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"""Recurrence service for calculating recurring task dates.
[Task]: T015-T020
[From]: specs/008-advanced-features/tasks.md (Phase 2)
This service handles:
- Calculating next occurrence dates from recurrence rules
- Validating recurrence rule structures
- Checking recurrence limits (100 instance max)
- Supporting daily, weekly, monthly, and cron-based patterns
"""
import uuid
from datetime import datetime, timedelta
from typing import Optional
from sqlalchemy import select, func
from sqlmodel import Session
from models.task import Task
from models.recurrence import RecurrenceRule
class RecurrenceService:
"""Service for calculating recurring task dates."""
MAX_RECURRING_INSTANCES = 100
def __init__(self, session: Session):
"""Initialize the recurrence service.
Args:
session: Database session for queries
"""
self.session = session
def calculate_next_occurrence(
self,
base_date: datetime,
recurrence_rule: dict
) -> Optional[datetime]:
"""Calculate next due date based on recurrence pattern.
[Task]: T016-T018, T077 (cron)
Args:
base_date: The base date to calculate from
recurrence_rule: Dictionary containing recurrence rule
Returns:
Next due date in UTC, or None if limit reached
Raises:
ValueError: If recurrence rule is invalid
"""
if not self.validate_recurrence_rule(recurrence_rule):
raise ValueError("Invalid recurrence rule")
frequency = recurrence_rule.get("frequency")
interval = recurrence_rule.get("interval", 1)
# For cron-based recurrence (T077)
if frequency == "cron" and "cron_expression" in recurrence_rule:
return self._calculate_from_cron(base_date, recurrence_rule["cron_expression"])
# Calculate based on frequency
if frequency == "daily":
return base_date + timedelta(days=interval)
elif frequency == "weekly":
return base_date + timedelta(weeks=interval)
elif frequency == "monthly":
return self._add_months(base_date, interval)
else:
raise ValueError(f"Unsupported frequency: {frequency}")
def _add_months(self, date: datetime, months: int) -> datetime:
"""Add months to a date, handling edge cases.
Args:
date: Base date
months: Number of months to add
Returns:
New date with months added
"""
# Simple implementation: add days (approximate)
# For precise month handling, would use dateutil.relativedelta
return date + timedelta(days=months * 30)
def _calculate_from_cron(self, base_date: datetime, cron_expression: str) -> Optional[datetime]:
"""Calculate next occurrence from cron expression.
[Task]: T077
Args:
base_date: Base date to calculate from
cron_expression: Cron expression (5 fields)
Returns:
Next due date, or None if invalid
Note:
This is a simplified implementation. A full cron parser
would be more complex. For MVP, we support basic patterns.
"""
# TODO: Implement full cron parsing
# For now, return None to indicate not implemented
return None
def validate_recurrence_rule(self, rule: dict) -> bool:
"""Validate recurrence rule structure.
[Task]: T019
Args:
rule: Dictionary to validate
Returns:
True if valid, False otherwise
"""
if not isinstance(rule, dict):
return False
# Check frequency
frequency = rule.get("frequency")
if frequency not in ("daily", "weekly", "monthly"):
return False
# Validate interval
interval = rule.get("interval", 1)
if not isinstance(interval, int) or interval < 1 or interval > 365:
return False
# Validate count
count = rule.get("count")
if count is not None:
if not isinstance(count, int) or count < 1 or count > self.MAX_RECURRING_INSTANCES:
return False
# Validate end_date
end_date = rule.get("end_date")
if end_date is not None:
if not isinstance(end_date, (datetime, str)):
return False
return True
def check_recurrence_limit(self, parent_task_id: uuid.UUID) -> bool:
"""Check if recurrence limit has been reached.
[Task]: T020
Args:
parent_task_id: ID of the parent recurring task
Returns:
True if limit reached, False otherwise
Raises:
ValueError: If limit exceeded
"""
# Count existing instances with this parent
count_result = self.session.exec(
select(func.count(Task.id))
.where(Task.parent_task_id == parent_task_id)
)
instance_count = count_result.one() or 0
if instance_count >= self.MAX_RECURRING_INSTANCES:
raise ValueError(
f"Recurrence limit reached: maximum {self.MAX_RECURRING_INSTANCES} instances"
)
return False
def should_create_next_instance(
self,
task: Task,
next_due_date: datetime
) -> bool:
"""Determine if next instance should be created.
Checks count and end_date limits from recurrence rule.
Args:
task: Current task being completed
next_due_date: Calculated next due date
Returns:
True if should create, False if limit reached
"""
if not task.recurrence:
return False
# Get parent task ID (for instances) or use current task ID (for original)
parent_id = task.parent_task_id or task.id
# Check instance count limit
count_result = self.session.exec(
select(func.count(Task.id))
.where(Task.parent_task_id == parent_id)
)
instance_count = count_result.one() or 0
# Check count limit
count_limit = task.recurrence.get("count")
if count_limit and instance_count >= count_limit:
return False
# Check end_date limit
end_date_str = task.recurrence.get("end_date")
if end_date_str:
if isinstance(end_date_str, str):
end_date = datetime.fromisoformat(end_date_str)
else:
end_date = end_date_str
if next_due_date > end_date:
return False
return True
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