from sqlalchemy import Column, Integer, String, Boolean, DateTime, Enum, ForeignKey
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


class Priority(str, enum.Enum):
    LOW = "low"
    MEDIUM = "medium"
    HIGH = "high"


class Todo(Base):
    __tablename__ = "todos"

    id = Column(Integer, primary_key=True, index=True)
    title = Column(String(200), nullable=False)
    description = Column(String(500), nullable=True)
    completed = Column(Boolean, default=False)
    priority = Column(Enum(Priority), default=Priority.MEDIUM)
    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())

    # Relationship to project
    project = relationship("Project", back_populates="todos")

    # Relationship to category
    category = relationship("Category", back_populates="todos")

    # Self-referential relationship for subtasks
    parent = relationship("Todo", remote_side=[id], back_populates="children")
    children = relationship(
        "Todo", back_populates="parent", cascade="all, delete-orphan"
    )

    @property
    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