feat: add realtime GNSS monitor with telemetry websocket

backend/app/mqtt/parsers/nmea.py

@@ -3,6 +3,16 @@ from __future__ import annotations
 from typing import Any
 
 SUPPORTED_NMEA_TYPES = {"GGA", "RMC", "GSV", "GSA", "GST"}
+TALKER_TO_CONSTELLATION = {
+    "GP": "GPS",
+    "GL": "GLONASS",
+    "GA": "Galileo",
+    "GB": "BeiDou",
+    "BD": "BeiDou",
+    "GQ": "QZSS",
+    "GI": "NavIC",
+    "GN": "Mixed",
+}
 
 
 def _to_float(value: str) -> float | None:
@@ -40,19 +50,46 @@ def _parse_lat_lon(value: str, hemisphere: str) -> float | None:
     return decimal
 
 
-def _extract_sentence_type(sentence: str) -> str | None:
+def _extract_sentence_meta(sentence: str) -> tuple[str, str] | None:
     if not sentence.startswith("$"):
         return None
     if len(sentence) < 6:
         return None
+    talker = sentence[1:3].upper()
     nmea_type = sentence[3:6].upper()
     if nmea_type not in SUPPORTED_NMEA_TYPES:
         return None
-    return nmea_type
+    return talker, nmea_type
 
 
-def _parse_nmea_fields(nmea_type: str, fields: list[str]) -> dict[str, Any]:
-    payload: dict[str, Any] = {"sentence_type": nmea_type, "raw_fields": fields}
+def _parse_satellite_blocks(fields: list[str]) -> list[dict[str, Any]]:
+    satellites: list[dict[str, Any]] = []
+    for i in range(4, len(fields), 4):
+        if i + 3 >= len(fields):
+            continue
+        satellite_id = fields[i]
+        if not satellite_id:
+            continue
+        satellites.append(
+            {
+                "satellite_id": satellite_id,
+                "elevation_deg": _to_int(fields[i + 1]),
+                "azimuth_deg": _to_int(fields[i + 2]),
+                "snr_dbhz": _to_int(fields[i + 3]),
+            }
+        )
+    return satellites
+
+
+def _parse_nmea_fields(
+    *, talker: str, nmea_type: str, fields: list[str]
+) -> dict[str, Any]:
+    payload: dict[str, Any] = {
+        "sentence_type": nmea_type,
+        "talker": talker,
+        "constellation": TALKER_TO_CONSTELLATION.get(talker, "Unknown"),
+        "raw_fields": fields,
+    }
 
     if nmea_type == "GGA":
         payload.update(
@@ -91,23 +128,27 @@ def _parse_nmea_fields(nmea_type: str, fields: list[str]) -> dict[str, Any]:
             }
         )
     elif nmea_type == "GSV":
+        satellites = _parse_satellite_blocks(fields)
         payload.update(
             {
                 "total_messages": _to_int(fields[1] if len(fields) > 1 else ""),
                 "message_index": _to_int(fields[2] if len(fields) > 2 else ""),
                 "satellites_in_view": _to_int(fields[3] if len(fields) > 3 else ""),
+                "satellites": satellites,
                 "snr_values": [
-                    _to_int(fields[i])
-                    for i in range(7, len(fields), 4)
-                    if i < len(fields)
+                    satellite["snr_dbhz"]
+                    for satellite in satellites
+                    if satellite["snr_dbhz"] is not None
                 ],
             }
         )
     elif nmea_type == "GSA":
+        used_satellite_ids = [sat_id for sat_id in fields[3:15] if sat_id]
         payload.update(
             {
                 "mode": fields[1] if len(fields) > 1 else None,
                 "fix_type": _to_int(fields[2] if len(fields) > 2 else ""),
+                "used_satellite_ids": used_satellite_ids,
                 "pdop": _to_float(fields[15] if len(fields) > 15 else ""),
                 "hdop": _to_float(fields[16] if len(fields) > 16 else ""),
                 "vdop": _to_float(fields[17] if len(fields) > 17 else ""),
@@ -134,13 +175,16 @@ def parse_nmea_sentences(payload: bytes) -> list[dict[str, Any]]:
             continue
 
         sentence = raw_line.decode("ascii", errors="ignore").strip()
-        nmea_type = _extract_sentence_type(sentence)
-        if nmea_type is None:
+        sentence_meta = _extract_sentence_meta(sentence)
+        if sentence_meta is None:
             continue
+        talker, nmea_type = sentence_meta
 
         main_part = sentence.split("*", 1)[0]
         fields = main_part.split(",")
-        parsed_payload = _parse_nmea_fields(nmea_type, fields)
+        parsed_payload = _parse_nmea_fields(
+            talker=talker, nmea_type=nmea_type, fields=fields
+        )
         events.append(
             {"event_type": f"nmea_{nmea_type.lower()}", "payload": parsed_payload}
         )