from enum import IntEnum
from flask_hashids import HashidMixin
from typing import Union
from app import db


class Permission(IntEnum):
    '''
    Defines User permissions as integers by the power of 2. User permission
    can be evaluated using the bitwise operator &.
    '''
    ADMINISTRATE = 1
    CONTRIBUTE = 2
    USE_API = 4

    @staticmethod
    def get(permission: Union['Permission', int, str]) -> 'Permission':
        if isinstance(permission, Permission):
            return permission
        if isinstance(permission, int):
            return Permission(permission)
        if isinstance(permission, str):
            return Permission[permission]
        raise TypeError('permission must be Permission, int, or str')


class Role(HashidMixin, db.Model):
    __tablename__ = 'roles'
    # Primary key
    id = db.Column(db.Integer, primary_key=True)
    # Fields
    name = db.Column(db.String(64), unique=True)
    default = db.Column(db.Boolean, default=False, index=True)
    permissions = db.Column(db.Integer, default=0)
    # Relationships
    users = db.relationship('User', back_populates='role', lazy='dynamic')

    def __repr__(self):
        return f'<Role {self.name}>'

    def has_permission(self, permission: Union[Permission, int, str]):
        p = Permission.get(permission)
        return self.permissions & p.value == p.value
    
    def add_permission(self, permission: Union[Permission, int, str]):
        p = Permission.get(permission)
        if not self.has_permission(p):
            self.permissions += p.value
    
    def remove_permission(self, permission: Union[Permission, int, str]):
        p = Permission.get(permission)
        if self.has_permission(p):
            self.permissions -= p.value

    def reset_permissions(self):
        self.permissions = 0

    def to_json_serializeable(self, backrefs=False, relationships=False):
        json_serializeable = {
            'id': self.hashid,
            'default': self.default,
            'name': self.name,
            'permissions': [
                x.name for x in Permission
                if self.has_permission(x.value)
            ]
        }
        if backrefs:
            pass
        if relationships:
            json_serializeable['users'] = {
                x.hashid: x.to_json_serializeable(relationships=True)
                for x in self.users
            }
        return json_serializeable

    @staticmethod
    def insert_defaults():
        roles = {
            'User': [],
            'API user': [Permission.USE_API],
            'Contributor': [Permission.CONTRIBUTE],
            'Administrator': [
                Permission.ADMINISTRATE,
                Permission.CONTRIBUTE,
                Permission.USE_API
            ],
            'System user': []
        }
        default_role_name = 'User'
        for role_name, permissions in roles.items():
            role = Role.query.filter_by(name=role_name).first()
            if role is None:
                role = Role(name=role_name)
            role.reset_permissions()
            for permission in permissions:
                role.add_permission(permission)
            role.default = role.name == default_role_name
            db.session.add(role)
        db.session.commit()