Add Todo Priorities, Deadlines & Filtering to FastAPI Backend

[Copilot]

Summary

This PR implements priority levels, due dates, and filtering/sorting capabilities for the Todo API, transforming it from a basic demo into a production-ready task management backend.

Features Added

🎯 Priority Levels

Todos now support three priority levels with automatic validation:

• High - Urgent tasks requiring immediate attention
• Medium - Default priority for standard tasks
• Low - Nice-to-have tasks

class Todo(BaseModel):
    priority: Optional[str] = Field(default="medium", pattern="^(low|medium|high)$")
    due_date: Optional[datetime] = None

📅 Due Dates

Todos can have optional deadlines in ISO 8601 format (YYYY-MM-DDTHH:MM:SS), enabling time-based task organization.

🔍 Advanced Filtering & Sorting

The GET /todos endpoint now supports powerful query parameters:

Filtering:

• completed - Filter by completion status (true/false)
• priority - Filter by priority level (low/medium/high)
• before - Show tasks due before a specific date
• after - Show tasks due after a specific date

Sorting:

• sort=due_date - Sort by deadline (earliest first, null values last)
• sort=priority - Sort by importance (high → medium → low)

Combined Queries:

# Get all high-priority incomplete tasks due within the next week, sorted by deadline
GET /todos?priority=high&completed=false&before=2025-10-15T00:00:00&sort=due_date

Example Usage

Create a High-Priority Todo with Deadline

curl -X POST http://localhost:8000/todos \
  -H "Content-Type: application/json" \
  -d '{
    "id": 1,
    "title": "Submit report",
    "description": "Monthly project update",
    "completed": false,
    "priority": "high",
    "due_date": "2025-10-08T17:00:00"
  }'

Response:

{
  "id": 1,
  "title": "Submit report",
  "description": "Monthly project update",
  "completed": false,
  "priority": "high",
  "due_date": "2025-10-08T17:00:00"
}

Filter and Sort Tasks

# Get high-priority tasks due before Oct 15, sorted by due date
curl -X GET 'http://localhost:8000/todos?priority=high&before=2025-10-15T00:00:00&sort=due_date'

# Get all completed tasks
curl -X GET 'http://localhost:8000/todos?completed=true'

# Sort all tasks by priority
curl -X GET 'http://localhost:8000/todos?sort=priority'

Implementation Details

Changes Made

• main.py (34 lines added):

  • Enhanced Todo model with priority and due_date fields
  • Added filtering and sorting logic to GET /todos endpoint
  • Updated PUT /todos/{id} to support priority and due_date updates

• README.md (53 lines added):

  • Updated Features section with new capabilities
  • Enhanced API documentation with query parameter descriptions
  • Added 10 comprehensive cURL examples

Total: 83 lines changed across 2 files

Key Features

• ✅ Backward Compatible - All existing functionality remains unchanged
• ✅ Input Validation - Pydantic patterns ensure data integrity (invalid priorities are rejected)
• ✅ Auto-Generated Docs - Swagger UI at /docs automatically shows all new parameters
• ✅ No New Dependencies - Uses only existing FastAPI/Pydantic features
• ✅ Clean Implementation - Follows existing code patterns and conventions

Testing

All features have been thoroughly tested:

• ✅ Create/update todos with priority and due dates
• ✅ Default priority ("medium") applied automatically
• ✅ Filter by completion, priority, and date ranges
• ✅ Sort by due_date and priority
• ✅ Combined filtering and sorting
• ✅ Input validation (rejects invalid priority values)

Benefits

This enhancement enables:

• 📊 Better Task Organization - Organize work by urgency and importance
• ⏰ Deadline Tracking - Never miss important due dates
• 🔎 Powerful Queries - Find exactly the tasks you need
• 🎯 Production Readiness - Real-world task management capabilities
• 📚 API Demo - Excellent showcase of FastAPI's query parameter features

Fixes

Closes #[issue_number] - Implements the complete feature specification including:

• Priority levels (low/medium/high)
• Due dates with ISO 8601 format
• Filtering by completion, priority, and date ranges
• Sorting by priority or due_date
• Updated interactive API documentation
• Comprehensive examples and testing

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Feature Proposal: Todo Priorities, Deadlines & Filtering</issue_title>
<issue_description>

Feature Proposal: Todo Priorities, Deadlines & Filtering

Labels: enhancement feature backend frontend api
Milestone: v0.2 (proposed)

---

Summary

Add priority levels, due dates, and filtering/sorting capabilities to the existing FastAPI Todo backend. This will turn the demo into a more realistic, production-ready task tracker where users can manage importance and deadlines effectively.

---

Why

Currently, each todo item only supports title, description, and completed. Adding deadlines and priorities allows:

• Task organization by urgency.

• Improved API demonstrations with query parameters.

• Easier extension into a frontend or team dashboard.

---

<h2 style="font-style: normal; font-variant-caps: normal; letter-spacing: normal; ...

Fixes #1

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