"Misc. utility functions/classes for admin documentation generator."

import re
from email.errors import HeaderParseError
from email.parser import HeaderParser

from django.core.urlresolvers import reverse
from django.utils.encoding import force_bytes
from django.utils.safestring import mark_safe

try:
    import docutils.core
    import docutils.nodes
    import docutils.parsers.rst.roles
except ImportError:
    docutils_is_available = False
else:
    docutils_is_available = True


def trim_docstring(docstring):
    """
    Uniformly trim leading/trailing whitespace from docstrings.

    Based on https://www.python.org/dev/peps/pep-0257/#handling-docstring-indentation
    """
    if not docstring or not docstring.strip():
        return ''
    # Convert tabs to spaces and split into lines
    lines = docstring.expandtabs().splitlines()
    indent = min(len(line) - len(line.lstrip()) for line in lines if line.lstrip())
    trimmed = [lines[0].lstrip()] + [line[indent:].rstrip() for line in lines[1:]]
    return "\n".join(trimmed).strip()


def parse_docstring(docstring):
    """
    Parse out the parts of a docstring.  Return (title, body, metadata).
    """
    docstring = trim_docstring(docstring)
    parts = re.split(r'\n{2,}', docstring)
    title = parts[0]
    if len(parts) == 1:
        body = ''
        metadata = {}
    else:
        parser = HeaderParser()
        try:
            metadata = parser.parsestr(parts[-1])
        except HeaderParseError:
            metadata = {}
            body = "\n\n".join(parts[1:])
        else:
            metadata = dict(metadata.items())
            if metadata:
                body = "\n\n".join(parts[1:-1])
            else:
                body = "\n\n".join(parts[1:])
    return title, body, metadata


def parse_rst(text, default_reference_context, thing_being_parsed=None):
    """
    Convert the string from reST to an XHTML fragment.
    """
    overrides = {
        'doctitle_xform': True,
        'inital_header_level': 3,
        "default_reference_context": default_reference_context,
        "link_base": reverse('django-admindocs-docroot').rstrip('/')
    }
    if thing_being_parsed:
        thing_being_parsed = force_bytes("<%s>" % thing_being_parsed)
    # Wrap ``text`` in some reST that sets the default role to ``cmsreference``,
    # then restores it.
    source = """
.. default-role:: cmsreference

%s

.. default-role::
"""
    parts = docutils.core.publish_parts(source % text,
                source_path=thing_being_parsed, destination_path=None,
                writer_name='html', settings_overrides=overrides)
    return mark_safe(parts['fragment'])

#
# reST roles
#
ROLES = {
    'model': '%s/models/%s/',
    'view': '%s/views/%s/',
    'template': '%s/templates/%s/',
    'filter': '%s/filters/#%s',
    'tag': '%s/tags/#%s',
}


def create_reference_role(rolename, urlbase):
    def _role(name, rawtext, text, lineno, inliner, options=None, content=None):
        if options is None:
            options = {}
        if content is None:
            content = []
        node = docutils.nodes.reference(
            rawtext,
            text,
            refuri=(urlbase % (
                inliner.document.settings.link_base,
                text.lower(),
            )),
            **options
        )
        return [node], []
    docutils.parsers.rst.roles.register_canonical_role(rolename, _role)


def default_reference_role(name, rawtext, text, lineno, inliner, options=None, content=None):
    if options is None:
        options = {}
    if content is None:
        content = []
    context = inliner.document.settings.default_reference_context
    node = docutils.nodes.reference(
        rawtext,
        text,
        refuri=(ROLES[context] % (
            inliner.document.settings.link_base,
            text.lower(),
        )),
        **options
    )
    return [node], []

if docutils_is_available:
    docutils.parsers.rst.roles.register_canonical_role('cmsreference', default_reference_role)

    for name, urlbase in ROLES.items():
        create_reference_role(name, urlbase)