"""

Example code for connecting to Stardog (http://stardog.com/) with
Python's RDFLib (http://github.com/rdflib).

See longer description: http://lawlesst.github.io/notebook/rdflib-stardog.html

"""


from rdflib import Graph, Literal, URIRef
from rdflib.namespace import RDF, SKOS
from rdflib.plugins.stores import sparqlstore

#Define the Stardog store
endpoint = 'http://localhost:5820/demo/query'
store = sparqlstore.SPARQLUpdateStore()
store.open((endpoint, endpoint))

#Identify a named graph where we will be adding our instances.
default_graph = URIRef('http://example.org/default-graph')
ng = Graph(store, identifier=default_graph)

#Load our SKOS data from a file into an in-memory graph.
g = Graph()
g.parse('./sample-concepts.ttl', format='turtle')

#Serialize our named graph to make sure we got what we expect.
print g.serialize(format='turtle')


#Issue a SPARQL INSERT update query to add the assertions
#to Stardog.
ng.update(
    u'INSERT DATA { %s }' % g.serialize(format='nt')
)

#Query the data using the RDFLib API.

#All concepts in the Stardog named graph.
for subj in ng.subjects(predicate=RDF.type, object=SKOS.Concept):
    print 'Concept: ', subj

#Find concepts that are broader than others
for ob in ng.objects(predicate=SKOS.broader):
    print 'Broader: ', ob

#Use RDFLib to issue SPARQL read queries.

#Bind a prefixe for SKOS so we can use it in our SPARQL queries
store.bind('skos', SKOS)

rq = """
SELECT ?s ?label
WHERE {
    ?s a skos:Concept ;
       skos:preferredLabel ?label .
}
"""
for s, l in ng.query(rq):
    print s.n3(), l.n3()


#Add a new assertion using the RDFLib API
soccer = URIRef('http://example.org/n1000')
ng.add((soccer, SKOS.altLabel, Literal('Football')))


#Read statements about soccer
for s, p, o in ng.triples((soccer, None, None)):
    print s.n3(), p.n3(), o.n3()