#!/usr/bin/env python3

import os, sys, json, traceback, subprocess

# Definitions
def stdout(string, end='\n', flush=False):
    print(string, end=end, file=sys.stdout, flush=flush)

def stderr(string, end='\n', flush=False):
    print(string, end=end, file=sys.stderr, flush=flush)

exit_codes = {
  "normal exit":            0,
  "wrong usage":            1,
  "error while processing": 2
}

stderr("\nVariable Grabbler - version 5.0\n--------------------------------------------------------------------------------")
################################################################################
# Chnages in this version:
# - complete rewrite in Python 3
# - output to stdout instead of rewriting the file
#===============================================================================
# Full documentation: tbd
#===============================================================================

# Command line input handling
usage = "Usage: python3 "+sys.argv[0]+" <macro config file> <file to be processed>"
if not len(sys.argv)==3:
    stderr("E: Wrong amount of arguments.")
    stderr(usage)
    sys.exit(exit_codes["wrong usage"])
if sys.argv[1] == sys.argv[2]:
    stderr("E: Both input files are the same.")
    stderr(usage)
    sys.exit(exit_codes["wrong usage"])

# load macros into a dict
stderr("I: Reading macro definitions... ")
macros = {}
try:
    if os.path.isfile(sys.argv[1]):
        macro_file = open(sys.argv[1], "r")
        macros = json.loads(macro_file.read())
        macro_file.close()
    elif sys.argv[1] == '-':
        macros = json.loads(sys.stdin.read())
    else:
        stderr("E: Not a valid file: "+sys.argv[1])
        sys.exit(exit_codes["error while processing"])
except:
    stderr("E: An exception occurred while trying to read macro definitions:")
    traceback.print_exc()
    sys.exit(exit_codes["error while processing"])

# process "file" and "exec" macros
stderr("I: Loading templates and processing commands...")
for macro in macros:
    if macros[macro][0] == "file":
        if os.path.isfile(macros[macro][1]):
            try:
                stderr("I: Loading template: " + macro)
                template = open(macros[macro][1], "r")
                macros[macro] = template.read()
                template.close()
            except:
                stderr("E: An exception occurred while trying to read the template:")
                traceback.print_exc()
                sys.exit(exit_codes["error while processing"])
        else:
            stderr("E: Macro \"" + macro + "\": template \"" + macros[macro][1] + "\" is not a valid file.")
            sys.exit(exit_codes["error while processing"])
    elif macros[macro][0] == "exec":
        try:
            stderr("I: Running command: " + macro)
            process = subprocess.Popen(macros[macro][1], shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
            process_stdout, process_stderr = process.communicate()
            macros[macro] = process_stdout.decode("utf-8")
            if len(process_stderr) > 0:
                stderr("Output on stderr:\n"+process_stderr)
            if not process.returncode == 0:
                stderr("E: Command execution failed with exit code "+str(process.returncode))
                sys.exit(exit_codes["error while processing"])
        except:
            stderr("E: An exception occurred while trying to process the command:")
            traceback.print_exc()
            sys.exit(exit_codes["error while processing"])

# open file to be processed and iterate over it
stderr("I: Preparing to process input file...")
try:
    input_file = sys.stdin
    if os.path.isfile(sys.argv[2]):
        input_file = open(sys.argv[2], "r")
    elif sys.argv[2] == '-':
        # nothing to do here bc input_file is already set to sys.stdin
        pass
    else:
        stderr("E: Not a valid file: "+sys.argv[2])
        sys.exit(exit_codes["error while processing"])
    # make the magic happen
    stderr("I: Processing input file...")
    for line in input_file:
        for macro in macros:
            line = line.replace("%" + macro + "%", str(macros[macro]))
        stdout(line, end="")
    # close input file if it's not sys.stdin, assume sys.stdin is being handled for us
    if not input_file==sys.stdin:
        input_file.close()
except:
    stderr("E: An exception occured while processing " + input_file.name + ":")
    traceback.print_exc()
    sys.exit(exit_codes["error while processing"])