#!/usr/bin/env python

import sys
import yaml
import yaml.constructor as yamlc
import json
import optparse

parser = optparse.OptionParser()

parser.add_option('-i', '--input', metavar='FILE')
parser.add_option('-o', '--output', metavar='FILE')

options, args = parser.parse_args()

if len(args) >= 3:
    parser.exit(1, 'Too many inputs!\n')

if args and (options.input or options.output):
    parser.exit(1, "Can't specify both args and options\n")

def open_file(name, mode):
    try:
        return open(name, mode, 1)
    except:
        parser.exit(2, "Could not open file %s\n" % name)

if options.input:
    input = open_file(options.input,'r')
elif len(args) >= 1:
    input = open_file(args[0],'r')
else:
    input = sys.stdin

if options.output:
    out = open_file(options.output,'w')
elif len(args) == 2:
    out = open_file(args[1],'w')
else:
    out = sys.stdout

indent = 2

with input, out:
    try:
        value = json.load(input)
        yaml.safe_dump(value, out, indent=indent, default_style=None, default_flow_style=False)
        out.write('\n')
    except:
        import traceback
        traceback.print_exception(*sys.exc_info())
        sys.exit(3)
sys.exit(0)