rewrite autolink script

Finally updated script to python3. Changed how the script works.
The old version made a symlink for each directory in the dot-files.
The new version:
 • makes directories for each folder in the dot-files in home directory
   • a folder [dot-files]/foo/bar will make folder ~/.foo/bar
 • makes symlinks for each file in the dot-files
   • a file [dot-files]/foo/bar/baz will make symlink
    ~/.foo/bar/baz → [dot-files]/foo/bar/baz

autolink

@@ -1,62 +1,80 @@
-#!/usr/bin/env python2
-"""
-A simple script to create a symlinks in your home directory for every filename
-in this directory.
+#!/usr/bin/env python3
 
-For example:
-    ~/.bashrc -> dot-files/bashrc
-"""
+import os
+from os import path
 
-from os import getcwd, listdir, getenv, symlink, remove
-from os.path import (dirname, basename, join, expanduser, lexists, exists,
-                     relpath, normpath, isfile, islink, realpath, abspath)
+SCRIPT_ABS_PATH = path.abspath(__file__)
+SCRIPT_NAME = path.basename(SCRIPT_ABS_PATH)
+DOT_FILES_DIR = path.dirname(SCRIPT_ABS_PATH)
+HOME_DIR = path.expanduser('~')
 
-def log(filename, message):
-    """Simple logging function"""
-    name = "'{0}':".format(filename).ljust(30, ' ')
-    print "{0}\t{0}".format(name, message)
+class ExistingFileError(OSError):
+    pass
 
-def dir_filter(file_name):
-    return file_name != basename(__file__) and \
-           file_name != 'README.md' and \
-           file_name[0] != '.'
+class ExistingSymlinkError(OSError):
+    pass
 
-def main():
-    """Create the symlinks"""
-    dir_path = dirname(__file__)
-    base_name = dirname(normpath(join(getenv('PWD'), __file__)))
-    home_dir = expanduser('~')
-    rel_path = normpath(relpath(base_name, home_dir))
+def main(*, dot_files=DOT_FILES_DIR, home_dir=HOME_DIR):
+    for directory in walk_directories(dot_files):
+        hidden_dir = path.join(home_dir, '.' + directory)
+        make_directory(hidden_dir)
 
-    for filename in filter(dir_filter, listdir(dirname(abspath(__file__)))):
-        config_path = join(home_dir, ".{0}".format(filename))
-        file_path = join(rel_path, filename)
+    for filename in walk_files(dot_files):
+        dot_file = path.join(dot_files, filename)
+        new_file = path.join(home_dir, '.' + filename)
+        link_to(dot_file, new_file)
 
-        # If the current file is going to be linked deeper in the
-        # home directory, for example, we want to link
-        # `~/.ssh/config` instead of the whole `~/.ssh` directory.
-        if filename[0] == '_':
-            deep_dirs = filename[1:].split('_')
-            link_file = deep_dirs[-1]
-            dir_name = join(*deep_dirs[:-1])
-            config_path = join(home_dir, ".{0}".format(dir_name), link_file)
-            file_path = join("..", file_path)
-
-        if lexists(config_path):
-            if not exists(config_path):
-                # If it does not exists but lexists is true, that means this
-                # is a broken symlink
-                remove(config_path)
-            elif islink(config_path):
-                if realpath(config_path) != file_path:
-                    continue
-            elif isfile(config_path):
-                log(config_path, 'existing file, consider merge')
+def walk_directories(directory):
+    visited = set()
+    for root, dirs, _ in os.walk(directory):
+        for d in (path.join(root, d) for d in dirs):
+            rel_dir = path.join(root, d).replace(directory + os.sep, '')
+            if rel_dir in visited:
                 continue
+            if path_contains(rel_dir, '.git'):
+                continue
+            yield rel_dir
+            visited.add(rel_dir)
 
-        log(config_path, "now linking to '{0}'".format(file_path))
-        symlink(file_path, config_path)
+def walk_files(directory):
+    visited = set()
+    for root, _, files in os.walk(directory):
+        for f in (path.join(root, f) for f in files if not f.startswith('.')):
+            relative_file = path.join(root, f).replace(directory + os.sep, '')
+            if relative_file in visited:
+                continue
+            if path_contains(relative_file, '.git', 'README.md', SCRIPT_NAME):
+                continue
+            yield relative_file
+            visited.add(relative_file)
+
+def make_directory(directory):
+    if path.isdir(directory):
+        return
+    if path.exists(directory):
+        raise ExistingFileError('expected no file or directory: {0}'.format(directory))
+    os.mkdir(directory, mode=0o755)
+
+def link_to(src, dest):
+    if path.islink(dest):
+        if path.realpath(src) == path.realpath(dest):
+            return
+        if path.exists(dest):
+            raise ExistingSymlinkError('found unexpected symlink: {0}'.format(dest))
+        # we have a broken symlink, remove it
+        os.remove(dest)
+    if path.isfile(dest):
+        raise ExistingSymlinkError('found unexpected file: {0}'.format(dest))
+    src_rel = path.relpath(src, start=path.dirname(dest))
+    dir_fd = os.open(path.dirname(dest), os.O_RDONLY)
+    os.symlink(src_rel, dest, dir_fd=dir_fd)
+
+def path_contains(directory, *strings):
+    directories = directory.split(os.sep)
+    for s in strings:
+        if s in directories:
+            return True
+    return False
 
 if __name__ == '__main__':
     main()
-