# Source code for rdflib.plugins.sparql.sparql

    import collections
    import itertools
    import datetime

    import isodate

    from rdflib.compat import Mapping, MutableMapping
    from rdflib.namespace import NamespaceManager
    from rdflib import Variable, BNode, Graph, ConjunctiveGraph, URIRef, Literal
    from rdflib.term import Node

    from rdflib.plugins.sparql.parserutils import CompValue

    import rdflib.plugins.sparql

    class SPARQLError(Exception):

        def __init__(self, msg=None):
            Exception.__init__(self, msg)

    class NotBoundError(SPARQLError):

        def __init__(self, msg=None):
            SPARQLError.__init__(self, msg)

    class AlreadyBound(SPARQLError):
        """Raised when trying to bind a variable that is already bound!"""

        def __init__(self):
            SPARQLError.__init__(self)

    class SPARQLTypeError(SPARQLError):

        def __init__(self, msg):
            SPARQLError.__init__(self, msg)

    class Bindings(MutableMapping):

        """

        A single level of a stack of variable-value bindings.
        Each dict keeps a reference to the dict below it,
        any failed lookup is propegated back

        In python 3.3 this could be a collections.ChainMap
        """

        def __init__(self, outer=None, d=[]):
            self._d = dict(d)
            self.outer = outer

        def __getitem__(self, key):
            if key in self._d:
                return self._d[key]

            if not self.outer:
                raise KeyError()
            return self.outer[key]

        def __contains__(self, key):
            try:
                self[key]
                return True
            except KeyError:
                return False

        def __setitem__(self, key, value):
            self._d[key] = value

        def __delitem__(self, key):
            raise Exception("DelItem is not implemented!")

        def __len__(self) -> int:
            i = 0
            d = self
            while d is not None:
                i += len(d._d)
                d = d.outer
            return i  # type: ignore[unreachable]

        def __iter__(self):
            d = self
            while d is not None:
                yield from d._d
                d = d.outer

        def __str__(self):
            return "Bindings({" + ", ".join((k, self[k]) for k in self) + "})"

        def __repr__(self):
            return str(self)

    class FrozenDict(Mapping):
        """
        An immutable hashable dict

        Taken from http://stackoverflow.com/a/2704866/81121

        """

        def __init__(self, *args, **kwargs):
            self._d = dict(*args, **kwargs)
            self._hash = None

        def __iter__(self):
            return iter(self._d)

        def __len__(self):
            return len(self._d)

        def __getitem__(self, key):
            return self._d[key]

        def __hash__(self):
            # It would have been simpler and maybe more obvious to
            # use hash(tuple(sorted(self._d.items()))) from this discussion
            # so far, but this solution is O(n). I don't know what kind of
            # n we are going to run into, but sometimes it's hard to resist the
            # urge to optimize when it will gain improved algorithmic performance.
            if self._hash is None:
                self._hash = 0
                for key, value in self.items():
                    self._hash ^= hash(key)
                    self._hash ^= hash(value)
            return self._hash

        def project(self, vars):
            return FrozenDict((x for x in self.items() if x[0] in vars))

        def disjointDomain(self, other):
            return not bool(set(self).intersection(other))

        def compatible(self, other):
            for k in self:
                try:
                    if self[k] != other[k]:
                        return False
                except KeyError:
                    pass

            return True

        def merge(self, other):
            res = FrozenDict(itertools.chain(self.items(), other.items()))

            return res

        def __str__(self):
            return str(self._d)

        def __repr__(self):
            return repr(self._d)

    class FrozenBindings(FrozenDict):

        def __init__(self, ctx, *args, **kwargs):
            FrozenDict.__init__(self, *args, **kwargs)
            self.ctx = ctx

        def __getitem__(self, key):

            if not isinstance(key, Node):
                key = Variable(key)

            if not isinstance(key, (BNode, Variable)):
                return key

            if key not in self._d:
                return self.ctx.initBindings[key]
            else:
                return self._d[key]

        def project(self, vars):
            return FrozenBindings(self.ctx, (x for x in self.items() if x[0] in vars))

        def merge(self, other):
            res = FrozenBindings(self.ctx, itertools.chain(self.items(), other.items()))
            return res

        @property
        def now(self):
            return self.ctx.now

        @property
        def bnodes(self):
            return self.ctx.bnodes

        @property
        def prologue(self):
            return self.ctx.prologue

        def forget(self, before, _except=None):
            """
            return a frozen dict only of bindings made in self
            since before
            """
            if not _except:
                _except = []

            # bindings from initBindings are newer forgotten
            return FrozenBindings(
                self.ctx,
                (
                    x
                    for x in self.items()
                    if (
                        x[0] in _except
                        or x[0] in self.ctx.initBindings
                        or before[x[0]] is None
                    )
                ),
            )

        def remember(self, these):
            """
            return a frozen dict only of bindings in these
            """
            return FrozenBindings(self.ctx, (x for x in self.items() if x[0] in these))

    class QueryContext(object):
        """
        Query context - passed along when evaluating the query
        """

        def __init__(self, graph=None, bindings=None, initBindings=None):
            self.initBindings = initBindings
            self.bindings = Bindings(d=bindings or [])
            if initBindings:
                self.bindings.update(initBindings)

            if isinstance(graph, ConjunctiveGraph):
                self._dataset = graph
                if rdflib.plugins.sparql.SPARQL_DEFAULT_GRAPH_UNION:
                    self.graph = self.dataset
                else:
                    self.graph = self.dataset.default_context
            else:
                self._dataset = None
                self.graph = graph

            self.prologue = None
            self._now = None

            self.bnodes = collections.defaultdict(BNode)

        @property
        def now(self) -> datetime.datetime:
            if self._now is None:
                self._now = datetime.datetime.now(isodate.tzinfo.UTC)
            return self._now

        def clone(self, bindings=None):
            r = QueryContext(
                self._dataset if self._dataset is not None else self.graph,
                bindings or self.bindings,
                initBindings=self.initBindings,
            )
            r.prologue = self.prologue
            r.graph = self.graph
            r.bnodes = self.bnodes
            return r

        @property
        def dataset(self):
            """ "current dataset"""
            if self._dataset is None:
                raise Exception(
                    "You performed a query operation requiring "
                    + "a dataset (i.e. ConjunctiveGraph), but "
                    + "operating currently on a single graph."
                )
            return self._dataset

        def load(self, source, default=False, **kwargs):
            def _load(graph, source):
                try:
                    return graph.parse(source, format="turtle", **kwargs)
                except Exception:
                    pass
                try:
                    return graph.parse(source, format="xml", **kwargs)
                except Exception:
                    pass
                try:
                    return graph.parse(source, format="n3", **kwargs)
                except Exception:
                    pass
                try:
                    return graph.parse(source, format="nt", **kwargs)
                except Exception:
                    raise Exception(
                        "Could not load %s as either RDF/XML, N3 or NTriples" % source
                    )

            if not rdflib.plugins.sparql.SPARQL_LOAD_GRAPHS:
                # we are not loading - if we already know the graph
                # being "loaded", just add it to the default-graph
                if default:
                    self.graph += self.dataset.get_context(source)
            else:

                if default:
                    _load(self.graph, source)
                else:
                    _load(self.dataset, source)

        def __getitem__(self, key):
            # in SPARQL BNodes are just labels
            if not isinstance(key, (BNode, Variable)):
                return key
            try:
                return self.bindings[key]
            except KeyError:
                return None

        def get(self, key, default=None):
            try:
                return self[key]
            except KeyError:
                return default

        def solution(self, vars=None):
            """
            Return a static copy of the current variable bindings as dict
            """
            if vars:
                return FrozenBindings(
                    self, ((k, v) for k, v in self.bindings.items() if k in vars)
                )
            else:
                return FrozenBindings(self, self.bindings.items())

        def __setitem__(self, key, value):
            if key in self.bindings and self.bindings[key] != value:
                raise AlreadyBound()

            self.bindings[key] = value

        def pushGraph(self, graph):
            r = self.clone()
            r.graph = graph
            return r

        def push(self):
            r = self.clone(Bindings(self.bindings))
            return r

        def clean(self):
            return self.clone([])

        def thaw(self, frozenbindings):
            """
            Create a new read/write query context from the given solution
            """
            c = self.clone(frozenbindings)

            return c

    class Prologue:
        """
        A class for holding prefixing bindings and base URI information
        """

        def __init__(self):
            self.base = None
            self.namespace_manager = NamespaceManager(Graph())  # ns man needs a store

        def resolvePName(self, prefix, localname):
            ns = self.namespace_manager.store.namespace(prefix or "")
            if ns is None:
                raise Exception("Unknown namespace prefix : %s" % prefix)
            return URIRef(ns + (localname or ""))

        def bind(self, prefix, uri):
            self.namespace_manager.bind(prefix, uri, replace=True)

        def absolutize(self, iri):
            """
            Apply BASE / PREFIXes to URIs
            (and to datatypes in Literals)

            TODO: Move resolving URIs to pre-processing
            """

            if isinstance(iri, CompValue):
                if iri.name == "pname":
                    return self.resolvePName(iri.prefix, iri.localname)
                if iri.name == "literal":
                    return Literal(
                        iri.string, lang=iri.lang, datatype=self.absolutize(iri.datatype)
                    )
            elif isinstance(iri, URIRef) and not ":" in iri:
                return URIRef(iri, base=self.base)

            return iri

    class Query:
        """
        A parsed and translated query
        """

        def __init__(self, prologue, algebra):
            self.prologue = prologue
            self.algebra = algebra