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

from app.database import get_db
from app.deps import get_current_admin
from app.models.group import Group, GroupMembership
from app.models.user import User
from app.schemas.group import GroupCreate, GroupDetailOut, GroupMemberAdminUpdate, GroupMemberOut, GroupOut, GroupUpdate

router = APIRouter()


def _to_group_out(group: Group) -> GroupOut:
    return GroupOut(
        id=group.id,
        name=group.name,
        description=group.description,
        created_at=group.created_at,
        member_count=len(group.memberships),
    )


def _to_group_detail(group: Group) -> GroupDetailOut:
    members = []
    for m in group.memberships:
        # memberships are loaded with joined user via selectinload
        user = m.__dict__.get("_user") or getattr(m, "user", None)
        if user is None:
            continue
        members.append(GroupMemberOut(
            id=user.id,
            email=user.email,
            full_name=user.full_name,
            is_active=user.is_active,
            joined_at=m.joined_at,
        ))
    return GroupDetailOut(
        id=group.id,
        name=group.name,
        description=group.description,
        created_at=group.created_at,
        member_count=len(members),
        members=members,
    )


@router.get("", response_model=list[GroupOut])
async def list_groups(
    _admin: User = Depends(get_current_admin),
    db: AsyncSession = Depends(get_db),
) -> list[GroupOut]:
    result = await db.execute(
        select(Group).options(selectinload(Group.memberships)).order_by(Group.name)
    )
    groups = list(result.scalars().all())
    return [_to_group_out(g) for g in groups]


@router.post("", response_model=GroupOut, status_code=status.HTTP_201_CREATED)
async def create_group(
    body: GroupCreate,
    _admin: User = Depends(get_current_admin),
    db: AsyncSession = Depends(get_db),
) -> GroupOut:
    existing = await db.execute(select(Group).where(Group.name == body.name))
    if existing.scalar_one_or_none():
        raise HTTPException(status_code=400, detail="A group with that name already exists")

    group = Group(name=body.name, description=body.description)
    db.add(group)
    await db.commit()
    await db.refresh(group)
    # refresh doesn't load relationships — load fresh with memberships
    result = await db.execute(
        select(Group).options(selectinload(Group.memberships)).where(Group.id == group.id)
    )
    group = result.scalar_one()
    return _to_group_out(group)


@router.get("/{group_id}", response_model=GroupDetailOut)
async def get_group(
    group_id: str,
    _admin: User = Depends(get_current_admin),
    db: AsyncSession = Depends(get_db),
) -> GroupDetailOut:
    result = await db.execute(
        select(Group)
        .options(
            selectinload(Group.memberships).joinedload(GroupMembership.group),
        )
        .where(Group.id == group_id)
    )
    group = result.scalar_one_or_none()
    if not group:
        raise HTTPException(status_code=404, detail="Group not found")

    # Load members separately for simplicity
    mem_result = await db.execute(
        select(GroupMembership, User)
        .join(User, User.id == GroupMembership.user_id)
        .where(GroupMembership.group_id == group_id)
        .order_by(User.email)
    )
    rows = mem_result.all()
    members = [
        GroupMemberOut(
            id=user.id,
            email=user.email,
            full_name=user.full_name,
            is_active=user.is_active,
            is_group_admin=membership.is_group_admin,
            joined_at=membership.joined_at,
        )
        for membership, user in rows
    ]
    return GroupDetailOut(
        id=group.id,
        name=group.name,
        description=group.description,
        created_at=group.created_at,
        member_count=len(members),
        members=members,
    )


@router.patch("/{group_id}", response_model=GroupOut)
async def update_group(
    group_id: str,
    body: GroupUpdate,
    _admin: User = Depends(get_current_admin),
    db: AsyncSession = Depends(get_db),
) -> GroupOut:
    result = await db.execute(
        select(Group).options(selectinload(Group.memberships)).where(Group.id == group_id)
    )
    group = result.scalar_one_or_none()
    if not group:
        raise HTTPException(status_code=404, detail="Group not found")

    if body.name is not None and body.name != group.name:
        dupe = await db.execute(select(Group).where(Group.name == body.name))
        if dupe.scalar_one_or_none():
            raise HTTPException(status_code=400, detail="A group with that name already exists")
        group.name = body.name
    if body.description is not None:
        group.description = body.description

    await db.commit()
    await db.refresh(group)
    result2 = await db.execute(
        select(Group).options(selectinload(Group.memberships)).where(Group.id == group.id)
    )
    group = result2.scalar_one()
    return _to_group_out(group)


@router.delete("/{group_id}", status_code=status.HTTP_204_NO_CONTENT)
async def delete_group(
    group_id: str,
    _admin: User = Depends(get_current_admin),
    db: AsyncSession = Depends(get_db),
) -> None:
    result = await db.execute(select(Group).where(Group.id == group_id))
    group = result.scalar_one_or_none()
    if not group:
        raise HTTPException(status_code=404, detail="Group not found")
    await db.delete(group)
    await db.commit()


@router.post("/{group_id}/members/{user_id}", status_code=status.HTTP_204_NO_CONTENT)
async def add_member(
    group_id: str,
    user_id: str,
    _admin: User = Depends(get_current_admin),
    db: AsyncSession = Depends(get_db),
) -> None:
    group_result = await db.execute(select(Group).where(Group.id == group_id))
    if not group_result.scalar_one_or_none():
        raise HTTPException(status_code=404, detail="Group not found")

    user_result = await db.execute(select(User).where(User.id == user_id))
    if not user_result.scalar_one_or_none():
        raise HTTPException(status_code=404, detail="User not found")

    existing = await db.execute(
        select(GroupMembership).where(
            GroupMembership.group_id == group_id, GroupMembership.user_id == user_id
        )
    )
    if existing.scalar_one_or_none():
        raise HTTPException(status_code=400, detail="User is already a member of this group")

    db.add(GroupMembership(group_id=group_id, user_id=user_id))
    await db.commit()


@router.patch("/{group_id}/members/{user_id}/admin", status_code=status.HTTP_204_NO_CONTENT)
async def set_member_admin(
    group_id: str,
    user_id: str,
    body: GroupMemberAdminUpdate,
    _admin: User = Depends(get_current_admin),
    db: AsyncSession = Depends(get_db),
) -> None:
    result = await db.execute(
        select(GroupMembership).where(
            GroupMembership.group_id == group_id, GroupMembership.user_id == user_id
        )
    )
    membership = result.scalar_one_or_none()
    if not membership:
        raise HTTPException(status_code=404, detail="User is not a member of this group")
    membership.is_group_admin = body.is_group_admin
    await db.commit()


@router.delete("/{group_id}/members/{user_id}", status_code=status.HTTP_204_NO_CONTENT)
async def remove_member(
    group_id: str,
    user_id: str,
    _admin: User = Depends(get_current_admin),
    db: AsyncSession = Depends(get_db),
) -> None:
    result = await db.execute(
        select(GroupMembership).where(
            GroupMembership.group_id == group_id, GroupMembership.user_id == user_id
        )
    )
    membership = result.scalar_one_or_none()
    if not membership:
        raise HTTPException(status_code=404, detail="User is not a member of this group")
    await db.delete(membership)
    await db.commit()