import uuid
from datetime import datetime, timezone
from typing import Sequence

from sqlalchemy import select, update as sa_update
from sqlalchemy.ext.asyncio import AsyncSession

from app.models.task import Task
from app.schemas.task import TaskCreate, TaskUpdate


async def create(
    db: AsyncSession,
    study_id: uuid.UUID,
    task_in: TaskCreate,
    *,
    created_by: uuid.UUID,
) -> Task:
    task = Task(
        study_id=study_id,
        milestone_id=task_in.milestone_id,
        title=task_in.title,
        description=task_in.description,
        assignee_id=task_in.assignee_id,
        priority=task_in.priority,
        due_date=task_in.due_date,
        status="TODO",
        created_by=created_by,
    )
    db.add(task)
    await db.commit()
    await db.refresh(task)
    return task


async def get(db: AsyncSession, task_id: uuid.UUID) -> Task | None:
    result = await db.execute(select(Task).where(Task.id == task_id))
    return result.scalar_one_or_none()


async def list_tasks(
    db: AsyncSession,
    study_id: uuid.UUID,
    milestone_id: uuid.UUID | None = None,
    assignee_id: uuid.UUID | None = None,
    status: str | None = None,
) -> Sequence[Task]:
    stmt = select(Task).where(Task.study_id == study_id)
    if milestone_id:
        stmt = stmt.where(Task.milestone_id == milestone_id)
    if assignee_id:
        stmt = stmt.where(Task.assignee_id == assignee_id)
    if status:
        stmt = stmt.where(Task.status == status)
    stmt = stmt.order_by(Task.due_date)
    result = await db.execute(stmt)
    return result.scalars().all()


async def update(db: AsyncSession, task: Task, task_in: TaskUpdate) -> Task:
    update_data = task_in.model_dump(exclude_unset=True)
    if "status" in update_data:
        status_change = update_data["status"]
        if status_change == "DONE":
            update_data["completed_at"] = datetime.now(timezone.utc)
        else:
            update_data["completed_at"] = None

    if update_data:
        await db.execute(
            sa_update(Task)
            .where(Task.id == task.id)
            .values(**update_data)
        )
        await db.commit()
    await db.refresh(task)
    return task