Implement todo recurrence logic with auto-reset scheduling

Backend:
- Add reset_at (datetime) and next_due_date (date) columns to todos
- Toggle endpoint calculates reset schedule when completing recurring todos:
  daily resets next day, weekly resets start of next week (respects
  first_day_of_week setting), monthly resets 1st of next month
- GET /todos auto-reactivates recurring todos whose reset_at has passed,
  updating due_date to next_due_date and clearing completion state
- Alembic migration 014

Frontend:
- Add reset_at and next_due_date to Todo type
- TodoItem shows recurrence badge (Daily/Weekly/Monthly) in purple
- Completed recurring todos display reset info:
  "Resets Mon 02/03/26 · Next due 06/03/26"

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/alembic/versions/014_add_todo_recurrence_fields.py

@@ -0,0 +1,26 @@
+"""Add reset_at and next_due_date to todos for recurrence
+
+Revision ID: 014
+Revises: 013
+Create Date: 2026-02-23
+
+"""
+from alembic import op
+import sqlalchemy as sa
+
+
+# revision identifiers, used by Alembic.
+revision = "014"
+down_revision = "013"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column("todos", sa.Column("reset_at", sa.DateTime(), nullable=True))
+    op.add_column("todos", sa.Column("next_due_date", sa.Date(), nullable=True))
+
+
+def downgrade() -> None:
+    op.drop_column("todos", "next_due_date")
+    op.drop_column("todos", "reset_at")

backend/app/models/todo.py

@@ -17,6 +17,8 @@ class Todo(Base):
     completed_at: Mapped[Optional[datetime]] = mapped_column(nullable=True)
     category: Mapped[Optional[str]] = mapped_column(String(100), nullable=True)
     recurrence_rule: Mapped[Optional[str]] = mapped_column(String(255), nullable=True)
+    reset_at: Mapped[Optional[datetime]] = mapped_column(nullable=True)
+    next_due_date: Mapped[Optional[date]] = mapped_column(Date, nullable=True)
     project_id: Mapped[Optional[int]] = mapped_column(Integer, ForeignKey("projects.id"), nullable=True)
     created_at: Mapped[datetime] = mapped_column(default=func.now())
     updated_at: Mapped[datetime] = mapped_column(default=func.now(), onupdate=func.now())

backend/app/routers/todos.py

@@ -1,8 +1,9 @@
 from fastapi import APIRouter, Depends, HTTPException, Query
 from sqlalchemy.ext.asyncio import AsyncSession
-from sqlalchemy import select
+from sqlalchemy import select, and_
 from typing import Optional, List
-from datetime import datetime
+from datetime import datetime, date, timedelta
+import calendar
 
 from app.database import get_db
 from app.models.todo import Todo
@@ -13,6 +14,90 @@ from app.models.settings import Settings
 router = APIRouter()
 
 
+def _calculate_recurrence(
+    recurrence_rule: str,
+    current_due_date: date | None,
+    first_day_of_week: int = 0,
+) -> tuple[datetime | None, date | None]:
+    """Calculate reset_at and next_due_date for a recurring todo.
+
+    Args:
+        recurrence_rule: "daily", "weekly", or "monthly"
+        current_due_date: The todo's current due date (may be None)
+        first_day_of_week: 0=Sunday, 1=Monday
+    Returns:
+        (reset_at, next_due_date) or (None, None) if rule is invalid
+    """
+    today = date.today()
+
+    if recurrence_rule == "daily":
+        reset_date = today + timedelta(days=1)
+        next_due = reset_date
+
+    elif recurrence_rule == "weekly":
+        # Find the start of the next week based on first_day_of_week setting.
+        # Python weekday(): Monday=0 ... Sunday=6
+        # Setting: 0=Sunday, 1=Monday
+        target_weekday = 6 if first_day_of_week == 0 else 0  # Python weekday for start
+        days_ahead = (target_weekday - today.weekday()) % 7
+        if days_ahead == 0:
+            days_ahead = 7  # Always push to *next* week
+        reset_date = today + timedelta(days=days_ahead)
+
+        if current_due_date:
+            # Preserve the day-of-week: place it in the reset week
+            dow_offset = (current_due_date.weekday() - target_weekday) % 7
+            next_due = reset_date + timedelta(days=dow_offset)
+        else:
+            next_due = reset_date
+
+    elif recurrence_rule == "monthly":
+        # First day of next month
+        if today.month == 12:
+            reset_date = date(today.year + 1, 1, 1)
+        else:
+            reset_date = date(today.year, today.month + 1, 1)
+
+        if current_due_date:
+            # Same day-of-month, clamped to month length
+            max_day = calendar.monthrange(reset_date.year, reset_date.month)[1]
+            day = min(current_due_date.day, max_day)
+            next_due = date(reset_date.year, reset_date.month, day)
+        else:
+            next_due = reset_date
+    else:
+        return None, None
+
+    reset_at = datetime(reset_date.year, reset_date.month, reset_date.day, 0, 0, 0)
+    return reset_at, next_due
+
+
+async def _reactivate_recurring_todos(db: AsyncSession) -> None:
+    """Auto-reactivate recurring todos whose reset_at has passed."""
+    now = datetime.now()
+    query = select(Todo).where(
+        and_(
+            Todo.completed == True,
+            Todo.recurrence_rule.isnot(None),
+            Todo.reset_at.isnot(None),
+            Todo.reset_at <= now,
+        )
+    )
+    result = await db.execute(query)
+    todos = result.scalars().all()
+
+    for todo in todos:
+        todo.completed = False
+        todo.completed_at = None
+        if todo.next_due_date:
+            todo.due_date = todo.next_due_date
+        todo.reset_at = None
+        todo.next_due_date = None
+
+    if todos:
+        await db.commit()
+
+
 @router.get("/", response_model=List[TodoResponse])
 async def get_todos(
     completed: Optional[bool] = Query(None),
@@ -23,6 +108,9 @@ async def get_todos(
     current_user: Settings = Depends(get_current_session)
 ):
     """Get all todos with optional filters."""
+    # Reactivate any recurring todos whose reset time has passed
+    await _reactivate_recurring_todos(db)
+
     query = select(Todo)
 
     if completed is not None:
@@ -98,6 +186,8 @@ async def update_todo(
             update_data["completed_at"] = datetime.now()
         elif not update_data["completed"]:
             update_data["completed_at"] = None
+            update_data["reset_at"] = None
+            update_data["next_due_date"] = None
 
     for key, value in update_data.items():
         setattr(todo, key, value)
@@ -133,7 +223,7 @@ async def toggle_todo(
     db: AsyncSession = Depends(get_db),
     current_user: Settings = Depends(get_current_session)
 ):
-    """Toggle todo completion status."""
+    """Toggle todo completion status. For recurring todos, calculates reset schedule."""
     result = await db.execute(select(Todo).where(Todo.id == todo_id))
     todo = result.scalar_one_or_none()
 
@@ -141,7 +231,24 @@ async def toggle_todo(
         raise HTTPException(status_code=404, detail="Todo not found")
 
     todo.completed = not todo.completed
-    todo.completed_at = datetime.now() if todo.completed else None
+
+    if todo.completed:
+        todo.completed_at = datetime.now()
+
+        # If recurring, schedule the reset
+        if todo.recurrence_rule:
+            reset_at, next_due = _calculate_recurrence(
+                todo.recurrence_rule,
+                todo.due_date,
+                current_user.first_day_of_week,
+            )
+            todo.reset_at = reset_at
+            todo.next_due_date = next_due
+    else:
+        # Manual uncomplete — clear recurrence scheduling
+        todo.completed_at = None
+        todo.reset_at = None
+        todo.next_due_date = None
 
     await db.commit()
     await db.refresh(todo)

backend/app/schemas/todo.py

@@ -36,6 +36,8 @@ class TodoResponse(BaseModel):
     completed_at: Optional[datetime]
     category: Optional[str]
     recurrence_rule: Optional[str]
+    reset_at: Optional[datetime]
+    next_due_date: Optional[date]
     project_id: Optional[int]
     created_at: datetime
     updated_at: datetime

frontend/src/components/todos/TodoItem.tsx

@@ -1,6 +1,6 @@
 import { useMutation, useQueryClient } from '@tanstack/react-query';
 import { toast } from 'sonner';
-import { Trash2, Pencil, Calendar, AlertCircle } from 'lucide-react';
+import { Trash2, Pencil, Calendar, AlertCircle, RefreshCw } from 'lucide-react';
 import { format, isToday, isPast, parseISO, startOfDay } from 'date-fns';
 import api from '@/lib/api';
 import type { Todo } from '@/types';
@@ -20,6 +20,12 @@ const priorityStyles: Record<string, string> = {
   high: 'bg-red-500/20 text-red-400',
 };
 
+const recurrenceLabels: Record<string, string> = {
+  daily: 'Daily',
+  weekly: 'Weekly',
+  monthly: 'Monthly',
+};
+
 export default function TodoItem({ todo, onEdit }: TodoItemProps) {
   const queryClient = useQueryClient();
 
@@ -58,6 +64,10 @@ export default function TodoItem({ todo, onEdit }: TodoItemProps) {
   const isDueToday = dueDate ? isToday(dueDate) : false;
   const isOverdue = dueDate && !todo.completed ? isPast(startOfDay(dueDate)) && !isDueToday : false;
 
+  const resetDate = todo.reset_at ? parseISO(todo.reset_at) : null;
+  const nextDueDate = todo.next_due_date ? parseISO(todo.next_due_date) : null;
+  const showResetInfo = todo.completed && todo.recurrence_rule && resetDate;
+
   return (
     <div
       className={cn(
@@ -95,16 +105,22 @@ export default function TodoItem({ todo, onEdit }: TodoItemProps) {
               {todo.category}
             </span>
           )}
+          {todo.recurrence_rule && (
+            <span className="text-[9px] px-1.5 py-0.5 rounded font-medium uppercase tracking-wide bg-purple-500/15 text-purple-400 shrink-0">
+              {recurrenceLabels[todo.recurrence_rule] || todo.recurrence_rule}
+            </span>
+          )}
         </div>
 
         {todo.description && (
           <p className="text-sm text-muted-foreground mt-1 line-clamp-1">{todo.description}</p>
         )}
 
+        <div className="flex items-center gap-3 mt-1.5">
           {dueDate && (
             <div
               className={cn(
-              'flex items-center gap-1 mt-1.5 text-xs',
+                'flex items-center gap-1 text-xs',
                 isOverdue
                   ? 'text-red-400'
                   : isDueToday
@@ -121,6 +137,17 @@ export default function TodoItem({ todo, onEdit }: TodoItemProps) {
               {format(dueDate, 'MMM d, yyyy')}
             </div>
           )}
+
+          {showResetInfo && (
+            <div className="flex items-center gap-1 text-xs text-purple-400">
+              <RefreshCw className="h-3 w-3" />
+              <span>
+                Resets {format(resetDate, 'EEE dd/MM/yy')}
+                {nextDueDate && <> · Next due {format(nextDueDate, 'dd/MM/yy')}</>}
+              </span>
+            </div>
+          )}
+        </div>
       </div>
 
       <div className="flex items-center gap-1 shrink-0">

frontend/src/types/index.ts

@@ -29,6 +29,8 @@ export interface Todo {
   due_date?: string;
   category?: string;
   recurrence_rule?: string;
+  reset_at?: string;
+  next_due_date?: string;
   project_id?: number;
   created_at: string;
   updated_at: string;