"use strict";

// protocol.js — GC-110N K 格式协议层（精简版）
// 负责：校验和、CRLF 切包、K 格式解析。

const CRLF = Buffer.from("\r\n", "ascii");

function checksum(body) {
  let sum = 0;
  for (const byte of body) {
    sum = (sum + byte) & 0xff;
  }
  return sum.toString(16).padStart(2, "0");
}

const GC110N_FIELD_LABELS = {
  A: "目标除水量", B: "当前除水量", C: "除水速度",
  D: "血液流量", E: "注射器泵速度", F: "透析液温度",
  G: "透析液浓度", H: "静脉压", I: "透析液压",
  J: "TMP", K: "治疗经过时间", L: "透析液流量",
  a: "液温报警", b: "浓度报警", c: "静脉压报警",
  d: "液压报警", e: "TMP报警", f: "气泡检测报警",
  g: "漏血报警", h: "其他报警",
  M: "治疗中标志", N: "治疗模式",
  O: "目标补液量", P: "当前补液量", Q: "补液速度",
  R: "补液温度",
  S: "血压测量时刻",
  T: "收缩压", U: "舒张压", V: "脉搏",
  i: "血压报警",
  W: "注射器泵累计量",
};

const GC110N_FIELD_UNITS = {
  A: "L", B: "L", C: "L/h", D: "mL/min", E: "mL/h",
  F: "℃", G: "mS/cm", H: "mmHg", I: "mmHg",
  J: "mmHg", K: "min", L: "mL/min",
  O: "L", P: "L", Q: "L/h", R: "℃",
  S: "HHMMSS",
  T: "mmHg", U: "mmHg", V: "bpm",
  W: "mL",
};

const GC110N_FIELD_ORDER = [
  "A","B","C","D","E","F","G","H","I","J","K","L",
  "a","b","c","d","e","f","g","h",
  "M","N",
  "O","P","Q","R",
  "S","T","U","V",
  "i","W",
];

const GC110N_FIXED_WIDTHS = {
  A: 5, B: 5, C: 5, D: 5, E: 5, F: 5, G: 5, H: 5, I: 5, J: 5,
  K: 5, L: 5,
  a: 1, b: 1, c: 1, d: 1, e: 1, f: 1, g: 1, h: 1,
  M: 1, N: 1,
  O: 5, P: 5, Q: 5, R: 5,
  S: 6,
  T: 5, U: 5, V: 5,
  i: 1,
  W: 5,
};

function parseGC110NFrame(frame) {
  const text = frame.toString("ascii");
  if (text.length < 6 || text[0] !== "K") return null;

  const statusCode = text.substring(1, 5);
  let pos = 5;
  const items = [];
  const knownIds = new Set(Object.keys(GC110N_FIXED_WIDTHS));

  while (pos < text.length) {
    const id = text[pos];
    if (!knownIds.has(id)) break;

    pos++;

    let value;
    if (id === "S") {
      let end = text.length;
      for (let i = pos; i < text.length; i++) {
        if (knownIds.has(text[i])) { end = i; break; }
      }
      value = text.substring(pos, end);
    } else {
      const width = GC110N_FIXED_WIDTHS[id];
      if (pos + width > text.length) break;
      value = text.substring(pos, pos + width);
    }
    pos += value.length;

    const label = GC110N_FIELD_LABELS[id] || "";
    const unit = GC110N_FIELD_UNITS[id] || "";
    const displayValue = value.trim() || "(空)";

    items.push({ id, value, displayValue, name: label, unit });
  }

  return {
    type: "gc110n-status",
    prefix: "K",
    command: "STATUS",
    statusCode,
    items,
  };
}

function parseFrameAuto(frame) {
  if (Buffer.compare(frame, Buffer.from("K", "ascii")) === 0) {
    return { type: "request-status" };
  }

  const ascii = frame.toString("ascii");
  if (ascii.length >= 6 && ascii[0] === "K" && /^\d{4}/.test(ascii.substring(1, 5))) {
    return parseGC110NFrame(frame);
  }

  return null;
}

function extractFrames(buffer) {
  const frames = [];
  let remaining = buffer;
  let index;

  while ((index = remaining.indexOf(CRLF)) !== -1) {
    frames.push(remaining.subarray(0, index));
    remaining = remaining.subarray(index + CRLF.length);
  }

  return { frames, remaining };
}

module.exports = {
  CRLF,
  checksum,
  extractFrames,
  parseFrameAuto,
  parseGC110NFrame,
  GC110N_FIELD_LABELS,
  GC110N_FIELD_UNITS,
  GC110N_FIELD_ORDER,
  GC110N_FIXED_WIDTHS,
};