var s = 0,
  S = {
    PARSER_UNINITIALIZED: s++,
    START: s++,
    START_BOUNDARY: s++,
    HEADER_FIELD_START: s++,
    HEADER_FIELD: s++,
    HEADER_VALUE_START: s++,
    HEADER_VALUE: s++,
    HEADER_VALUE_ALMOST_DONE: s++,
    HEADERS_ALMOST_DONE: s++,
    PART_DATA_START: s++,
    PART_DATA: s++,
    PART_END: s++,
    END: s++
  },
  f = 1,
  F = {
    PART_BOUNDARY: f,
    LAST_BOUNDARY: (f *= 2)
  },
  LF = 10,
  CR = 13,
  SPACE = 32,
  HYPHEN = 45,
  COLON = 58,
  A = 97,
  Z = 122,
  lower = function (c) {
    return c | 0x20
  }

export class MultipartParser {
  boundary = null
  boundaryChars = null
  lookbehind = null
  state = S.PARSER_UNINITIALIZED

  index = null
  flags = 0

  static stateToString(stateNumber) {
    for (var state in S) {
      var number = S[state]
      if (number === stateNumber) return state
    }
  }

  initWithBoundary(str) {
    this.boundary = Buffer.alloc(str.length + 4)
    this.boundary.write('\r\n--', 0)
    this.boundary.write(str, 4)
    this.lookbehind = Buffer.alloc(this.boundary.length + 8)
    this.state = S.START

    this.boundaryChars = {}
    for (var i = 0; i < this.boundary.length; i++) {
      this.boundaryChars[this.boundary[i]] = true
    }
  }

  write(buffer) {
    var self = this,
      i = 0,
      len = buffer.length,
      prevIndex = this.index,
      index = this.index,
      state = this.state,
      flags = this.flags,
      lookbehind = this.lookbehind,
      boundary = this.boundary,
      boundaryChars = this.boundaryChars,
      boundaryLength = this.boundary.length,
      boundaryEnd = boundaryLength - 1,
      bufferLength = buffer.length,
      c,
      cl,
      mark = function (name) {
        self[name + 'Mark'] = i
      },
      clear = function (name) {
        delete self[name + 'Mark']
      },
      callback = function (name, buffer, start, end) {
        if (start !== undefined && start === end) {
          return
        }

        var callbackSymbol =
          'on' + name.substr(0, 1).toUpperCase() + name.substr(1)
        if (callbackSymbol in self) {
          self[callbackSymbol](buffer, start, end)
        }
      },
      dataCallback = function (name, clear) {
        var markSymbol = name + 'Mark'
        if (!(markSymbol in self)) {
          return
        }

        if (!clear) {
          callback(name, buffer, self[markSymbol], buffer.length)
          self[markSymbol] = 0
        } else {
          callback(name, buffer, self[markSymbol], i)
          delete self[markSymbol]
        }
      }

    for (i = 0; i < len; i++) {
      c = buffer[i]
      switch (state) {
        case S.PARSER_UNINITIALIZED:
          return i
        case S.START:
          index = 0
          state = S.START_BOUNDARY
        case S.START_BOUNDARY:
          if (index == boundary.length - 2) {
            if (c == HYPHEN) {
              flags |= F.LAST_BOUNDARY
            } else if (c != CR) {
              return i
            }
            index++
            break
          } else if (index - 1 == boundary.length - 2) {
            if (flags & F.LAST_BOUNDARY && c == HYPHEN) {
              callback('end')
              state = S.END
              flags = 0
            } else if (!(flags & F.LAST_BOUNDARY) && c == LF) {
              index = 0
              callback('partBegin')
              state = S.HEADER_FIELD_START
            } else {
              return i
            }
            break
          }

          if (c != boundary[index + 2]) {
            index = -2
          }
          if (c == boundary[index + 2]) {
            index++
          }
          break
        case S.HEADER_FIELD_START:
          state = S.HEADER_FIELD
          mark('headerField')
          index = 0
        case S.HEADER_FIELD:
          if (c == CR) {
            clear('headerField')
            state = S.HEADERS_ALMOST_DONE
            break
          }

          index++
          if (c == HYPHEN) {
            break
          }

          if (c == COLON) {
            if (index == 1) {
              // empty header field
              return i
            }
            dataCallback('headerField', true)
            state = S.HEADER_VALUE_START
            break
          }

          cl = lower(c)
          if (cl < A || cl > Z) {
            return i
          }
          break
        case S.HEADER_VALUE_START:
          if (c == SPACE) {
            break
          }

          mark('headerValue')
          state = S.HEADER_VALUE
        case S.HEADER_VALUE:
          if (c == CR) {
            dataCallback('headerValue', true)
            callback('headerEnd')
            state = S.HEADER_VALUE_ALMOST_DONE
          }
          break
        case S.HEADER_VALUE_ALMOST_DONE:
          if (c != LF) {
            return i
          }
          state = S.HEADER_FIELD_START
          break
        case S.HEADERS_ALMOST_DONE:
          if (c != LF) {
            return i
          }

          callback('headersEnd')
          state = S.PART_DATA_START
          break
        case S.PART_DATA_START:
          state = S.PART_DATA
          mark('partData')
        case S.PART_DATA:
          prevIndex = index

          if (index === 0) {
            // boyer-moore derrived algorithm to safely skip non-boundary data
            i += boundaryEnd
            while (i < bufferLength && !(buffer[i] in boundaryChars)) {
              i += boundaryLength
            }
            i -= boundaryEnd
            c = buffer[i]
          }

          if (index < boundary.length) {
            if (boundary[index] == c) {
              if (index === 0) {
                dataCallback('partData', true)
              }
              index++
            } else {
              index = 0
            }
          } else if (index == boundary.length) {
            index++
            if (c == CR) {
              // CR = part boundary
              flags |= F.PART_BOUNDARY
            } else if (c == HYPHEN) {
              // HYPHEN = end boundary
              flags |= F.LAST_BOUNDARY
            } else {
              index = 0
            }
          } else if (index - 1 == boundary.length) {
            if (flags & F.PART_BOUNDARY) {
              index = 0
              if (c == LF) {
                // unset the PART_BOUNDARY flag
                flags &= ~F.PART_BOUNDARY
                callback('partEnd')
                callback('partBegin')
                state = S.HEADER_FIELD_START
                break
              }
            } else if (flags & F.LAST_BOUNDARY) {
              if (c == HYPHEN) {
                callback('partEnd')
                callback('end')
                state = S.END
                flags = 0
              } else {
                index = 0
              }
            } else {
              index = 0
            }
          }

          if (index > 0) {
            // when matching a possible boundary, keep a lookbehind reference
            // in case it turns out to be a false lead
            lookbehind[index - 1] = c
          } else if (prevIndex > 0) {
            // if our boundary turned out to be rubbish, the captured lookbehind
            // belongs to partData
            callback('partData', lookbehind, 0, prevIndex)
            prevIndex = 0
            mark('partData')

            // reconsider the current character even so it interrupted the sequence
            // it could be the beginning of a new sequence
            i--
          }

          break
        case S.END:
          break
        default:
          return i
      }
    }

    dataCallback('headerField')
    dataCallback('headerValue')
    dataCallback('partData')

    this.index = index
    this.state = state
    this.flags = flags

    return len
  }

  end() {
    var callback = function (self, name) {
      var callbackSymbol =
        'on' + name.substr(0, 1).toUpperCase() + name.substr(1)
      if (callbackSymbol in self) {
        self[callbackSymbol]()
      }
    }
    if (
      (this.state == S.HEADER_FIELD_START && this.index === 0) ||
      (this.state == S.PART_DATA && this.index == this.boundary.length)
    ) {
      callback(this, 'partEnd')
      callback(this, 'end')
    } else if (this.state != S.END) {
      return new Error(
        'MultipartParser.end(): stream ended unexpectedly: ' + this.explain()
      )
    }
  }

  explain() {
    return 'state = ' + MultipartParser.stateToString(this.state)
  }
}