// Revoke removes privileges from this descriptor for a given list of users.
func (p *PrivilegeDescriptor) Revoke(user string, privList privilege.List) {
	userPriv, ok := p.findUser(user)
	if !ok || userPriv.Privileges == 0 {
		// Removing privileges from a user without privileges is a no-op.
		return
	}

	bits := privList.ToBitField()
	if isPrivilegeSet(bits, privilege.ALL) {
		// Revoking 'ALL' privilege: remove user.
		// TODO(marc): the grammar does not allow it, but we should
		// check if other privileges are being specified and error out.
		p.removeUser(user)
		return
	}

	if isPrivilegeSet(userPriv.Privileges, privilege.ALL) {
		// User has 'ALL' privilege. Remove it and set
		// all other privileges one.
		userPriv.Privileges = 0
		for _, v := range privilege.ByValue {
			if v != privilege.ALL {
				userPriv.Privileges |= v.Mask()
			}
		}
	}

	// One doesn't see "AND NOT" very often.
	userPriv.Privileges &^= bits

	if userPriv.Privileges == 0 {
		p.removeUser(user)
	}
}

// NewPrivilegeDescriptor returns a privilege descriptor for the given
// user with the specified list of privileges.
func NewPrivilegeDescriptor(user string, priv privilege.List) *PrivilegeDescriptor {
	return &PrivilegeDescriptor{
		Users: []UserPrivileges{
			{
				User:       user,
				Privileges: priv.ToBitField(),
			},
		},
	}
}

// Grant adds new privileges to this descriptor for a given list of users.
// TODO(marc): if all privileges other than ALL are set, should we collapse
// them into ALL?
func (p *PrivilegeDescriptor) Grant(user string, privList privilege.List) {
	userPriv := p.findOrCreateUser(user)
	if isPrivilegeSet(userPriv.Privileges, privilege.ALL) {
		// User already has 'ALL' privilege: no-op.
		return
	}

	bits := privList.ToBitField()
	if isPrivilegeSet(bits, privilege.ALL) {
		// Granting 'ALL' privilege: overwrite.
		// TODO(marc): the grammar does not allow it, but we should
		// check if other privileges are being specified and error out.
		userPriv.Privileges = privilege.ALL.Mask()
		return
	}
	userPriv.Privileges |= bits
}