// Query String Utilities

var QueryString = exports;
var urlDecode = process.binding("http_parser").urlDecode;


function charCode (c) {
  return c.charCodeAt(0);
}


// a safe fast alternative to decodeURIComponent
QueryString.unescapeBuffer = function (s, decodeSpaces) {
  var out = new Buffer(s.length);
  var state = "CHAR"; // states: CHAR, HEX0, HEX1
  var n, m, hexchar;

  for (var inIndex = 0, outIndex = 0; inIndex <= s.length; inIndex++) {
    var c = s.charCodeAt(inIndex);
    switch (state) {
      case 'CHAR':
        switch (c) {
          case charCode('%'):
            n = 0;
            m = 0;
            state = 'HEX0';
            break;
          case charCode('+'):
            if (decodeSpaces) c = charCode(' ');
            // pass thru
          default:
            out[outIndex++] = c;
            break;
        }
        break;

      case 'HEX0':
        state = 'HEX1';
        hexchar = c;
        if (charCode('0') <= c && c <= charCode('9')) {
          n = c - charCode('0');
        } else if (charCode('a') <= c && c <= charCode('f')) {
          n = c - charCode('a') + 10;
        } else if (charCode('A') <= c && c <= charCode('F')) {
          n = c - charCode('A') + 10;
        } else {
          out[outIndex++] = charCode('%');
          out[outIndex++] = c;
          state = 'CHAR';
          break;
        }
        break;

      case 'HEX1':
        state = 'CHAR';
        if (charCode('0') <= c && c <= charCode('9')) {
          m = c - charCode('0');
        } else if (charCode('a') <= c && c <= charCode('f')) {
          m = c - charCode('a') + 10;
        } else if (charCode('A') <= c && c <= charCode('F')) {
          m = c - charCode('A') + 10;
        } else {
          out[outIndex++] = charCode('%');
          out[outIndex++] = hexchar;
          out[outIndex++] = c;
          break;
        }
        out[outIndex++] = 16*n + m;
        break;
    }
  }

  // TODO support returning arbitrary buffers.

  return out.slice(0, outIndex-1);
};


QueryString.unescape = function (s, decodeSpaces) {
  return QueryString.unescapeBuffer(s, decodeSpaces).toString();
};


QueryString.escape = function (str) {
  return encodeURIComponent(str);
};

var stringifyPrimitive = function(v) {
  switch (typeof v) {
    case "string":
      return v;

    case "boolean":
      return v ? "true" : "false";

    case "number":
      return isFinite(v) ? v : "";

    default:
      return "";
  }
};

/**
 * <p>Converts an arbitrary value to a Query String representation.</p>
 *
 * <p>Objects with cyclical references will trigger an exception.</p>
 *
 * @method stringify
 * @param obj {Variant} any arbitrary value to convert to query string
 * @param sep {String} (optional) Character that should join param k=v pairs together. Default: "&"
 * @param eq  {String} (optional) Character that should join keys to their values. Default: "="
 * @param name {String} (optional) Name of the current key, for handling children recursively.
 * @static
 */
QueryString.stringify = QueryString.encode = function (obj, sep, eq, name) {
  sep = sep || "&";
  eq = eq || "=";
  obj = (obj === null) ? undefined : obj;

  switch (typeof obj) {
    case "object":
      return Object.keys(obj).map(function(k) {
        if (Array.isArray(obj[k])) {
          return obj[k].map(function(v) {
            return QueryString.escape(stringifyPrimitive(k)) +
                   eq +
                   QueryString.escape(stringifyPrimitive(v));
          }).join(sep);
        } else {
          return QueryString.escape(stringifyPrimitive(k)) + 
                 eq +
                 QueryString.escape(stringifyPrimitive(obj[k]));
        }
      }).join(sep);

    default:
      return (name) ?
        QueryString.escape(stringifyPrimitive(name)) + eq +
          QueryString.escape(stringifyPrimitive(obj)) :
        "";
  }
};

// Parse a key=val string.
QueryString.parse = QueryString.decode = function (qs, sep, eq) {
  sep = sep || "&";
  eq = eq || "=";
  var obj = {};

  if (typeof qs !== 'string') {
    return obj;
  }

  qs.split(sep).forEach(function(kvp) {
    var x = kvp.split(eq);
    var k = QueryString.unescape(x[0], true);
    var v = QueryString.unescape(x.slice(1).join(eq), true);

    if (!(k in obj)) {
        obj[k] = v;
    } else if (!Array.isArray(obj[k])) {
        obj[k] = [obj[k], v];
    } else {
        obj[k].push(v);
    }
  });

  return obj;
};