// Per-signal affine calibration: value = raw * scale + offset, with an optional
// unit override. Pure and dependency-free so it can be unit-tested under Node;
// in the browser it defines the global `Calib`.
(function (root) {
  'use strict';

  var MAX_UNIT_LEN = 16;
  var IDENTITY = Object.freeze({scale: 1, offset: 0, unit: ''});

  // The table is keyed by (source label, base signal name). U+0000 cannot occur
  // in either, so it is an unambiguous separator.
  function calKey(source, signal) {
    return source + '\u0000' + signal;
  }

  // 'Adc[3]' -> 'Adc'. One calibration covers every element of an array signal.
  function baseSignalName(name) {
    var s = String(name == null ? '' : name);
    var open = s.lastIndexOf('[');
    if (open > 0 && s.charAt(s.length - 1) === ']') {
      var idx = s.slice(open + 1, s.length - 1);
      if (idx.length > 0 && /^[0-9]+$/.test(idx)) return s.slice(0, open);
    }
    return s;
  }

  function isFiniteNum(v) {
    return typeof v === 'number' && isFinite(v);
  }

  // Mirrors the hub-side validation exactly (Go: CalConfig.Normalise,
  // C++: StreamHub::HandleSetCalibration). Returns null when the entry must be
  // rejected, so a caller can revert an input field to its last accepted value.
  function normaliseCal(obj) {
    if (obj === null || typeof obj !== 'object') return null;
    var source = String(obj.source == null ? '' : obj.source).trim();
    var signal = baseSignalName(String(obj.signal == null ? '' : obj.signal).trim());
    if (source === '' || signal === '') return null;
    var scale = obj.scale === undefined ? 1 : obj.scale;
    var offset = obj.offset === undefined ? 0 : obj.offset;
    if (!isFiniteNum(scale) || scale === 0) return null;
    if (!isFiniteNum(offset)) return null;
    var unit = String(obj.unit == null ? '' : obj.unit).trim();
    // Cap at MAX_UNIT_LEN UTF-8 bytes, matching both hubs' Normalise() exactly.
    // TextEncoder/TextDecoder are available natively in all modern browsers and
    // Node v11+; no build step or bundler is needed.
    var enc = new TextEncoder();
    var bytes = enc.encode(unit);
    if (bytes.length > MAX_UNIT_LEN) {
      // Truncate to MAX_UNIT_LEN bytes, then repair any split UTF-8 rune at the
      // tail.  Mirrors Go's utf8.DecodeLastRuneInString walk-back loop and the
      // C++ repair loop in StreamHub::SetCalibrationEntry:
      //   Drop continuation bytes (10xxxxxx) from the tail until the last byte
      //   is either an ASCII byte (< 0x80) or a lead byte whose sequence is
      //   complete (i.e. all expected continuation bytes are present).
      var b = bytes.slice(0, MAX_UNIT_LEN);
      var len = b.length;
      // Walk back over continuation bytes (up to 3) to find the lead byte of
      // the last sequence.
      var cont = 0;
      while (cont < 3 && cont < len && (b[len - 1 - cont] & 0xC0) === 0x80) {
        cont++;
      }
      if (cont < len) {
        var lead = b[len - 1 - cont];
        // Determine expected sequence length from the lead byte.
        var seqLen = lead < 0x80 ? 1 :   // 0xxxxxxx  ASCII
                     (lead & 0xE0) === 0xC0 ? 2 :  // 110xxxxx
                     (lead & 0xF0) === 0xE0 ? 3 :  // 1110xxxx
                     (lead & 0xF8) === 0xF0 ? 4 :  // 11110xxx
                     1; // orphaned continuation byte — treat as 1
        var haveBytes = cont + 1; // lead + continuation bytes present
        if (haveBytes < seqLen) {
          // Incomplete sequence: drop the lead byte and all its continuations.
          len = len - haveBytes;
        }
      }
      unit = new TextDecoder().decode(b.slice(0, len));
    }
    return {source: source, signal: signal, scale: scale, offset: offset, unit: unit};
  }

  function isIdentity(cal) {
    return cal.scale === 1 && cal.offset === 0 && cal.unit === '';
  }

  function applyCal(raw, cal) {
    return raw * cal.scale + cal.offset;
  }

  function invertCal(value, cal) {
    return (value - cal.offset) / cal.scale;
  }

  // A negative scale swaps the ends of a range, so re-order after calibrating.
  function calRange(min, max, cal) {
    var a = applyCal(min, cal), b = applyCal(max, cal);
    return a <= b ? [a, b] : [b, a];
  }

  function CalTable() {
    this._m = Object.create(null);
  }

  CalTable.prototype.get = function (source, signal) {
    var e = this._m[calKey(source, baseSignalName(signal))];
    return e === undefined ? IDENTITY : e;
  };

  // Returns false when the entry was rejected as invalid. An entry that reduces
  // to the identity is deleted rather than stored, so a Reset cleans the table
  // (and, once saved, the config file) instead of filling it with no-ops.
  CalTable.prototype.set = function (entry) {
    var c = normaliseCal(entry);
    if (c === null) return false;
    var k = calKey(c.source, c.signal);
    if (isIdentity(c)) delete this._m[k];
    else this._m[k] = c;
    return true;
  };

  CalTable.prototype.replaceAll = function (list) {
    this._m = Object.create(null);
    if (!list) return;
    for (var i = 0; i < list.length; i++) this.set(list[i]);
  };

  CalTable.prototype.list = function () {
    var out = [], k;
    for (k in this._m) out.push(this._m[k]);
    out.sort(function (a, b) {
      if (a.source !== b.source) return a.source < b.source ? -1 : 1;
      if (a.signal !== b.signal) return a.signal < b.signal ? -1 : 1;
      return 0;
    });
    return out;
  };

  var api = {
    MAX_UNIT_LEN: MAX_UNIT_LEN,
    IDENTITY: IDENTITY,
    calKey: calKey,
    baseSignalName: baseSignalName,
    normaliseCal: normaliseCal,
    isIdentity: isIdentity,
    applyCal: applyCal,
    invertCal: invertCal,
    calRange: calRange,
    CalTable: CalTable,
  };

  if (typeof module !== 'undefined' && module.exports) module.exports = api;
  else root.Calib = api;
})(typeof globalThis !== 'undefined' ? globalThis : this);