#! /usr/bin/env python
"""
replace variables in a template with specific variables
"""

import logging
import yaml


def parse_arguments():
    from argparse import ArgumentParser, FileType

    arg_parser = ArgumentParser()

    arg_parser.add_argument("--template", "-t", type=FileType("r"))
    arg_parser.add_argument(
        "--input", "-i", type=FileType("r"), help="yaml format template parameter"
    )
    arg_parser.add_argument(
        "--output", "-o", type=FileType("w"), help="filled in template", default="-"
    )

    return arg_parser.parse_args()


def inject(template, variables):
    import re

    variable_regex = re.compile("\$([a-zA-Z\_]+)")
    variables_in_template = variable_regex.findall(template)

    # we need to be able to fill in every variable
    assert (v in variables for v in variables_in_template)
    if not all(v in variables_in_template for v in variables):
        logging.warn(
            f"There are unused variables: {filter(lambda v: v not in variables_in_template, [v for v in variables])}"
        )
    
    filled_template = template
    for variable, value in variables.items():
        filled_template = filled_template.replace(f"${variable}", value)
    
    return filled_template
    

if __name__ == "__main__":
    argv = parse_arguments()

    with argv.input as yaml_stream:
        variables = yaml.safe_load(yaml_stream)

    with argv.template as string_stream:
        template = string_stream.read()

    with argv.output as output_stream:
        output_stream.write(
            inject(template, variables)
        )
        output_stream.close()