// According to RFC 3986, only characters from a set of reserved and a set
// of unreserved characters are allowed in a URL:
var unreserved = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-_.~";
var reserved   = "!*'();:@&=+$,/?%#[]";
var allowed    = unreserved + reserved;
var hexchars   = "0123456789ABCDEFabcdef";

// Found on http://www.hypergurl.com/urlencode.html. Thank you!
function o2escape(str) {
  var encoded = "";

  for (var i = 0; i < str.length; i++) {
    var ch = str.charAt(i);
    // Check if character is an unreserved character:
    if (unreserved.indexOf(ch) != -1) {
      encoded = encoded + ch;
    }
    else {

      // The position in the Unicode table tells us how many bytes are needed.
      // Note that if we talk about first, second, etc. in the following, we are
      // counting from left to right:
      //
      //   Position in   |  Bytes needed   | Binary representation
      //  Unicode table  |   for UTF-8     |       of UTF-8
      // ----------------------------------------------------------
      //     0 -     127 |    1 byte       | 0XXX.XXXX
      //   128 -    2047 |    2 bytes      | 110X.XXXX 10XX.XXXX
      //  2048 -   65535 |    3 bytes      | 1110.XXXX 10XX.XXXX 10XX.XXXX
      // 65536 - 2097151 |    4 bytes      | 1111.0XXX 10XX.XXXX 10XX.XXXX 10XX.XXXX

      var charcode = str.charCodeAt(i);

      // Position 0 - 127 is equal to percent-encoding with an ASCII character encoding:
      if (charcode < 128) {
        encoded = encoded + gethex(charcode);
      }

      // Position 128 - 2047: two bytes for UTF-8 character encoding.
      if (charcode > 127 && charcode < 2048) {
        // First UTF byte: Mask the first five bits of charcode with binary 110X.XXXX:
        encoded = encoded + gethex((charcode >> 6) | 0xC0);
        // Second UTF byte: Get last six bits of charcode and mask them with binary 10XX.XXXX:
        encoded = encoded + gethex((charcode & 0x3F) | 0x80);
      }

      // Position 2048 - 65535: three bytes for UTF-8 character encoding.
      if (charcode > 2047 && charcode < 65536) {
        // First UTF byte: Mask the first four bits of charcode with binary 1110.XXXX:
        encoded = encoded + gethex((charcode >> 12) | 0xE0);
        // Second UTF byte: Get the next six bits of charcode and mask them binary 10XX.XXXX:
        encoded = encoded + gethex(((charcode >> 6) & 0x3F) | 0x80);
        // Third UTF byte: Get the last six bits of charcode and mask them binary 10XX.XXXX:
        encoded = encoded + gethex((charcode & 0x3F) | 0x80);
      }

      // Position 65536 - : four bytes for UTF-8 character encoding.
      if (charcode > 65535) {
        // First UTF byte: Mask the first three bits of charcode with binary 1111.0XXX:
        encoded = encoded + gethex((charcode >> 18) | 0xF0);
        // Second UTF byte: Get the next six bits of charcode and mask them binary 10XX.XXXX:
        encoded = encoded + gethex(((charcode >> 12) & 0x3F) | 0x80);
        // Third UTF byte: Get the last six bits of charcode and mask them binary 10XX.XXXX:
        encoded = encoded + gethex(((charcode >> 6) & 0x3F) | 0x80);
        // Fourth UTF byte: Get the last six bits of charcode and mask them binary 10XX.XXXX:
        encoded = encoded + gethex((charcode & 0x3F) | 0x80);
      }

    }
  }
  // console.log(encoded);
  return encoded;
}

function gethex(decimal) {
  return "%" + hexchars.charAt(decimal >> 4) + hexchars.charAt(decimal & 0xF);
}