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

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

Maintainer: Glyph Lefkowitz
"""

# 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__