from datetime import datetime, timezone
from typing import Any

from sqlalchemy import CheckConstraint, ForeignKey, Index, JSON, String, Text
from sqlalchemy.ext.mutable import MutableList
from sqlalchemy.orm import Mapped, mapped_column, relationship

from app.extensions import db


TASK_STATUSES = ("not_started", "in_progress", "done")
TASK_PRIORITIES = ("urgent", "important", "normal")


class Task(db.Model):
    __table_args__ = (
        CheckConstraint(
            "status IN ('not_started', 'in_progress', 'done')",
            name="ck_task_status",
        ),
        CheckConstraint(
            "priority IN ('urgent', 'important', 'normal')",
            name="ck_task_priority",
        ),
        Index(
            "ix_task_owner_visibility_status_due",
            "user_id",
            "cleared_at",
            "status",
            "due_date",
        ),
    )

    id: Mapped[int] = mapped_column(primary_key=True)
    title: Mapped[str] = mapped_column(String(200))
    description: Mapped[str | None] = mapped_column(Text)
    status: Mapped[str] = mapped_column(String(20), default="not_started")
    priority: Mapped[str] = mapped_column(String(20), default="normal")
    created_at: Mapped[datetime] = mapped_column(
        default=lambda: datetime.now(timezone.utc)
    )
    due_date: Mapped[datetime | None]
    completed_at: Mapped[datetime | None]
    cleared_at: Mapped[datetime | None]
    clear_batch_id: Mapped[str | None] = mapped_column(String(36), index=True)
    user_id: Mapped[int] = mapped_column(
        ForeignKey("user.id", ondelete="CASCADE"), index=True
    )

    # Stored now so Phase 3 can add timers and chunking without reshaping CRUD.
    timer_seconds: Mapped[int] = mapped_column(default=0)
    context: Mapped[str | None] = mapped_column(String(100))
    chunk_sessions: Mapped[list[Any]] = mapped_column(
        MutableList.as_mutable(JSON), default=list
    )

    subtasks: Mapped[list["Subtask"]] = relationship(
        back_populates="task",
        cascade="all, delete-orphan",
        order_by="Subtask.id",
    )

    @property
    def progress_percentage(self) -> int:
        if not self.subtasks:
            return 100 if self.status == "done" else 0
        completed = sum(subtask.completed for subtask in self.subtasks)
        return round(completed / len(self.subtasks) * 100)


class Subtask(db.Model):
    id: Mapped[int] = mapped_column(primary_key=True)
    title: Mapped[str] = mapped_column(String(100))
    completed: Mapped[bool] = mapped_column(default=False)
    task_id: Mapped[int] = mapped_column(
        ForeignKey("task.id", ondelete="CASCADE"), index=True
    )

    task: Mapped[Task] = relationship(back_populates="subtasks")