"""
WSGI middleware

Application dispatching, based on URL.  An instance of `URLParser` is
an application that loads and delegates to other applications.  It
looks for files in its directory that match the first part of
PATH_INFO; these may have an extension, but are not required to have
one, in which case the available files are searched to find the
appropriate file.  If it is ambiguous, a 404 is returned and an error
logged.

Each URLParser has a set of options, which can be local to that
URLParser.  Also, there are default options:

``index_name``:
    The name of the index file, sans extension.

``hide_extensions``:
    A list of extensions (with leading ``.``) that should not ever
    be served.

``ignore_extensions``:
    Extensions that will be ignored when searching for a file.  If
    the extension is given explicitly, files with these extensions
    will still be served.

``constructors``:
    A dictionary of extensions as keys, and application constructors
    as values.  Also the key ``dir`` for directories, and ``*`` when
    no other constructor is found.

    Each constructor is called like ``constructor(environ, filename)``
    and should return an application or ``None``.

By default there is a constructor for .py files that loads the module,
and looks for an attribute ``application``, which is a ready
application object, or an attribute that matches the module name,
which is a factory for building applications, and is called with no
arguments.

URLParser will also look in __init__.py for special overrides.  Currently
the only override is urlparser_hook(environ), which can modify the
environment; its return value is ignored.  You can use this, for example,
to manipulate SCRIPT_NAME/PATH_INFO (try to keep them consistent with the
original URL -- but consuming PATH_INFO and moving that to SCRIPT_NAME
is ok).
"""

import os
import sys
import imp
import wsgilib

class NoDefault:
    pass

class URLParser(object):

    default_options = {
        'index_names': ['index', 'Index', 'main', 'Main'],
        'hide_extensions': ['.pyc', '.bak', '.py~'],
        'ignore_extensions': [],
        'constructors': {},
        }

    parsers_by_directory = {}

    # This is lazily initialized
    init_module = NoDefault

    def __init__(self, directory, base_python_name, add_options=None):
        if os.path.sep != '/':
            directory = directory.replace(os.path.sep, '/')
        self.directory = directory
        self.add_options = add_options
        self.base_python_name = base_python_name

    def __call__(self, environ, start_response):
        environ['paste.urlparser.base_python_name'] = self.base_python_name
        if self.add_options:
            if environ.has_key('paste.urlparser.options'):
                environ['paste.urlparser.options'].update(self.add_options)
            else:
                environ['paste.urlparser.options'] = self.add_options.copy()
        if self.init_module is NoDefault:
            self.init_module = self.find_init_module(environ)
        path_info = environ.get('PATH_INFO', '')
        if not path_info:
            return self.add_slash(environ, start_response)
        if (self.init_module
            and getattr(self.init_module, 'urlparser_hook', None)):
            self.init_module.urlparser_hook(environ)
        name, rest_of_path = wsgilib.path_info_split(environ['PATH_INFO'])
        orig_path_info = environ['PATH_INFO']
        orig_script_name = environ['SCRIPT_NAME']
        environ['PATH_INFO'] = rest_of_path
        if name is not None:
            environ['SCRIPT_NAME'] = environ.get('SCRIPT_NAME', '') + '/' + name
        if not name:
            names = self.option(environ, 'index_names') or []
            for index_name in names:
                filename = self.find_file(environ, index_name)
                if filename:
                    break
            else:
                # None of the index files found
                filename = None
        else:
            filename = self.find_file(environ, name)
        if filename is None:
            application = None
        else:
            application = self.get_application(environ, filename)
        if not application:
            if (self.init_module
                and getattr(self.init_module, 'not_found_hook', None)
                and environ.get('paste.urlparser.not_found_parser') is not self):
                not_found_hook = self.init_module.not_found_hook
                environ['paste.urlparser.not_found_parser'] = self
                environ['PATH_INFO'] = orig_path_info
                environ['SCRIPT_NAME'] = orig_script_name
                return not_found_hook(environ, start_response)
            if filename is None:
                if not name:
                    desc = 'one of %s' % ', '.join(
                        self.option(environ, 'index_names') or
                        ['(no index_names defined)'])
                else:
                    desc = name

                return self.not_found(
                    environ, start_response,
                    'Tried to load %s from directory %s'
                    % (desc, self.directory))
            else:
                environ['wsgi.errors'].write(
                    'Found resource %s, but could not construct application\n'
                    % filename)
                return self.not_found(
                    environ, start_response,
                    'Tried to load %s from directory %s'
                    % (filename, self.directory))
        return application(environ, start_response)

    def not_found(self, environ, start_response, debug_message=None):
        status, headers, body = wsgilib.error_response(
            environ,
            '404 Not Found',
            'The resource at %s could not be found'
            % wsgilib.construct_url(environ),
            debug_message=debug_message)
        start_response(status, headers)
        return [body]

    def option(self, environ, name):
        return environ.get('paste.urlparser.options', {}).get(
            name, self.default_options.get(name))

    def add_slash(self, environ, start_response):
        """
        This happens when you try to get to a directory
        without a trailing /
        """
        url = wsgilib.construct_url(environ, with_query_string=False)
        url += '/'
        if environ.get('QUERY_STRING'):
            url += '?' + environ['QUERY_STRING']
        status = '301 Moved Permanently'
        status, headers, body = wsgilib.error_response(
            environ,
            status,
            '''
            <p>The resource has moved to <a href="%s">%s</a>.  You should be redirected automatically.</p>''' % (url, url))
        start_response(status, headers + [('Location', url)])
        return [body]

    def find_file(self, environ, base_filename):
        possible = []
        """Cache a few values to reduce function call overhead"""
        ignore_extensions = self.option(environ, 'ignore_extensions')
        hide_extensions = self.option(environ, 'hide_extensions')
        for filename in os.listdir(self.directory):
            base, ext = os.path.splitext(filename)
            full_filename = os.path.join(self.directory, filename)
            if (ext in hide_extensions
                or not base):
                continue
            if filename == base_filename:
                possible.append(full_filename)
                continue
            if ext in ignore_extensions:
                continue
            if base == base_filename:
                possible.append(full_filename)
        if not possible:
            #environ['wsgi.errors'].write(
            #    'No file found matching %r in %s\n'
            #    % (base_filename, self.directory))
            return None
        if len(possible) > 1:
            environ['wsgi.errors'].write(
                'Ambiguous URL: %s; matches files %s\n'
                % (wsgilib.construct_url(environ),
                   ', '.join(possible)))
            return None
        return possible[0]

    def get_application(self, environ, filename):
        constructors = self.option(environ, 'constructors')
        if os.path.isdir(filename):
            t = 'dir'
        else:
            t = os.path.splitext(filename)[1]
        constructor = constructors.get(t, constructors.get('*'))
        if constructor is None:
            #environ['wsgi.errors'].write(
            #    'No constructor found for %s\n' % t)
            return constructor
        app = constructor(environ, filename)
        if app is None:
            #environ['wsgi.errors'].write(
            #    'Constructor %s return None for %s\n' %
            #    (constructor, filename))
            pass
        return app

    def register_constructor(cls, extension, constructor):
        d = cls.default_options['constructors']
        assert not d.has_key(extension), (
            "A constructor already exists for the extension %r (%r) "
            "when attemption to register constructor %r"
            % (extension, d[extension], constructor))
        d[extension] = constructor
    register_constructor = classmethod(register_constructor)

    def get_parser(cls, directory, base_python_name):
        try:
            return cls.parsers_by_directory[(directory, base_python_name)]
        except KeyError:
            parser = cls(directory, base_python_name)
            cls.parsers_by_directory[(directory, base_python_name)] = parser
            return parser
    get_parser = classmethod(get_parser)

    def find_init_module(self, environ):
        filename = os.path.join(self.directory, '__init__.py')
        if not os.path.exists(filename):
            return None
        return load_module(environ, filename)

    def __repr__(self):
        return '<%s directory=%r; module=%s at %s>' % (
            self.__class__.__name__,
            self.directory,
            self.base_python_name,
            hex(abs(id(self))))

def make_directory(environ, filename):
    base_python_name = environ['paste.urlparser.base_python_name']
    if base_python_name:
        base_python_name += "." + os.path.basename(filename)
    else:
        base_python_name = os.path.basename(filename)
    return URLParser.get_parser(filename, base_python_name)

URLParser.register_constructor('dir', make_directory)

def make_unknown(environ, filename):
    return wsgilib.send_file(filename)

URLParser.register_constructor('*', make_unknown)

def load_module(environ, filename):
    base_python_name = environ['paste.urlparser.base_python_name']
    module_name = os.path.splitext(os.path.basename(filename))[0]
    if base_python_name:
        module_name = base_python_name + '.' + module_name
    return load_module_from_name(environ, filename, module_name,
                                 environ['wsgi.errors'])

def load_module_from_name(environ, filename, module_name, errors):
    if sys.modules.has_key(module_name):
        return sys.modules[module_name]
    init_filename = os.path.join(os.path.dirname(filename), '__init__.py')
    if not os.path.exists(init_filename):
        try:
            f = open(init_filename, 'w')
        except (OSError, IOError), e:
            errors.write(
                'Cannot write __init__.py file into directory %s (%s)\n'
                % (os.path.dirname(filename), e))
            return None
        f.write('#\n')
        f.close()
    fp = None
    if sys.modules.has_key(module_name):
        return sys.modules[module_name]
    if '.' in module_name:
        parent_name = '.'.join(module_name.split('.')[:-1])
        base_name = module_name.split('.')[-1]
        parent = load_module_from_name(environ, os.path.dirname(filename),
                                       parent_name, errors)
    else:
        base_name = module_name
    fp = None
    try:
        fp, pathname, stuff = imp.find_module(
            base_name, [os.path.dirname(filename)])
        module = imp.load_module(module_name, fp, pathname, stuff)
    finally:
        if fp is not None:
            fp.close()
    return module

def make_py(environ, filename):
    module = load_module(environ, filename)
    if not module:
        return None
    if hasattr(module, 'application') and module.application:
        return module.application
    base_name = module.__name__.split('.')[-1]
    if hasattr(module, base_name):
        return getattr(module, base_name)()
    environ['wsgi.errors'].write(
        "Cound not find application or %s in %s\n"
        % (base_name, module))
    return None
    
URLParser.register_constructor('.py', make_py)