modelverse/wrappers/modelverse.py

import urllib
import urllib2
import json
import random
from urllib2 import URLError
import sys

# Bind to the compiler (might have to update path manually!)
sys.path.append("interface/HUTN")
from hutn_compiler.compiler import main as do_compile

# Helper functions and configuration: do not use yourself!
taskname = random.random()
address = None
last_output = None
mode = 0

def _input(value):
    # Ugly json encoding of primitives
    if isinstance(value, type([])):
        value = json.dumps(value)
        urllib2.urlopen(urllib2.Request(address, urllib.urlencode({"op": "set_input", "data": value, "taskname": taskname}))).read()
    else:
        value = json.dumps(value)
        #print("Set input: " + str(value))
        urllib2.urlopen(urllib2.Request(address, urllib.urlencode({"op": "set_input", "value": value, "taskname": taskname}))).read()

def _input_raw(value, taskname):
    # Ugly json encoding of primitives
    urllib2.urlopen(urllib2.Request(address, urllib.urlencode({"op": "set_input", "value": value, "taskname": taskname}))).read()

def _compile_AL(code):
    # Compile an action language file and send the compiled code
    code_fragments = code.split("\n")
    code_fragments = [i for i in code_fragments if i.strip() != ""]
    code_fragments = [i.replace("    ", "\t") for i in code_fragments]
    initial_tabs = min([len(i) - len(i.lstrip("\t")) for i in code_fragments])
    code_fragments = [i[initial_tabs:] for i in code_fragments]
    code_fragments.append("")
    code = "\n".join(code_fragments)

    with open("__constraint.alc", "w") as f:
        f.write(code)
        f.flush()

    return do_compile("__constraint.alc", "interface/HUTN/grammars/actionlanguage.g", "CS")

def _compile_model(code):
    # Compile a model and send the compiled graph
    # First change multiple spaces to a tab
    code_fragments = code.split("\n")
    code_fragments = [i for i in code_fragments if i.strip() != ""]
    code_fragments = [i.replace("    ", "\t") for i in code_fragments]
    initial_tabs = min([len(i) - len(i.lstrip("\t")) for i in code_fragments])
    code_fragments = [i[initial_tabs:] for i in code_fragments]
    code_fragments.append("")
    code = "\n".join(code_fragments)

    with open("__model.mvc", "w") as f:
        f.write(code)
        f.flush()

    return do_compile("__model.mvc", "interface/HUTN/grammars/modelling.g", "M") + ["exit"]

def _output(expected=None):
    try:
        global last_output
        last_output = json.loads(urllib2.urlopen(urllib2.Request(address, urllib.urlencode({"op": "get_output", "taskname": taskname}))).read())
        #print("Got output: " + str(last_output))
    except:
        raise UnknownError()
    if expected is not None and last_output != expected:
        raise InterfaceMismatch(_last_output(), expected)
    return last_output

def _last_output():
    return last_output

# Exceptions
class ModelverseException(Exception):
    pass

class UnknownException(ModelverseException):
    pass

class UnknownIdentifier(ModelverseException):
    pass

class UnknownType(ModelverseException):
    pass

class NotAnAssociation(ModelverseException):
    pass

class UnsupportedValue(ModelverseException):
    pass

class CompilationError(ModelverseException):
    pass

class NoSuchAttribute(ModelverseException):
    pass

class UnknownModel(ModelverseException):
    pass

class ConnectionError(ModelverseException):
    pass

class ModelExists(ModelverseException):
    pass

class PermissionDenied(ModelverseException):
    pass

class InvalidMode(ModelverseException):
    pass

class InterfaceMismatch(ModelverseException):
    pass

# Main MvC operations
def init(address_param="http://localhost:8001"):
    """Starts up the connection to the Modelverse."""
    # return None
    # raises ConnectionError
    # raises UnknownError
    # raises InvalidMode
    global mode
    if mode != 0:
        raise InvalidMode()
    global address
    address = address_param
    try:
        _input_raw('"%s"' % taskname, "task_manager")
        mode = 1
    except URLError as e:
        raise ConnectionError(e.reason)

def login(username, password):
    """Log in a user, if user doesn't exist, it is created."""
    # return None
    # raises UnknownError
    # raises PermissionDenied
    # raises InterfaceMismatch
    global mode
    if mode != 1:
        raise InvalidMode()
    _output("Log on as which user?")
    _input(username)
    if _output() == "Password for existing user?":
        _input(password)
        if _output() == "Welcome to the Model Management Interface v2.0!":
            _output("Use the 'help' command for a list of possible commands")
            _output("Ready for command...")
            mode = 2
        elif _last_output() == "Wrong password!":
            raise PermissionDenied()
        else:
            raise InterfaceMismatch(_last_output())
    elif _last_output() == "This is a new user: please give password!":
        _input(password)
        _output("Please repeat the password")
        _input(password)
        if _output() == "Passwords match!":
            _output("Welcome to the Model Management Interface v2.0!")
            _output("Use the 'help' command for a list of possible commands")
            _output("Ready for command...")
            mode = 2
        elif _last_output() == "Not the same password!":
            # We just sent the same password, so it should be identical, unless the interface changed
            raise InterfaceMismatch(_last_output())
        else:
            raise InterfaceMismatch(_last_output())
    else:
        raise InterfaceMismatch(_last_output())

def model_add(model_name, metamodel_name, model_code=None):
    """Instantiate a new model."""
    # return None
    # raises UnknownModel
    # raises ModelExists
    # raises UnknownError
    # raises PermissionDenied
    # raises CompilationError
    if mode != 2:
        raise InvalidMode()
    # Do this before creating the model, as otherwise compilation errors would make us inconsistent
    if model_code is not None:
        try:
            compiled = _compile_model(model_code)
        except:
            raise CompilationError()
    else:
        compiled = ["exit"]

    _input("model_add")
    _output("Creating new model!")
    _output("Model type?")
    _input(metamodel_name)
    if _output() == "Model name?":
        _input(model_name)
        if _output() == "Waiting for model constructors...":
            _input(compiled)
            _output("Model upload success!")
            _output("Ready for command...")
        elif _last_output() == "Model with that name already exists!":
            _output("Ready for command...")
            raise ModelExists()
        else:
            raise InterfaceMismatch(_last_output())
    elif _last_output().startswith("Could not find type model"):
        _output("Ready for command...")
        raise UnknownModel()
    elif _last_output() == "Permission denied":
        _output("Ready for command...")
        raise PermissionDenied()

def model_modify(model_name):
    """Modify an existing model."""
    # return is_write
    # raises UnknownModel
    # raises PermissionDenied
    # raises UnknownError
    global mode
    if mode != 2:
        raise InvalidMode()

    _input("model_modify")
    _output("Which model do you want to modify?")
    _input(model_name)
    if _output() == "Permission denied":
        _output("Ready for command...")
        raise PermissionDenied()
    elif _last_output() == "Could not find model!":
        _output("Ready for command...")
        raise UnknownModel()
    elif _last_output() == "Model loaded, ready for commands!":
        mode = 3
        if ("r/w" in _output()):
            write = True
        else:
            write = False
        _output("Use 'help' command for a list of possible commands")
        _output("Please give your command.")
        return write
    else:
        raise InterfaceMismatch()

def model_list():
    """List all models."""
    # return [(model1, metamodel1), (model2, metamodel2), ...]
    # raises UnknownError
    if mode != 2:
        raise InvalidMode()
    _input("model_list")
    lst = []
    while (_output() != "Ready for command..."):
        v = _last_output()
        m, mm = v.split(":")
        m = m.strip()
        mm = mm.strip()
        lst.append((m, mm))
    return lst

def model_list_full():
    """List full information on all models."""
    # return [(model1, metamodel1, owner1, group1, permissions1), (model2, metamodel2, owner2, group2, permissions2), ...]
    # raises UnknownError
    if mode != 2:
        raise InvalidMode()
    _input("model_list_full")
    lst = []
    while (_output() != "Ready for command..."):
        v = _last_output()
        m, mm = v.split(":")
        m = m.strip()
        mm = mm.strip()
        perm, own, grp, m = m.split(" ")
        lst.append((m, mm, own, grp, perm))
    return lst

def verify(model):
    """Verify if a model conforms to its metamodel."""
    # return "verification_result"
    # raises UnknownError
    # raises UnknownModel
    if mode != 2:
        raise InvalidMode()
    _input("verify")
    _output("Which model to verify?")
    _input(model)
    if _output() == "Verifying model...":
        result = _output()
        _output("Ready for command...")
        return result
    elif _last_output() == "Permission denied":
        _output("Ready for command...")
        raise PermissionDenied()
    elif _last_output() == "No such model":
        _output("Ready for command...")
        raise UnknownModel()
    else:
        raise InterfaceMismatch(_last_output())

def model_overwrite(model_name, new_model=None):
    """Upload a new model and overwrite an existing model."""
    # return None
    # raises UnknownModel
    # raises PermissionDenied
    # raises CompilationError
    # raises UnknownError
    if mode != 2:
        raise InvalidMode()

    if new_model is not None:
        try:
            compiled = _compile_model(new_model)
        except Exception as e:
            raise CompilationError(e)
    else:
        compiled = ["exit"]

    _input("model_overwrite")
    _output("Which model to overwrite?")
    _input(model_name)
    if _output() == "Permission denied":
        _output("Ready for command...")
        raise PermissionDenied()
    elif _last_output() == "No such model":
        _output("Ready for command...")
        raise UnknownModel()
    elif _last_output() == "Waiting for model constructors...":
        _input(compiled)
        _output("Model overwrite success")
        _output("Ready for command...")

def user_logout():
    """Log out the current user and break the connection."""
    # return None
    # raises UnknownException
    global mode
    if mode != 2:
        raise InvalidMode()
    _input("exit")
    mode = 0

def user_delete():
    """Removes the current user and break the connection."""
    # return None
    # raises UnknownException
    global mode
    if mode != 2:
        raise InvalidMode()
    _input("self-destruct")
    mode = 0

def model_render(model, mapper):
    """Fetch a rendered verion of a model."""
    # return JSON_representation
    # raises UnknownException
    # raises UnknownIdentifier
    # raises InterfaceMismatch
    global mode
    if mode != 2:
        raise InvalidMode()

    #TODO error handling!

    _input("model_render")
    _output()
    _input(model)
    _output()
    _input(mapper)
    _output("Mapping success")
    rendered = _output()
    _output("Ready for command...")
    return rendered

def transformation_between(source, target):
    global mode
    if mode != 2:
        raise InvalidMode()

    _input("transformation_between")
    _output("Source metamodel?")
    _input(source)
    if _output() == "Target metamodel?":
        _input(target)
        if _output() == "Searching transformations...":
            result = []
            while _output() != "Ready for command...":
                result.append(_last_output())
            return result
        elif _last_output() == "Target unknown!":
            raise UnknownModel()
        else:
            raise InterfaceMismatch(_last_output())
    elif _last_output() == "Source unknown!":
        raise UnknownModel()
    else:
        raise InterfaceMismatch(_last_output())

def transformation_add_MT_language():
    """Create a new Model Transformation language out of a set of metamodels."""
    raise NotImplementedError()

def transformation_add_MT():
    """Create a new model transformation."""
    raise NotImplementedError()

def transformation_add_AL():
    """Create a new action language fragment."""
    raise NotImplementedError()

def transformation_add_MANUAL():
    """Create a new manual model operation."""
    raise NotImplementedError()

def transformation_execute():
    """Execute an existing model operation."""
    raise NotImplementedError()

def transformation_list():
    """List existing model operations."""
    raise NotImplementedError()

def transformation_list_full():
    """List detailed information on model operations."""
    raise NotImplementedError()

def transformation_detail():
    """List full details of a a model operation."""
    raise NotImplementedError()

def transformation_RAMify():
    """Ramify an existing metamodel."""
    raise NotImplementedError()

def process_execute():
    """Execute a process model."""
    raise NotImplementedError()

def permission_modify():
    """Modify permissions of a model."""
    raise NotImplementedError()

def permission_owner():
    """Modify the owning user of a model."""
    raise NotImplementedError()

def permission_group():
    """Modify the owning group of a model."""
    raise NotImplementedError()

def group_create():
    """Create a new group."""
    raise NotImplementedError()

def group_delete():
    """Delete a group of which you are an owner."""
    raise NotImplementedError()

def group_owner_add():
    """Add a new owning user to a group you own."""
    raise NotImplementedError()

def group_owner_delete():
    """Delete an owning user to a group you own."""
    raise NotImplementedError()

def group_join():
    """Add a new user to a group you own."""
    raise NotImplementedError()

def group_kick():
    """Delete a user from a group you own."""
    raise NotImplementedError()

def group_list():
    """List existing groups."""
    raise NotImplementedError()

def admin_promote():
    """Promote a user to admin status."""
    raise NotImplementedError()

def admin_demote():
    """Demote a user from admin status."""
    raise NotImplementedError()

# Actual operations on the model
def element_list(model_name):
    """Return a list of all IDs and the type of the element"""
    # return [(name1, type1), (name2, type2), ...]
    # raises UnknownError
    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("list_full")
        lst = []
        _output("List of all elements:")
        while (_output() != "Please give your command."):
            v = _last_output()
            m, mm = v.split(":")
            m = m.strip()
            mm = mm.strip()
            lst.append((m, mm))
        return lst

    finally:
        model_exit()

def types(model_name):
    """Return a list of all types usable in the model"""
    # return [type1, type2, ...]
    # raises UnknownError
    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("types")
        _output("List of types:")
        lst = []
        while (_output() != "Please give your command."):
            v = _last_output()
            m, mm = v.split(":")
            m = m.strip()
            lst.append(m)
        return lst

    finally:
        model_exit()

def types_full(model_name):
    """Return a list of full types usable in the model"""
    # return [(type1, typetype1), (type2, typetype2), ...]
    # raises UnknownError
    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("types")
        _output("List of types:")
        lst = []
        while (_output() != "Please give your command."):
            v = _last_output()
            m, mm = v.split(":")
            m = m.strip()
            mm = mm.strip()
            lst.append((m, mm))
        return lst

    finally:
        model_exit()

def read(model_name, ID):
    """Return a tuple of information on the element: its type and source/target (None if not an edge)"""
    # return (type, (source, target))
    # raises UnknownError
    # raises UnknownIdentifier
    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("read")
        _output("Element to read?")
        _input(ID)
        if _output() == "Unknown element; aborting":
            _output("Please give your command.")
            raise UnknownIdentifier()
        elif _last_output() == "ID: " + str(ID):
            t = _output().split(":")[1].strip()
            if (not _output().startswith("Source:")):
                rval = (t, None)
            else:
                src = _last_output().split(":")[1].strip()
                trg = _output().split(":")[1].strip()
                rval = (t, (src, trg))
            while (_output() != "Please give your command."):
                pass
            return rval

    finally:
        model_exit()

def read_attrs(model_name, ID):
    """Return a dictionary of attribute value pairs"""
    # return {attr1: value1, attr2: value2, ...}
    # raises UnknownError
    # raises UnknownIdentifier
    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("read")
        _output("Element to read?")
        _input(ID)
        if _output() == "Unknown element; aborting":
            _output("Please give your command.")
            raise UnknownIdentifier()
        elif _last_output() == "ID: " + str(ID):
            rval = {}
            # Skip until attributes
            while (_output() != "Attributes:"):
                pass
            while (_output() != "Please give your command."):
                r = _last_output()
                key, value = r.split(":")
                _, value = value.split("=")
                key = json.loads(key.strip())
                value = value.strip()
                value = None if value == "None" else json.loads(value)
                rval[key] = value
            return rval
    finally:
        model_exit()

def instantiate(model_name, typename, edge=None, ID=""):
    """Create a new instance of the specified typename, between the selected elements (if not None), and with the provided ID (if any)"""
    # return instantiated_ID
    # raises UnknownError
    # raises UnknownType
    # raises UnknownIdentifier
    # raises NotAnEdge
    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("instantiate")
        if (_output() == "Permission denied"):
            _output("Please give your command.")
            raise PermissionDenied()
        else:
            _input(typename)
            if (_output() == "Name of new element?"):
                _input(ID)
                if (_output() == "Element already exists; aborting"):
                    _output("Please give your command.")
                    raise ElementExists()

                if (edge is not None) and (_last_output() == "Source name?"):
                    # Is an edge and we have data
                    _input(edge[0])
                    if _output() == "Destination name?":
                        _input(edge[1])
                        if _output() == "Instantiation successful!":
                            ID = _output()
                            _output("Please give your command.")
                            return ID
                        elif _last_output() == "Unknown destination; aborting":
                            _output("Please give your command.")
                            raise UnknownIdentifier()
                        else:
                            raise InterfaceMismatch(_last_output())
                    elif _last_output() == "Unknown source; aborting":
                        _output("Please give your command.")
                        raise UnknownIdentifier()
                    else:
                        raise InterfaceMismatch(_last_output())
                elif (edge is None) and (_last_output() != "Source name?"):
                    # Is no edge and we don't have data
                    if _last_output() == "Instantiation successful!":
                        ID = _output()
                        _output("Please give your command.")
                        return ID
                    else:
                        raise InterfaceMismatch(_last_output())
                elif (edge is not None) and (_last_output() != "Source name?"):
                    # Is no edge, but we have edge data to input: ERROR
                    # Delete the element again
                    ID = _last_output()
                    _output("Please give your command.")
                    delete_element(ID)
                    raise NotAnEdge()
                elif (edge is None) and (_last_output() == "Source name?"):
                    # Is an edge, but we have no edge data to input: ERROR
                    # Add an empty source, which is guaranteed not to be there
                    _input("")
                    _output("Unknown source; aborting")
                    _output("Please give your command.")
                    raise NotAnEdge()

            elif (_last_output() == "Permission denied"):
                _output("Please give your command.")
                raise PermissionDenied()
            elif (_last_output() == "Unknown type specified; aborting"):
                _output("Please give your command.")
                raise UnknownType()
            else:
                raise InterfaceMismatch(_last_output())

    finally:
        model_exit()

def delete_element(model_name, ID):
    """Delete the element with the given ID"""
    # return None
    # raises UnknownError
    # raises UnknownIdentifier
    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("delete")
        if _output() == "What is the name of the element you want to delete?":
            _input(ID)
            if _output() == "Deleted!":
                _output("Please give your command.")
            elif _last_output() == "No such element; aborting":
                _output("Please give your command.")
                raise UnknownIdentifier()
            else:
                raise InterfaceMismatch(_last_output())
        elif _last_output() == "Permission denied":
            _output("Please give your command.")
            raise PermissionDenied()
        else:
            raise InterfaceMismatch(_last_output())

    finally:
        model_exit()

def attr_assign(model_name, ID, attr, value):
    """Assign a value to an attribute"""
    # return None
    # raises UnknownError
    # raises UnknownIdentifier
    # raises NoSuchAttribute
    # raises UnsupportedValue
    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("attr_add")
        if _output() == "Which element do you want to assign an attribute to?":
            _input(ID)
            if _output() == "Which attribute do you wish to assign?":
                _input(attr)
                if _output() == "Value of attribute?":
                    _input(value)
                    _output("Added attribute!")
                    _output("Please give your command.")
                elif _last_output() == "No such attribute!":
                    _output("Please give your command.")
                    raise NoSuchAttribute()
                else:
                    raise InterfaceMismatch(_last_output())

            elif _last_output() == "No such element!":
                _output("Please give your command.")
                raise UnknownIdentifier()
            else:
                raise InterfaceMismatch(_last_output())

        elif _last_output() == "Permission denied":
            _output("Please give your command.")
            raise PermissionDenied()
        else:
            raise InterfaceMismatch(_last_output())

    finally:
        model_exit()

def attr_assign_code(model_name, ID, attr, code):
    """Assign a piece of Action Language code to the attribute"""
    # return None
    # raises UnknownError
    # raises UnknownIdentifier
    # raises NoSuchAttribute
    # raises UnsupportedValue
    try:
        compiled = _compile_AL(code)
    except Exception as e:
        raise CompilationError(e)

    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("attr_add")
        if _output() == "Which element do you want to assign an attribute to?":
            _input(ID)
            if _output() == "Which attribute do you want to assign?":
                _input(attr)
                if _output() == "Waiting for code constructors...":
                    _input(compiled)
                    _output("Added attribute!")
                    _output("Please give your command.")
                elif _last_output() == "No such attribute!":
                    _output("Please give your command.")
                    raise NoSuchAttribute()
                else:
                    raise InterfaceMismatch(_last_output())

            elif _last_output() == "No such element!":
                _output("Please give your command.")
                raise UnknownIdentifier()
            else:
                raise InterfaceMismatch(_last_output())

        elif _last_output() == "Permission denied":
            _output("Please give your command.")
            raise PermissionDenied()
        else:
            raise InterfaceMismatch(_last_output())
    finally:
        model_exit()

def attr_delete(model_name, ID, attr):
    """Remove an attribute."""
    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("attr_del")
        if _output() == "Which element do you want to remove an attribute of?":
            _input(ID)
            if _output() == "Which attribute do you want to delete?":
                _input(attr)
                if _output() == "Attribute deleted!":
                    _output("Please give your command.")
                elif _last_output() == "No such attribute!":
                    _output("Please give your command.")
                    raise NoSuchAttribute()
                else:
                    raise InterfaceMismatch(_last_output())
            elif _last_output() == "No such element!":
                _output("Please give your command.")
                raise UnknownIdentifier()
            else:
                raise InterfaceMismatch(_last_output())
        elif _last_output() == "Permission denied":
            _output("Please give your command.")
            raise PermissionDenied()
        else:
            raise InterfaceMismatch(_last_output())

    finally:
        model_exit()

def read_outgoing(model_name, ID, typename):
    """Returns a list of all outgoing associations of a specific type ("" = all)"""
    # return [name1, name2, ...]
    # raises UnknownError
    # raises UnknownIdentifier
    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("read_outgoing")
        _output("Element to read from?")
        _input(ID)
        if _output() == "Type of outgoing edge (empty for all)?":
            _input(typename)
            lst = []
            while (_output() != "Please give your command."):
                lst.append(_last_output())
            return lst
        elif _last_output() == "Unknown element; aborting":
            _output("Please give your command.")
            raise UnknownIdentifier()
        else:
            raise InterfaceMismatch()

    finally:
        model_exit()

def read_incoming(model_name, ID, typename):
    """Returns a list of all incoming associations of a specific type ("" = all)"""
    # return [name1, name2, ...]
    # raises UnknownError
    # raises UnknownIdentifier
    # raises UnknownType
    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("read_incoming")
        _output("Element to read from?")
        _input(ID)
        if _output() == "Type of incoming edge (empty for all)?":
            _input(typename)
            lst = []
            while (_output() != "Please give your command."):
                lst.append(_last_output())
            return lst
        elif _last_output() == "Unknown element; aborting":
            _output("Please give your command.")
            raise UnknownIdentifier()
        else:
            raise InterfaceMismatch()
    finally:
        model_exit()

def read_association_source(model_name, ID):
    """Returns the source of an association."""
    # returns name
    # raises UnknownError
    # raises UnknownIdentifier
    # raises NotAnAssociation
    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("read_association_source")
        _output("Association to read source of?")
        _input(ID)
        if _output() == "Read source:":
            result = _output()
            _output("Please give your command.")
            return result
        elif _last_output() == "Unknown element; aborting":
            _output("Please give your command.")
            raise UnknownIdentifier()
        elif _last_output() == "Not an association; aborting":
            _output("Please give your command.")
            raise NotAnEdge()
        else:
            raise InterfaceMismatch(_last_output())
    finally:
        model_exit()

def read_association_destination(model_name, ID):
    """Returns the destination of an association."""
    # returns name
    # raises UnknownError
    # raises UnknownIdentifier
    # raises NotAnAssociation
    model_modify(model_name)

    if mode != 3:
        raise InvalidMode()

    try:
        _input("read_association_destination")
        _output("Association to read destination of?")
        _input(ID)
        if _output() == "Read destination:":
            result = _output()
            _output("Please give your command.")
            return result
        elif _last_output() == "Unknown element; aborting":
            _output("Please give your command.")
            raise UnknownIdentifier()
        elif _last_output() == "Not an association; aborting":
            _output("Please give your command.")
            raise NotAnEdge()
        else:
            raise InterfaceMismatch(_last_output())
    finally:
        model_exit()

def model_exit():
    """Leave model modify mode."""
    # return None
    # raises UnknownError
    global mode
    if mode != 3:
        raise InvalidMode()
    _input("exit")
    _output("Ready for command...")
    mode = 2