text: 'use strict';
  
  var libcharset = require('./charset');
  var libbase64 = require('libbase64');
  var libqp = require('libqp');
  var mimetypes = require('./mimetypes');
  
  var libmime = module.exports = {
  
      /**
       * Checks if a value is plaintext string (uses only printable 7bit chars)
       *
       * @param {String} value String to be tested
       * @returns {Boolean} true if it is a plaintext string
       */
      isPlainText: function(value) {
          if (typeof value !== 'string' || /[\x00-\x08\x0b\x0c\x0e-\x1f\u0080-\uFFFF]/.test(value)) {
              return false;
          } else {
              return true;
          }
      },
  
      /**
       * Checks if a multi line string containes lines longer than the selected value.
       *
       * Useful when detecting if a mail message needs any processing at all –
       * if only plaintext characters are used and lines are short, then there is
       * no need to encode the values in any way. If the value is plaintext but has
       * longer lines then allowed, then use format=flowed
       *
       * @param {Number} lineLength Max line length to check for
       * @returns {Boolean} Returns true if there is at least one line longer than lineLength chars
       */
      hasLongerLines: function(str, lineLength) {
          return new RegExp('^.{' + (lineLength + 1) + ',}', 'm').test(str);
      },
  
      /**
       * Decodes a string from a format=flowed soft wrapping.
       *
       * @param {String} str Plaintext string with format=flowed to decode
       * @param {Boolean} [delSp] If true, delete leading spaces (delsp=yes)
       * @return {String} Mime decoded string
       */
      decodeFlowed: function(str, delSp) {
          str = (str || '').toString();
  
          return str.
          split(/\r?\n/).
          // remove soft linebreaks
          // soft linebreaks are added after space symbols
          reduce(function(previousValue, currentValue, index) {
              var body = previousValue;
              if (delSp) {
                  // delsp adds spaces to text to be able to fold it
                  // these spaces can be removed once the text is unfolded
                  body = body.replace(/[ ]+$/, '');
              }
              if (/ $/.test(previousValue) && !/(^|\n)\-\- $/.test(previousValue) || index === 1) {
                  return body + currentValue;
              } else {
                  return body + '\n' + currentValue;
              }
          }).
          // remove whitespace stuffing
          // http://tools.ietf.org/html/rfc3676#section-4.4
          replace(/^ /gm, '');
      },
  
      /**
       * Adds soft line breaks to content marked with format=flowed to
       * ensure that no line in the message is never longer than lineLength
       *
       * @param {String} str Plaintext string that requires wrapping
       * @param {Number} [lineLength=76] Maximum length of a line
       * @return {String} String with forced line breaks
       */
      encodeFlowed: function(str, lineLength) {
          lineLength = lineLength || 76;
  
          var flowed = [];
          str.split(/\r?\n/).forEach(function(line) {
              flowed.push(libmime.foldLines(line.
                  // space stuffing http://tools.ietf.org/html/rfc3676#section-4.2
                  replace(/^( |From|>)/igm, ' $1'),
                  lineLength, true));
          });
          return flowed.join('\r\n');
      },
  
      /**
       * Encodes a string or an Buffer to an UTF-8 MIME Word (rfc2047)
       *
       * @param {String|Buffer} data String to be encoded
       * @param {String} mimeWordEncoding='Q' Encoding for the mime word, either Q or B
       * @param {Number} [maxLength=0] If set, split mime words into several chunks if needed
       * @return {String} Single or several mime words joined together
       */
      encodeWord: function(data, mimeWordEncoding, maxLength) {
          mimeWordEncoding = (mimeWordEncoding || 'Q').toString().toUpperCase().trim().charAt(0);
          maxLength = maxLength || 0;
  
          var encodedStr,
              toCharset = 'UTF-8',
              i, len, parts;
  
          if (maxLength && maxLength > 7 + toCharset.length) {
              maxLength -= (7 + toCharset.length);
          }
  
          if (mimeWordEncoding === 'Q') {
              encodedStr = libqp.encode(data).replace(/[_?\r\n\t"]/g, function(chr) {
                  var ord = chr.charCodeAt(0).toString(16).toUpperCase();
                  return '=' + (ord.length === 1 ? '0' + ord : ord);
              }).replace(/%20| /g, '_');
          } else if (mimeWordEncoding === 'B') {
              encodedStr = typeof data === 'string' ? data : libbase64.encode(data);
              maxLength = Math.max(3, (maxLength - maxLength % 4) / 4 * 3);
          }
  
          if (maxLength && encodedStr.length > maxLength) {
              if (mimeWordEncoding === 'Q') {
                  encodedStr = splitMimeEncodedString(encodedStr, maxLength).join('?= =?' + toCharset + '?' + mimeWordEncoding + '?');
              } else {
  
                  // RFC2047 6.3 (2) states that encoded-word must include an integral number of characters, so no chopping unicode sequences
                  parts = [];
                  for (i = 0, len = encodedStr.length; i < len; i += maxLength) {
                      parts.push(libbase64.encode(encodedStr.substr(i, maxLength)));
                  }
  
                  if (parts.length > 1) {
                      encodedStr = parts.join('?= =?' + toCharset + '?' + mimeWordEncoding + '?');
                  } else {
                      encodedStr = parts.join('');
                  }
              }
          } else if (mimeWordEncoding === 'B') {
              encodedStr = libbase64.encode(data);
          }
  
          return '=?' + toCharset + '?' + mimeWordEncoding + '?' + encodedStr + (encodedStr.substr(-2) === '?=' ? '' : '?=');
      },
  
      /**
       * Decode a complete mime word encoded string
       *
       * @param {String} str Mime word encoded string
       * @return {String} Decoded unicode string
       */
      decodeWord: function(str) {
          str = (str || '').toString().trim();
  
          var fromCharset, encoding, match;
  
          match = str.match(/^\=\?([\w_\-\*]+)\?([QqBb])\?([^\?]+)\?\=$/i);
          if (!match) {
              return str;
          }
  
          // RFC2231 added language tag to the encoding
          // see: https://tools.ietf.org/html/rfc2231#section-5
          // this implementation silently ignores this tag
          fromCharset = match[1].split('*').shift();
  
          encoding = (match[2] || 'Q').toString().toUpperCase();
          str = (match[3] || '').replace(/_/g, ' ').replace(/ $/, '=20');
  
          if (encoding === 'B') {
              return libcharset.decode(libbase64.decode(str), fromCharset);
          } else if (encoding === 'Q') {
              return libcharset.decode(libqp.decode(str), fromCharset);
          } else {
              return str;
          }
      },
  
      /**
       * Finds word sequences with non ascii text and converts these to mime words
       *
       * @param {String|Buffer} data String to be encoded
       * @param {String} mimeWordEncoding='Q' Encoding for the mime word, either Q or B
       * @param {Number} [maxLength=0] If set, split mime words into several chunks if needed
       * @param {String} [fromCharset='UTF-8'] Source sharacter set
       * @return {String} String with possible mime words
       */
      encodeWords: function(data, mimeWordEncoding, maxLength, fromCharset) {
          if (!fromCharset && typeof maxLength === 'string' && !maxLength.match(/^[0-9]+$/)) {
              fromCharset = maxLength;
              maxLength = undefined;
          }
  
          maxLength = maxLength || 0;
  
          var decodedValue = libcharset.decode(libcharset.convert((data || ''), fromCharset)),
              encodedValue;
  
          encodedValue = decodedValue.replace(/([^\s\u0080-\uFFFF]*[\u0080-\uFFFF]+[^\s\u0080-\uFFFF]*(?:\s+[^\s\u0080-\uFFFF]*[\u0080-\uFFFF]+[^\s\u0080-\uFFFF]*\s*)?)+/g, function(match) {
              return match.length ? libmime.encodeWord(match, mimeWordEncoding || 'Q', maxLength) : '';
          });
  
          return encodedValue;
      },
  
      /**
       * Decode a string that might include one or several mime words
       *
       * @param {String} str String including some mime words that will be encoded
       * @return {String} Decoded unicode string
       */
      decodeWords: function(str) {
          str = (str || '').toString();
          str = str.
          replace(/(=\?[^?]+\?[QqBb]\?[^?]+\?=)\s+(?==\?[^?]+\?[QqBb]\?[^?]+\?=)/g, '$1').
          replace(/\=\?([\w_\-\*]+)\?([QqBb])\?[^\?]+\?\=/g, function(mimeWord) {
              return libmime.decodeWord(mimeWord);
          });
  
          return str;
      },
  
      /**
       * Splits a string by :
       * The result is not mime word decoded, you need to do your own decoding based
       * on the rules for the specific header key
       *
       * @param {String} headerLine Single header line, might include linebreaks as well if folded
       * @return {Object} And object of {key, value}
       */
      decodeHeader: function(headerLine) {
          var line = (headerLine || '').toString().replace(/(?:\r?\n|\r)[ \t]*/g, ' ').trim(),
              match = line.match(/^\s*([^:]+):(.*)$/),
              key = (match && match[1] || '').trim().toLowerCase(),
              value = (match && match[2] || '').trim();
  
          return {
              key: key,
              value: value
          };
      },
  
      /**
       * Parses a block of header lines. Does not decode mime words as every
       * header might have its own rules (eg. formatted email addresses and such)
       *
       * @param {String} headers Headers string
       * @return {Object} An object of headers, where header keys are object keys. NB! Several values with the same key make up an Array
       */
      decodeHeaders: function(headers) {
          var lines = headers.split(/\r?\n|\r/),
              headersObj = {},
              header,
              i, len;
  
          for (i = lines.length - 1; i >= 0; i--) {
              if (i && lines[i].match(/^\s/)) {
                  lines[i - 1] += '\r\n' + lines[i];
                  lines.splice(i, 1);
              }
          }
  
          for (i = 0, len = lines.length; i < len; i++) {
              header = libmime.decodeHeader(lines[i]);
              if (!headersObj[header.key]) {
                  headersObj[header.key] = [header.value];
              } else {
                  headersObj[header.key].push(header.value);
              }
          }
  
          return headersObj;
      },
  
      /**
       * Joins parsed header value together as 'value; param1=value1; param2=value2'
       *
       * @param {Object} structured Parsed header value
       * @return {String} joined header value
       */
      buildHeaderValue: function(structured) {
          var paramsArray = [];
  
          Object.keys(structured.params || {}).forEach(function(param) {
              // filename might include unicode characters so it is a special case
              var value = structured.params[param];
              if (param === 'filename' || !libmime.isPlainText(value) || value.length >= 75) {
                  libmime.buildHeaderParam(param, value, 50).forEach(function(encodedParam) {
                      if (encodedParam.key === param) {
                          paramsArray.push(encodedParam.key + '=' + encodedParam.value);
                      } else {
                          paramsArray.push(encodedParam.key + '="' + encodedParam.value + '"');
                      }
                  });
              } else {
                  if (value.match(/[\s'"\\;\/=]|^\-/g)) {
                      paramsArray.push(param + '="' + value.replace(/(["\\])/g, "\\$1") + '"');
                  } else {
                      paramsArray.push(param + '=' + value);
                  }
              }
          }.bind(this));
  
          return structured.value + (paramsArray.length ? '; ' + paramsArray.join('; ') : '');
      },
  
      /**
       * Parses a header value with key=value arguments into a structured
       * object.
       *
       *   parseHeaderValue('content-type: text/plain; CHARSET='UTF-8'') ->
       *   {
       *     'value': 'text/plain',
       *     'params': {
       *       'charset': 'UTF-8'
       *     }
       *   }
       *
       * @param {String} str Header value
       * @return {Object} Header value as a parsed structure
       */
      parseHeaderValue: function(str) {
          var response = {
                  value: false,
                  params: {}
              },
              key = false,
              value = '',
              type = 'value',
              quote = false,
              escaped = false,
              chr;
  
          for (var i = 0, len = str.length; i < len; i++) {
              chr = str.charAt(i);
              if (type === 'key') {
                  if (chr === '=') {
                      key = value.trim().toLowerCase();
                      type = 'value';
                      value = '';
                      continue;
                  }
                  value += chr;
              } else {
                  if (escaped) {
                      value += chr;
                  } else if (chr === '\\') {
                      escaped = true;
                      continue;
                  } else if (quote && chr === quote) {
                      quote = false;
                  } else if (!quote && chr === '"') {
                      quote = chr;
                  } else if (!quote && chr === ';') {
                      if (key === false) {
                          response.value = value.trim();
                      } else {
                          response.params[key] = value.trim();
                      }
                      type = 'key';
                      value = '';
                  } else {
                      value += chr;
                  }
                  escaped = false;
  
              }
          }
  
          if (type === 'value') {
              if (key === false) {
                  response.value = value.trim();
              } else {
                  response.params[key] = value.trim();
              }
          } else if (value.trim()) {
              response.params[value.trim().toLowerCase()] = '';
          }
  
          // handle parameter value continuations
          // https://tools.ietf.org/html/rfc2231#section-3
  
          // preprocess values
          Object.keys(response.params).forEach(function(key) {
              var actualKey, nr, match, value;
              if ((match = key.match(/(\*(\d+)|\*(\d+)\*|\*)$/))) {
                  actualKey = key.substr(0, match.index);
                  nr = Number(match[2] || match[3]) || 0;
  
                  if (!response.params[actualKey] || typeof response.params[actualKey] !== 'object') {
                      response.params[actualKey] = {
                          charset: false,
                          values: []
                      };
                  }
  
                  value = response.params[key];
  
                  if (nr === 0 && match[0].substr(-1) === '*' && (match = value.match(/^([^']*)'[^']*'(.*)$/))) {
                      response.params[actualKey].charset = match[1] || 'iso-8859-1';
                      value = match[2];
                  }
  
                  response.params[actualKey].values[nr] = value;
  
                  // remove the old reference
                  delete response.params[key];
              }
          });
  
          // concatenate split rfc2231 strings and convert encoded strings to mime encoded words
          Object.keys(response.params).forEach(function(key) {
              var value;
              if (response.params[key] && Array.isArray(response.params[key].values)) {
                  value = response.params[key].values.map(function(val) {
                      return val || '';
                  }).join('');
  
                  if (response.params[key].charset) {
                      // convert "%AB" to "=?charset?Q?=AB?="
                      response.params[key] = '=?' +
                          response.params[key].charset +
                          '?Q?' +
                          value.
                      // fix invalidly encoded chars
                      replace(/[=\?_\s]/g, function(s) {
                          var c = s.charCodeAt(0).toString(16);
                          if (s === ' ') {
                              return '_';
                          } else {
                              return '%' + (c.length < 2 ? '0' : '') + c;
                          }
                      }).
                      // change from urlencoding to percent encoding
                      replace(/%/g, '=') +
                          '?=';
                  } else {
                      response.params[key] = value;
                  }
              }
          }.bind(this));
  
          return response;
      },
  
      /**
       * Encodes a string or an Buffer to an UTF-8 Parameter Value Continuation encoding (rfc2231)
       * Useful for splitting long parameter values.
       *
       * For example
       *      title="unicode string"
       * becomes
       *     title*0*="utf-8''unicode"
       *     title*1*="%20string"
       *
       * @param {String|Buffer} data String to be encoded
       * @param {Number} [maxLength=50] Max length for generated chunks
       * @param {String} [fromCharset='UTF-8'] Source sharacter set
       * @return {Array} A list of encoded keys and headers
       */
      buildHeaderParam: function(key, data, maxLength, fromCharset) {
          var list = [];
          var encodedStr = typeof data === 'string' ? data : libmime.decode(data, fromCharset);
          var chr;
          var line;
          var startPos = 0;
          var isEncoded = false;
  
          maxLength = maxLength || 50;
  
          // process ascii only text
          if (/^[\w.\- ]*$/.test(data)) {
  
              // check if conversion is even needed
              if (encodedStr.length <= maxLength) {
                  return [{
                      key: key,
                      value: encodedStr
                  }];
              }
  
              encodedStr = encodedStr.replace(new RegExp('.{' + maxLength + '}', 'g'), function(str) {
                  list.push({
                      line: str
                  });
                  return '';
              });
  
              if (encodedStr) {
                  list.push({
                      line: encodedStr
                  });
              }
  
          } else {
  
              // first line includes the charset and language info and needs to be encoded
              // even if it does not contain any unicode characters
              line = 'utf-8\'\'';
              isEncoded = true;
              startPos = 0;
              // process text with unicode or special chars
              for (var i = 0, len = encodedStr.length; i < len; i++) {
  
                  chr = encodedStr[i];
  
                  if (isEncoded) {
                      chr = encodeURIComponent(chr);
                  } else {
                      // try to urlencode current char
                      chr = chr === ' ' ? chr : encodeURIComponent(chr);
                      // By default it is not required to encode a line, the need
                      // only appears when the string contains unicode or special chars
                      // in this case we start processing the line over and encode all chars
                      if (chr !== encodedStr[i]) {
                          // Check if it is even possible to add the encoded char to the line
                          // If not, there is no reason to use this line, just push it to the list
                          // and start a new line with the char that needs encoding
                          if ((encodeURIComponent(line) + chr).length >= maxLength) {
                              list.push({
                                  line: line,
                                  encoded: isEncoded
                              });
                              line = '';
                              startPos = i - 1;
                          } else {
                              isEncoded = true;
                              i = startPos;
                              line = '';
                              continue;
                          }
                      }
                  }
  
                  // if the line is already too long, push it to the list and start a new one
                  if ((line + chr).length >= maxLength) {
                      list.push({
                          line: line,
                          encoded: isEncoded
                      });
                      line = chr = encodedStr[i] === ' ' ? ' ' : encodeURIComponent(encodedStr[i]);
                      if (chr === encodedStr[i]) {
                          isEncoded = false;
                          startPos = i - 1;
                      } else {
                          isEncoded = true;
                      }
                  } else {
                      line += chr;
                  }
              }
  
              if (line) {
                  list.push({
                      line: line,
                      encoded: isEncoded
                  });
              }
          }
  
          return list.map(function(item, i) {
              return {
                  // encoded lines: {name}*{part}*
                  // unencoded lines: {name}*{part}
                  // if any line needs to be encoded then the first line (part==0) is always encoded
                  key: key + '*' + i + (item.encoded ? '*' : ''),
                  value: item.line
              };
          });
      },
  
      /**
       * Returns file extension for a content type string. If no suitable extensions
       * are found, 'bin' is used as the default extension
       *
       * @param {String} mimeType Content type to be checked for
       * @return {String} File extension
       */
      detectExtension: function(mimeType) {
          mimeType = (mimeType || '').toString().toLowerCase().replace(/\s/g, '');
          if (!(mimeType in mimetypes.list)) {
              return 'bin';
          }
  
          if (typeof mimetypes.list[mimeType] === 'string') {
              return mimetypes.list[mimeType];
          }
  
          var mimeParts = mimeType.split('/');
  
          // search for name match
          for (var i = 0, len = mimetypes.list[mimeType].length; i < len; i++) {
              if (mimeParts[1] === mimetypes.list[mimeType][i]) {
                  return mimetypes.list[mimeType][i];
              }
          }
  
          // use the first one
          return mimetypes.list[mimeType][0] !== '*' ? mimetypes.list[mimeType][0] : 'bin';
      },
  
      /**
       * Returns content type for a file extension. If no suitable content types
       * are found, 'application/octet-stream' is used as the default content type
       *
       * @param {String} extension Extension to be checked for
       * @return {String} File extension
       */
      detectMimeType: function(extension) {
          extension = (extension || '').toString().toLowerCase().replace(/\s/g, '').replace(/^\./g, '').split('.').pop();
  
          if (!(extension in mimetypes.extensions)) {
              return 'application/octet-stream';
          }
  
          if (typeof mimetypes.extensions[extension] === 'string') {
              return mimetypes.extensions[extension];
          }
  
          var mimeParts;
  
          // search for name match
          for (var i = 0, len = mimetypes.extensions[extension].length; i < len; i++) {
              mimeParts = mimetypes.extensions[extension][i].split('/');
              if (mimeParts[1] === extension) {
                  return mimetypes.extensions[extension][i];
              }
          }
  
          // use the first one
          return mimetypes.extensions[extension][0];
      },
  
      /**
       * Folds long lines, useful for folding header lines (afterSpace=false) and
       * flowed text (afterSpace=true)
       *
       * @param {String} str String to be folded
       * @param {Number} [lineLength=76] Maximum length of a line
       * @param {Boolean} afterSpace If true, leave a space in th end of a line
       * @return {String} String with folded lines
       */
      foldLines: function(str, lineLength, afterSpace) {
          str = (str || '').toString();
          lineLength = lineLength || 76;
  
          var pos = 0,
              len = str.length,
              result = '',
              line, match;
  
          while (pos < len) {
              line = str.substr(pos, lineLength);
              if (line.length < lineLength) {
                  result += line;
                  break;
              }
              if ((match = line.match(/^[^\n\r]*(\r?\n|\r)/))) {
                  line = match[0];
                  result += line;
                  pos += line.length;
                  continue;
              } else if ((match = line.match(/(\s+)[^\s]*$/)) && match[0].length - (afterSpace ? (match[1] || '').length : 0) < line.length) {
                  line = line.substr(0, line.length - (match[0].length - (afterSpace ? (match[1] || '').length : 0)));
              } else if ((match = str.substr(pos + line.length).match(/^[^\s]+(\s*)/))) {
                  line = line + match[0].substr(0, match[0].length - (!afterSpace ? (match[1] || '').length : 0));
              }
  
              result += line;
              pos += line.length;
              if (pos < len) {
                  result += '\r\n';
              }
          }
  
          return result;
      }
  };
  
  /**
   * Splits a mime encoded string. Needed for dividing mime words into smaller chunks
   *
   * @param {String} str Mime encoded string to be split up
   * @param {Number} maxlen Maximum length of characters for one part (minimum 12)
   * @return {Array} Split string
   */
  function splitMimeEncodedString(str, maxlen) {
      var curLine, match, chr, done,
          lines = [];
  
      // require at least 12 symbols to fit possible 4 octet UTF-8 sequences
      maxlen = Math.max(maxlen || 0, 12);
  
      while (str.length) {
          curLine = str.substr(0, maxlen);
  
          // move incomplete escaped char back to main
          if ((match = curLine.match(/\=[0-9A-F]?$/i))) {
              curLine = curLine.substr(0, match.index);
          }
  
          done = false;
          while (!done) {
              done = true;
              // check if not middle of a unicode char sequence
              if ((match = str.substr(curLine.length).match(/^\=([0-9A-F]{2})/i))) {
                  chr = parseInt(match[1], 16);
                  // invalid sequence, move one char back anc recheck
                  if (chr < 0xC2 && chr > 0x7F) {
                      curLine = curLine.substr(0, curLine.length - 3);
                      done = false;
                  }
              }
          }
  
          if (curLine.length) {
              lines.push(curLine);
          }
          str = str.substr(curLine.length);
      }
  
      return lines;
  }