#!/usr/bin/python

"""A FOAF checker that takes a URI of a signed FOAF file, confirms the
signature, and returns the name, email address, other selected
properties of the foaf:Person in that instance with an rdf:seeAlso
that matches the URI.

Repeat: the FOAF instance must have a
  <rdf:seeAlso rdf:resource="" />
or equivalent in the foaf:Person that this URI describes.

PGP Signing FOAF Files
  http://usefulinc.com/foaf/signingFoafFiles

FoafCheck requires GnuPG.

See also:
  http://www.sixapart.com/log/2003/01/fun_with_foaf.shtml
"""

import os, rdfxml, sys, urllib

RDF = rdfxml.Namespace('http://www.w3.org/1999/02/22-rdf-syntax-ns#')
FOAF = rdfxml.Namespace('http://xmlns.com/foaf/0.1/')
WOT = rdfxml.Namespace('http://xmlns.com/wot/0.1/')

class World(object): 
   def __init__(self): self.subjects = {}
   def triple(self, s, p, o):
       if s[0] == '<': s = s[1:-1]
       if p[0] == '<': p = p[1:-1]
       if o[0] == '<': o = o[1:-1]
       if o[0] == '"': o = o[1:-1]
       if not self.subjects.has_key(s):
           self.subjects[s] = { RDF.about: [ s ] }
       if not self.subjects[s].has_key(p):
           self.subjects[s][p] = []
       self.subjects[s][p].append(o)

class FoafCheckError(Exception): pass

def check_uri(uri):
    try:
        foaf_instance = urllib.urlopen(uri).read()
    except OSError:
        raise FoafCheckError("Could not read FOAF instance '%s'" % uri)
    foaf = World()
    rdfxml.parseRDF(foaf_instance, uri, foaf)

    if not foaf.subjects.has_key(uri):
        raise FoafCheckError('FOAF instance missing resource for "this" URI')
    if not foaf.subjects[uri].has_key(WOT.assurance):
        raise FoafCheckError('FOAF instance missing wot:assurance in resource for "this" URI')
    foaf_signature_uri = foaf.subjects[uri][WOT.assurance][0]
    try:
        foaf_signature = urllib.urlopen(foaf_signature_uri).read()
    except OSError:
        raise FoafCheckError("Could not read FOAF signature '%s'" % foaf_signature_uri)
    open('/tmp/foaf-check-temp-file.rdf', 'w').write(foaf_instance)
    open('/tmp/foaf-check-temp-file.rdf.asc', 'w').write(foaf_signature)
    result = os.system('''/usr/bin/gpg --no-options --homedir=/tmp --verify \
                            /tmp/foaf-check-temp-file.rdf.asc /tmp/foaf-check-temp-file.rdf \
                            >/tmp/foaf-check-temp-file.log 2>&1''')
    if result != 0:
        print open('/tmp/foaf-check-temp-file.log').read()
        raise FoafCheckError('FOAF signature does not verify')

    found = 0
    for node in foaf.subjects.values():
        if node.has_key(RDF.seeAlso):
            if node[RDF.seeAlso][0] == uri:
                found = 1
                break

    if not found:
        raise FoafCheckError('No foaf:Person found in FOAF instance')

    return node

if __name__ == "__main__":
   if len(sys.argv) != 2:
       print __doc__
       sys.exit(1)

   try:
       node = check_uri(sys.argv[1])
   except FoafCheckError:
       print sys.exc_info()[1]
       sys.exit(1)

   for ii in "name firstName surname nick mbox homepage depiction".split():
       if node.has_key(FOAF + ii):
           print "%s: %s" % (ii, node[FOAF + ii][0])