import uuid
from typing import Sequence

from sqlalchemy import delete, func, select, update
from sqlalchemy.ext.asyncio import AsyncSession

from app.core.config import (
    PROTECTED_ADMIN_CLINICAL_DEPARTMENT,
    PROTECTED_ADMIN_DEFAULT_PASSWORD,
    PROTECTED_ADMIN_EMAIL,
    PROTECTED_ADMIN_FULL_NAME,
)
from app.core.security import hash_password
from app.models.study_member import StudyMember
from app.models.user import User, UserRole, UserStatus
from app.schemas.user import UserCreate, UserRegisterRequest, UserUpdate


async def get_by_email(db: AsyncSession, email: str) -> User | None:
    result = await db.execute(select(User).where(User.email == email))
    return result.scalar_one_or_none()


def is_protected_admin_email(email: str | None) -> bool:
    return (email or "").strip().lower() == PROTECTED_ADMIN_EMAIL


def is_protected_admin_user(user: User | None) -> bool:
    return user is not None and is_protected_admin_email(user.email)


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


async def create_user(
    db: AsyncSession, user_in: UserCreate, *, status: UserStatus | None = UserStatus.ACTIVE
) -> User:
    status_value = status or UserStatus(user_in.status)
    user = User(
        email=user_in.email,
        password_hash=hash_password(user_in.password),
        full_name=user_in.full_name,
        role=UserRole(user_in.role),
        clinical_department=user_in.clinical_department,
        status=status_value,
    )
    db.add(user)
    await db.commit()
    await db.refresh(user)
    return user


async def create_pending_user(db: AsyncSession, user_in: UserRegisterRequest) -> User:
    return await create_user(db, UserCreate(**user_in.model_dump()), status=UserStatus.PENDING)


async def update_user(db: AsyncSession, user: User, user_in: UserUpdate) -> User:
    update_data = {}
    if user_in.role is not None:
        update_data["role"] = UserRole(user_in.role)
    if user_in.status is not None:
        update_data["status"] = UserStatus(user_in.status)
    if user_in.is_active is not None:
        update_data["status"] = UserStatus.ACTIVE if user_in.is_active else UserStatus.DISABLED
    if user_in.avatar_url is not None:
        update_data["avatar_url"] = user_in.avatar_url
    if user_in.password:
        update_data["password_hash"] = hash_password(user_in.password)
    if user_in.full_name is not None:
        update_data["full_name"] = user_in.full_name
    if user_in.clinical_department is not None:
        update_data["clinical_department"] = user_in.clinical_department

    if update_data:
        await db.execute(update(User).where(User.id == user.id).values(**update_data))
        await db.commit()
    await db.refresh(user)
    return user


async def list_users(db: AsyncSession, skip: int = 0, limit: int = 100) -> Sequence[User]:
    result = await db.execute(select(User).offset(skip).limit(limit))
    return result.scalars().all()


async def list_active_member_candidates_for_study(
    db: AsyncSession,
    study_id: uuid.UUID,
    skip: int = 0,
    limit: int = 100,
) -> Sequence[User]:
    existing_member = (
        select(StudyMember.id)
        .where(StudyMember.study_id == study_id, StudyMember.user_id == User.id)
        .exists()
    )
    stmt = (
        select(User)
        .where(User.status == UserStatus.ACTIVE)
        .where(~existing_member)
        .order_by(User.full_name.asc(), User.email.asc())
        .offset(skip)
        .limit(limit)
    )
    result = await db.execute(stmt)
    return result.scalars().all()


async def count_active_admins(db: AsyncSession) -> int:
    result = await db.execute(
        select(func.count())
        .select_from(User)
        .where(User.role == UserRole.ADMIN, User.status == UserStatus.ACTIVE)
    )
    return int(result.scalar_one() or 0)


async def list_users_by_status(
    db: AsyncSession, status: UserStatus | None = None, skip: int = 0, limit: int = 100
) -> Sequence[User]:
    stmt = select(User).offset(skip).limit(limit)
    if status:
        stmt = stmt.where(User.status == status)
    result = await db.execute(stmt.order_by(User.created_at.desc()))
    return result.scalars().all()


async def ensure_admin_exists(db: AsyncSession, *, default_password: str = PROTECTED_ADMIN_DEFAULT_PASSWORD) -> None:
    result = await db.execute(select(User).where(User.email == PROTECTED_ADMIN_EMAIL))
    admin = result.scalar_one_or_none()
    if admin:
        return
    new_admin = User(
        email=PROTECTED_ADMIN_EMAIL,
        password_hash=hash_password(default_password),
        full_name=PROTECTED_ADMIN_FULL_NAME,
        role=UserRole.ADMIN,
        clinical_department=PROTECTED_ADMIN_CLINICAL_DEPARTMENT,
        status=UserStatus.ACTIVE,
    )
    db.add(new_admin)
    await db.commit()


async def get_users_by_ids(db: AsyncSession, ids: set[uuid.UUID]) -> dict[uuid.UUID, User]:
    if not ids:
        return {}
    result = await db.execute(select(User).where(User.id.in_(ids)))
    users = result.scalars().all()
    return {u.id: u for u in users}


async def delete_user(db: AsyncSession, user: User) -> None:
    await db.execute(delete(StudyMember).where(StudyMember.user_id == user.id))
    await db.delete(user)
    await db.commit()


async def approve_user(db: AsyncSession, user: User, admin_id: uuid.UUID) -> User:
    await db.execute(
        update(User)
        .where(User.id == user.id)
        .values(status=UserStatus.ACTIVE, approved_by=admin_id, approved_at=func.now())
    )
    await db.commit()
    await db.refresh(user)
    return user


async def reject_user(db: AsyncSession, user: User, admin_id: uuid.UUID) -> User:
    await db.execute(
        update(User)
        .where(User.id == user.id)
        .values(status=UserStatus.REJECTED, approved_by=admin_id, approved_at=func.now())
    )
    await db.commit()
    await db.refresh(user)
    return user