from fastapi import APIRouter, Depends, HTTPException, status
from sqlalchemy.ext.asyncio import AsyncSession
from sqlalchemy import select
from sqlalchemy.orm import selectinload

from app.dependencies import get_db, get_current_user
from app.models.subject import Subject, SubjectOption
from app.models.user import User
from app.schemas.subject import (
    SubjectCreate, SubjectOut, SubjectUpdate,
    SubjectOptionCreate, SubjectOptionUpdate, SubjectOptionOut,
)

router = APIRouter(prefix="/api/subjects", tags=["subjects"])


def _opts():
    return selectinload(Subject.options)


@router.get("", response_model=list[SubjectOut])
async def list_subjects(
    current_user: User = Depends(get_current_user),
    db: AsyncSession = Depends(get_db),
):
    result = await db.execute(
        select(Subject)
        .where(Subject.user_id == current_user.id)
        .options(_opts())
        .order_by(Subject.name)
    )
    return result.scalars().all()


@router.post("", response_model=SubjectOut, status_code=status.HTTP_201_CREATED)
async def create_subject(
    body: SubjectCreate,
    current_user: User = Depends(get_current_user),
    db: AsyncSession = Depends(get_db),
):
    subject = Subject(**body.model_dump(), user_id=current_user.id)
    db.add(subject)
    await db.commit()
    result = await db.execute(
        select(Subject).where(Subject.id == subject.id).options(_opts())
    )
    return result.scalar_one()


@router.get("/{subject_id}", response_model=SubjectOut)
async def get_subject(
    subject_id: int,
    current_user: User = Depends(get_current_user),
    db: AsyncSession = Depends(get_db),
):
    result = await db.execute(
        select(Subject)
        .where(Subject.id == subject_id, Subject.user_id == current_user.id)
        .options(_opts())
    )
    subject = result.scalar_one_or_none()
    if not subject:
        raise HTTPException(status_code=404, detail="Subject not found")
    return subject


@router.patch("/{subject_id}", response_model=SubjectOut)
async def update_subject(
    subject_id: int,
    body: SubjectUpdate,
    current_user: User = Depends(get_current_user),
    db: AsyncSession = Depends(get_db),
):
    result = await db.execute(
        select(Subject)
        .where(Subject.id == subject_id, Subject.user_id == current_user.id)
        .options(_opts())
    )
    subject = result.scalar_one_or_none()
    if not subject:
        raise HTTPException(status_code=404, detail="Subject not found")

    for field, value in body.model_dump(exclude_none=True).items():
        setattr(subject, field, value)
    await db.commit()
    result = await db.execute(
        select(Subject).where(Subject.id == subject.id).options(_opts())
    )
    return result.scalar_one()


@router.delete("/{subject_id}", status_code=status.HTTP_204_NO_CONTENT)
async def delete_subject(
    subject_id: int,
    current_user: User = Depends(get_current_user),
    db: AsyncSession = Depends(get_db),
):
    result = await db.execute(
        select(Subject).where(Subject.id == subject_id, Subject.user_id == current_user.id)
    )
    subject = result.scalar_one_or_none()
    if not subject:
        raise HTTPException(status_code=404, detail="Subject not found")
    if subject.is_system:
        raise HTTPException(status_code=403, detail="System subjects cannot be deleted")
    await db.delete(subject)
    await db.commit()


# --- Subject Option sub-routes ---

@router.post("/{subject_id}/options", response_model=SubjectOptionOut, status_code=status.HTTP_201_CREATED)
async def add_option(
    subject_id: int,
    body: SubjectOptionCreate,
    current_user: User = Depends(get_current_user),
    db: AsyncSession = Depends(get_db),
):
    result = await db.execute(
        select(Subject).where(Subject.id == subject_id, Subject.user_id == current_user.id)
    )
    if not result.scalar_one_or_none():
        raise HTTPException(status_code=404, detail="Subject not found")

    option = SubjectOption(subject_id=subject_id, **body.model_dump())
    db.add(option)
    await db.commit()
    await db.refresh(option)
    return option


@router.patch("/{subject_id}/options/{option_id}", response_model=SubjectOptionOut)
async def update_option(
    subject_id: int,
    option_id: int,
    body: SubjectOptionUpdate,
    current_user: User = Depends(get_current_user),
    db: AsyncSession = Depends(get_db),
):
    result = await db.execute(
        select(SubjectOption)
        .join(Subject)
        .where(
            SubjectOption.id == option_id,
            SubjectOption.subject_id == subject_id,
            Subject.user_id == current_user.id,
        )
    )
    option = result.scalar_one_or_none()
    if not option:
        raise HTTPException(status_code=404, detail="Option not found")

    for field, value in body.model_dump(exclude_unset=True).items():
        setattr(option, field, value)
    await db.commit()
    await db.refresh(option)
    return option


@router.delete("/{subject_id}/options/{option_id}", status_code=status.HTTP_204_NO_CONTENT)
async def delete_option(
    subject_id: int,
    option_id: int,
    current_user: User = Depends(get_current_user),
    db: AsyncSession = Depends(get_db),
):
    result = await db.execute(
        select(SubjectOption)
        .join(Subject)
        .where(
            SubjectOption.id == option_id,
            SubjectOption.subject_id == subject_id,
            Subject.user_id == current_user.id,
        )
    )
    option = result.scalar_one_or_none()
    if not option:
        raise HTTPException(status_code=404, detail="Option not found")
    await db.delete(option)
    await db.commit()