from datetime import datetime
from app.extensions import db


class Folder(db.Model):
    __tablename__ = 'folders'
    __table_args__ = (
        # 同一用户同一父目录下名称唯一
        # 注意：MySQL 对 NULL 不强制唯一，根目录重名由路由层补充校验
        db.UniqueConstraint('user_id', 'parent_id', 'name',
                            name='uq_folder_user_parent_name'),
    )

    id         = db.Column(db.Integer, primary_key=True)
    user_id    = db.Column(db.Integer,
                           db.ForeignKey('users.id', ondelete='CASCADE'),
                           nullable=False, index=True)
    name       = db.Column(db.String(128), nullable=False)
    parent_id  = db.Column(db.Integer,
                           db.ForeignKey('folders.id', ondelete='CASCADE'),
                           nullable=True, index=True)
    created_at = db.Column(db.DateTime, default=datetime.utcnow, nullable=False)
    updated_at = db.Column(db.DateTime, default=datetime.utcnow,
                           onupdate=datetime.utcnow, nullable=False)

    # 自引用关系：父删 → 子自动删
    children = db.relationship(
        'Folder',
        backref=db.backref('parent', remote_side=[id]),
        lazy='select',
        cascade='all, delete-orphan'
    )
    # 文件夹内的资源
    resources = db.relationship(
        'Resource',
        backref='folder',
        lazy='dynamic',
        foreign_keys='Resource.folder_id'
    )

    # ── 业务方法 ─────────────────────────────────────────────────

    def is_ancestor_of(self, target_id: int) -> bool:
        """检测 self 是否是 target_id 的祖先（防止移动到自身子树产生循环引用）"""
        visited = set()
        current = Folder.query.get(target_id)
        while current is not None:
            if current.id == self.id:
                return True
            if current.id in visited:
                break
            visited.add(current.id)
            current = current.parent
        return False

    def get_breadcrumb(self) -> list:
        """从根到当前节点的路径列表（用于面包屑导航）"""
        path, node = [], self
        while node is not None:
            path.append(node)
            node = node.parent
        path.reverse()
        return path

    def to_dict(self) -> dict:
        return {
            'id': self.id,
            'name': self.name,
            'parent_id': self.parent_id,
            'resource_count': self.resources.count(),
            'children': [c.to_dict() for c in sorted(self.children, key=lambda x: x.name)]
        }

    @staticmethod
    def get_user_tree(user_id: int) -> list:
        """返回某用户所有根文件夹的完整树（递归序列化）"""
        roots = (Folder.query
                 .filter_by(user_id=user_id, parent_id=None)
                 .order_by(Folder.name)
                 .all())
        return [f.to_dict() for f in roots]

    def __repr__(self):
        return f'<Folder {self.id} {self.name!r}>'