# imports
import os
import typing

# bsfs imports
from bsfs.query import ast, validate
from bsfs import schema as bsc
from bsfs.triple_store import TripleStoreBase
from bsfs.utils import URI, typename

# inner-module imports
from . import ac
from . import nodes as _nodes
from . import resolve

# exports
__all__: typing.Sequence[str] = (
    'Graph',
    )


## code ##

class Graph():
    """The Graph class provides a convenient interface to query and access a graph.
    Since it logically builds on the concept of graphs it is easier to
    navigate than raw triple stores. Naturally, it uses a triple store
    as *backend*. It also controls actions via access permissions to a *user*.

    """

    # link to the triple storage backend.
    _backend: TripleStoreBase

    # access controls.
    _ac: ac.AccessControlBase

    def __init__(
            self,
            backend: TripleStoreBase,
            access_control: ac.AccessControlBase,
            ):
        # store members
        self._backend = backend
        self._ac = access_control
        # ensure Graph schema requirements
        self.migrate(self._backend.schema)

    def __hash__(self) -> int:
        return hash((type(self), self._backend, self._ac))

    def __eq__(self, other) -> bool:
        return isinstance(other, type(self)) \
           and self._backend == other._backend \
           and self._ac == other._ac

    def __repr__(self) -> str:
        return f'{typename(self)}({repr(self._backend)}, {self._ac})'

    def __str__(self) -> str:
        return f'{typename(self)}({str(self._backend)})'

    @property
    def schema(self) -> bsc.Schema:
        """Return the store's local schema."""
        return self._backend.schema

    def migrate(self, schema: bsc.Schema, append: bool = True) -> 'Graph':
        """Migrate the current schema to a new *schema*.

        Appends to the current schema by default; control this via *append*.
        The `Graph` may add additional classes to the schema that are required for its interals.

        """
        # check args
        if not isinstance(schema, bsc.Schema):
            raise TypeError(schema)
        # append to current schema
        if append:
            schema = schema + self._backend.schema
        # add Graph schema requirements
        with open(os.path.join(os.path.dirname(__file__), 'schema.nt'), mode='rt', encoding='UTF-8') as ifile:
            schema = schema + bsc.from_string(ifile.read())
        # migrate schema in backend
        # FIXME: consult access controls!
        self._backend.schema = schema
        # return self
        return self

    def nodes(self, node_type: URI, guids: typing.Iterable[URI]) -> _nodes.Nodes:
        """Return nodes *guids* of type *node_type* as a `bsfs.graph.Nodes` instance.

        Note that the *guids* need not to exist (however, the *node_type* has
        to be part of the schema). Inexistent guids will be created (using
        *node_type*) once some data is assigned to them.

        """
        # get node type
        type_ = self.schema.node(node_type)
        # NOTE: Nodes constructor materializes guids.
        return _nodes.Nodes(self._backend, self._ac, type_, guids)

    def node(self, node_type: URI, guid: URI) -> _nodes.Nodes:
        """Return node *guid* of type *node_type* as a `bsfs.graph.Nodes` instance.

        Note that the *guid* need not to exist (however, the *node_type* has
        to be part of the schema). An inexistent guid will be created (using
        *node_type*) once some data is assigned to them.

        """
        return self.nodes(node_type, {guid})

    def empty(self, node_type: URI) -> _nodes.Nodes:
        """Return a `Nodes` instance with type *node_type* but no nodes."""
        return self.nodes(node_type, set())

    def get(
            self,
            node_type: URI,
            query: typing.Optional[ast.filter.FilterExpression],
            ) -> _nodes.Nodes:
        """Return a `Nodes` instance over all nodes of type *node_type* that match the *query*."""
        # return Nodes instance
        type_ = self.schema.node(node_type)
        return _nodes.Nodes(self._backend, self._ac, type_, self.__get(node_type, query))

    def sorted(
            self,
            node_type: URI,
            query: typing.Optional[ast.filter.FilterExpression],
            # FIXME: sort ast
            ) -> typing.Iterator[_nodes.Nodes]:
        """Return a iterator over `Nodes` instances over all nodes of type *node_type* that match the *query*."""
        # FIXME: Order should be a parameter
        # return iterator over Nodes instances
        type_ = self.schema.node(node_type)
        for guid in self.__get(node_type, query):
            yield _nodes.Nodes(self._backend, self._ac, type_, {guid})

    def all(self, node_type: URI) -> _nodes.Nodes:
        """Return all instances of type *node_type*."""
        type_ = self.schema.node(node_type)
        return _nodes.Nodes(self._backend, self._ac, type_, self.__get(node_type, None))

    def __get(
            self,
            node_type: URI,
            query: typing.Optional[ast.filter.FilterExpression],
            ) -> typing.Iterator[URI]:
        """Build and execute a get query."""
        # get node type
        type_ = self.schema.node(node_type)
        # resolve Nodes instances
        query = resolve.Filter(self._backend.schema).resolve(type_, query)
        # add access controls to query
        query = self._ac.filter_read(type_, query)
        # validate query
        if query is not None:
            validate.Filter(self._backend.schema).validate(type_, query)
        # query the backend and return the (non-materialized) result
        return self._backend.get(type_, query)

## EOF ##