#!/usr/bin/env python3
import sys, re, os
from argparse import ArgumentParser
from argparse import RawTextHelpFormatter


def setup_options():
    parser = ArgumentParser(
        description="""Template Filler

=== Template example: ===
  Hello [[name]]!
[[letter]]

== Value file/Value pair example: ==
[[name]]=John
[[letter]]=@letter.txt
    """,
        formatter_class=RawTextHelpFormatter,
    )
    parser.add_argument(
        "-e",
        action="store_true",
        dest="env",
        default=False,
        help="Use the environment to replace ${env} style variables.",
    )
    parser.add_argument(
        "-f", action="store", dest="file", help="File name to read keys/values."
    )
    parser.add_argument(
        "-p",
        action="append",
        dest="values",
        default=[],
        help="key=value pairs. This option may be issued several times.",
    )
    parser.add_argument(
        "template",
        action="store",
        nargs="?",
        help="Template file to be filled. If not defined, stdin used.",
    )
    options = parser.parse_args()
    return options


def parse_file(filename):
    pairs = []
    with open(filename, "r") as reader:
        for i, l in enumerate(reader):
            l = l.rstrip("\n\r")
            if len(l) == 0:
                continue
            tokens = l.split("=", 1)
            if len(tokens) != 2:
                print(
                    "File %s:%i key=value pair '%s' does not parse"
                    % (
                        filename,
                        i + 1,
                        l,
                    )
                )
                sys.exit(1)
            pairs.append((tokens[0], tokens[1]))
    return pairs


def parse_arguments(args):
    pairs = []
    for p in args:
        tokens = p.split("=", 1)
        if len(tokens) != 2:
            print("Argument key=value pair '%s' does not parse" % (p,))
            sys.exit(1)
        pairs.append((tokens[0], tokens[1]))
    return pairs


if __name__ == "__main__":
    options = setup_options()
    pairs = []
    if options.file != None:
        pairs.extend(parse_file(options.file))
    pairs.extend(parse_arguments(options.values))
    if options.template == None:
        in_reader = sys.stdin
    else:
        in_reader = open(options.template, "rb")
    for l in in_reader:
        for p in pairs:
            value = p[1]
            if len(value) > 0:
                if value[0] == "@":
                    value = open(value[1:], "rt").read()
                elif value[0:2] == "\\@":
                    value = value[1:]
            l = l.replace(p[0].encode("utf-8"), value.encode("utf-8"))
        if options.env:
            var_list = [m.group(0) for m in re.finditer("\${[^ ]+}", l)]
            for v in var_list:
                l = l.replace(v, os.environ.get(v[:-1][2:], ""))
        sys.stdout.write(l.decode("utf-8"))