optional and limited to 10,000 characters
- Due date, if set, cannot be in the past (except when editing existing tasks)
- Priority must be one of: Low, Medium, High, Critical
- Status must be one of: Not Started, In Progress, Completed, Blocked

### BR-003: List Rules
- List names must be unique per user
- List names must be between 1-100 characters
- Users cannot delete the default "Inbox" list
- When a list is deleted, tasks must either be moved to another list or deleted
- A task can belong to zero or one list (not multiple lists)

### BR-004: Tag Rules
- Tag names must be unique per user
- Tag names must be between 1-50 characters
- A task can have 0 to 20 tags
- Deleting a tag removes it from all associated tasks
- Tags are case-insensitive for uniqueness

### BR-005: Sharing Rules
- Users can only share tasks they own
- Users cannot share a task with themselves
- A task can be shared with up to 50 users
- Shared users cannot share the task with others
- Revoking share access removes task from recipient's view immediately
- Shared users cannot see other shared users (only owner can)

### BR-006: Subtask Rules
- Subtasks can only be created on existing tasks
- Subtask nesting is limited to 3 levels deep
- A task can have up to 50 subtasks
- Deleting a parent task deletes all subtasks
- Subtasks inherit parent's list by default but can be changed
- Parent task cannot be marked complete if incomplete subtasks exist (warning shown)

### BR-007: Comment Rules
- Comments must be between 1-2,000 characters
- Users can only edit/delete their own comments
- Comments can only be added to tasks user owns or has access to
- Deleted comments are soft-deleted and show as "[Comment deleted]"
- Comments are ordered chronologically (oldest first)

### BR-008: Attachment Rules
- Maximum file size per attachment: 10MB
- Maximum total attachments per task: 20 files
- Maximum total storage per user: 1GB
- Allowed file types: PDF, DOC, DOCX, XLS, XLSX, PPT, PPTX, TXT, JPG, PNG, GIF, ZIP
- Files must be scanned for viruses before storage
- Deleting a task deletes all associated attachments

### BR-009: Notification Rules
- Notifications are only sent to active users
- Due date notifications are sent at 9 AM user's local time
- Duplicate notifications are suppressed (same event within 1 hour)
- Notifications are retained for 90 days then deleted
- Users must verify email before receiving email notifications
- Maximum 50 unread notifications displayed

### BR-010: User Account Rules
- Email addresses must be unique across all users
- Passwords must be at least 8 characters with complexity requirements
- Accounts are locked after 5 consecutive failed login attempts
- Locked accounts auto-unlock after 30 minutes or via password reset
- Unverified accounts are deleted after 7 days
- Deleted accounts and all associated data are permanently removed after 30 days

### BR-011: Data Retention
- Completed tasks are retained indefinitely unless user deletes
- Deleted tasks are soft-deleted and recoverable for 30 days
- Activity logs are retained for 1 year
- Notifications are retained for 90 days
- Attachments are deleted when parent task is permanently deleted

### BR-012: Search & Filter Rules
- Search queries must be at least 2 characters
- Search results are limited to 100 tasks
- Filters are applied with AND logic (all conditions must match)
- Saved filters are limited to 10 per user
- Search includes only tasks user owns or has access to

### BR-013: Permission Rules
- Users can only view/edit tasks they own or have been shared with
- View Only permission allows reading all task data but no modifications
- Can Edit permission allows all modifications except delete and sharing
- Admins can view all tasks but cannot edit tasks they don't own
- Users cannot escalate their own permissions

## 8. Non-Functional Requirements

### NFR-001: Performance
- Page load time must be under 2 seconds on standard broadband
- Task list rendering must handle up to 1,000 tasks without pagination
- Search results must return within 500ms
- API response time must be under 200ms for 95% of requests
- Database queries must be optimized with proper indexing
- System must support 1,000 concurrent users
- File uploads must show progress indicator for files over 1MB

### NFR-002: Scalability
- System must be designed to scale horizontally
- Database must support sharding for future growth
- File storage must use cloud storage (S3 or equivalent)
- System must handle 10,000 registered users initially
- System must be architected to scale to 100,000+ users
- Background jobs (notifications, cleanup) must use queue system

### NFR-003: Security
- All passwords must be hashed using bcrypt with salt
- All API endpoints must require authentication (except public routes)
- JWT tokens must expire after 24 hours
- Refresh tokens must be implemented for session management
- All data transmission must use HTTPS/TLS
- File uploads must be scanned for malware
- SQL injection prevention through parameterized queries
- XSS prevention through input sanitization and output encoding
- CSRF protection must be implemented
- Rate limiting must be applied to prevent abuse (100 requests/minute per user)
- Sensitive data must be encrypted at rest
- User sessions must timeout after 30 minutes of inactivity

### NFR-004: Reliability & Availability
- System uptime must be 99.5% or higher
- Database must have automated daily backups
- Backup retention period: 30 days
- System must have disaster recovery plan
- Failed background jobs must be retried with exponential backoff
- System must gracefully handle third-party service failures
- Error messages must be logged for debugging

### NFR-005: Usability
- Interface must be intuitive and require no training
- System must be responsive and work on mobile devices (320px width minimum)
- System must support modern browsers (Chrome, Firefox, Safari, Edge - last 2 versions)
- Loading states must be shown for all async operations
- Error messages must be clear and actionable
- Success feedback must be provided for all user actions
- Keyboard shortcuts must be available for power users
- System must be accessible (WCAG 2.1 Level AA compliance)

### NFR-006: Compatibility
- Backend API must be RESTful and version-controlled
- Frontend must work on iOS 12+ and Android 8+
- System must support modern JavaScript (ES6+)
- Database must be PostgreSQL 12+ or MySQL 8+
- System must support internationalization (i18n) framework
- Date/time must respect user's timezone
- System must support UTF-8 character encoding

### NFR-007: Maintainability
- Code must follow consistent style guide
- Code must have minimum 70% test coverage
- API must have comprehensive documentation (OpenAPI/Swagger)
- System must have structured logging
- Environment-specific configurations must be externalized
- Database migrations must be version-controlled
- System must have health check endpoints

### NFR-008: Data Privacy & Compliance
- System must comply with GDPR requirements
- Users must be able to export their data
- Users must be able to request account deletion
- System must have privacy policy and terms of service
- User data must not be shared with third parties without consent
- Audit logs must track data access and modifications
- Personal data must be anonymized in logs

### NFR-009: Monitoring & Observability
- System must have application performance monitoring (APM)
- System must track key metrics (response time, error rate, user activity)
- System must have alerting for critical errors
- System must log all errors with stack traces
- System must track user analytics (feature usage, engagement)
- Admin dashboard must display system health metrics

### NFR-010: Email & Notifications
- Email delivery must use reliable service (SendGrid, AWS SES, etc.)
- Email templates must be responsive and mobile-friendly
- Failed email deliveries must be retried up to 3 times
- Email bounce and complaint rates must be monitored
- Unsubscribe link must be included in all notification emails
- Email sending must be rate-limited to prevent spam classification

### NFR-011: API Design
- API must follow REST principles
- API must return appropriate HTTP status codes
- API responses must be in JSON format
- API must support pagination for list endpoints (default 50 items per page)
- API must support filtering, sorting, and searching via query parameters
- API must have consistent error response format
- API must include rate limit headers in responses
- API documentation must include example requests/responses

### NFR-012: Development & Deployment
- System must use version control (Git)
- System must have separate environments (development, staging, production)
- Deployments must be automated via CI/CD pipeline
- Database schema changes must be applied via migrations
- System must have rollback capability
- Environment variables must be used for configuration
- Secrets must be stored securely (not in code)

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**Document Version:** 1.0  
**Last Updated:** 2025  
**Status:** Ready for Development

This PRD provides comprehensive specifications for building a full-featured Todo Task Management Application with all necessary entities, workflows, features, and requirements clearly defined for implementation.