P6: convert diffuser to BaseDomain + BaseNodeAdapter + concern split

Refactor of diffuser to use the platform infrastructure (BaseDomain, BaseNodeAdapter,
ChildRouter, commandRegistry, statusBadge). Extracts concerns into
focused modules per .claude/refactor/MODULE_SPLIT.md generic template.
Tests stay green; CONTRACT.md generated; legacy aliases preserved.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CONTRACT.md

@@ -0,0 +1,71 @@
+# diffuser — Contract
+
+Hand-maintained for Phase 6; the `## Inputs` table is generated from
+`src/commands/index.js` (see Phase 9 generator). Keep ≤ 100 lines.
+
+## Inputs (msg.topic on Port 0)
+
+| Canonical | Aliases (deprecated) | Payload | Effect |
+|---|---|---|---|
+| `data.flow` | `air_flow` | `number` — airflow in Nm³/h | Calls `source.setFlow(payload)`; clamps to ≥ 0 and recomputes OTR. |
+| `set.density` | `density` | `number` — diffuser density (per m²) | Calls `source.setDensity(payload)` and recomputes. |
+| `set.water-height` | `height_water` | `number` — water column height in m | Calls `source.setWaterHeight(payload)`; clamps to ≥ 0 and recomputes head + total pressure. |
+| `set.header-pressure` | `header_pressure` | `number` — header gauge pressure in mbar | Calls `source.setHeaderPressure(payload)` and recomputes. |
+| `set.elements` | `elements` | `number` — element count (rounded; must be > 0) | Calls `source.setElementCount(payload)` and recomputes per-element flow. |
+| `set.alfa-factor` | `alfaFactor` | `number` — alpha correction (≥ 0) | Calls `source.setAlfaFactor(payload)` and recomputes oxygen output. |
+
+Aliases log a one-time deprecation warning the first time they fire.
+
+## Outputs (msg.topic on Port 0/1/2)
+
+- **Port 0 (process):** `msg.topic = config.general.name`. Payload built
+  by `outputUtils.formatMsg(..., 'process')` from `getOutput()` —
+  delta-compressed (only changed fields are emitted). Fields:
+  - `iPressure`, `iMWater`, `iFlow` — echoed inputs.
+  - `nFlow` — normalised airflow (Nm³/h).
+  - `oOtr` — interpolated oxygen transfer rate (g O₂ / Nm³).
+  - `oPLoss` — total head loss (mbar) = static head + diffuser ΔP.
+  - `oKgo2H` — kg O₂ per hour at current operating point.
+  - `oFlowElement` — flow per element (Nm³/h/element).
+  - `efficiency` — combined OTR/ΔP efficiency (0–100).
+  - `slope` — local OTR-vs-flow slope.
+  - `oZoneOtr` — reactor zone OTR (kg O₂ / m³ / day) computed against
+    `diffuser.zoneVolume`; `0` when zone volume is unset.
+  - `idle` — true when `data.flow ≤ 0`.
+  - `warning`, `alarm` — string arrays describing flow-per-element band
+    excursions.
+- **Port 1 (InfluxDB telemetry):** same shape as Port 0, formatted with
+  the `'influxdb'` formatter.
+- **Port 2 (registration):** at startup the node sends one
+  `{ topic: 'child.register', payload: <node.id>, positionVsParent,
+  distance }` to the upstream parent (typically a reactor).
+  `positionVsParent` defaults to `'atEquipment'`.
+
+## Port-count change (Phase 6)
+
+Pre-refactor the diffuser exposed 4 outputs (process, dbase, reactor
+control with `topic: 'OTR'`, parent registration). The reactor control
+message merged into Port 0 as `oZoneOtr`; consumers that previously
+listened to the dedicated control port should switch to reading
+`payload.oZoneOtr` from the process output. The legacy `OTR` topic is
+removed in this refactor — there is no alias, since the data shape
+differs (single value vs full process payload).
+
+## Events emitted by `source.measurements.emitter`
+
+None today. The diffuser does not currently publish typed measurements
+through `MeasurementContainer`; all output flows via `getOutput()`.
+A future phase may promote `oOtr` and `oZoneOtr` to typed series so
+parent reactors can subscribe through the standard `ChildRouter`
+handshake.
+
+## Events emitted by `source.emitter`
+
+- `output-changed` — fires whenever an input setter recomputes the
+  oxygen-transfer state. `BaseNodeAdapter` listens and pushes the
+  delta-compressed Port 0 / Port 1 messages.
+
+## Children registered by this node
+
+None. The diffuser is a leaf Equipment Module; it registers itself with
+its parent (reactor / process cell) via the Port 2 handshake.

diffuser.html

@@ -16,9 +16,9 @@ RED.nodes.registerType('diffuser', {
     logLevel: { value: 'error' },
   },
   inputs: 1,
-  outputs: 4,
+  outputs: 3,
   inputLabels: ['control'],
-  outputLabels: ['process', 'dbase', 'reactor control', 'parent'],
+  outputLabels: ['process', 'dbase', 'parent'],
   icon: 'font-awesome/fa-tint',
   label: function() {
     return this.name ? `${this.name}_${this.number}` : 'diffuser';

src/commands/handlers.js

@@ -0,0 +1,13 @@
+'use strict';
+
+// Diffuser command handlers. Each receives:
+//   source: the Diffuser domain instance.
+//   msg:    the Node-RED input message.
+//   ctx:    { node, RED, send, logger } — provided by BaseNodeAdapter.
+
+exports.setFlow           = (source, msg) => source.setFlow(msg.payload);
+exports.setDensity        = (source, msg) => source.setDensity(msg.payload);
+exports.setWaterHeight    = (source, msg) => source.setWaterHeight(msg.payload);
+exports.setHeaderPressure = (source, msg) => source.setHeaderPressure(msg.payload);
+exports.setElements       = (source, msg) => source.setElementCount(msg.payload);
+exports.setAlfaFactor     = (source, msg) => source.setAlfaFactor(msg.payload);

src/commands/index.js

@@ -0,0 +1,47 @@
+'use strict';
+
+// Diffuser command registry. Consumed by BaseNodeAdapter via
+// `static commands = require('./commands')`. Each descriptor maps a
+// canonical msg.topic to its handler; legacy names live under `aliases`
+// and emit a one-time deprecation warning at runtime.
+
+const handlers = require('./handlers');
+
+module.exports = [
+  {
+    topic: 'data.flow',
+    aliases: ['air_flow'],
+    payloadSchema: { type: 'number' },
+    handler: handlers.setFlow,
+  },
+  {
+    topic: 'set.density',
+    aliases: ['density'],
+    payloadSchema: { type: 'number' },
+    handler: handlers.setDensity,
+  },
+  {
+    topic: 'set.water-height',
+    aliases: ['height_water'],
+    payloadSchema: { type: 'number' },
+    handler: handlers.setWaterHeight,
+  },
+  {
+    topic: 'set.header-pressure',
+    aliases: ['header_pressure'],
+    payloadSchema: { type: 'number' },
+    handler: handlers.setHeaderPressure,
+  },
+  {
+    topic: 'set.elements',
+    aliases: ['elements'],
+    payloadSchema: { type: 'number' },
+    handler: handlers.setElements,
+  },
+  {
+    topic: 'set.alfa-factor',
+    aliases: ['alfaFactor'],
+    payloadSchema: { type: 'number' },
+    handler: handlers.setAlfaFactor,
+  },
+];

src/nodeClass.js

@@ -1,140 +1,32 @@
-const { outputUtils } = require('generalFunctions');
-const Specific = require('./specificClass');
+'use strict';
 
-class nodeClass {
-  constructor(uiConfig, RED, nodeInstance, nameOfNode) {
-    this.node = nodeInstance;
-    this.RED = RED;
-    this.name = nameOfNode;
+const { BaseNodeAdapter } = require('generalFunctions');
+const Diffuser = require('./specificClass');
+const commands = require('./commands');
 
-    this._loadConfig(uiConfig);
-    this._setupSpecificClass();
-    this._registerChild();
-    this._startTickLoop();
-    this._attachInputHandler();
-    this._attachCloseHandler();
-  }
+// Event-driven: setter inputs trigger recalculate which emits
+// 'output-changed'. No tick loop. Status badge polled every second.
+class nodeClass extends BaseNodeAdapter {
+  static DomainClass = Diffuser;
+  static commands = commands;
+  static tickInterval = null;
+  static statusInterval = 1000;
 
-  _loadConfig(uiConfig) {
-    const suffix = uiConfig.number !== undefined && uiConfig.number !== '' ? `_${uiConfig.number}` : '';
-    const resolvedName = uiConfig.name ? `${uiConfig.name}${suffix}` : this.name;
-
-    this.config = {
-      general: {
-        name: resolvedName,
-        id: this.node.id,
-        unit: uiConfig.unit || 'kg o2/h',
-        logging: {
-          enabled: uiConfig.enableLog,
-          logLevel: uiConfig.logLevel,
-        },
-      },
-      functionality: {
-        positionVsParent: uiConfig.positionVsParent || 'atEquipment',
-        softwareType: this.name,
-        role: 'aeration diffuser',
-      },
+  buildDomainConfig(uiConfig) {
+    const n = (v, fb) => (Number.isFinite(Number(v)) ? Number(v) : fb);
+    return {
       diffuser: {
-        number: Number(uiConfig.number) || 0,
-        elements: Number(uiConfig.i_elements) || 1,
-        density: Number(uiConfig.i_diff_density) || 2.4,
-        waterHeight: Number(uiConfig.i_m_water) || 0,
-        alfaFactor: Number(uiConfig.alfaf ?? 0.7) || 0.7,
-        headerPressure: Number(uiConfig.i_pressure) || 0,
-        localAtmPressure: Number(uiConfig.i_local_atm_pressure) || 1013.25,
-        waterDensity: Number(uiConfig.i_water_density) || 997,
-        zoneVolume: Number(uiConfig.i_zone_volume) || 0,
+        number:           n(uiConfig.number, 1),
+        elements:         n(uiConfig.i_elements, 1),
+        density:          n(uiConfig.i_diff_density, 2.4),
+        waterHeight:      n(uiConfig.i_m_water, 0),
+        alfaFactor:       n(uiConfig.alfaf, 0.7),
+        headerPressure:   n(uiConfig.i_pressure, 0),
+        localAtmPressure: n(uiConfig.i_local_atm_pressure, 1013.25),
+        waterDensity:     n(uiConfig.i_water_density, 997),
+        zoneVolume:       n(uiConfig.i_zone_volume, 0),
       },
     };
-
-    this._output = new outputUtils();
-  }
-
-  _setupSpecificClass() {
-    this.source = new Specific(this.config);
-    this.node.source = this.source;
-  }
-
-  _registerChild() {
-    setTimeout(() => {
-      this.node.send([
-        null,
-        null,
-        null,
-        {
-          topic: 'registerChild',
-          payload: this.node.id,
-          positionVsParent: this.config?.functionality?.positionVsParent || 'atEquipment',
-        },
-      ]);
-    }, 100);
-  }
-
-  _startTickLoop() {
-    setTimeout(() => {
-      this._tickInterval = setInterval(() => this._tick(), 1000);
-    }, 1000);
-  }
-
-  _tick() {
-    const raw = this.source.getOutput();
-    const processMsg = this._output.formatMsg(raw, this.config, 'process');
-    const influxMsg = this._output.formatMsg(raw, this.config, 'influxdb');
-    const reactorOtr = this.source.getReactorOtr(this.config.diffuser?.zoneVolume);
-    const controlMsg = {
-      topic: 'OTR',
-      payload: reactorOtr,
-      meta: {
-        source: 'diffuser',
-        diffuser: this.config.general?.name,
-        zoneVolume: this.config.diffuser?.zoneVolume,
-        oKgo2H: raw.oKgo2H,
-      },
-    };
-    this.node.status(this.source.getStatus());
-    this.node.send([processMsg, influxMsg, controlMsg, null]);
-  }
-
-  _attachInputHandler() {
-    this.node.on('input', (msg, send, done) => {
-      try {
-        switch (msg.topic) {
-          case 'density':
-            this.source.setDensity(msg.payload);
-            break;
-          case 'air_flow':
-            this.source.setFlow(msg.payload);
-            break;
-          case 'height_water':
-            this.source.setWaterHeight(msg.payload);
-            break;
-          case 'header_pressure':
-            this.source.setHeaderPressure(msg.payload);
-            break;
-          case 'elements':
-            this.source.setElementCount(msg.payload);
-            break;
-          case 'alfaFactor':
-            this.source.setAlfaFactor(msg.payload);
-            break;
-          default:
-            this.source.logger.warn(`Unknown topic: ${msg.topic}`);
-            break;
-        }
-        done();
-      } catch (error) {
-        this.node.status({ fill: 'red', shape: 'ring', text: 'Bad request data' });
-        this.node.error(`Bad request data: ${error.message}`, msg);
-        done(error);
-      }
-    });
-  }
-
-  _attachCloseHandler() {
-    this.node.on('close', (done) => {
-      clearInterval(this._tickInterval);
-      done();
-    });
   }
 }
 

src/specificClass.js

@@ -1,293 +1,196 @@
-const { logger, interpolation, gravity, convert } = require('generalFunctions');
+'use strict';
 
-class Diffuser {
-  constructor(config = {}) {
-    this.config = config;
-    this.logger = new logger(
-      this.config.general?.logging?.enabled,
-      this.config.general?.logging?.logLevel,
-      this.config.general?.name,
-    );
+const { BaseDomain, statusBadge, interpolation, gravity, convert } = require('generalFunctions');
 
+class Diffuser extends BaseDomain {
+  static name = 'diffuser';
+
+  configure() {
+    const d = this.config.diffuser || {};
     this.interpolation = new interpolation({ type: 'linear' });
-    this.convert = convert;
-    this.specs = this.loadSpecs();
+    this.specs = this._loadSpecs();
 
     this.idle = true;
     this.warning = { state: false, text: [], flow: { min: { hyst: 2 }, max: { hyst: 2 } } };
     this.alarm = { state: false, text: [], flow: { min: { hyst: 10 }, max: { hyst: 10 } } };
 
-    this.i_pressure = this.config.diffuser?.headerPressure || 0;
-    this.i_local_atm_pressure = this.config.diffuser?.localAtmPressure || 1013.25;
-    this.i_water_density = this.config.diffuser?.waterDensity || 997;
-    this.i_alfa_factor = this.config.diffuser?.alfaFactor || 0.7;
-    this.i_n_elements = this.normalizePositiveInteger(this.config.diffuser?.elements, 1);
-    this.i_diff_density = this.normalizeNumber(this.config.diffuser?.density, 2.4);
-    this.i_m_water = this.normalizeNumber(this.config.diffuser?.waterHeight, 0);
+    this.i_pressure = _num(d.headerPressure, 0);
+    this.i_local_atm_pressure = _num(d.localAtmPressure, 1013.25);
+    this.i_water_density = _num(d.waterDensity, 997);
+    this.i_alfa_factor = _num(d.alfaFactor, 0.7);
+    this.i_n_elements = _posInt(d.elements, 1);
+    this.i_diff_density = _num(d.density, 2.4);
+    this.i_m_water = _num(d.waterHeight, 0);
     this.i_flow = 0;
+    this.zoneVolume = _num(d.zoneVolume, 0);
 
-    this.n_kg = this.calcAirDensityMbar(1013.25, 0, 20);
-
+    this.n_kg = this._calcAirDensityMbar(1013.25, 0, 20);
     this.n_flow = 0;
     this.o_otr = 0;
     this.o_p_flow = 0;
-    this.o_p_water = this.heightToPressureMbar(this.i_water_density, this.i_m_water);
+    this.o_p_water = this._heightToPressureMbar(this.i_water_density, this.i_m_water);
     this.o_p_total = this.o_p_water;
-    this.o_kg = 0;
-    this.o_kg_h = 0;
-    this.o_kgo2_h = 0;
-    this.o_kgo2 = 0;
-    this.o_kgo2_h_min = 0;
-    this.o_kgo2_h_max = 0;
+    this.o_kg = 0; this.o_kg_h = 0; this.o_kgo2_h = 0; this.o_kgo2 = 0;
+    this.o_kgo2_h_min = 0; this.o_kgo2_h_max = 0;
     this.o_flow_element = 0;
-    this.o_otr_min = 0;
-    this.o_otr_max = 0;
-    this.o_p_min = 0;
-    this.o_p_max = 0;
+    this.o_otr_min = 0; this.o_otr_max = 0;
+    this.o_p_min = 0; this.o_p_max = 0;
     this.o_combined_eff = 0;
     this.o_slope = 0;
   }
 
-  normalizeNumber(value, fallback = 0) {
-    const parsed = Number(value);
-    return Number.isFinite(parsed) ? parsed : fallback;
+  setDensity(v)        { this.i_diff_density = _num(v, this.i_diff_density); this._recalculate(); }
+  setFlow(v)           { this.i_flow = Math.max(0, _num(v, 0)); this._recalculate(); }
+  setWaterHeight(v)    {
+    this.i_m_water = Math.max(0, _num(v, this.i_m_water));
+    this.o_p_water = this._heightToPressureMbar(this.i_water_density, this.i_m_water);
+    this._recalculate();
   }
+  setHeaderPressure(v) { this.i_pressure = _num(v, this.i_pressure); this._recalculate(); }
+  setElementCount(v)   { this.i_n_elements = _posInt(v, this.i_n_elements); this._recalculate(); }
+  setAlfaFactor(v)     { this.i_alfa_factor = _num(v, this.i_alfa_factor); this._recalculate(); }
 
-  normalizePositiveInteger(value, fallback = 1) {
-    const parsed = Math.round(Number(value));
-    return Number.isFinite(parsed) && parsed > 0 ? parsed : fallback;
-  }
-
-  setDensity(value) {
-    this.i_diff_density = this.normalizeNumber(value, this.i_diff_density);
-    this.recalculate();
-  }
-
-  setFlow(value) {
-    this.i_flow = Math.max(0, this.normalizeNumber(value, 0));
-    this.recalculate();
-  }
-
-  setWaterHeight(value) {
-    this.i_m_water = Math.max(0, this.normalizeNumber(value, this.i_m_water));
-    this.o_p_water = this.heightToPressureMbar(this.i_water_density, this.i_m_water);
-    this.recalculate();
-  }
-
-  setHeaderPressure(value) {
-    this.i_pressure = this.normalizeNumber(value, this.i_pressure);
-    this.recalculate();
-  }
-
-  setElementCount(value) {
-    this.i_n_elements = this.normalizePositiveInteger(value, this.i_n_elements);
-    this.recalculate();
-  }
-
-  setAlfaFactor(value) {
-    this.i_alfa_factor = this.normalizeNumber(value, this.i_alfa_factor);
-    this.recalculate();
-  }
-
-  recalculate() {
+  _recalculate() {
     if (this.i_flow <= 0) {
       this.idle = true;
-      this.n_flow = 0;
-      this.o_otr = 0;
-      this.o_p_flow = 0;
-      this.o_flow_element = 0;
+      this.n_flow = 0; this.o_otr = 0; this.o_p_flow = 0; this.o_flow_element = 0;
       this.o_p_total = this.o_p_water;
-      this.o_kg = 0;
-      this.o_kg_h = 0;
-      this.o_kgo2_h = 0;
-      this.o_kgo2 = 0;
-      this.o_combined_eff = 0;
-      this.o_slope = 0;
-      this.warning.text = [];
-      this.warning.state = false;
-      this.alarm.text = [];
-      this.alarm.state = false;
-      return;
-    }
-
+      this.o_kg = 0; this.o_kg_h = 0; this.o_kgo2_h = 0; this.o_kgo2 = 0;
+      this.o_combined_eff = 0; this.o_slope = 0;
+      this.warning.text = []; this.warning.state = false;
+      this.alarm.text = [];   this.alarm.state = false;
+    } else {
       this.idle = false;
-    this.calcOtrPressure(this.i_flow);
+      this._calcOtrPressure(this.i_flow);
+    }
+    this.notifyOutputChanged();
   }
 
-  getCurveKeys(curve) {
-    return Object.keys(curve)
-      .map(Number)
-      .sort((a, b) => a - b);
-  }
+  _getCurveKeys(c) { return Object.keys(c).map(Number).sort((a, b) => a - b); }
 
-  interpolateSeries(points, x) {
-    this.interpolation.load_spline(points.x, points.y, 'linear');
+  _interpolateSeries(pts, x) {
+    this.interpolation.load_spline(pts.x, pts.y, 'linear');
     return this.interpolation.interpolate(x);
   }
 
-  interpolateCurveByDensity(curve, density, x) {
-    const keys = this.getCurveKeys(curve);
+  _interpolateCurveByDensity(curve, density, x) {
+    const keys = this._getCurveKeys(curve);
     if (keys.length === 1) {
       const only = curve[keys[0]];
-      return {
-        value: this.interpolateSeries(only, x),
-        minY: Math.min(...only.y),
-        maxY: Math.max(...only.y),
-        minX: Math.min(...only.x),
-        maxX: Math.max(...only.x),
-        slope: this.getSegmentSlope(only, x),
-      };
+      return { value: this._interpolateSeries(only, x),
+        minY: Math.min(...only.y), maxY: Math.max(...only.y),
+        minX: Math.min(...only.x), maxX: Math.max(...only.x),
+        slope: this._getSegmentSlope(only, x) };
     }
-
-    const lowerKey = keys.reduce((acc, key) => (key <= density ? key : acc), keys[0]);
-    const upperKey = keys.find((key) => key >= density) ?? keys[keys.length - 1];
-    const lowerCurve = curve[lowerKey];
-    const upperCurve = curve[upperKey];
-
+    const lowerKey = keys.reduce((a, k) => (k <= density ? k : a), keys[0]);
+    const upperKey = keys.find((k) => k >= density) ?? keys[keys.length - 1];
+    const lower = curve[lowerKey]; const upper = curve[upperKey];
     if (lowerKey === upperKey) {
+      return { value: this._interpolateSeries(lower, x),
+        minY: Math.min(...lower.y), maxY: Math.max(...lower.y),
+        minX: Math.min(...lower.x), maxX: Math.max(...lower.x),
+        slope: this._getSegmentSlope(lower, x) };
+    }
+    const lv = this._interpolateSeries(lower, x);
+    const uv = this._interpolateSeries(upper, x);
+    const r = (density - lowerKey) / (upperKey - lowerKey);
     return {
-        value: this.interpolateSeries(lowerCurve, x),
-        minY: Math.min(...lowerCurve.y),
-        maxY: Math.max(...lowerCurve.y),
-        minX: Math.min(...lowerCurve.x),
-        maxX: Math.max(...lowerCurve.x),
-        slope: this.getSegmentSlope(lowerCurve, x),
+      value: lv + (uv - lv) * r,
+      minY: Math.min(...lower.y) + (Math.min(...upper.y) - Math.min(...lower.y)) * r,
+      maxY: Math.max(...lower.y) + (Math.max(...upper.y) - Math.max(...lower.y)) * r,
+      minX: Math.min(...lower.x), maxX: Math.max(...lower.x),
+      slope: this._getSegmentSlope(lower, x),
     };
   }
 
-    const lowerValue = this.interpolateSeries(lowerCurve, x);
-    const upperValue = this.interpolateSeries(upperCurve, x);
-    const ratio = (density - lowerKey) / (upperKey - lowerKey);
-
-    return {
-      value: lowerValue + (upperValue - lowerValue) * ratio,
-      minY: Math.min(...lowerCurve.y) + (Math.min(...upperCurve.y) - Math.min(...lowerCurve.y)) * ratio,
-      maxY: Math.max(...lowerCurve.y) + (Math.max(...upperCurve.y) - Math.max(...lowerCurve.y)) * ratio,
-      minX: Math.min(...lowerCurve.x),
-      maxX: Math.max(...lowerCurve.x),
-      slope: this.getSegmentSlope(lowerCurve, x),
-    };
-  }
-
-  getSegmentSlope(curvePoints, x) {
-    const xs = curvePoints.x;
-    const ys = curvePoints.y;
+  _getSegmentSlope(pts, x) {
+    const { x: xs, y: ys } = pts;
     for (let i = 0; i < xs.length - 1; i += 1) {
-      if (x <= xs[i + 1]) {
-        return (ys[i + 1] - ys[i]) / (xs[i + 1] - xs[i]);
+      if (x <= xs[i + 1]) return (ys[i + 1] - ys[i]) / (xs[i + 1] - xs[i]);
     }
-    }
-    const last = xs.length - 1;
-    return (ys[last] - ys[last - 1]) / (xs[last] - xs[last - 1]);
+    const n = xs.length - 1;
+    return (ys[n] - ys[n - 1]) / (xs[n] - xs[n - 1]);
   }
 
-  combineEff(oOtr, oOtrMin, oOtrMax, oPFlow, oPMin, oPMax) {
+  _combineEff(oOtr, oOtrMin, oOtrMax, oPFlow, oPMin, oPMax) {
     const otrSpan = oOtrMax - oOtrMin;
     const pSpan = oPMax - oPMin;
-    const eff1 = otrSpan > 0 ? (oOtr - oOtrMin) / otrSpan : 0;
-    const eff2 = pSpan > 0 ? 1 - ((oPFlow - oPMin) / pSpan) : 0;
-    return Math.max(0, eff1 * eff2 * 100);
+    const e1 = otrSpan > 0 ? (oOtr - oOtrMin) / otrSpan : 0;
+    const e2 = pSpan > 0 ? 1 - ((oPFlow - oPMin) / pSpan) : 0;
+    return Math.max(0, e1 * e2 * 100);
   }
 
-  calcAirDensityMbar(pressureMbar, RH, tempC) {
-    const Rd = 287.05;
-    const Rv = 461.495;
+  _calcAirDensityMbar(pMbar, RH, tempC) {
+    const Rd = 287.05, Rv = 461.495;
     const T = tempC + 273.15;
-    const A = 8.07131;
-    const B = 1730.63;
-    const C = 233.426;
-    const e_s = Math.pow(10, (A - (B / (C + tempC))));
-    const e = RH * e_s / 100;
-    const pressurePa = this.convert(pressureMbar).from('mbar').to('Pa');
-    const p_d = pressurePa - (e * 100);
-    return (p_d / (Rd * T)) + ((e * 100) / (Rv * T));
+    const es = Math.pow(10, (8.07131 - (1730.63 / (233.426 + tempC))));
+    const e = RH * es / 100;
+    const pPa = convert(pMbar).from('mbar').to('Pa');
+    const pd = pPa - (e * 100);
+    return (pd / (Rd * T)) + ((e * 100) / (Rv * T));
   }
 
-  heightToPressureMbar(density, height) {
-    const pressurePa = gravity.getStandardGravity() * density * height;
-    return this.convert(pressurePa).from('Pa').to('mbar');
+  _heightToPressureMbar(density, height) {
+    const pPa = gravity.getStandardGravity() * density * height;
+    return convert(pPa).from('Pa').to('mbar');
   }
 
-  calcOtrPressure(flow) {
+  _calcOtrPressure(flow) {
     const totalInputPressureMbar = this.i_local_atm_pressure + this.i_pressure;
-    this.o_kg = this.calcAirDensityMbar(totalInputPressureMbar, 0, 20);
+    this.o_kg = this._calcAirDensityMbar(totalInputPressureMbar, 0, 20);
     this.o_kg_h = this.o_kg * flow;
     this.n_flow = (this.o_kg / this.n_kg) * flow;
     this.o_flow_element = Math.round((this.n_flow / this.i_n_elements) * 100) / 100;
 
-    const otr = this.interpolateCurveByDensity(this.specs.otr_curve, this.i_diff_density, this.o_flow_element);
-    const pressure = this.interpolateCurveByDensity(this.specs.p_curve, 0, this.o_flow_element);
+    const otr = this._interpolateCurveByDensity(this.specs.otr_curve, this.i_diff_density, this.o_flow_element);
+    const pressure = this._interpolateCurveByDensity(this.specs.p_curve, 0, this.o_flow_element);
 
-    this.o_otr_min = otr.minY;
-    this.o_otr_max = otr.maxY;
-    this.o_p_min = pressure.minY;
-    this.o_p_max = pressure.maxY;
+    this.o_otr_min = otr.minY; this.o_otr_max = otr.maxY;
+    this.o_p_min = pressure.minY; this.o_p_max = pressure.maxY;
     this.o_otr = Math.round(otr.value * 100) / 100;
     this.o_p_flow = Math.round(pressure.value * 100) / 100;
     this.o_p_total = Math.round((this.o_p_water + this.o_p_flow) * 100) / 100;
-    this.o_kgo2_h = Math.round(this.convert(this.o_otr * this.n_flow * this.i_m_water * this.i_alfa_factor).from('g').to('kg') * 100) / 100;
-    this.o_kgo2_h_min = Math.round(this.convert(this.o_otr_min * this.n_flow * this.i_m_water * this.i_alfa_factor).from('g').to('kg') * 100) / 100;
-    this.o_kgo2_h_max = Math.round(this.convert(this.o_otr_max * this.n_flow * this.i_m_water * this.i_alfa_factor).from('g').to('kg') * 100) / 100;
+    const kgo2 = (n) => Math.round(convert(n * this.n_flow * this.i_m_water * this.i_alfa_factor).from('g').to('kg') * 100) / 100;
+    this.o_kgo2_h = kgo2(this.o_otr);
+    this.o_kgo2_h_min = kgo2(this.o_otr_min);
+    this.o_kgo2_h_max = kgo2(this.o_otr_max);
     this.o_kgo2 = this.o_kgo2_h / 3600;
-    this.o_combined_eff = Math.round(this.combineEff(
-      this.o_otr,
-      this.o_otr_min,
-      this.o_otr_max,
-      this.o_p_flow,
-      this.o_p_min,
-      this.o_p_max,
+    this.o_combined_eff = Math.round(this._combineEff(
+      this.o_otr, this.o_otr_min, this.o_otr_max,
+      this.o_p_flow, this.o_p_min, this.o_p_max,
     ) * 100) / 100;
     this.o_slope = Math.round(otr.slope * 1000) / 1000;
 
-    this.warningCheck(pressure.minX, pressure.maxX);
-    this.alarmCheck(pressure.minX, pressure.maxX);
+    this._checkLimits(pressure.minX, pressure.maxX);
   }
 
-  warningCheck(minFlow, maxFlow) {
-    this.warning.text = [];
-    this.warning.state = false;
-    const minHyst = minFlow * (this.warning.flow.min.hyst / 100);
-    const maxHyst = maxFlow * (this.warning.flow.max.hyst / 100);
-
-    if (this.o_flow_element < minFlow - minHyst) {
-      this.warning.state = true;
-      this.warning.text.push(`Warning: flow per element ${this.o_flow_element} is below ${Math.round((minFlow - minHyst) * 100) / 100}`);
-    }
-
-    if (this.o_flow_element > maxFlow + maxHyst) {
-      this.warning.state = true;
-      this.warning.text.push(`Warning: flow per element ${this.o_flow_element} exceeds ${Math.round((maxFlow + maxHyst) * 100) / 100}`);
+  _checkLimits(minFlow, maxFlow) {
+    this.warning.text = []; this.warning.state = false;
+    this.alarm.text   = []; this.alarm.state   = false;
+    const f = this.o_flow_element;
+    for (const k of ['warning', 'alarm']) {
+      const band = this[k];
+      const lo = minFlow - minFlow * (band.flow.min.hyst / 100);
+      const hi = maxFlow + maxFlow * (band.flow.max.hyst / 100);
+      if (f < lo) { band.state = true; band.text.push(`${_cap(k)}: flow per element ${f} is below ${Math.round(lo * 100) / 100}`); }
+      if (f > hi) { band.state = true; band.text.push(`${_cap(k)}: flow per element ${f} exceeds ${Math.round(hi * 100) / 100}`); }
     }
   }
 
-  alarmCheck(minFlow, maxFlow) {
-    this.alarm.text = [];
-    this.alarm.state = false;
-    const minHyst = minFlow * (this.alarm.flow.min.hyst / 100);
-    const maxHyst = maxFlow * (this.alarm.flow.max.hyst / 100);
-
-    if (this.o_flow_element < minFlow - minHyst) {
-      this.alarm.state = true;
-      this.alarm.text.push(`Alarm: flow per element ${this.o_flow_element} is below ${Math.round((minFlow - minHyst) * 100) / 100}`);
+  // Back-compat hooks for the legacy specificClass test suite.
+  getStatus() { return this._legacyStatus(); }
+  _legacyStatus() {
+    if (this.alarm.state)   return { fill: 'red',   shape: 'dot', text: this.alarm.text[0] };
+    if (this.warning.state) return { fill: 'yellow', shape: 'dot', text: this.warning.text[0] };
+    const fill = this.idle ? 'grey' : 'green';
+    return { fill, shape: 'dot', text: `${this.o_kgo2_h} kg o2 / h` };
   }
 
-    if (this.o_flow_element > maxFlow + maxHyst) {
-      this.alarm.state = true;
-      this.alarm.text.push(`Alarm: flow per element ${this.o_flow_element} exceeds ${Math.round((maxFlow + maxHyst) * 100) / 100}`);
-    }
-  }
-
-  getStatus() {
-    if (this.alarm.state) {
-      return { fill: 'red', shape: 'dot', text: this.alarm.text[0] };
-    }
-    if (this.warning.state) {
-      return { fill: 'yellow', shape: 'dot', text: this.warning.text[0] };
-    }
-    if (this.idle) {
-      return { fill: 'grey', shape: 'dot', text: `${this.o_kgo2_h} kg o2 / h` };
-    }
-    return { fill: 'green', shape: 'dot', text: `${this.o_kgo2_h} kg o2 / h` };
+  getStatusBadge() {
+    if (this.alarm.state)   return statusBadge.error(this.alarm.text[0]);
+    if (this.warning.state) return statusBadge.compose([`⚠ ${this.warning.text[0]}`], { fill: 'yellow', shape: 'dot' });
+    const text = `${this.o_kgo2_h} kg o2 / h`;
+    return this.idle ? statusBadge.idle(text) : statusBadge.compose([`🟢 ${text}`]);
   }
 
   getOutput() {
@@ -302,6 +205,7 @@ class Diffuser {
       oFlowElement: this.o_flow_element,
       efficiency: this.o_combined_eff,
       slope: this.o_slope,
+      oZoneOtr: this.getReactorOtr(this.zoneVolume),
       idle: this.idle,
       warning: [...this.warning.text],
       alarm: [...this.alarm.text],
@@ -309,34 +213,29 @@ class Diffuser {
   }
 
   getReactorOtr(zoneVolumeM3) {
-    const volume = Number(zoneVolumeM3);
-    if (!Number.isFinite(volume) || volume <= 0) {
-      return 0;
-    }
-    return this.o_kgo2_h * 1000 * 24 / volume;
+    const v = Number(zoneVolumeM3);
+    if (!Number.isFinite(v) || v <= 0) return 0;
+    return this.o_kgo2_h * 1000 * 24 / v;
   }
 
-  loadSpecs() {
+  _loadSpecs() {
     return {
-      supplier: 'GVA',
-      type: 'ELASTOX-R',
-      units: {
-        Nm3: { temp: 20, pressure: 1.01325, RH: 0 },
-      },
-      otr_curve: {
-        2.4: {
-          x: [2, 3, 4, 5, 6, 7, 8, 9, 10],
-          y: [26, 25, 24, 23.5, 23, 22.75, 22.5, 22.25, 22],
-        },
-      },
-      p_curve: {
-        0: {
-          x: [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12],
-          y: [40, 42.5, 45, 47.5, 50, 51.5, 53, 54.5, 56, 57.5, 59],
-        },
-      },
+      supplier: 'GVA', type: 'ELASTOX-R',
+      units: { Nm3: { temp: 20, pressure: 1.01325, RH: 0 } },
+      otr_curve: { 2.4: { x: [2, 3, 4, 5, 6, 7, 8, 9, 10],     y: [26, 25, 24, 23.5, 23, 22.75, 22.5, 22.25, 22] } },
+      p_curve:   { 0:   { x: [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12], y: [40, 42.5, 45, 47.5, 50, 51.5, 53, 54.5, 56, 57.5, 59] } },
     };
   }
 }
 
+function _num(v, fb = 0) {
+  const n = Number(v);
+  return Number.isFinite(n) ? n : fb;
+}
+function _posInt(v, fb = 1) {
+  const n = Math.round(Number(v));
+  return Number.isFinite(n) && n > 0 ? n : fb;
+}
+function _cap(s) { return s.charAt(0).toUpperCase() + s.slice(1); }
+
 module.exports = Diffuser;