class Status(object):
    lookup_table = {}

    def __init__(self, value, name):
        self._value = value
        self._name = name
        Status.lookup_table[value] = self

    def invert(self):
        if self is REACHABLE:
            return UNREACHABLE
        elif self is UNREACHABLE:
            return REACHABLE
        else:
            return UNSURE

    def __and__(self, other):
        if UNSURE in (self, other):
            return UNSURE
        else:
            return REACHABLE if self._value and other._value else UNREACHABLE

    def __repr__(self):
        return '<%s: %s>' % (type(self).__name__, self._name)


REACHABLE = Status(True, 'reachable')
UNREACHABLE = Status(False, 'unreachable')
UNSURE = Status(None, 'unsure')


def _get_flow_scopes(node):
    while True:
        node = node.get_parent_scope(include_flows=True)
        if node is None or node.is_scope():
            return
        yield node


def reachability_check(context, context_scope, node, origin_scope=None):
    first_flow_scope = node.get_parent_scope(include_flows=True)
    if origin_scope is not None:
        origin_flow_scopes = list(_get_flow_scopes(origin_scope))
        node_flow_scopes = list(_get_flow_scopes(node))

        branch_matches = True
        for flow_scope in origin_flow_scopes:
            if flow_scope in node_flow_scopes:
                node_keyword = flow_scope.get_branch_keyword(node)
                origin_keyword = flow_scope.get_branch_keyword(origin_scope)
                branch_matches = node_keyword == origin_keyword
                if flow_scope.type == 'if_stmt':
                    if not branch_matches:
                        return UNREACHABLE
                elif flow_scope.type == 'try_stmt':
                    if not branch_matches and origin_keyword == 'else' \
                            and node_keyword == 'except':
                        return UNREACHABLE
                break

        # Direct parents get resolved, we filter scopes that are separate
        # branches.  This makes sense for autocompletion and static analysis.
        # For actual Python it doesn't matter, because we're talking about
        # potentially unreachable code.
        # e.g. `if 0:` would cause all name lookup within the flow make
        # unaccessible. This is not a "problem" in Python, because the code is
        # never called. In Jedi though, we still want to infer types.
        while origin_scope is not None:
            if first_flow_scope == origin_scope and branch_matches:
                return REACHABLE
            origin_scope = origin_scope.parent

    return _break_check(context, context_scope, first_flow_scope, node)


def _break_check(context, context_scope, flow_scope, node):
    reachable = REACHABLE
    if flow_scope.type == 'if_stmt':
        if flow_scope.node_after_else(node):
            for check_node in flow_scope.check_nodes():
                reachable = _check_if(context, check_node)
                if reachable in (REACHABLE, UNSURE):
                    break
            reachable = reachable.invert()
        else:
            flow_node = flow_scope.node_in_which_check_node(node)
            if flow_node is not None:
                reachable = _check_if(context, flow_node)
    elif flow_scope.type in ('try_stmt', 'while_stmt'):
        return UNSURE

    # Only reachable branches need to be examined further.
    if reachable in (UNREACHABLE, UNSURE):
        return reachable

    if context_scope != flow_scope and context_scope != flow_scope.parent:
        flow_scope = flow_scope.get_parent_scope(include_flows=True)
        return reachable & _break_check(context, context_scope, flow_scope, node)
    else:
        return reachable


def _check_if(context, node):
    types = context.eval_node(node)
    values = set(x.py__bool__() for x in types)
    if len(values) == 1:
        return Status.lookup_table[values.pop()]
    else:
        return UNSURE
