Add due date functionality to Todo model

- Add due_date field as nullable DateTime with timezone support
- Add is_overdue property to check if task is overdue
- Add days_until_due property for time calculations
- Create migration 007 to add due_date column with index
- Maintain backward compatibility with nullable due_date

alembic/versions/007_add_due_date.py

@@ -0,0 +1,32 @@
+"""Add due_date field to todos table
+
+Revision ID: 007
+Revises: 006
+Create Date: 2025-06-19 12:00:00.000000
+
+"""
+
+from alembic import op
+import sqlalchemy as sa
+
+# revision identifiers, used by Alembic.
+revision = "007"
+down_revision = "006"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    # Add due_date column to todos table
+    op.add_column(
+        "todos",
+        sa.Column("due_date", sa.DateTime(timezone=True), nullable=True),
+    )
+
+    # Add index for better performance on due date queries
+    op.create_index(op.f("ix_todos_due_date"), "todos", ["due_date"], unique=False)
+
+
+def downgrade() -> None:
+    op.drop_index(op.f("ix_todos_due_date"), table_name="todos")
+    op.drop_column("todos", "due_date")

app/models/todo.py

@@ -2,6 +2,8 @@ from sqlalchemy import Column, Integer, String, Boolean, DateTime, Enum, Foreign
 from sqlalchemy.orm import relationship
 from sqlalchemy.sql import func
 import enum
+from datetime import datetime, timezone
+from typing import Optional
 
 from app.db.base import Base
 
@@ -23,6 +25,7 @@ class Todo(Base):
     project_id = Column(Integer, ForeignKey("projects.id"), nullable=True)
     category_id = Column(Integer, ForeignKey("categories.id"), nullable=True)
     parent_id = Column(Integer, ForeignKey("todos.id"), nullable=True)
+    due_date = Column(DateTime(timezone=True), nullable=True)
     created_at = Column(DateTime(timezone=True), server_default=func.now())
     updated_at = Column(DateTime(timezone=True), onupdate=func.now())
 
@@ -42,3 +45,25 @@ class Todo(Base):
     def is_subtask(self) -> bool:
         """Check if this todo is a subtask of another todo."""
         return self.parent_id is not None
+
+    @property
+    def is_overdue(self) -> bool:
+        """Check if this todo is overdue."""
+        if self.due_date is None or self.completed:
+            return False
+        return datetime.now(timezone.utc) > self.due_date
+
+    @property
+    def days_until_due(self) -> Optional[int]:
+        """Calculate the number of days until the due date.
+        
+        Returns:
+            int: Number of days until due (negative if overdue)
+            None: If no due date is set
+        """
+        if self.due_date is None:
+            return None
+        
+        now = datetime.now(timezone.utc)
+        delta = (self.due_date - now).days
+        return delta