"""
This module converts requested URLs to callback view functions.

RegexURLResolver is the main class here. Its resolve() method takes a URL (as
a string) and returns a tuple in this format:

    (view_function, function_args, function_kwargs)
"""

import re

from django.http import Http404
from django.core.exceptions import ImproperlyConfigured, ViewDoesNotExist
from django.utils.encoding import iri_to_uri, force_unicode, smart_str
from django.utils.functional import memoize
from django.utils.regex_helper import normalize
from django.utils.thread_support import currentThread

try:
    reversed
except NameError:
    from django.utils.itercompat import reversed     # Python 2.3 fallback
    from sets import Set as set

_resolver_cache = {} # Maps urlconf modules to RegexURLResolver instances.
_callable_cache = {} # Maps view and url pattern names to their view functions.

# SCRIPT_NAME prefixes for each thread are stored here. If there's no entry for
# the current thread (which is the only one we ever access), it is assumed to
# be empty.
_prefixes = {}

class Resolver404(Http404):
    pass

class NoReverseMatch(Exception):
    # Don't make this raise an error when used in a template.
    silent_variable_failure = True

def get_callable(lookup_view, can_fail=False):
    """
    Convert a string version of a function name to the callable object.

    If the lookup_view is not an import path, it is assumed to be a URL pattern
    label and the original string is returned.

    If can_fail is True, lookup_view might be a URL pattern label, so errors
    during the import fail and the string is returned.
    """
    if not callable(lookup_view):
        try:
            # Bail early for non-ASCII strings (they can't be functions).
            lookup_view = lookup_view.encode('ascii')
            mod_name, func_name = get_mod_func(lookup_view)
            if func_name != '':
                lookup_view = getattr(__import__(mod_name, {}, {}, ['']), func_name)
                if not callable(lookup_view):
                    raise AttributeError("'%s.%s' is not a callable." % (mod_name, func_name))
        except (ImportError, AttributeError):
            if not can_fail:
                raise
        except UnicodeEncodeError:
            pass
    return lookup_view
get_callable = memoize(get_callable, _callable_cache, 1)

def get_resolver(urlconf):
    if urlconf is None:
        from django.conf import settings
        urlconf = settings.ROOT_URLCONF
    return RegexURLResolver(r'^/', urlconf)
get_resolver = memoize(get_resolver, _resolver_cache, 1)

def get_mod_func(callback):
    # Converts 'django.views.news.stories.story_detail' to
    # ['django.views.news.stories', 'story_detail']
    try:
        dot = callback.rindex('.')
    except ValueError:
        return callback, ''
    return callback[:dot], callback[dot+1:]

class RegexURLPattern(object):
    def __init__(self, regex, callback, default_args=None, name=None):
        # regex is a string representing a regular expression.
        # callback is either a string like 'foo.views.news.stories.story_detail'
        # which represents the path to a module and a view function name, or a
        # callable object (view).
        self.regex = re.compile(regex, re.UNICODE)
        if callable(callback):
            self._callback = callback
        else:
            self._callback = None
            self._callback_str = callback
        self.default_args = default_args or {}
        self.name = name

    def __repr__(self):
        return '<%s %s %s>' % (self.__class__.__name__, self.name, self.regex.pattern)

    def add_prefix(self, prefix):
        """
        Adds the prefix string to a string-based callback.
        """
        if not prefix or not hasattr(self, '_callback_str'):
            return
        self._callback_str = prefix + '.' + self._callback_str

    def resolve(self, path):
        match = self.regex.search(path)
        if match:
            # If there are any named groups, use those as kwargs, ignoring
            # non-named groups. Otherwise, pass all non-named arguments as
            # positional arguments.
            kwargs = match.groupdict()
            if kwargs:
                args = ()
            else:
                args = match.groups()
            # In both cases, pass any extra_kwargs as **kwargs.
            kwargs.update(self.default_args)

            return self.callback, args, kwargs

    def _get_callback(self):
        if self._callback is not None:
            return self._callback
        try:
            self._callback = get_callable(self._callback_str)
        except ImportError, e:
            mod_name, _ = get_mod_func(self._callback_str)
            raise ViewDoesNotExist, "Could not import %s. Error was: %s" % (mod_name, str(e))
        except AttributeError, e:
            mod_name, func_name = get_mod_func(self._callback_str)
            raise ViewDoesNotExist, "Tried %s in module %s. Error was: %s" % (func_name, mod_name, str(e))
        return self._callback
    callback = property(_get_callback)

class RegexURLResolver(object):
    def __init__(self, regex, urlconf_name, default_kwargs=None):
        # regex is a string representing a regular expression.
        # urlconf_name is a string representing the module containing urlconfs.
        self.regex = re.compile(regex, re.UNICODE)
        self.urlconf_name = urlconf_name
        self.callback = None
        self.default_kwargs = default_kwargs or {}
        self._reverse_dict = {}

    def __repr__(self):
        return '<%s %s %s>' % (self.__class__.__name__, self.urlconf_name, self.regex.pattern)

    def _get_reverse_dict(self):
        if not self._reverse_dict and hasattr(self.urlconf_module, 'urlpatterns'):
            for pattern in reversed(self.urlconf_module.urlpatterns):
                p_pattern = pattern.regex.pattern
                if p_pattern.startswith('^'):
                    p_pattern = p_pattern[1:]
                if isinstance(pattern, RegexURLResolver):
                    parent = normalize(pattern.regex.pattern)
                    for name, (matches, pat) in pattern.reverse_dict.iteritems():
                        new_matches = []
                        for piece, p_args in parent:
                            new_matches.extend([(piece + suffix, p_args + args)
                                    for (suffix, args) in matches])
                        self._reverse_dict[name] = new_matches, p_pattern + pat
                else:
                    bits = normalize(p_pattern)
                    self._reverse_dict[pattern.callback] = bits, p_pattern
                    self._reverse_dict[pattern.name] = bits, p_pattern
        return self._reverse_dict
    reverse_dict = property(_get_reverse_dict)

    def resolve(self, path):
        tried = []
        match = self.regex.search(path)
        if match:
            new_path = path[match.end():]
            for pattern in self.urlconf_module.urlpatterns:
                try:
                    sub_match = pattern.resolve(new_path)
                except Resolver404, e:
                    tried.extend([(pattern.regex.pattern + '   ' + t) for t in e.args[0]['tried']])
                else:
                    if sub_match:
                        sub_match_dict = dict([(smart_str(k), v) for k, v in match.groupdict().items()])
                        sub_match_dict.update(self.default_kwargs)
                        for k, v in sub_match[2].iteritems():
                            sub_match_dict[smart_str(k)] = v
                        return sub_match[0], sub_match[1], sub_match_dict
                    tried.append(pattern.regex.pattern)
            raise Resolver404, {'tried': tried, 'path': new_path}

    def _get_urlconf_module(self):
        try:
            return self._urlconf_module
        except AttributeError:
            self._urlconf_module = __import__(self.urlconf_name, {}, {}, [''])
            return self._urlconf_module
    urlconf_module = property(_get_urlconf_module)

    def _get_url_patterns(self):
        return self.urlconf_module.urlpatterns
    url_patterns = property(_get_url_patterns)

    def _resolve_special(self, view_type):
        callback = getattr(self.urlconf_module, 'handler%s' % view_type)
        mod_name, func_name = get_mod_func(callback)
        try:
            return getattr(__import__(mod_name, {}, {}, ['']), func_name), {}
        except (ImportError, AttributeError), e:
            raise ViewDoesNotExist, "Tried %s. Error was: %s" % (callback, str(e))

    def resolve404(self):
        return self._resolve_special('404')

    def resolve500(self):
        return self._resolve_special('500')

    def reverse(self, lookup_view, *args, **kwargs):
        if args and kwargs:
            raise ValueError("Don't mix *args and **kwargs in call to reverse()!")
        try:
            lookup_view = get_callable(lookup_view, True)
        except (ImportError, AttributeError), e:
            raise NoReverseMatch("Error importing '%s': %s." % (lookup_view, e))
        possibilities, pattern = self.reverse_dict.get(lookup_view, [(), ()])
        for result, params in possibilities:
            if args:
                if len(args) != len(params):
                    continue
                unicode_args = [force_unicode(val) for val in args]
                candidate =  result % dict(zip(params, unicode_args))
            else:
                if set(kwargs.keys()) != set(params):
                    continue
                unicode_kwargs = dict([(k, force_unicode(v)) for (k, v) in kwargs.items()])
                candidate = result % unicode_kwargs
            if re.search(u'^%s' % pattern, candidate, re.UNICODE):
                return candidate
        raise NoReverseMatch("Reverse for '%s' with arguments '%s' and keyword "
                "arguments '%s' not found." % (lookup_view, args, kwargs))

def resolve(path, urlconf=None):
    return get_resolver(urlconf).resolve(path)

def reverse(viewname, urlconf=None, args=None, kwargs=None, prefix=None):
    args = args or []
    kwargs = kwargs or {}
    if prefix is None:
        prefix = get_script_prefix()
    return iri_to_uri(u'%s%s' % (prefix, get_resolver(urlconf).reverse(viewname,
            *args, **kwargs)))

def clear_url_caches():
    global _resolver_cache
    global _callable_cache
    _resolver_cache.clear()
    _callable_cache.clear()

def set_script_prefix(prefix):
    """
    Sets the script prefix for the current thread.
    """
    if not prefix.endswith('/'):
        prefix += '/'
    _prefixes[currentThread()] = prefix

def get_script_prefix():
    """
    Returns the currently active script prefix. Useful for client code that
    wishes to construct their own URLs manually (although accessing the request
    instance is normally going to be a lot cleaner).
    """
    return _prefixes.get(currentThread(), u'/')

