From d9c4af6b37b5c1d6e3afa4db35f4d60af5107c38 Mon Sep 17 00:00:00 2001
From: Adrian Holovaty <adrian@holovaty.com>
Date: Tue, 16 May 2006 04:05:55 +0000
Subject: [PATCH] Added first stab at reverse matching to urlresolvers.py

git-svn-id: http://code.djangoproject.com/svn/django/trunk@2910 bcc190cf-cafb-0310-a4f2-bffc1f526a37
---
 django/core/urlresolvers.py | 78 +++++++++++++++++++++++++++++++++++++
 1 file changed, 78 insertions(+)

diff --git a/django/core/urlresolvers.py b/django/core/urlresolvers.py
index e11b63e977..db4967e1c5 100644
--- a/django/core/urlresolvers.py
+++ b/django/core/urlresolvers.py
@@ -14,12 +14,56 @@ import re
 class Resolver404(Http404):
     pass
 
+class NoReverseMatch(Exception):
+    pass
+
 def get_mod_func(callback):
     # Converts 'django.views.news.stories.story_detail' to
     # ['django.views.news.stories', 'story_detail']
     dot = callback.rindex('.')
     return callback[:dot], callback[dot+1:]
 
+class MatchChecker(object):
+    "Class used in reverse RegexURLPattern lookup."
+    def __init__(self, args, kwargs):
+        self.args, self.kwargs = args, kwargs
+        self.current_arg = 0
+
+    def __call__(self, match_obj):
+        # match_obj.group(1) is the contents of the parenthesis.
+        # First we need to figure out whether it's a named or unnamed group.
+        #
+        grouped = match_obj.group(1)
+        m = re.search(r'^\?P<(\w+)>(.*?)$', grouped)
+        if m: # If this was a named group...
+            # m.group(1) is the name of the group
+            # m.group(2) is the regex.
+            try:
+                value = self.kwargs[m.group(1)]
+            except KeyError:
+                # It was a named group, but the arg was passed in as a
+                # positional arg or not at all.
+                try:
+                    value = self.args[self.current_arg]
+                    self.current_arg += 1
+                except IndexError:
+                    # The arg wasn't passed in.
+                    raise NoReverseMatch('Not enough positional arguments passed in')
+            test_regex = m.group(2)
+        else: # Otherwise, this was a positional (unnamed) group.
+            try:
+                value = self.args[self.current_arg]
+                self.current_arg += 1
+            except IndexError:
+                # The arg wasn't passed in.
+                raise NoReverseMatch('Not enough positional arguments passed in')
+            test_regex = grouped
+        # Note we're using re.match here on purpose because the start of
+        # to string needs to match.
+        if not re.match(test_regex + '$', str(value)): # TODO: Unicode?
+            raise NoReverseMatch("Value %r didn't match regular expression %r" % (value, test_regex))
+        return str(value) # TODO: Unicode?
+
 class RegexURLPattern:
     def __init__(self, regex, callback, default_args=None):
         # regex is a string representing a regular expression.
@@ -58,12 +102,37 @@ class RegexURLPattern:
         except AttributeError, e:
             raise ViewDoesNotExist, "Tried %s in module %s. Error was: %s" % (func_name, mod_name, str(e))
 
+    def reverse(self, viewname, *args, **kwargs):
+        if viewname != self.callback:
+            raise NoReverseMatch
+        return self.reverse_helper(*args, **kwargs)
+
+    def reverse_helper(self, *args, **kwargs):
+        """
+        Does a "reverse" lookup -- returns the URL for the given args/kwargs.
+        The args/kwargs are applied to the regular expression in this
+        RegexURLPattern. For example:
+
+            >>> RegexURLPattern('^places/(\d+)/$').reverse_helper(3)
+            'places/3/'
+            >>> RegexURLPattern('^places/(?P<id>\d+)/$').reverse_helper(id=3)
+            'places/3/'
+            >>> RegexURLPattern('^people/(?P<state>\w\w)/(\w+)/$').reverse_helper('adrian', state='il')
+            'people/il/adrian/'
+
+        Raises NoReverseMatch if the args/kwargs aren't valid for the RegexURLPattern.
+        """
+        # TODO: Handle nested parenthesis in the following regex.
+        result = re.sub(r'\(([^)]+)\)', MatchChecker(args, kwargs), self.regex.pattern)
+        return result.replace('^', '').replace('$', '')
+
 class RegexURLResolver(object):
     def __init__(self, regex, urlconf_name):
         # regex is a string representing a regular expression.
         # urlconf_name is a string representing the module containing urlconfs.
         self.regex = re.compile(regex)
         self.urlconf_name = urlconf_name
+        self.callback = None
 
     def resolve(self, path):
         tried = []
@@ -110,3 +179,12 @@ class RegexURLResolver(object):
 
     def resolve500(self):
         return self._resolve_special('500')
+
+    def reverse(self, viewname, *args, **kwargs):
+        for pattern in self.urlconf_module.urlpatterns:
+            if pattern.callback == viewname:
+                try:
+                    return pattern.reverse_helper(*args, **kwargs)
+                except NoReverseMatch:
+                    continue
+        raise NoReverseMatch