var json = typeof JSON !== 'undefined' ? JSON : require('jsonify');
  
  module.exports = function (obj, opts) {
      if (!opts) opts = {};
      if (typeof opts === 'function') opts = { cmp: opts };
      var space = opts.space || '';
      if (typeof space === 'number') space = Array(space+1).join(' ');
      var cycles = (typeof opts.cycles === 'boolean') ? opts.cycles : false;
      var replacer = opts.replacer || function(key, value) { return value; };
  
      var cmp = opts.cmp && (function (f) {
          return function (node) {
              return function (a, b) {
                  var aobj = { key: a, value: node[a] };
                  var bobj = { key: b, value: node[b] };
                  return f(aobj, bobj);
              };
          };
      })(opts.cmp);
  
      var seen = [];
      return (function stringify (parent, key, node, level) {
          var indent = space ? ('
  ' + new Array(level + 1).join(space)) : '';
          var colonSeparator = space ? ': ' : ':';
  
          if (node && node.toJSON && typeof node.toJSON === 'function') {
              node = node.toJSON();
          }
  
          node = replacer.call(parent, key, node);
  
          if (node === undefined) {
              return;
          }
          if (typeof node !== 'object' || node === null) {
              return json.stringify(node);
          }
          if (isArray(node)) {
              var out = [];
              for (var i = 0; i < node.length; i++) {
                  var item = stringify(node, i, node[i], level+1) || json.stringify(null);
                  out.push(indent + space + item);
              }
              return '[' + out.join(',') + indent + ']';
          }
          else {
              if (seen.indexOf(node) !== -1) {
                  if (cycles) return json.stringify('__cycle__');
                  throw new TypeError('Converting circular structure to JSON');
              }
              else seen.push(node);
  
              var keys = objectKeys(node).sort(cmp && cmp(node));
              var out = [];
              for (var i = 0; i < keys.length; i++) {
                  var key = keys[i];
                  var value = stringify(node, key, node[key], level+1);
  
                  if(!value) continue;
  
                  var keyValue = json.stringify(key)
                      + colonSeparator
                      + value;
                  ;
                  out.push(indent + space + keyValue);
              }
              seen.splice(seen.indexOf(node), 1);
              return '{' + out.join(',') + indent + '}';
          }
      })({ '': obj }, '', obj, 0);
  };
  
  var isArray = Array.isArray || function (x) {
      return {}.toString.call(x) === '[object Array]';
  };
  
  var objectKeys = Object.keys || function (obj) {
      var has = Object.prototype.hasOwnProperty || function () { return true };
      var keys = [];
      for (var key in obj) {
          if (has.call(obj, key)) keys.push(key);
      }
      return keys;
  };