# $Id: references.py 6167 2009-10-11 14:51:42Z grubert $
# Author: David Goodger <goodger@python.org>
# Copyright: This module has been placed in the public domain.

"""
Transforms for resolving references.
"""

__docformat__ = 'reStructuredText'

import sys
import re
from docutils import nodes, utils
from docutils.transforms import TransformError, Transform


class PropagateTargets(Transform):

    """
    Propagate empty internal targets to the next element.

    Given the following nodes::

        <target ids="internal1" names="internal1">
        <target anonymous="1" ids="id1">
        <target ids="internal2" names="internal2">
        <paragraph>
            This is a test.

    PropagateTargets propagates the ids and names of the internal
    targets preceding the paragraph to the paragraph itself::

        <target refid="internal1">
        <target anonymous="1" refid="id1">
        <target refid="internal2">
        <paragraph ids="internal2 id1 internal1" names="internal2 internal1">
            This is a test.
    """

    default_priority = 260

    def apply(self):
        for target in self.document.traverse(nodes.target):
            # Only block-level targets without reference (like ".. target:"):
            if (isinstance(target.parent, nodes.TextElement) or
                (target.hasattr('refid') or target.hasattr('refuri') or
                 target.hasattr('refname'))):
                continue
            assert len(target) == 0, 'error: block-level target has children'
            next_node = target.next_node(ascend=1)
            # Do not move names and ids into Invisibles (we'd lose the
            # attributes) or different Targetables (e.g. footnotes).
            if (next_node is not None and
                ((not isinstance(next_node, nodes.Invisible) and
                  not isinstance(next_node, nodes.Targetable)) or
                 isinstance(next_node, nodes.target))):
                next_node['ids'].extend(target['ids'])
                next_node['names'].extend(target['names'])
                # Set defaults for next_node.expect_referenced_by_name/id.
                if not hasattr(next_node, 'expect_referenced_by_name'):
                    next_node.expect_referenced_by_name = {}
                if not hasattr(next_node, 'expect_referenced_by_id'):
                    next_node.expect_referenced_by_id = {}
                for id in target['ids']:
                    # Update IDs to node mapping.
                    self.document.ids[id] = next_node
                    # If next_node is referenced by id ``id``, this
                    # target shall be marked as referenced.
                    next_node.expect_referenced_by_id[id] = target
                for name in target['names']:
                    next_node.expect_referenced_by_name[name] = target
                # If there are any expect_referenced_by_... attributes
                # in target set, copy them to next_node.
                next_node.expect_referenced_by_name.update(
                    getattr(target, 'expect_referenced_by_name', {}))
                next_node.expect_referenced_by_id.update(
                    getattr(target, 'expect_referenced_by_id', {}))
                # Set refid to point to the first former ID of target
                # which is now an ID of next_node.
                target['refid'] = target['ids'][0]
                # Clear ids and names; they have been moved to
                # next_node.
                target['ids'] = []
                target['names'] = []
                self.document.note_refid(target)


class AnonymousHyperlinks(Transform):

    """
    Link anonymous references to targets.  Given::

        <paragraph>
            <reference anonymous="1">
                internal
            <reference anonymous="1">
                external
        <target anonymous="1" ids="id1">
        <target anonymous="1" ids="id2" refuri="http://external">

    Corresponding references are linked via "refid" or resolved via "refuri"::

        <paragraph>
            <reference anonymous="1" refid="id1">
                text
            <reference anonymous="1" refuri="http://external">
                external
        <target anonymous="1" ids="id1">
        <target anonymous="1" ids="id2" refuri="http://external">
    """

    default_priority = 440

    def apply(self):
        anonymous_refs = []
        anonymous_targets = []
        for node in self.document.traverse(nodes.reference):
            if node.get('anonymous'):
                anonymous_refs.append(node)
        for node in self.document.traverse(nodes.target):
            if node.get('anonymous'):
                anonymous_targets.append(node)
        if len(anonymous_refs) \
              != len(anonymous_targets):
            msg = self.document.reporter.error(
                  'Anonymous hyperlink mismatch: %s references but %s '
                  'targets.\nSee "backrefs" attribute for IDs.'
                  % (len(anonymous_refs), len(anonymous_targets)))
            msgid = self.document.set_id(msg)
            for ref in anonymous_refs:
                prb = nodes.problematic(
                      ref.rawsource, ref.rawsource, refid=msgid)
                prbid = self.document.set_id(prb)
                msg.add_backref(prbid)
                ref.replace_self(prb)
            return
        for ref, target in zip(anonymous_refs, anonymous_targets):
            target.referenced = 1
            while 1:
                if target.hasattr('refuri'):
                    ref['refuri'] = target['refuri']
                    ref.resolved = 1
                    break
                else:
                    if not target['ids']:
                        # Propagated target.
                        target = self.document.ids[target['refid']]
                        continue
                    ref['refid'] = target['ids'][0]
                    self.document.note_refid(ref)
                    break


class IndirectHyperlinks(Transform):

    """
    a) Indirect external references::

           <paragraph>
               <reference refname="indirect external">
                   indirect external
           <target id="id1" name="direct external"
               refuri="http://indirect">
           <target id="id2" name="indirect external"
               refname="direct external">

       The "refuri" attribute is migrated back to all indirect targets
       from the final direct target (i.e. a target not referring to
       another indirect target)::

           <paragraph>
               <reference refname="indirect external">
                   indirect external
           <target id="id1" name="direct external"
               refuri="http://indirect">
           <target id="id2" name="indirect external"
               refuri="http://indirect">

       Once the attribute is migrated, the preexisting "refname" attribute
       is dropped.

    b) Indirect internal references::

           <target id="id1" name="final target">
           <paragraph>
               <reference refname="indirect internal">
                   indirect internal
           <target id="id2" name="indirect internal 2"
               refname="final target">
           <target id="id3" name="indirect internal"
               refname="indirect internal 2">

       Targets which indirectly refer to an internal target become one-hop
       indirect (their "refid" attributes are directly set to the internal
       target's "id"). References which indirectly refer to an internal
       target become direct internal references::

           <target id="id1" name="final target">
           <paragraph>
               <reference refid="id1">
                   indirect internal
           <target id="id2" name="indirect internal 2" refid="id1">
           <target id="id3" name="indirect internal" refid="id1">
    """

    default_priority = 460

    def apply(self):
        for target in self.document.indirect_targets:
            if not target.resolved:
                self.resolve_indirect_target(target)
            self.resolve_indirect_references(target)

    def resolve_indirect_target(self, target):
        refname = target.get('refname')
        if refname is None:
            reftarget_id = target['refid']
        else:
            reftarget_id = self.document.nameids.get(refname)
            if not reftarget_id:
                # Check the unknown_reference_resolvers
                for resolver_function in \
                        self.document.transformer.unknown_reference_resolvers:
                    if resolver_function(target):
                        break
                else:
                    self.nonexistent_indirect_target(target)
                return
        reftarget = self.document.ids[reftarget_id]
        reftarget.note_referenced_by(id=reftarget_id)
        if isinstance(reftarget, nodes.target) \
               and not reftarget.resolved and reftarget.hasattr('refname'):
            if hasattr(target, 'multiply_indirect'):
                #and target.multiply_indirect):
                #del target.multiply_indirect
                self.circular_indirect_reference(target)
                return
            target.multiply_indirect = 1
            self.resolve_indirect_target(reftarget) # multiply indirect
            del target.multiply_indirect
        if reftarget.hasattr('refuri'):
            target['refuri'] = reftarget['refuri']
            if 'refid' in target:
                del target['refid']
        elif reftarget.hasattr('refid'):
            target['refid'] = reftarget['refid']
            self.document.note_refid(target)
        else:
            if reftarget['ids']:
                target['refid'] = reftarget_id
                self.document.note_refid(target)
            else:
                self.nonexistent_indirect_target(target)
                return
        if refname is not None:
            del target['refname']
        target.resolved = 1

    def nonexistent_indirect_target(self, target):
        if target['refname'] in self.document.nameids:
            self.indirect_target_error(target, 'which is a duplicate, and '
                                       'cannot be used as a unique reference')
        else:
            self.indirect_target_error(target, 'which does not exist')

    def circular_indirect_reference(self, target):
        self.indirect_target_error(target, 'forming a circular reference')

    def indirect_target_error(self, target, explanation):
        naming = ''
        reflist = []
        if target['names']:
            naming = '"%s" ' % target['names'][0]
        for name in target['names']:
            reflist.extend(self.document.refnames.get(name, []))
        for id in target['ids']:
            reflist.extend(self.document.refids.get(id, []))
        naming += '(id="%s")' % target['ids'][0]
        msg = self.document.reporter.error(
              'Indirect hyperlink target %s refers to target "%s", %s.'
              % (naming, target['refname'], explanation), base_node=target)
        msgid = self.document.set_id(msg)
        for ref in utils.uniq(reflist):
            prb = nodes.problematic(
                  ref.rawsource, ref.rawsource, refid=msgid)
            prbid = self.document.set_id(prb)
            msg.add_backref(prbid)
            ref.replace_self(prb)
        target.resolved = 1

    def resolve_indirect_references(self, target):
        if target.hasattr('refid'):
            attname = 'refid'
            call_method = self.document.note_refid
        elif target.hasattr('refuri'):
            attname = 'refuri'
            call_method = None
        else:
            return
        attval = target[attname]
        for name in target['names']:
            reflist = self.document.refnames.get(name, [])
            if reflist:
                target.note_referenced_by(name=name)
            for ref in reflist:
                if ref.resolved:
                    continue
                del ref['refname']
                ref[attname] = attval
                if call_method:
                    call_method(ref)
                ref.resolved = 1
                if isinstance(ref, nodes.target):
                    self.resolve_indirect_references(ref)
        for id in target['ids']:
            reflist = self.document.refids.get(id, [])
            if reflist:
                target.note_referenced_by(id=id)
            for ref in reflist:
                if ref.resolved:
                    continue
                del ref['refid']
                ref[attname] = attval
                if call_method:
                    call_method(ref)
                ref.resolved = 1
                if isinstance(ref, nodes.target):
                    self.resolve_indirect_references(ref)


class ExternalTargets(Transform):

    """
    Given::

        <paragraph>
            <reference refname="direct external">
                direct external
        <target id="id1" name="direct external" refuri="http://direct">

    The "refname" attribute is replaced by the direct "refuri" attribute::

        <paragraph>
            <reference refuri="http://direct">
                direct external
        <target id="id1" name="direct external" refuri="http://direct">
    """

    default_priority = 640

    def apply(self):
        for target in self.document.traverse(nodes.target):
            if target.hasattr('refuri'):
                refuri = target['refuri']
                for name in target['names']:
                    reflist = self.document.refnames.get(name, [])
                    if reflist:
                        target.note_referenced_by(name=name)
                    for ref in reflist:
                        if ref.resolved:
                            continue
                        del ref['refname']
                        ref['refuri'] = refuri
                        ref.resolved = 1


class InternalTargets(Transform):

    default_priority = 660

    def apply(self):
        for target in self.document.traverse(nodes.target):
            if not target.hasattr('refuri') and not target.hasattr('refid'):
                self.resolve_reference_ids(target)

    def resolve_reference_ids(self, target):
        """
        Given::

            <paragraph>
                <reference refname="direct internal">
                    direct internal
            <target id="id1" name="direct internal">

        The "refname" attribute is replaced by "refid" linking to the target's
        "id"::

            <paragraph>
                <reference refid="id1">
                    direct internal
            <target id="id1" name="direct internal">
        """
        for name in target['names']:
            refid = self.document.nameids[name]
            reflist = self.document.refnames.get(name, [])
            if reflist:
                target.note_referenced_by(name=name)
            for ref in reflist:
                if ref.resolved:
                    continue
                del ref['refname']
                ref['refid'] = refid
                ref.resolved = 1


class Footnotes(Transform):

    """
    Assign numbers to autonumbered footnotes, and resolve links to footnotes,
    citations, and their references.

    Given the following ``document`` as input::

        <document>
            <paragraph>
                A labeled autonumbered footnote referece:
                <footnote_reference auto="1" id="id1" refname="footnote">
            <paragraph>
                An unlabeled autonumbered footnote referece:
                <footnote_reference auto="1" id="id2">
            <footnote auto="1" id="id3">
                <paragraph>
                    Unlabeled autonumbered footnote.
            <footnote auto="1" id="footnote" name="footnote">
                <paragraph>
                    Labeled autonumbered footnote.

    Auto-numbered footnotes have attribute ``auto="1"`` and no label.
    Auto-numbered footnote_references have no reference text (they're
    empty elements). When resolving the numbering, a ``label`` element
    is added to the beginning of the ``footnote``, and reference text
    to the ``footnote_reference``.

    The transformed result will be::

        <document>
            <paragraph>
                A labeled autonumbered footnote referece:
                <footnote_reference auto="1" id="id1" refid="footnote">
                    2
            <paragraph>
                An unlabeled autonumbered footnote referece:
                <footnote_reference auto="1" id="id2" refid="id3">
                    1
            <footnote auto="1" id="id3" backrefs="id2">
                <label>
                    1
                <paragraph>
                    Unlabeled autonumbered footnote.
            <footnote auto="1" id="footnote" name="footnote" backrefs="id1">
                <label>
                    2
                <paragraph>
                    Labeled autonumbered footnote.

    Note that the footnotes are not in the same order as the references.

    The labels and reference text are added to the auto-numbered ``footnote``
    and ``footnote_reference`` elements.  Footnote elements are backlinked to
    their references via "refids" attributes.  References are assigned "id"
    and "refid" attributes.

    After adding labels and reference text, the "auto" attributes can be
    ignored.
    """

    default_priority = 620

    autofootnote_labels = None
    """Keep track of unlabeled autonumbered footnotes."""

    symbols = [
          # Entries 1-4 and 6 below are from section 12.51 of
          # The Chicago Manual of Style, 14th edition.
          '*',                          # asterisk/star
          u'\u2020',                    # dagger &dagger;
          u'\u2021',                    # double dagger &Dagger;
          u'\u00A7',                    # section mark &sect;
          u'\u00B6',                    # paragraph mark (pilcrow) &para;
                                        # (parallels ['||'] in CMoS)
          '#',                          # number sign
          # The entries below were chosen arbitrarily.
          u'\u2660',                    # spade suit &spades;
          u'\u2665',                    # heart suit &hearts;
          u'\u2666',                    # diamond suit &diams;
          u'\u2663',                    # club suit &clubs;
          ]

    def apply(self):
        self.autofootnote_labels = []
        startnum = self.document.autofootnote_start
        self.document.autofootnote_start = self.number_footnotes(startnum)
        self.number_footnote_references(startnum)
        self.symbolize_footnotes()
        self.resolve_footnotes_and_citations()

    def number_footnotes(self, startnum):
        """
        Assign numbers to autonumbered footnotes.

        For labeled autonumbered footnotes, copy the number over to
        corresponding footnote references.
        """
        for footnote in self.document.autofootnotes:
            while 1:
                label = str(startnum)
                startnum += 1
                if label not in self.document.nameids:
                    break
            footnote.insert(0, nodes.label('', label))
            for name in footnote['names']:
                for ref in self.document.footnote_refs.get(name, []):
                    ref += nodes.Text(label)
                    ref.delattr('refname')
                    assert len(footnote['ids']) == len(ref['ids']) == 1
                    ref['refid'] = footnote['ids'][0]
                    footnote.add_backref(ref['ids'][0])
                    self.document.note_refid(ref)
                    ref.resolved = 1
            if not footnote['names'] and not footnote['dupnames']:
                footnote['names'].append(label)
                self.document.note_explicit_target(footnote, footnote)
                self.autofootnote_labels.append(label)
        return startnum

    def number_footnote_references(self, startnum):
        """Assign numbers to autonumbered footnote references."""
        i = 0
        for ref in self.document.autofootnote_refs:
            if ref.resolved or ref.hasattr('refid'):
                continue
            try:
                label = self.autofootnote_labels[i]
            except IndexError:
                msg = self.document.reporter.error(
                      'Too many autonumbered footnote references: only %s '
                      'corresponding footnotes available.'
                      % len(self.autofootnote_labels), base_node=ref)
                msgid = self.document.set_id(msg)
                for ref in self.document.autofootnote_refs[i:]:
                    if ref.resolved or ref.hasattr('refname'):
                        continue
                    prb = nodes.problematic(
                          ref.rawsource, ref.rawsource, refid=msgid)
                    prbid = self.document.set_id(prb)
                    msg.add_backref(prbid)
                    ref.replace_self(prb)
                break
            ref += nodes.Text(label)
            id = self.document.nameids[label]
            footnote = self.document.ids[id]
            ref['refid'] = id
            self.document.note_refid(ref)
            assert len(ref['ids']) == 1
            footnote.add_backref(ref['ids'][0])
            ref.resolved = 1
            i += 1

    def symbolize_footnotes(self):
        """Add symbols indexes to "[*]"-style footnotes and references."""
        labels = []
        for footnote in self.document.symbol_footnotes:
            reps, index = divmod(self.document.symbol_footnote_start,
                                 len(self.symbols))
            labeltext = self.symbols[index] * (reps + 1)
            labels.append(labeltext)
            footnote.insert(0, nodes.label('', labeltext))
            self.document.symbol_footnote_start += 1
            self.document.set_id(footnote)
        i = 0
        for ref in self.document.symbol_footnote_refs:
            try:
                ref += nodes.Text(labels[i])
            except IndexError:
                msg = self.document.reporter.error(
                      'Too many symbol footnote references: only %s '
                      'corresponding footnotes available.' % len(labels),
                      base_node=ref)
                msgid = self.document.set_id(msg)
                for ref in self.document.symbol_footnote_refs[i:]:
                    if ref.resolved or ref.hasattr('refid'):
                        continue
                    prb = nodes.problematic(
                          ref.rawsource, ref.rawsource, refid=msgid)
                    prbid = self.document.set_id(prb)
                    msg.add_backref(prbid)
                    ref.replace_self(prb)
                break
            footnote = self.document.symbol_footnotes[i]
            assert len(footnote['ids']) == 1
            ref['refid'] = footnote['ids'][0]
            self.document.note_refid(ref)
            footnote.add_backref(ref['ids'][0])
            i += 1

    def resolve_footnotes_and_citations(self):
        """
        Link manually-labeled footnotes and citations to/from their
        references.
        """
        for footnote in self.document.footnotes:
            for label in footnote['names']:
                if label in self.document.footnote_refs:
                    reflist = self.document.footnote_refs[label]
                    self.resolve_references(footnote, reflist)
        for citation in self.document.citations:
            for label in citation['names']:
                if label in self.document.citation_refs:
                    reflist = self.document.citation_refs[label]
                    self.resolve_references(citation, reflist)

    def resolve_references(self, note, reflist):
        assert len(note['ids']) == 1
        id = note['ids'][0]
        for ref in reflist:
            if ref.resolved:
                continue
            ref.delattr('refname')
            ref['refid'] = id
            assert len(ref['ids']) == 1
            note.add_backref(ref['ids'][0])
            ref.resolved = 1
        note.resolved = 1


class CircularSubstitutionDefinitionError(Exception): pass


class Substitutions(Transform):

    """
    Given the following ``document`` as input::

        <document>
            <paragraph>
                The
                <substitution_reference refname="biohazard">
                    biohazard
                 symbol is deservedly scary-looking.
            <substitution_definition name="biohazard">
                <image alt="biohazard" uri="biohazard.png">

    The ``substitution_reference`` will simply be replaced by the
    contents of the corresponding ``substitution_definition``.

    The transformed result will be::

        <document>
            <paragraph>
                The
                <image alt="biohazard" uri="biohazard.png">
                 symbol is deservedly scary-looking.
            <substitution_definition name="biohazard">
                <image alt="biohazard" uri="biohazard.png">
    """

    default_priority = 220
    """The Substitutions transform has to be applied very early, before
    `docutils.tranforms.frontmatter.DocTitle` and others."""

    def apply(self):
        defs = self.document.substitution_defs
        normed = self.document.substitution_names
        subreflist = self.document.traverse(nodes.substitution_reference)
        nested = {}
        for ref in subreflist:
            refname = ref['refname']
            key = None
            if refname in defs:
                key = refname
            else:
                normed_name = refname.lower()
                if normed_name in normed:
                    key = normed[normed_name]
            if key is None:
                msg = self.document.reporter.error(
                      'Undefined substitution referenced: "%s".'
                      % refname, base_node=ref)
                msgid = self.document.set_id(msg)
                prb = nodes.problematic(
                      ref.rawsource, ref.rawsource, refid=msgid)
                prbid = self.document.set_id(prb)
                msg.add_backref(prbid)
                ref.replace_self(prb)
            else:
                subdef = defs[key]
                parent = ref.parent
                index = parent.index(ref)
                if  ('ltrim' in subdef.attributes
                     or 'trim' in subdef.attributes):
                    if index > 0 and isinstance(parent[index - 1],
                                                nodes.Text):
                        parent.replace(parent[index - 1],
                                       parent[index - 1].rstrip())
                if  ('rtrim' in subdef.attributes
                     or 'trim' in subdef.attributes):
                    if  (len(parent) > index + 1
                         and isinstance(parent[index + 1], nodes.Text)):
                        parent.replace(parent[index + 1],
                                       parent[index + 1].lstrip())
                subdef_copy = subdef.deepcopy()
                try:
                    # Take care of nested substitution references:
                    for nested_ref in subdef_copy.traverse(
                          nodes.substitution_reference):
                        nested_name = normed[nested_ref['refname'].lower()]
                        if nested_name in nested.setdefault(nested_name, []):
                            raise CircularSubstitutionDefinitionError
                        else:
                            nested[nested_name].append(key)
                            subreflist.append(nested_ref)
                except CircularSubstitutionDefinitionError:
                    parent = ref.parent
                    if isinstance(parent, nodes.substitution_definition):
                        msg = self.document.reporter.error(
                            'Circular substitution definition detected:',
                            nodes.literal_block(parent.rawsource,
                                                parent.rawsource),
                            line=parent.line, base_node=parent)
                        parent.replace_self(msg)
                    else:
                        msg = self.document.reporter.error(
                            'Circular substitution definition referenced: "%s".'
                            % refname, base_node=ref)
                        msgid = self.document.set_id(msg)
                        prb = nodes.problematic(
                            ref.rawsource, ref.rawsource, refid=msgid)
                        prbid = self.document.set_id(prb)
                        msg.add_backref(prbid)
                        ref.replace_self(prb)
                else:
                    ref.replace_self(subdef_copy.children)
                    # register refname of the replacment node(s)
                    # (needed for resolution of references)
                    for node in subdef_copy.children:
                        if isinstance(node, nodes.Referential):
                            # HACK: verify refname attribute exists.
                            # Test with docs/dev/todo.txt, see. |donate|
                            if 'refname' in node:
                                self.document.note_refname(node)


class TargetNotes(Transform):

    """
    Creates a footnote for each external target in the text, and corresponding
    footnote references after each reference.
    """

    default_priority = 540
    """The TargetNotes transform has to be applied after `IndirectHyperlinks`
    but before `Footnotes`."""


    def __init__(self, document, startnode):
        Transform.__init__(self, document, startnode=startnode)

        self.classes = startnode.details.get('class', [])

    def apply(self):
        notes = {}
        nodelist = []
        for target in self.document.traverse(nodes.target):
            # Only external targets.
            if not target.hasattr('refuri'):
                continue
            names = target['names']
            refs = []
            for name in names:
                refs.extend(self.document.refnames.get(name, []))
            if not refs:
                continue
            footnote = self.make_target_footnote(target['refuri'], refs,
                                                 notes)
            if target['refuri'] not in notes:
                notes[target['refuri']] = footnote
                nodelist.append(footnote)
        # Take care of anonymous references.
        for ref in self.document.traverse(nodes.reference):
            if not ref.get('anonymous'):
                continue
            if ref.hasattr('refuri'):
                footnote = self.make_target_footnote(ref['refuri'], [ref],
                                                     notes)
                if ref['refuri'] not in notes:
                    notes[ref['refuri']] = footnote
                    nodelist.append(footnote)
        self.startnode.replace_self(nodelist)

    def make_target_footnote(self, refuri, refs, notes):
        if refuri in notes:  # duplicate?
            footnote = notes[refuri]
            assert len(footnote['names']) == 1
            footnote_name = footnote['names'][0]
        else:                           # original
            footnote = nodes.footnote()
            footnote_id = self.document.set_id(footnote)
            # Use uppercase letters and a colon; they can't be
            # produced inside names by the parser.
            footnote_name = 'TARGET_NOTE: ' + footnote_id
            footnote['auto'] = 1
            footnote['names'] = [footnote_name]
            footnote_paragraph = nodes.paragraph()
            footnote_paragraph += nodes.reference('', refuri, refuri=refuri)
            footnote += footnote_paragraph
            self.document.note_autofootnote(footnote)
            self.document.note_explicit_target(footnote, footnote)
        for ref in refs:
            if isinstance(ref, nodes.target):
                continue
            refnode = nodes.footnote_reference(
                refname=footnote_name, auto=1)
            refnode['classes'] += self.classes
            self.document.note_autofootnote_ref(refnode)
            self.document.note_footnote_ref(refnode)
            index = ref.parent.index(ref) + 1
            reflist = [refnode]
            if not utils.get_trim_footnote_ref_space(self.document.settings):
                if self.classes:
                    reflist.insert(0, nodes.inline(text=' ', Classes=self.classes))
                else:
                    reflist.insert(0, nodes.Text(' '))
            ref.parent.insert(index, reflist)
        return footnote


class DanglingReferences(Transform):

    """
    Check for dangling references (incl. footnote & citation) and for
    unreferenced targets.
    """

    default_priority = 850

    def apply(self):
        visitor = DanglingReferencesVisitor(
            self.document,
            self.document.transformer.unknown_reference_resolvers)
        self.document.walk(visitor)
        # *After* resolving all references, check for unreferenced
        # targets:
        for target in self.document.traverse(nodes.target):
            if not target.referenced:
                if target.get('anonymous'):
                    # If we have unreferenced anonymous targets, there
                    # is already an error message about anonymous
                    # hyperlink mismatch; no need to generate another
                    # message.
                    continue
                if target['names']:
                    naming = target['names'][0]
                elif target['ids']:
                    naming = target['ids'][0]
                else:
                    # Hack: Propagated targets always have their refid
                    # attribute set.
                    naming = target['refid']
                self.document.reporter.info(
                    'Hyperlink target "%s" is not referenced.'
                    % naming, base_node=target)


class DanglingReferencesVisitor(nodes.SparseNodeVisitor):
    
    def __init__(self, document, unknown_reference_resolvers):
        nodes.SparseNodeVisitor.__init__(self, document)
        self.document = document
        self.unknown_reference_resolvers = unknown_reference_resolvers

    def unknown_visit(self, node):
        pass

    def visit_reference(self, node):
        if node.resolved or not node.hasattr('refname'):
            return
        refname = node['refname']
        id = self.document.nameids.get(refname)
        if id is None:
            for resolver_function in self.unknown_reference_resolvers:
                if resolver_function(node):
                    break
            else:
                if refname in self.document.nameids:
                    msg = self.document.reporter.error(
                        'Duplicate target name, cannot be used as a unique '
                        'reference: "%s".' % (node['refname']), base_node=node)
                else:
                    msg = self.document.reporter.error(
                        'Unknown target name: "%s".' % (node['refname']),
                        base_node=node)
                msgid = self.document.set_id(msg)
                prb = nodes.problematic(
                      node.rawsource, node.rawsource, refid=msgid)
                prbid = self.document.set_id(prb)
                msg.add_backref(prbid)
                node.replace_self(prb)
        else:
            del node['refname']
            node['refid'] = id
            self.document.ids[id].note_referenced_by(id=id)
            node.resolved = 1

    visit_footnote_reference = visit_citation_reference = visit_reference
