#!/usr/bin/env python
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].decode('string_escape')) )
    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].decode('string_escape')) )
    return pairs

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],value)
    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)