text: /* eslint no-control-regex:0 */
  
  'use strict';
  
  const base64 = require('../base64');
  const qp = require('../qp');
  const mimeTypes = require('./mime-types');
  
  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(value, isParam) {
          const re = isParam ? /[\x00-\x08\x0b\x0c\x0e-\x1f"\u0080-\uFFFF]/ : /[\x00-\x08\x0b\x0c\x0e-\x1f\u0080-\uFFFF]/;
          if (typeof value !== 'string' || re.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(str, lineLength) {
          if (str.length > 128 * 1024) {
              // do not test strings longer than 128kB
              return true;
          }
          return new RegExp('^.{' + (lineLength + 1) + ',}', 'm').test(str);
      },
  
      /**
       * 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(data, mimeWordEncoding, maxLength) {
          mimeWordEncoding = (mimeWordEncoding || 'Q').toString().toUpperCase().trim().charAt(0);
          maxLength = maxLength || 0;
  
          let encodedStr;
          let toCharset = 'UTF-8';
  
          if (maxLength && maxLength > 7 + toCharset.length) {
              maxLength -= 7 + toCharset.length;
          }
  
          if (mimeWordEncoding === 'Q') {
              // https://tools.ietf.org/html/rfc2047#section-5 rule (3)
              encodedStr = qp.encode(data).replace(/[^a-z0-9!*+\-/=]/gi, chr => {
                  let ord = chr.charCodeAt(0).toString(16).toUpperCase();
                  if (chr === ' ') {
                      return '_';
                  } else {
                      return '=' + (ord.length === 1 ? '0' + ord : ord);
                  }
              });
          } else if (mimeWordEncoding === 'B') {
              encodedStr = typeof data === 'string' ? data : base64.encode(data);
              maxLength = maxLength ? Math.max(3, ((maxLength - (maxLength % 4)) / 4) * 3) : 0;
          }
  
          if (maxLength && (mimeWordEncoding !== 'B' ? encodedStr : base64.encode(data)).length > maxLength) {
              if (mimeWordEncoding === 'Q') {
                  encodedStr = this.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
                  let parts = [];
                  let lpart = '';
                  for (let i = 0, len = encodedStr.length; i < len; i++) {
                      let chr = encodedStr.charAt(i);
                      // check if we can add this character to the existing string
                      // without breaking byte length limit
                      if (Buffer.byteLength(lpart + chr) <= maxLength || i === 0) {
                          lpart += chr;
                      } else {
                          // we hit the length limit, so push the existing string and start over
                          parts.push(base64.encode(lpart));
                          lpart = chr;
                      }
                  }
                  if (lpart) {
                      parts.push(base64.encode(lpart));
                  }
  
                  if (parts.length > 1) {
                      encodedStr = parts.join('?= =?' + toCharset + '?' + mimeWordEncoding + '?');
                  } else {
                      encodedStr = parts.join('');
                  }
              }
          } else if (mimeWordEncoding === 'B') {
              encodedStr = base64.encode(data);
          }
  
          return '=?' + toCharset + '?' + mimeWordEncoding + '?' + encodedStr + (encodedStr.substr(-2) === '?=' ? '' : '?=');
      },
  
      /**
       * Finds word sequences with non ascii text and converts these to mime words
       *
       * @param {String} value 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 {Boolean} [encodeAll=false] If true and the value needs encoding then encodes entire string, not just the smallest match
       * @return {String} String with possible mime words
       */
      encodeWords(value, mimeWordEncoding, maxLength, encodeAll) {
          maxLength = maxLength || 0;
  
          let encodedValue;
  
          // find first word with a non-printable ascii or special symbol in it
          let firstMatch = value.match(/(?:^|\s)([^\s]*["\u0080-\uFFFF])/);
          if (!firstMatch) {
              return value;
          }
  
          if (encodeAll) {
              // if it is requested to encode everything or the string contains something that resebles encoded word, then encode everything
  
              return this.encodeWord(value, mimeWordEncoding, maxLength);
          }
  
          // find the last word with a non-printable ascii in it
          let lastMatch = value.match(/(["\u0080-\uFFFF][^\s]*)[^"\u0080-\uFFFF]*$/);
          if (!lastMatch) {
              // should not happen
              return value;
          }
  
          let startIndex =
              firstMatch.index +
              (
                  firstMatch[0].match(/[^\s]/) || {
                      index: 0
                  }
              ).index;
          let endIndex = lastMatch.index + (lastMatch[1] || '').length;
  
          encodedValue =
              (startIndex ? value.substr(0, startIndex) : '') +
              this.encodeWord(value.substring(startIndex, endIndex), mimeWordEncoding || 'Q', maxLength) +
              (endIndex < value.length ? value.substr(endIndex) : '');
  
          return encodedValue;
      },
  
      /**
       * Joins parsed header value together as 'value; param1=value1; param2=value2'
       * PS: We are following RFC 822 for the list of special characters that we need to keep in quotes.
       *      Refer: https://www.w3.org/Protocols/rfc1341/4_Content-Type.html
       * @param {Object} structured Parsed header value
       * @return {String} joined header value
       */
      buildHeaderValue(structured) {
          let paramsArray = [];
  
          Object.keys(structured.params || {}).forEach(param => {
              // filename might include unicode characters so it is a special case
              // other values probably do not
              let value = structured.params[param];
              if (!this.isPlainText(value, true) || value.length >= 75) {
                  this.buildHeaderParam(param, value, 50).forEach(encodedParam => {
                      if (!/[\s"\\;:/=(),<>@[\]?]|^[-']|'$/.test(encodedParam.value) || encodedParam.key.substr(-1) === '*') {
                          paramsArray.push(encodedParam.key + '=' + encodedParam.value);
                      } else {
                          paramsArray.push(encodedParam.key + '=' + JSON.stringify(encodedParam.value));
                      }
                  });
              } else if (/[\s'"\\;:/=(),<>@[\]?]|^-/.test(value)) {
                  paramsArray.push(param + '=' + JSON.stringify(value));
              } else {
                  paramsArray.push(param + '=' + value);
              }
          });
  
          return structured.value + (paramsArray.length ? '; ' + paramsArray.join('; ') : '');
      },
  
      /**
       * 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(key, data, maxLength) {
          let list = [];
          let encodedStr = typeof data === 'string' ? data : (data || '').toString();
          let encodedStrArr;
          let chr, ord;
          let line;
          let startPos = 0;
          let i, len;
  
          maxLength = maxLength || 50;
  
          // process ascii only text
          if (this.isPlainText(data, true)) {
              // check if conversion is even needed
              if (encodedStr.length <= maxLength) {
                  return [
                      {
                          key,
                          value: encodedStr
                      }
                  ];
              }
  
              encodedStr = encodedStr.replace(new RegExp('.{' + maxLength + '}', 'g'), str => {
                  list.push({
                      line: str
                  });
                  return '';
              });
  
              if (encodedStr) {
                  list.push({
                      line: encodedStr
                  });
              }
          } else {
              if (/[\uD800-\uDBFF]/.test(encodedStr)) {
                  // string containts surrogate pairs, so normalize it to an array of bytes
                  encodedStrArr = [];
                  for (i = 0, len = encodedStr.length; i < len; i++) {
                      chr = encodedStr.charAt(i);
                      ord = chr.charCodeAt(0);
                      if (ord >= 0xd800 && ord <= 0xdbff && i < len - 1) {
                          chr += encodedStr.charAt(i + 1);
                          encodedStrArr.push(chr);
                          i++;
                      } else {
                          encodedStrArr.push(chr);
                      }
                  }
                  encodedStr = encodedStrArr;
              }
  
              // 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\x27\x27';
              let encoded = true;
              startPos = 0;
  
              // process text with unicode or special chars
              for (i = 0, len = encodedStr.length; i < len; i++) {
                  chr = encodedStr[i];
  
                  if (encoded) {
                      chr = this.safeEncodeURIComponent(chr);
                  } else {
                      // try to urlencode current char
                      chr = chr === ' ' ? chr : this.safeEncodeURIComponent(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 ((this.safeEncodeURIComponent(line) + chr).length >= maxLength) {
                              list.push({
                                  line,
                                  encoded
                              });
                              line = '';
                              startPos = i - 1;
                          } else {
                              encoded = 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,
                          encoded
                      });
                      line = chr = encodedStr[i] === ' ' ? ' ' : this.safeEncodeURIComponent(encodedStr[i]);
                      if (chr === encodedStr[i]) {
                          encoded = false;
                          startPos = i - 1;
                      } else {
                          encoded = true;
                      }
                  } else {
                      line += chr;
                  }
              }
  
              if (line) {
                  list.push({
                      line,
                      encoded
                  });
              }
          }
  
          return list.map((item, i) => ({
              // 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
          }));
      },
  
      /**
       * 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(str) {
          let response = {
              value: false,
              params: {}
          };
          let key = false;
          let value = '';
          let type = 'value';
          let quote = false;
          let escaped = false;
          let chr;
  
          for (let 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(key => {
              let 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(key => {
              let value;
              if (response.params[key] && Array.isArray(response.params[key].values)) {
                  value = response.params[key].values.map(val => 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, s => {
                                  let 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;
                  }
              }
          });
  
          return response;
      },
  
      /**
       * 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: mimeType => mimeTypes.detectExtension(mimeType),
  
      /**
       * 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: extension => mimeTypes.detectMimeType(extension),
  
      /**
       * 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(str, lineLength, afterSpace) {
          str = (str || '').toString();
          lineLength = lineLength || 76;
  
          let 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
       */
      splitMimeEncodedString: (str, maxlen) => {
          let 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;
      },
  
      encodeURICharComponent: chr => {
          let res = '';
          let ord = chr.charCodeAt(0).toString(16).toUpperCase();
  
          if (ord.length % 2) {
              ord = '0' + ord;
          }
  
          if (ord.length > 2) {
              for (let i = 0, len = ord.length / 2; i < len; i++) {
                  res += '%' + ord.substr(i, 2);
              }
          } else {
              res += '%' + ord;
          }
  
          return res;
      },
  
      safeEncodeURIComponent(str) {
          str = (str || '').toString();
  
          try {
              // might throw if we try to encode invalid sequences, eg. partial emoji
              str = encodeURIComponent(str);
          } catch (E) {
              // should never run
              return str.replace(/[^\x00-\x1F *'()<>@,;:\\"[\]?=\u007F-\uFFFF]+/g, '');
          }
  
          // ensure chars that are not handled by encodeURICompent are converted as well
          return str.replace(/[\x00-\x1F *'()<>@,;:\\"[\]?=\u007F-\uFFFF]/g, chr => this.encodeURICharComponent(chr));
      }
  };
  