from flask import current_app
from flask_login import UserMixin, AnonymousUserMixin
from itsdangerous import TimedJSONWebSignatureSerializer as Serializer
from werkzeug.security import generate_password_hash, check_password_hash
from . import db
from . import login_manager


class Permission:
    """
    Defines User permissions as integers by the power of 2. User permission
    can be evaluated using the bitwise operator &. 3 equals to CREATE_JOB and
    DELETE_JOB and so on.
    """
    CREATE_JOB = 1
    DELETE_JOB = 2
    # WRITE = 4
    # MODERATE = 8
    ADMIN = 16


class Role(db.Model):
    """
    Model for the different roles Users can have. Is a one-to-many relationship.
    A Role can be associated with many User rows.
    """
    __tablename__ = 'roles'
    # Primary key
    id = db.Column(db.Integer, primary_key=True)
    default = db.Column(db.Boolean, default=False, index=True)
    name = db.Column(db.String(64), unique=True)
    permissions = db.Column(db.Integer)
    # Relationships
    users = db.relationship('User', backref='role', lazy='dynamic')

    def __init__(self, **kwargs):
        super(Role, self).__init__(**kwargs)
        if self.permissions is None:
            self.permissions = 0

    def __repr__(self):
        """
        String representation of the Role. For human readability.
        """
        return '<Role %r>' % self.name

    def add_permission(self, perm):
        """
        Add new permission to Role. Input is a Permission.
        """
        if not self.has_permission(perm):
            self.permissions += perm

    def remove_permission(self, perm):
        """
        Removes permission from a Role. Input a Permission.
        """
        if self.has_permission(perm):
            self.permissions -= perm

    def reset_permissions(self):
        """
        Resets permissions to zero. Zero equals no permissions at all.
        """
        self.permissions = 0

    def has_permission(self, perm):
        """
        Checks if a Role has a specific Permission. Does this wit hthe bitwise
        operator.
        """
        return self.permissions & perm == perm

    @staticmethod
    def insert_roles():
        """
        Inserts roles into the databes. This has to be executed befor Users are
        added to the database. Otherwiese Users will not have a Role assigned
        to them. Order of the roles dictionary determines the ID of each role.
        User hast the ID 1 and Administrator has the ID 2.
        """
        roles = {
                    'User': [Permission.CREATE_JOB],
                    'Administrator': [Permission.ADMIN,
                                      Permission.CREATE_JOB,
                                      Permission.DELETE_JOB]
        }
        default_role = 'User'
        for r in roles:
            role = Role.query.filter_by(name=r).first()
            if role is None:
                role = Role(name=r)
            role.reset_permissions()
            for perm in roles[r]:
                role.add_permission(perm)
            role.default = (role.name == default_role)
            db.session.add(role)
        db.session.commit()


class User(UserMixin, db.Model):
    """
    Model for Users that are registered to Opaque.
    """
    __tablename__ = 'users'
    # Primary key
    id = db.Column(db.Integer, primary_key=True)
    confirmed = db.Column(db.Boolean, default=False)
    email = db.Column(db.String(64), unique=True, index=True)
    password_hash = db.Column(db.String(128))
    role_id = db.Column(db.Integer, db.ForeignKey('roles.id'))
    username = db.Column(db.String(64), unique=True, index=True)
    # Relationships
    jobs = db.relationship('Job', backref='job', lazy='dynamic')

    def __repr__(self):
        """
        String representation of the User. For human readability.
        """
        return '<User %r>' % self.username

    def __init__(self, **kwargs):
        super(User, self).__init__(**kwargs)
        if self.role is None:
            if self.email == current_app.config['OPAQUE_ADMIN']:
                self.role = Role.query.filter_by(name='Administrator').first()
            if self.role is None:
                self.role = Role.query.filter_by(default=True).first()

    def generate_confirmation_token(self, expiration=3600):
        """
        Generates a confirmation token for user confirmation via email.
        """
        s = Serializer(current_app.config['SECRET_KEY'], expiration)
        return s.dumps({'confirm': self.id}).decode('utf-8')

    def generate_reset_token(self, expiration=3600):
        """
        Generates a reset token for password reset via email.
        """
        s = Serializer(current_app.config['SECRET_KEY'], expiration)
        return s.dumps({'reset': self.id}).decode('utf-8')

    def confirm(self, token):
        """
        Confirms User if the given token is valid and not expired.
        """
        s = Serializer(current_app.config['SECRET_KEY'])
        try:
            data = s.loads(token.encode('utf-8'))
        except:
            return False
        if data.get('confirm') != self.id:
            return False
        self.confirmed = True
        db.session.add(self)
        return True

    @staticmethod
    def reset_password(token, new_password):
        """
        Resets password for User if the given token is valid and not expired.
        """
        s = Serializer(current_app.config['SECRET_KEY'])
        try:
            data = s.loads(token.encode('utf-8'))
        except:
            return False
        user = User.query.get(data.get('reset'))
        if user is None:
            return False
        user.password = new_password
        db.session.add(user)
        return True

    @property
    def password(self):
        raise AttributeError('password is not a readable attribute')

    @password.setter
    def password(self, password):
        self.password_hash = generate_password_hash(password)

    def verify_password(self, password):
        return check_password_hash(self.password_hash, password)

    def can(self, perm):
        """
        Checks if a User with its current role can doe something. Checks if the
        associated role actually has the needed Permission.
        """
        return self.role is not None and self.role.has_permission(perm)

    def is_administrator(self):
        """
        Checks if User has Admin permissions.
        """
        return self.can(Permission.ADMIN)


class AnonymousUser(AnonymousUserMixin):
    """
    Model replaces the default AnonymousUser.
    """
    def can(self, permissions):
        return False

    def is_administrator(self):
        return False


class Job(db.Model):
    """
    Class to define Jobs.
    """
    __tablename__ = 'jobs'
    # Primary key
    id = db.Column(db.Integer, primary_key=True)
    description = db.Column(db.String(64))
    '''
    ' Requested ressources.
    ' Example: {"n_cores": 2,
    '           "mem_mb": 4096
    '           }
    '''
    ressources = db.Column(db.String(255))
    service = db.Column(db.String(64))
    '''
    ' Service specific arguments in JSON format.
    ' Example: {"args": ["--keep-intermediates", "skip-binarization"],
    '           "lang": "eng",
    '           "version": "latest"
    '           }
    '''
    service_args = db.Column(db.String(255))
    status = db.Column(db.String(8))
    title = db.Column(db.String(32))
    user_id = db.Column(db.Integer, db.ForeignKey('users.id'))

    def __init__(self, **kwargs):
        super(Job, self).__init__(**kwargs)

    def __repr__(self):
        """
        String representation of the Job. For human readability.
        """
        return '<Job %r>' % self.title


'''
' Flask-Login is told to use the application’s custom anonymous user by setting
' its class in the login_manager.anonymous_user attribute.
'''
login_manager.anonymous_user = AnonymousUser


@login_manager.user_loader
def load_user(user_id):
    return User.query.get(int(user_id))