implement basic NMEA stream parsing

take into account only GGA packets and export all locations as a single
track

lib/import.js

@@ -1,4 +1,32 @@
+const makeStream = require('./stream');
+
 module.exports = importNmea;
 
-function importNmea() {
+/* global WritableStream */
+
+/**
+ * Parses ASCII stream containing NMEA messages into Furkot's trip
+ * @param {ReadableStream} from
+ */
+async function importNmea(from) {
+  const stream = makeStream({ GGA: true });
+  const track = [];
+
+  await from.pipeThrough(stream).pipeTo(new WritableStream({
+    write: packet => track.push(toStop(packet))
+  }));
+
+  return {
+    track: [track]
+  };
+}
+
+function toStop({ longitude, latitude, time }) {
+  return {
+    coordinates: {
+      lon: longitude,
+      lat: latitude
+    },
+    timestamp: time.toISOString()
+  };
 }

lib/stream.js

@@ -0,0 +1,49 @@
+const nmea = require("nmea-simple");
+
+module.exports = makeStream;
+
+/* global TransformStream */
+
+function makeStream(types) {
+  return new TransformStream(makeSource(types));
+}
+
+function makeSource(types) {
+  let prefix = '';
+  return {
+    transform,
+    flush
+  };
+
+  /**
+   * @param {String} chunk
+   * @param {TransformStreamDefaultController} controller
+   */
+  function transform(chunk, controller) {
+    const lines = chunk.split(/[\n\r]+/);
+    if (prefix) {
+      lines[0] = prefix + lines[0];
+    }
+    prefix = lines.length > 0 ? lines.pop() : '';
+    for (const line of lines) {
+      processSentence(line, controller);
+    }
+  }
+
+  /**
+   * @param {TransformStreamDefaultController} controller
+   */
+  function flush(controller) {
+    processSentence(prefix, controller);
+  }
+
+  function processSentence(line, controller) {
+    if (line[0] === '$') {
+      const packet = nmea.parseNmeaSentence(line);
+      const { sentenceId } = packet;
+      if (types[sentenceId]) {
+        controller.enqueue(packet);
+      }
+    }
+  }
+}

package.json

@@ -14,7 +14,9 @@
     "nmea",
     "furkot"
   ],
-  "dependencies": {},
+  "dependencies": {
+    "nmea-simple": "^3.3.0"
+  },
   "devDependencies": {
     "@pirxpilot/jshint": "^3.0.1"
   },