webcache/importer.py

import web
import re
import os.path

from cache import Cache, to_dir, assert_file_exists


ALIAS_PREFIX = '@'


def separate_imports(content):
    """
    Separate the import section from the rest of the content of a file. Returns
    a tuple with a list of imports, and the remaning part of the string.

    Imports are located in the beginning of a file, and can take the following
    forms:
    # No imports
    content

    # Single file import
    import foo

    content

    # Multiple files import
    import foo, bar

    content

    # Multiline import
    import foo, bar, \
           baz

    content
    """
    content = content.lstrip()
    imports = []

    comma = re.compile(' *, *(?:\\\\\r?\n *)?')
    file_list = '\w+(?:%s\w+?)*' % comma.pattern
    m = re.match('^import (%s)(?:(?:\r?\n)+(.*))?$' % file_list, content, re.M)

    if m:
        imports = comma.split(m.group(1))
        content = m.group(2)

        if not content:
            content = ''

    return imports, content


class Importer(Cache):
    def __init__(self, root, extension=None):
        Cache.__init__(self)
        self.root = to_dir(root + '/')
        self.aliases = {}

        if extension:
            self.extension = '.' + extension
        else:
            self.extension = ''

    def set_alias(self, name, path):
        """
        Add an alias for the path to a file, relative to the importer's root
        directory. Aliases are used to shorten the names of imports. E.g. using
        "@jquery" in an import could point to "static/js/jquery-min-1.7.1.js".
        """
        path = self.root + path + self.extension
        assert_file_exists(path)
        self.aliases[name] = path

    def create_full_paths(self, files, relative_file=None):
        """
        Create full paths out of a file list:
        1. Replace any aliases.
        2. Look for direct siblings of the loaded file, if any (relative_file).
        3. Look in the root folder of the Import object.
        """
        replaced = []
        alias_len = len(ALIAS_PREFIX)

        if relative_file:
            relative_dir = to_dir(relative_file)

        for i, path in enumerate(files):
            if path[:alias_len] == ALIAS_PREFIX:
                # Alias syntax is used, assert that the alias exists
                alias = path[alias_len:]

                if alias not in self.aliases:
                    raise ValueError('Alias "%s" has not been set.' % alias)

                # Alias exists, translate is to a full path
                replaced.append(self.aliases[alias])
            else:
                if relative_file:
                    relative_path = relative_dir + path + self.extension

                    if os.path.exists(relative_path):
                        # Relative import
                        replaced.append(relative_path)
                        continue

                # Import from root
                path = self.root + path + self.extension
                assert_file_exists(path)
                replaced.append(path)

        return replaced

    def concatenate(self, files):
        files = self.create_full_paths(files)
        map(assert_file_exists, files)
        self.loaded = []
        self.import_map = {}
        concat = ''

        for path in files:
            f = open(path, 'r')
            raw = f.read()
            f.close()

            # Parse imports from file content
            imports, content = separate_imports(raw)
            self.import_map.update({path: imports})

            # Only add imported files that have not been loaded yet
            new_imports = filter(lambda i: i not in self.loaded, imports)

            # Prepend imports that have not been loaded yet before the file's
            # content
            if new_imports:
                new_imports = self.create_full_paths(new_imports, path)

                # Check if there is a recursive import
                for f in new_imports:
                    if f == path:
                        raise ImportError('Recursive import in file "%s".' % f)

                    if f in self.import_map and path in self.import_map[f]:
                        raise ImportError('Recursive import in of "%s" in ' \
                                          + 'file "%s".' % (f, path))

                concat += self.concatenate(new_imports)

            concat += content
            self.loaded += path

        return concat

    def content(self):
        return self.concatenate(self.files)