#!/usr/bin/env python
"""Stitch together the letsencrypt-auto script.

Implement a simple templating language in which {{ some/file }} turns into the
contents of the file at ./pieces/some/file except for certain tokens which have
other, special definitions.

"""
from os.path import abspath, dirname, join
import re
from sys import argv


DIR = dirname(abspath(__file__))


def le_version(build_script_dir):
    """Return the version number stamped in letsencrypt/__init__.py."""
    return re.search('''^__version__ = ['"](.+)['"].*''',
                     file_contents(join(dirname(build_script_dir),
                                        'letsencrypt',
                                        '__init__.py')),
                     re.M).group(1)


def file_contents(path):
    with open(path) as file:
        return file.read()


def build(version=None, requirements=None):
    """Return the built contents of the letsencrypt-auto script.

    :arg version: The version to attach to the script. Default: the version of
        the letsencrypt package
    :arg requirements: The contents of the requirements file to embed. Default:
        contents of letsencrypt-auto-requirements.txt

    """
    special_replacements = {
        'LE_AUTO_VERSION': version or le_version(DIR)
    }
    if requirements:
        special_replacements['letsencrypt-auto-requirements.txt'] = requirements

    def replacer(match):
        token = match.group(1)
        if token in special_replacements:
            return special_replacements[token]
        else:
            return file_contents(join(DIR, 'pieces', token))

    return re.sub(r'{{\s*([A-Za-z0-9_./-]+)\s*}}',
                  replacer,
                  file_contents(join(DIR, 'letsencrypt-auto.template')))


def main():
    with open(join(DIR, 'letsencrypt-auto'), 'w') as out:
        out.write(build())


if __name__ == '__main__':
    main()