Add Label BA FANS 1/A CPDLC Downlink decoder plugin

lib/MessageDecoder.ts

@@ -78,6 +78,7 @@ const pluginClasses = [
   Plugins.Label_QQ,
   Plugins.Label_QR,
   Plugins.Label_QS,
+  Plugins.Label_BA_CPDLC,
 ];
 
 export class MessageDecoder {

lib/plugins/Label_BA_CPDLC.ts

@@ -0,0 +1,186 @@
+import { DecoderPlugin } from '../DecoderPlugin';
+import { DecodeResult, Message, Options } from '../DecoderPluginInterface';
+import { ResultFormatter } from '../utils/result_formatter';
+
+/**
+ * Label BA — FANS-1/A CPDLC Downlink (aircraft → ground)
+ *
+ * The downlink companion to label AA (uplink). Carried inside the ARINC 622
+ * framework. Observed service qualifiers:
+ *   DR1 — CPDLC Downlink Response Type 1 (most common)
+ *   CC1 — CPDLC Connection / Connect-Confirm
+ *   AT1 — ATC Type 1 (occasional)
+ *
+ * Wire format:
+ *
+ *   / USADCXA . DR1 . N887QS <payload-hex> 0CAF
+ *   | |       |  |  | |      |              |
+ *   | |       |  |  | |      |              └ 4-char CRC (hex) — message integrity
+ *   | |       |  |  | |      └──────────────── CPDLC payload, ASN.1 PER hex (may be empty)
+ *   | |       |  |  | └─────────────────────── Aircraft registration / tail (typ. 6 chars)
+ *   | |       |  |  └───────────────────────── Separator
+ *   | |       |  └──────────────────────────── Service qualifier (DR1, CC1, ATN, ...)
+ *   | |       └─────────────────────────────── Separator
+ *   | └─────────────────────────────────────── Ground-station ARINC address (5–9 chars)
+ *   └───────────────────────────────────────── ARINC-622 routing delimiter '/'
+ *
+ * The trailing 4 characters are always the CRC. When `payload-hex` is empty
+ * the message is typically a link-status / acknowledgement / keep-alive
+ * (e.g. `/USADCXA.DR1.N887QS0CAF` — tail directly followed by CRC).
+ *
+ * Direction: aircraft → ground (downlink) — the BA label semantics.
+ */
+export class Label_BA_CPDLC extends DecoderPlugin {
+  name = 'label-ba-cpdlc';
+
+  qualifiers() {
+    return {
+      labels: ['BA'],
+    };
+  }
+
+  decode(message: Message, options: Options = {}): DecodeResult {
+    const decodeResult = this.initResult(
+      message,
+      'FANS-1/A CPDLC Downlink — Controller–Pilot Data Link Communications',
+    );
+
+    const text = (message.text || '').trim();
+    if (!text) {
+      this.setDecodeLevel(decodeResult, false);
+      return decodeResult;
+    }
+
+    // Envelope: /GROUND.QUALIFIER.REST
+    const envelope =
+      /^\/(?<ground>[A-Z0-9]{5,9})\.(?<qual>[A-Z0-9]{2,4})\.(?<rest>.+)$/;
+    const env = text.match(envelope);
+    if (!env?.groups) {
+      this.setDecodeLevel(decodeResult, false);
+      return decodeResult;
+    }
+
+    const { ground, qual, rest } = env.groups;
+    decodeResult.raw.ground_address = ground;
+    decodeResult.raw.service_qualifier = qual;
+
+    // Tail/payload split heuristic: tails on label BA can be all-hex
+    // (e.g. C-XXXXX) so a strict "find the first non-hex char" approach
+    // fails. We scan the leading 8 chars for a non-hex character to mark
+    // the end of the tail; if none, default to the first 6 chars.
+    let tail = '';
+    let payloadAndCrc = '';
+    const window = rest.substring(0, Math.min(8, rest.length));
+    const nonHexIdx = window.search(/[G-Zg-z]/);
+    if (nonHexIdx >= 2) {
+      // Tail is rest[0 .. nonHexIdx], payload+CRC follows
+      tail = rest.substring(0, nonHexIdx + 1);
+      payloadAndCrc = rest.substring(nonHexIdx + 1);
+    } else {
+      // All-hex window — assume 6-char tail
+      tail = rest.substring(0, 6);
+      payloadAndCrc = rest.substring(6);
+    }
+
+    decodeResult.raw.tail = tail;
+    ResultFormatter.tail(decodeResult, tail);
+
+    // Trailing 4 chars are the CRC; everything before is the CPDLC payload.
+    let payload = '';
+    let crc = '';
+    if (payloadAndCrc.length >= 4) {
+      crc = payloadAndCrc.slice(-4).toUpperCase();
+      payload = payloadAndCrc.slice(0, -4);
+    } else {
+      // Malformed — too short to contain a CRC; expose verbatim and bail at partial.
+      decodeResult.raw.cpdlc_payload_hex = payloadAndCrc;
+      decodeResult.formatted.items.unshift(
+        {
+          type: 'message_type',
+          code: 'MSGTYP',
+          label: 'Message Type',
+          value: 'FANS-1/A CPDLC Downlink',
+        },
+        {
+          type: 'ground_address',
+          code: 'GND',
+          label: 'Ground Address',
+          value: ground,
+        },
+        {
+          type: 'service_qualifier',
+          code: 'QUAL',
+          label: 'Service Qualifier',
+          value: qual,
+        },
+        {
+          type: 'tail',
+          code: 'TAIL',
+          label: 'Tail',
+          value: tail,
+        },
+      );
+      this.setDecodeLevel(decodeResult, true, 'partial');
+      return decodeResult;
+    }
+
+    decodeResult.raw.cpdlc_payload_hex = payload;
+    decodeResult.raw.crc = crc;
+
+    // Direction
+    decodeResult.raw.direction = 'aircraft-to-ground (downlink)';
+
+    decodeResult.formatted.items.unshift(
+      {
+        type: 'message_type',
+        code: 'MSGTYP',
+        label: 'Message Type',
+        value: 'FANS-1/A CPDLC Downlink',
+      },
+      {
+        type: 'direction',
+        code: 'DIR',
+        label: 'Direction',
+        value: 'Aircraft → Ground (downlink)',
+      },
+      {
+        type: 'ground_address',
+        code: 'GND',
+        label: 'Ground Address',
+        value: ground,
+      },
+      {
+        type: 'service_qualifier',
+        code: 'QUAL',
+        label: 'Service Qualifier',
+        value: qual,
+      },
+    );
+
+    if (payload) {
+      decodeResult.formatted.items.push({
+        type: 'cpdlc_payload',
+        code: 'PAYLOAD',
+        label: 'CPDLC Payload (ASN.1 PER hex)',
+        value: payload,
+      });
+    } else {
+      decodeResult.formatted.items.push({
+        type: 'cpdlc_payload',
+        code: 'PAYLOAD',
+        label: 'CPDLC Payload',
+        value: '(none — likely link status / acknowledgement / keep-alive)',
+      });
+    }
+
+    decodeResult.formatted.items.push({
+      type: 'crc',
+      code: 'CRC',
+      label: 'CRC',
+      value: crc,
+    });
+
+    this.setDecodeLevel(decodeResult, true, 'full');
+    return decodeResult;
+  }
+}

lib/plugins/official.ts

@@ -64,3 +64,4 @@ export * from './Label_QR';
 export * from './Label_QP';
 export * from './Label_QS';
 export * from './Label_QQ';
+export * from './Label_BA_CPDLC';