# -*- test-case-name: twisted.test.test_roots -*-
#
# Copyright (c) 2001-2004 Twisted Matrix Laboratories.
# See LICENSE for details.


"""Twisted Python Roots: an abstract hierarchy representation for Twisted.

Maintainer: Glyph Lefkowitz

Stability: Unstable

Future Plans: Removing distinction between 'static' and 'dynamic' entities,
which never made much sense anyway and bloats the API horribly.  This probably
involves updating all of Coil to have tree widgets that can be dynamically
expanded, which probably involves porting all of Coil to Woven, so it might not
happen for a while.

"""

# System imports
import types
from twisted.python import reflect

class NotSupportedError(NotImplementedError):
    """
    An exception meaning that the tree-manipulation operation
    you're attempting to perform is not supported.
    """


class Request:
    """I am an abstract representation of a request for an entity.

    I also function as the response.  The request is responded to by calling
    self.write(data) until there is no data left and then calling
    self.finish().
    """
    # This attribute should be set to the string name of the protocol being
    # responded to (e.g. HTTP or FTP)
    wireProtocol = None
    def write(self, data):
        """Add some data to the response to this request.
        """
        raise NotImplementedError("%s.write" % reflect.qual(self.__class__))

    def finish(self):
        """The response to this request is finished; flush all data to the network stream.
        """
        raise NotImplementedError("%s.finish" % reflect.qual(self.__class__))


class Entity:
    """I am a terminal object in a hierarchy, with no children.

    I represent a null interface; certain non-instance objects (strings and
    integers, notably) are Entities.

    Methods on this class are suggested to be implemented, but are not
    required, and will be emulated on a per-protocol basis for types which do
    not handle them.
    """
    def render(self, request):
        """
        I produce a stream of bytes for the request, by calling request.write()
        and request.finish().
        """
        raise NotImplementedError("%s.render" % reflect.qual(self.__class__))


class Collection:
    """I represent a static collection of entities.

    I contain methods designed to represent collections that can be dynamically
    created.
    """

    def __init__(self, entities=None):
        """Initialize me.
        """
        if entities is not None:
            self.entities = entities
        else:
            self.entities = {}

    def getStaticEntity(self, name):
        """Get an entity that was added to me using putEntity.

        This method will return 'None' if it fails.
        """
        return self.entities.get(name)

    def getDynamicEntity(self, name, request):
        """Subclass this to generate an entity on demand.

        This method should return 'None' if it fails.
        """

    def getEntity(self, name, request):
        """Retrieve an entity from me.

        I will first attempt to retrieve an entity statically; static entities
        will obscure dynamic ones.  If that fails, I will retrieve the entity
        dynamically.

        If I cannot retrieve an entity, I will return 'None'.
        """
        ent = self.getStaticEntity(name)
        if ent is not None:
            return ent
        ent = self.getDynamicEntity(name, request)
        if ent is not None:
            return ent
        return None

    def putEntity(self, name, entity):
        """Store a static reference on 'name' for 'entity'.

        Raises a KeyError if the operation fails.
        """
        self.entities[name] = entity

    def delEntity(self, name):
        """Remove a static reference for 'name'.

        Raises a KeyError if the operation fails.
        """
        del self.entities[name]

    def storeEntity(self, name, request):
        """Store an entity for 'name', based on the content of 'request'.
        """
        raise NotSupportedError("%s.storeEntity" % reflect.qual(self.__class__))

    def removeEntity(self, name, request):
        """Remove an entity for 'name', based on the content of 'request'.
        """
        raise NotSupportedError("%s.removeEntity" % reflect.qual(self.__class__))

    def listStaticEntities(self):
        """Retrieve a list of all name, entity pairs that I store references to.

        See getStaticEntity.
        """
        return self.entities.items()

    def listDynamicEntities(self, request):
        """A list of all name, entity that I can generate on demand.

        See getDynamicEntity.
        """
        return []

    def listEntities(self, request):
        """Retrieve a list of all name, entity pairs I contain.

        See getEntity.
        """
        return self.listStaticEntities() + self.listDynamicEntities(request)

    def listStaticNames(self):
        """Retrieve a list of the names of entities that I store references to.

        See getStaticEntity.
        """
        return self.entities.keys()


    def listDynamicNames(self):
        """Retrieve a list of the names of entities that I store references to.

        See getDynamicEntity.
        """
        return []


    def listNames(self, request):
        """Retrieve a list of all names for entities that I contain.

        See getEntity.
        """
        return self.listStaticNames()


class ConstraintViolation(Exception):
    """An exception raised when a constraint is violated.
    """


class Constrained(Collection):
    """A collection that has constraints on its names and/or entities."""

    def nameConstraint(self, name):
        """A method that determines whether an entity may be added to me with a given name.

        If the constraint is satisfied, return 1; if the constraint is not
        satisfied, either return 0 or raise a descriptive ConstraintViolation.
        """
        return 1

    def entityConstraint(self, entity):
        """A method that determines whether an entity may be added to me.

        If the constraint is satisfied, return 1; if the constraint is not
        satisfied, either return 0 or raise a descriptive ConstraintViolation.
        """
        return 1

    def reallyPutEntity(self, name, entity):
        Collection.putEntity(self, name, entity)

    def putEntity(self, name, entity):
        """Store an entity if it meets both constraints.

        Otherwise raise a ConstraintViolation.
        """
        if self.nameConstraint(name):
            if self.entityConstraint(entity):
                self.reallyPutEntity(name, entity)
            else:
                raise ConstraintViolation("Entity constraint violated.")
        else:
            raise ConstraintViolation("Name constraint violated.")


class Locked(Constrained):
    """A collection that can be locked from adding entities."""

    locked = 0

    def lock(self):
        self.locked = 1

    def entityConstraint(self, entity):
        return not self.locked


class Homogenous(Constrained):
    """A homogenous collection of entities.

    I will only contain entities that are an instance of the class or type
    specified by my 'entityType' attribute.
    """

    entityType = types.InstanceType

    def entityConstraint(self, entity):
        if isinstance(entity, self.entityType):
            return 1
        else:
            raise ConstraintViolation("%s of incorrect type (%s)" %
                                      (entity, self.entityType))

    def getNameType(self):
        return "Name"

    def getEntityType(self):
        return self.entityType.__name__
