"""

Part of the BlackStar filesystem (bsfs) module.
A copy of the license is provided with the project.
Author: Matthias Baumgartner, 2022
"""
# imports
import os
import typing

# bsfs imports
from bsfs.schema import Schema
from bsfs.triple_store import TripleStoreBase
from bsfs.utils import URI, typename

# inner-module imports
from . import nodes as _nodes

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


## code ##

class Graph():
    """The Graph class is

    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

    # user uri.
    _user: URI

    def __init__(self, backend: TripleStoreBase, user: URI):
        self._backend = backend
        self._user = user
        # ensure Graph schema requirements
        self.migrate(self._backend.schema)

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

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

    def __repr__(self) -> str:
        return f'{typename(self)}(backend={repr(self._backend)}, user={self._user})'

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

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

    def migrate(self, schema: 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, 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 + Schema.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.

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

        """
        type_ = self.schema.node(node_type)
        return _nodes.Nodes(self._backend, self._user, type_, {guid})

## EOF ##