#!/usr/bin/env python3

import os
from os import path

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('~')

class ExistingFileError(OSError):
    pass

class ExistingSymlinkError(OSError):
    pass

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 walk_files(dot_files):
        dot_file = path.join(dot_files, filename)
        new_file = path.join(home_dir, '.' + filename)
        link_to(dot_file, new_file)

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)

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()