import * as net from "node:net";

const buildHuffmanTree = (values) => {
  const root = [];
  for (const [value, path] of values) {
    let cur = root;
    for (let i = 0; i < path.length; i++) {
      const decision = Number(path[i]);

      if (i === path.length - 1) {
        cur[decision] = value;
      } else {
        if (!cur[decision]) {
          cur[decision] = [];
        }
      }

      cur = cur[decision];
    }
  }

  return root;
};

const HUFFMAN_EOS = Symbol("EOS");
const HUFFMAN_TREE = buildHuffmanTree([
  [String.fromCharCode(0), "1111111111000"],
  [String.fromCharCode(1), "11111111111111111011000"],
  [String.fromCharCode(2), "1111111111111111111111100010"],
  [String.fromCharCode(3), "1111111111111111111111100011"],
  [String.fromCharCode(4), "1111111111111111111111100100"],
  [String.fromCharCode(5), "1111111111111111111111100101"],
  [String.fromCharCode(6), "1111111111111111111111100110"],
  [String.fromCharCode(7), "1111111111111111111111100111"],
  [String.fromCharCode(8), "1111111111111111111111101000"],
  [String.fromCharCode(9), "111111111111111111101010"],
  [String.fromCharCode(10), "111111111111111111111111111100"],
  [String.fromCharCode(11), "1111111111111111111111101001"],
  [String.fromCharCode(12), "1111111111111111111111101010"],
  [String.fromCharCode(13), "111111111111111111111111111101"],
  [String.fromCharCode(14), "1111111111111111111111101011"],
  [String.fromCharCode(15), "1111111111111111111111101100"],
  [String.fromCharCode(16), "1111111111111111111111101101"],
  [String.fromCharCode(17), "1111111111111111111111101110"],
  [String.fromCharCode(18), "1111111111111111111111101111"],
  [String.fromCharCode(19), "1111111111111111111111110000"],
  [String.fromCharCode(20), "1111111111111111111111110001"],
  [String.fromCharCode(21), "1111111111111111111111110010"],
  [String.fromCharCode(22), "111111111111111111111111111110"],
  [String.fromCharCode(23), "1111111111111111111111110011"],
  [String.fromCharCode(24), "1111111111111111111111110100"],
  [String.fromCharCode(25), "1111111111111111111111110101"],
  [String.fromCharCode(26), "1111111111111111111111110110"],
  [String.fromCharCode(27), "1111111111111111111111110111"],
  [String.fromCharCode(28), "1111111111111111111111111000"],
  [String.fromCharCode(29), "1111111111111111111111111001"],
  [String.fromCharCode(30), "1111111111111111111111111010"],
  [String.fromCharCode(31), "1111111111111111111111111011"],
  [String.fromCharCode(32), "010100"],
  [String.fromCharCode(33), "1111111000"],
  [String.fromCharCode(34), "1111111001"],
  [String.fromCharCode(35), "111111111010"],
  [String.fromCharCode(36), "1111111111001"],
  [String.fromCharCode(37), "010101"],
  [String.fromCharCode(38), "11111000"],
  [String.fromCharCode(39), "11111111010"],
  [String.fromCharCode(40), "1111111010"],
  [String.fromCharCode(41), "1111111011"],
  [String.fromCharCode(42), "11111001"],
  [String.fromCharCode(43), "11111111011"],
  [String.fromCharCode(44), "11111010"],
  [String.fromCharCode(45), "010110"],
  [String.fromCharCode(46), "010111"],
  [String.fromCharCode(47), "011000"],
  [String.fromCharCode(48), "00000"],
  [String.fromCharCode(49), "00001"],
  [String.fromCharCode(50), "00010"],
  [String.fromCharCode(51), "011001"],
  [String.fromCharCode(52), "011010"],
  [String.fromCharCode(53), "011011"],
  [String.fromCharCode(54), "011100"],
  [String.fromCharCode(55), "011101"],
  [String.fromCharCode(56), "011110"],
  [String.fromCharCode(57), "011111"],
  [String.fromCharCode(58), "1011100"],
  [String.fromCharCode(59), "11111011"],
  [String.fromCharCode(60), "111111111111100"],
  [String.fromCharCode(61), "100000"],
  [String.fromCharCode(62), "111111111011"],
  [String.fromCharCode(63), "1111111100"],
  [String.fromCharCode(64), "1111111111010"],
  [String.fromCharCode(65), "100001"],
  [String.fromCharCode(66), "1011101"],
  [String.fromCharCode(67), "1011110"],
  [String.fromCharCode(68), "1011111"],
  [String.fromCharCode(69), "1100000"],
  [String.fromCharCode(70), "1100001"],
  [String.fromCharCode(71), "1100010"],
  [String.fromCharCode(72), "1100011"],
  [String.fromCharCode(73), "1100100"],
  [String.fromCharCode(74), "1100101"],
  [String.fromCharCode(75), "1100110"],
  [String.fromCharCode(76), "1100111"],
  [String.fromCharCode(77), "1101000"],
  [String.fromCharCode(78), "1101001"],
  [String.fromCharCode(79), "1101010"],
  [String.fromCharCode(80), "1101011"],
  [String.fromCharCode(81), "1101100"],
  [String.fromCharCode(82), "1101101"],
  [String.fromCharCode(83), "1101110"],
  [String.fromCharCode(84), "1101111"],
  [String.fromCharCode(85), "1110000"],
  [String.fromCharCode(86), "1110001"],
  [String.fromCharCode(87), "1110010"],
  [String.fromCharCode(88), "11111100"],
  [String.fromCharCode(89), "1110011"],
  [String.fromCharCode(90), "11111101"],
  [String.fromCharCode(91), "1111111111011"],
  [String.fromCharCode(92), "1111111111111110000"],
  [String.fromCharCode(93), "1111111111100"],
  [String.fromCharCode(94), "11111111111100"],
  [String.fromCharCode(95), "100010"],
  [String.fromCharCode(96), "111111111111101"],
  [String.fromCharCode(97), "00011"],
  [String.fromCharCode(98), "100011"],
  [String.fromCharCode(99), "00100"],
  [String.fromCharCode(100), "100100"],
  [String.fromCharCode(101), "00101"],
  [String.fromCharCode(102), "100101"],
  [String.fromCharCode(103), "100110"],
  [String.fromCharCode(104), "100111"],
  [String.fromCharCode(105), "00110"],
  [String.fromCharCode(106), "1110100"],
  [String.fromCharCode(107), "1110101"],
  [String.fromCharCode(108), "101000"],
  [String.fromCharCode(109), "101001"],
  [String.fromCharCode(110), "101010"],
  [String.fromCharCode(111), "00111"],
  [String.fromCharCode(112), "101011"],
  [String.fromCharCode(113), "1110110"],
  [String.fromCharCode(114), "101100"],
  [String.fromCharCode(115), "01000"],
  [String.fromCharCode(116), "01001"],
  [String.fromCharCode(117), "101101"],
  [String.fromCharCode(118), "1110111"],
  [String.fromCharCode(119), "1111000"],
  [String.fromCharCode(120), "1111001"],
  [String.fromCharCode(121), "1111010"],
  [String.fromCharCode(122), "1111011"],
  [String.fromCharCode(123), "111111111111110"],
  [String.fromCharCode(124), "11111111100"],
  [String.fromCharCode(125), "11111111111101"],
  [String.fromCharCode(126), "1111111111101"],
  [String.fromCharCode(127), "1111111111111111111111111100"],
  [String.fromCharCode(128), "11111111111111100110"],
  [String.fromCharCode(129), "1111111111111111010010"],
  [String.fromCharCode(130), "11111111111111100111"],
  [String.fromCharCode(131), "11111111111111101000"],
  [String.fromCharCode(132), "1111111111111111010011"],
  [String.fromCharCode(133), "1111111111111111010100"],
  [String.fromCharCode(134), "1111111111111111010101"],
  [String.fromCharCode(135), "11111111111111111011001"],
  [String.fromCharCode(136), "1111111111111111010110"],
  [String.fromCharCode(137), "11111111111111111011010"],
  [String.fromCharCode(138), "11111111111111111011011"],
  [String.fromCharCode(139), "11111111111111111011100"],
  [String.fromCharCode(140), "11111111111111111011101"],
  [String.fromCharCode(141), "11111111111111111011110"],
  [String.fromCharCode(142), "111111111111111111101011"],
  [String.fromCharCode(143), "11111111111111111011111"],
  [String.fromCharCode(144), "111111111111111111101100"],
  [String.fromCharCode(145), "111111111111111111101101"],
  [String.fromCharCode(146), "1111111111111111010111"],
  [String.fromCharCode(147), "11111111111111111100000"],
  [String.fromCharCode(148), "111111111111111111101110"],
  [String.fromCharCode(149), "11111111111111111100001"],
  [String.fromCharCode(150), "11111111111111111100010"],
  [String.fromCharCode(151), "11111111111111111100011"],
  [String.fromCharCode(152), "11111111111111111100100"],
  [String.fromCharCode(153), "111111111111111011100"],
  [String.fromCharCode(154), "1111111111111111011000"],
  [String.fromCharCode(155), "11111111111111111100101"],
  [String.fromCharCode(156), "1111111111111111011001"],
  [String.fromCharCode(157), "11111111111111111100110"],
  [String.fromCharCode(158), "11111111111111111100111"],
  [String.fromCharCode(159), "111111111111111111101111"],
  [String.fromCharCode(160), "1111111111111111011010"],
  [String.fromCharCode(161), "111111111111111011101"],
  [String.fromCharCode(162), "11111111111111101001"],
  [String.fromCharCode(163), "1111111111111111011011"],
  [String.fromCharCode(164), "1111111111111111011100"],
  [String.fromCharCode(165), "11111111111111111101000"],
  [String.fromCharCode(166), "11111111111111111101001"],
  [String.fromCharCode(167), "111111111111111011110"],
  [String.fromCharCode(168), "11111111111111111101010"],
  [String.fromCharCode(169), "1111111111111111011101"],
  [String.fromCharCode(170), "1111111111111111011110"],
  [String.fromCharCode(171), "111111111111111111110000"],
  [String.fromCharCode(172), "111111111111111011111"],
  [String.fromCharCode(173), "1111111111111111011111"],
  [String.fromCharCode(174), "11111111111111111101011"],
  [String.fromCharCode(175), "11111111111111111101100"],
  [String.fromCharCode(176), "111111111111111100000"],
  [String.fromCharCode(177), "111111111111111100001"],
  [String.fromCharCode(178), "1111111111111111100000"],
  [String.fromCharCode(179), "111111111111111100010"],
  [String.fromCharCode(180), "11111111111111111101101"],
  [String.fromCharCode(181), "1111111111111111100001"],
  [String.fromCharCode(182), "11111111111111111101110"],
  [String.fromCharCode(183), "11111111111111111101111"],
  [String.fromCharCode(184), "11111111111111101010"],
  [String.fromCharCode(185), "1111111111111111100010"],
  [String.fromCharCode(186), "1111111111111111100011"],
  [String.fromCharCode(187), "1111111111111111100100"],
  [String.fromCharCode(188), "11111111111111111110000"],
  [String.fromCharCode(189), "1111111111111111100101"],
  [String.fromCharCode(190), "1111111111111111100110"],
  [String.fromCharCode(191), "11111111111111111110001"],
  [String.fromCharCode(192), "11111111111111111111100000"],
  [String.fromCharCode(193), "11111111111111111111100001"],
  [String.fromCharCode(194), "11111111111111101011"],
  [String.fromCharCode(195), "1111111111111110001"],
  [String.fromCharCode(196), "1111111111111111100111"],
  [String.fromCharCode(197), "11111111111111111110010"],
  [String.fromCharCode(198), "1111111111111111101000"],
  [String.fromCharCode(199), "1111111111111111111101100"],
  [String.fromCharCode(200), "11111111111111111111100010"],
  [String.fromCharCode(201), "11111111111111111111100011"],
  [String.fromCharCode(202), "11111111111111111111100100"],
  [String.fromCharCode(203), "111111111111111111111011110"],
  [String.fromCharCode(204), "111111111111111111111011111"],
  [String.fromCharCode(205), "11111111111111111111100101"],
  [String.fromCharCode(206), "111111111111111111110001"],
  [String.fromCharCode(207), "1111111111111111111101101"],
  [String.fromCharCode(208), "1111111111111110010"],
  [String.fromCharCode(209), "111111111111111100011"],
  [String.fromCharCode(210), "11111111111111111111100110"],
  [String.fromCharCode(211), "111111111111111111111100000"],
  [String.fromCharCode(212), "111111111111111111111100001"],
  [String.fromCharCode(213), "11111111111111111111100111"],
  [String.fromCharCode(214), "111111111111111111111100010"],
  [String.fromCharCode(215), "111111111111111111110010"],
  [String.fromCharCode(216), "111111111111111100100"],
  [String.fromCharCode(217), "111111111111111100101"],
  [String.fromCharCode(218), "11111111111111111111101000"],
  [String.fromCharCode(219), "11111111111111111111101001"],
  [String.fromCharCode(220), "1111111111111111111111111101"],
  [String.fromCharCode(221), "111111111111111111111100011"],
  [String.fromCharCode(222), "111111111111111111111100100"],
  [String.fromCharCode(223), "111111111111111111111100101"],
  [String.fromCharCode(224), "11111111111111101100"],
  [String.fromCharCode(225), "111111111111111111110011"],
  [String.fromCharCode(226), "11111111111111101101"],
  [String.fromCharCode(227), "111111111111111100110"],
  [String.fromCharCode(228), "1111111111111111101001"],
  [String.fromCharCode(229), "111111111111111100111"],
  [String.fromCharCode(230), "111111111111111101000"],
  [String.fromCharCode(231), "11111111111111111110011"],
  [String.fromCharCode(232), "1111111111111111101010"],
  [String.fromCharCode(233), "1111111111111111101011"],
  [String.fromCharCode(234), "1111111111111111111101110"],
  [String.fromCharCode(235), "1111111111111111111101111"],
  [String.fromCharCode(236), "111111111111111111110100"],
  [String.fromCharCode(237), "111111111111111111110101"],
  [String.fromCharCode(238), "11111111111111111111101010"],
  [String.fromCharCode(239), "11111111111111111110100"],
  [String.fromCharCode(240), "11111111111111111111101011"],
  [String.fromCharCode(241), "111111111111111111111100110"],
  [String.fromCharCode(242), "11111111111111111111101100"],
  [String.fromCharCode(243), "11111111111111111111101101"],
  [String.fromCharCode(244), "111111111111111111111100111"],
  [String.fromCharCode(245), "111111111111111111111101000"],
  [String.fromCharCode(246), "111111111111111111111101001"],
  [String.fromCharCode(247), "111111111111111111111101010"],
  [String.fromCharCode(248), "111111111111111111111101011"],
  [String.fromCharCode(249), "1111111111111111111111111110"],
  [String.fromCharCode(250), "111111111111111111111101100"],
  [String.fromCharCode(251), "111111111111111111111101101"],
  [String.fromCharCode(252), "111111111111111111111101110"],
  [String.fromCharCode(253), "111111111111111111111101111"],
  [String.fromCharCode(254), "111111111111111111111110000"],
  [String.fromCharCode(255), "11111111111111111111101110"],
  [HUFFMAN_EOS, "111111111111111111111111111111"],
]);

class HPackCtx {
  #dynamicTable;

  static #STATIC_TABLE = {
    1: [":authority", ""],
    2: [":method", "GET"],
    3: [":method", "POST"],
    4: [":path", "/"],
    5: [":path", "/index.html"],
    6: [":scheme", "http"],
    7: [":scheme", "https"],
    8: [":status", "200"],
    9: [":status", "204"],
    10: [":status", "206"],
    11: [":status", "304"],
    12: [":status", "400"],
    13: [":status", "404"],
    14: [":status", "500"],
    15: ["accept-charset", ""],
    16: ["accept-encoding", "gzip, deflate"],
    17: ["accept-language", ""],
    18: ["accept-ranges", ""],
    19: ["accept", ""],
    20: ["access-control-allow-origin", ""],
    21: ["age", ""],
    22: ["allow", ""],
    23: ["authorization", ""],
    24: ["cache-control", ""],
    25: ["content-disposition", ""],
    26: ["content-encoding", ""],
    27: ["content-language", ""],
    28: ["content-length", ""],
    29: ["content-location", ""],
    30: ["content-range", ""],
    31: ["content-type", ""],
    32: ["cookie", ""],
    33: ["date", ""],
    34: ["etag", ""],
    35: ["expect", ""],
    36: ["expires", ""],
    37: ["from", ""],
    38: ["host", ""],
    39: ["if-match", ""],
    40: ["if-modified-since", ""],
    41: ["if-none-match", ""],
    42: ["if-range", ""],
    43: ["if-unmodified-since", ""],
    44: ["last-modified", ""],
    45: ["link", ""],
    46: ["location", ""],
    47: ["max-forwards", ""],
    48: ["proxy-authenticate", ""],
    49: ["proxy-authorization", ""],
    50: ["range", ""],
    51: ["referer", ""],
    52: ["refresh", ""],
    53: ["retry-after", ""],
    54: ["server", ""],
    55: ["set-cookie", ""],
    56: ["strict-transport-security", ""],
    57: ["transfer-encoding", ""],
    58: ["user-agent", ""],
    59: ["vary", ""],
    60: ["via", ""],
    61: ["www-authenticate", ""],
  };
  static #STATIC_TABLE_MAX = 61;

  constructor() {
    this.#dynamicTable = {};
  }

  #indexTable = (index) => {
    return index < HPackCtx.#STATIC_TABLE_MAX
      ? HPackCtx.#STATIC_TABLE[index]
      : this.#dynamicTable[index - HPackCtx.#STATIC_TABLE_MAX];
  };

  decode = (block) => {
    const fields = [];

    while (block.length > 0) {
      let size = 0;

      const firstBit = block[0] & 128;
      const secondBit = block[0] & 64;
      const thirdBit = block[0] & 32;
      const fourthBit = block[0] & 16;

      let field;

      const decodeInteger = (mask) => {
        const int = block[size] & (0xff >> mask);

        if (int === 0xff >> mask) {
          throw new Error("long integer, todo");
        }
        size += 1;
        return int;
      };

      const decodeHuffman = (length) => {
        let string = "";
        let remaining = length;

        let cur = HUFFMAN_TREE;

        while (remaining > 0) {
          const nextOctet = block[size];

          for (let i = 7; i >= 0; i--) {
            const nextBit = (nextOctet >> i) & 0x01;
            cur = cur[nextBit ? 1 : 0];

            if (typeof cur === "string") {
              string += cur;
              cur = HUFFMAN_TREE;
            } else if (typeof cur === "symbol" && cur === HUFFMAN_EOS) {
              throw new Error("what");
            }
          }

          size++;
          remaining--;
        }

        return string;
      };

      const decodeString = () => {
        const huffman = block[size] & 128;

        const length = decodeInteger(1);

        if (huffman) {
          return decodeHuffman(length);
        } else {
          size += length;
          return new TextDecoder().decode(block.subarray(size, length));
        }
      };

      // Indexed Header Field Representation
      if (firstBit) {
        const index = decodeInteger(1);

        const tabled = this.#indexTable(index);

        field = tabled;
      } else {
        // Literal Header Field with Incremental Indexing
        if (secondBit) {
          const index = decodeInteger(2);

          let headerName;
          if (index === 0) {
            headerName = decodeString();
          } else {
            headerName = this.#indexTable(index)[0];
          }

          const headerValue = decodeString();

          field = [headerName, headerValue];
        } else {
          throw new Error("some other encoding");
        }
      }

      if (typeof field === "undefined") {
        throw new Error("field was not set");
      }
      fields.push(field);

      if (size === 0) {
        throw new Error("size was not set");
      }
      block = block.subarray(size);
    }

    return fields;
  };
  encode = () => {};
}

const FRAME_TYPE = {
  DATA: 0x0,
  HEADERS: 0x1,
  PRIORITY: 0x2,
  RST_STREAM: 0x3,
  SETTINGS: 0x04,
  PUSH_PROMISE: 0x5,
  PING: 0x6,
  GOAWAY: 0x7,
  WINDOW_UPDATE: 0x08,
  CONTINUATION: 0x09,
};
const FRAME_TYPE_NAME = Object.fromEntries(
  Object.entries(FRAME_TYPE).map(([k, v]) => [v, k])
);

const SETTING = {
  SETTINGS_HEADER_TABLE_SIZE: 0x01,
  SETTINGS_ENABLE_PUSH: 0x02,
  SETTINGS_MAX_CONCURRENT_STREAMS: 0x03,
  SETTINGS_INITIAL_WINDOW_SIZE: 0x04,
  SETTINGS_MAX_FRAME_SIZE: 0x05,
  SETTINGS_MAX_HEADER_LIST_SIZE: 0x06,
};
const SETTING_NAME = Object.fromEntries(
  Object.entries(SETTING).map(([k, v]) => [v, k])
);
const FRAME_HEADER_SIZE = 3 + 1 + 1 + 4;

const frameReader = (frameCb) => {
  const STATE = {
    PREFACE: 0,
    FRAME_HEAD: 1,
    FRAME_PAYLOAD: 2,
  };
  const CONNECTION_PREFACE = new TextEncoder().encode(
    "PRI * HTTP/2.0\r\n\r\nSM\r\n\r\n"
  );

  let state = STATE.PREFACE;
  let frameHead;
  let buf = Buffer.from([]);

  return (data) => {
    buf = Buffer.concat([buf, data]);

    while (true) {
      switch (state) {
        case STATE.PREFACE: {
          if (buf.length < 24) {
            return;
          }

          const preface = buf.subarray(0, 24);
          buf = buf.subarray(24);
          if (Buffer.compare(preface, CONNECTION_PREFACE) !== 0) {
            frameCb(new Error(`invalid preface from ${peer}`));
            return;
          }

          state = STATE.FRAME_HEAD;

          break;
        }
        case STATE.FRAME_HEAD: {
          if (buf.length < FRAME_HEADER_SIZE) {
            return;
          }

          const frameHeader = buf.subarray(0, FRAME_HEADER_SIZE);
          buf = buf.subarray(FRAME_HEADER_SIZE);

          const length =
            (frameHeader[0] << 16) | (frameHeader[1] << 8) | frameHeader[2];
          const type = frameHeader[3];
          const flags = frameHeader[4];
          const streamIdentifier =
            frameHeader.readUint32BE(5) & (0xff_ff_ff_ff >> 1);

          state = STATE.FRAME_PAYLOAD;
          frameHead = {
            length,
            type,
            flags,
            streamIdentifier,
          };

          break;
        }
        case STATE.FRAME_PAYLOAD: {
          if (buf.length < frameHead.length) {
            return;
          }

          const payload = buf.subarray(0, frameHead.length);
          buf = buf.subarray(frameHead.length);

          frameCb(null, {
            ...frameHead,
            payload,
          });

          state = STATE.FRAME_HEAD;

          break;
        }
        default:
          throw new Error("unknown state", state);
      }
    }
  };
};

const encodeFrame = (frame) => {
  if (typeof frame.flags !== "number") {
    throw new Error(`Flags of frame are not number: ${frame.flags}`);
  }
  if (typeof frame.type !== "number") {
    throw new Error(`Type of frame is not a number: ${frame.type}`);
  }
  const length = frame.payload.length;
  const buffer = Buffer.alloc(FRAME_HEADER_SIZE + length);
  if (length > 2 ** 24) {
    throw new Error(`Frame is too long: ${length}`);
  }
  buffer[0] = length >> 16;
  buffer[1] = (length >> 8) & 0xff;
  buffer[2] = length & 0xff;
  if (!(frame.type in FRAME_TYPE_NAME)) {
    throw new Error(`Trying to write unknown frame type: ${frame.type}`);
  }
  buffer[3] = frame.type;
  if (frame.flags > 0xff) {
    throw new Error(`Frame flags do not fit in a byte: ${frame.flags}`);
  }
  buffer[4] = frame.flags;
  buffer.writeUint32BE(length, 5);

  frame.payload.copy(buffer, FRAME_HEADER_SIZE);

  return buffer;
};

/**
 * @param {net.Socket} socket
 */
const handleConnection = (socket) => {
  const peer = `${socket.remoteAddress}:${socket.remotePort}`;

  console.log(`received connection from ${peer}`);

  const hpackDecode = new HPackCtx();
  const hpackEncode = new HPackCtx();
  const peerSettings = new Map();
  const streams = new Map();

  socket.write(
    encodeFrame({
      type: FRAME_TYPE.SETTINGS,
      flags: 0,
      payload: Buffer.from([]),
    })
  );

  const onData = frameReader((err, frame) => {
    if (err) {
      console.warn("error from frame layer", err);
      socket.destroy();
      return;
    }
    console.log("received frame", FRAME_TYPE_NAME[frame.type], frame);

    switch (frame.type) {
      case FRAME_TYPE.HEADERS: {
        if (!streams.has(frame.streamIdentifier)) {
          streams.set(frame.streamIdentifier, {
            headerBuffer: Buffer.from([]),
            endHeaders: false,
          });
        }

        // END_HEADERS
        if ((frame.flags & 0x04) !== 0) {
          streams.get(frame.streamIdentifier).endHeaders = true;
        }

        // PRIORITY
        const priorityFlag = (frame.flags & 0x20) !== 0;
        // PADDED
        const paddedFlag = (frame.flags & 0x08) !== 0;

        let payload = frame.payload;

        let paddingLength = 0;
        if (paddedFlag) {
          paddingLength = payload[0];
          payload = payload.subarray(1);
        }

        if (priorityFlag) {
          // skip over Exclusive/Stream Dependency, Weight
          payload = payload.subarray(5);
        }

        if (paddedFlag) {
          if (paddingLength > payload.length) {
            console.warn("too much padding");
            socket.destroy();
            return;
          }
          payload = payload.subarray(0, payload.length - paddingLength);
        }

        if (streams.get(frame.streamIdentifier).endHeaders) {
          const fieldBlockFragement = payload;
          const fields = hpackDecode.decode(fieldBlockFragement);

          console.log("headers", fields);

          // we got a request!!!
        } else {
          throw new Error("expecting CONTINUATION is not yet supported");
        }

        break;
      }
      case FRAME_TYPE.SETTINGS: {
        // ACK
        if ((frame.flags & 0x1) !== 0) {
          if (frame.length !== 0) {
            console.warn("received non-empty SETTINGS ack frame");
            socket.destroy();
            return;
          }

          break;
        }

        if (frame.streamIdentifier !== 0) {
          console.warn("stream identifier for a SETTINGS");
          socket.destroy();
          return;
        }
        if (frame.length % 6 !== 0) {
          console.warn("invalid length for SETTINGS frame");
          socket.destroy();
          return;
        }

        for (let i = 0; i < frame.length; i += 6) {
          const identifier = frame.payload.readUint16BE(i);
          const value = frame.payload.readUint32BE(i + 2);
          console.log("SETTINGS setting", SETTING_NAME[identifier], "=", value);

          peerSettings[SETTING_NAME[identifier]] = value;
        }

        break;
      }
      case FRAME_TYPE.WINDOW_UPDATE: {
        // whatever
        const increment = frame.payload.readUint32BE();
        console.log("incrementing transfer window by", increment);
        break;
      }
      default: {
        console.warn(
          `unsupported frame type ${FRAME_TYPE_NAME[frame.type] ?? frame.type}`
        );
      }
    }
  });

  socket.on("data", onData);

  socket.on("error", (err) => {
    console.warn(`error from ${peer}:`, err);
  });

  socket.on("close", () => {
    console.log(`connection closed for ${peer}`);
  });
};

const server = net.createServer(handleConnection).on("error", (err) => {
  console.error(`error: ${err}`);
});

server.listen(8080, () => {
  console.log("Listening on", server.address());
});