from datetime import datetime

from sqlalchemy import select, func
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy.orm import selectinload

from app.db.models import Assignment, AssignmentSubmission, User
from app.schemas.assignment import AssignmentCreate, AssignmentUpdate, SubmissionCreate, SubmissionGrade
from app.services.notification_service import create_notifications_for_class


async def create_assignment(
    db: AsyncSession, class_id: int, creator_id: int, data: AssignmentCreate
) -> Assignment:
    assignment = Assignment(
        class_id=class_id,
        creator_id=creator_id,
        title=data.title,
        description=data.description,
        deadline=data.deadline,
    )
    db.add(assignment)
    await db.commit()
    await db.refresh(assignment)

    await create_notifications_for_class(
        db, class_id, "assignment", f"新作业: {data.title}",
        content=data.description,
        related_id=assignment.id,
        email_subject=f"HKU ICB - 新作业: {data.title}",
        email_body=f"<p>{data.description or data.title}</p>",
        email_action_path="/assignments",
    )

    return assignment


async def update_assignment(
    db: AsyncSession, assignment: Assignment, data: AssignmentUpdate
) -> Assignment:
    for field, value in data.model_dump(exclude_unset=True).items():
        setattr(assignment, field, value)
    await db.commit()
    await db.refresh(assignment)
    return assignment


async def delete_assignment(db: AsyncSession, assignment: Assignment):
    await db.delete(assignment)
    await db.commit()


async def get_assignment_by_id(db: AsyncSession, assignment_id: int) -> Assignment | None:
    result = await db.execute(
        select(Assignment)
        .options(
            selectinload(Assignment.creator),
            selectinload(Assignment.submissions).selectinload(AssignmentSubmission.student),
        )
        .where(Assignment.id == assignment_id)
    )
    return result.scalar_one_or_none()


async def list_assignments(
    db: AsyncSession, class_id: int, page: int = 1, page_size: int = 20
) -> tuple[list[Assignment], int]:
    total_result = await db.execute(
        select(func.count(Assignment.id)).where(Assignment.class_id == class_id)
    )
    total = total_result.scalar() or 0

    result = await db.execute(
        select(Assignment)
        .options(
            selectinload(Assignment.creator),
            selectinload(Assignment.submissions),
        )
        .where(Assignment.class_id == class_id)
        .order_by(Assignment.created_at.desc())
        .offset((page - 1) * page_size)
        .limit(page_size)
    )
    return list(result.scalars().all()), total


async def add_attachments(db: AsyncSession, assignment: Assignment, urls: list[str]):
    existing = assignment.get_attachment_urls_list()
    existing.extend(urls)
    assignment.set_attachment_urls_list(existing)
    await db.commit()
    await db.refresh(assignment)


async def create_submission(
    db: AsyncSession,
    assignment_id: int,
    student_id: int,
    notes: str | None,
    file_url: str | None = None,
    file_name: str | None = None,
    file_type: str | None = None,
    file_size: int | None = None,
) -> AssignmentSubmission:
    # Check assignment exists and is open
    a_result = await db.execute(select(Assignment).where(Assignment.id == assignment_id))
    assignment = a_result.scalar_one_or_none()
    if assignment is None:
        raise ValueError("作业不存在")
    if assignment.status != "open":
        raise ValueError("作业已关闭提交")
    if assignment.deadline and datetime.now() > assignment.deadline:
        raise ValueError("作业已过截止日期")

    # Check no existing submission
    existing = await db.execute(
        select(AssignmentSubmission).where(
            AssignmentSubmission.assignment_id == assignment_id,
            AssignmentSubmission.student_id == student_id,
        )
    )
    if existing.scalar_one_or_none():
        raise ValueError("你已经提交过作业了")

    submission = AssignmentSubmission(
        assignment_id=assignment_id,
        student_id=student_id,
        notes=notes,
        file_url=file_url,
        file_name=file_name,
        file_type=file_type,
        file_size=file_size,
    )
    db.add(submission)
    await db.commit()
    await db.refresh(submission)

    # Reload with student relationship
    result = await db.execute(
        select(AssignmentSubmission)
        .options(selectinload(AssignmentSubmission.student))
        .where(AssignmentSubmission.id == submission.id)
    )
    return result.scalar_one()


async def get_submission_by_student(
    db: AsyncSession, assignment_id: int, student_id: int
) -> AssignmentSubmission | None:
    result = await db.execute(
        select(AssignmentSubmission)
        .options(selectinload(AssignmentSubmission.student))
        .where(
            AssignmentSubmission.assignment_id == assignment_id,
            AssignmentSubmission.student_id == student_id,
        )
    )
    return result.scalar_one_or_none()


async def grade_submission(
    db: AsyncSession, submission: AssignmentSubmission, data: SubmissionGrade
) -> AssignmentSubmission:
    submission.grade = data.grade
    submission.feedback = data.feedback
    submission.graded_at = datetime.now()
    await db.commit()
    await db.refresh(submission)
    return submission


async def list_submissions(db: AsyncSession, assignment_id: int) -> list[AssignmentSubmission]:
    result = await db.execute(
        select(AssignmentSubmission)
        .options(selectinload(AssignmentSubmission.student))
        .where(AssignmentSubmission.assignment_id == assignment_id)
        .order_by(AssignmentSubmission.created_at.desc())
    )
    return list(result.scalars().all())