var Buffer = require('buffer').Buffer,
    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;
    };

for (var s in S) {
  exports[s] = S[s];
}

function MultipartParser() {
  this.boundary = null;
  this.boundaryChars = null;
  this.lookbehind = null;
  this.state = S.PARSER_UNINITIALIZED;

  this.index = null;
  this.flags = 0;
};
exports.MultipartParser = MultipartParser;

MultipartParser.stateToString = function(stateNumber) {
  for (var state in S) {
    var number = S[state];
    if (number === stateNumber) return state;
  }
};

MultipartParser.prototype.initWithBoundary = function(str) {
  this.boundary = new Buffer(str.length+4);
  this.boundary.write('\r\n--', 'ascii', 0);
  this.boundary.write(str, 'ascii', 4);
  this.lookbehind = new Buffer(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;
  }
};

MultipartParser.prototype.write = function(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 != CR) {
            return i;
          }
          index++;
          break;
        } else if (index - 1 == boundary.length - 2) {
          if (c != LF) {
            return i;
          }
          index = 0;
          callback('partBegin');
          state = S.HEADER_FIELD_START;
          break;
        }

        if (c != boundary[index+2]) {
          return i;
        }
        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;
            } 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;
};

MultipartParser.prototype.end = function() {
  if (this.state != S.END) {
    return new Error('MultipartParser.end(): stream ended unexpectedly: ' + this.explain());
  }
};

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