A proof of concept for automatic dependency detection

autodepends.py

import re
from os import path, stat
from webassets import Bundle
from webassets.exceptions import BundleError


DEPENDS_REGEXES = map(re.compile, [
    # http://stackoverflow.com/questions/4652777/java-regex-to-get-the-urls-from-css
    # With addon to handle quotes
    r'url[\s]*\([\s\'\"]*(?P<url>[^\)\'\"]*)[\s\'\"]*\)[\s]*',
    r'@import[\s]*[\"|\'](?P<url>[^\'\"]*)[\"|\']',
])
PARSE_FILETYPES = ('css', 'scss', 'sass')


def cache_key(resolved_path):
    return (resolved_path, str(stat(resolved_path).st_mtime))


def resolve_dependency(item, env):
    try:
        result = env.resolver.resolve_source(item)
    except IOError, e:
        raise BundleError(e)
    if not isinstance(result, list):
        result = [result]
    return result


def get_dependencies(subject_path, env):
    resolved_sources = resolve_dependency(subject_path, env)
    subject_dir = path.dirname(subject_path)

    depends = []
    for resolved_path in resolved_sources:
        cached = env.cache.get(cache_key(resolved_path), python=True) or {}
        if cached:
            return cached.keys()

        with open(resolved_path) as source:
            source_data = source.read()

        for regex in DEPENDS_REGEXES:
            for match in regex.findall(source_data):
                normalized = path.normpath(path.join(subject_dir, match))
                resolved = resolve_dependency(normalized, env)
                depends.extend(resolved)
                for dep in resolved:
                    cached[dep] = stat(dep).st_mtime

        env.cache.set(cache_key(resolved_path), cached)
    return depends


def recurse_dependencies(sources, global_depends, env):
    for source in sources:
        if source.rsplit('.', 1)[-1] in PARSE_FILETYPES:
            depends = [d for d in get_dependencies(source, env=env) if d not in global_depends]
            if depends:
                global_depends.extend(depends)
                recurse_dependencies(depends, global_depends, env=env)


class AutoDependsBundle(Bundle):
    def resolve_depends(self, env):
        depends = super(AutoDependsBundle, self).resolve_depends(env)
        recurse_dependencies(list(self.contents) + depends, depends, env=env)
        return depends