From bfc6ba247cf075ff02ff701818f898068f6dc822 Mon Sep 17 00:00:00 2001
From: Akos Becsey <becsey.a@gmail.com>
Date: Thu, 9 Feb 2023 16:52:04 +0100
Subject: [PATCH] FIX: RMC failed to parse milliseconds

---
 codecs/RMC.ts    |  4 +--
 helpers.ts       | 67 +++++++++++++++++++++---------------------------
 tests/RMCtest.ts | 11 +++++++-
 3 files changed, 41 insertions(+), 41 deletions(-)

diff --git a/codecs/RMC.ts b/codecs/RMC.ts
index 1eeaf57..878cbad 100644
--- a/codecs/RMC.ts
+++ b/codecs/RMC.ts
@@ -26,7 +26,7 @@
  * 13. Checksum
  */
 
-import { parseDatetime, parseFloatSafe, parseLatitude, parseLongitude } from "../helpers";
+import { parseFloatSafe, parseLatitude, parseLongitude, parseTime } from "../helpers";
 import { initStubFields, PacketStub } from "./PacketStub";
 
 
@@ -50,7 +50,7 @@ export interface RMCPacket extends PacketStub<typeof sentenceId> {
 export function decodeSentence(stub: PacketStub, fields: string[]): RMCPacket {
     return {
         ...initStubFields(stub, sentenceId, sentenceName),
-        datetime: parseDatetime(fields[9], fields[1]),
+        datetime: parseTime(fields[1], fields[9], true),
         status: fields[2] === "A" ? "valid" : "warning",
         latitude: parseLatitude(fields[3], fields[4]),
         longitude: parseLongitude(fields[5], fields[6]),
diff --git a/helpers.ts b/helpers.ts
index 6f26b25..dd837c3 100644
--- a/helpers.ts
+++ b/helpers.ts
@@ -337,6 +337,33 @@ export function parseLongitude(lon: string, hemi: string): number {
     return parseDmCoordinate(lon) * hemisphere;
 }
 
+function getYearFromString(yearString: string, rmcCompatible: boolean): number {
+    if (yearString.length === 4) {
+        return Number(yearString);
+    } else if (yearString.length === 2) {
+        if (rmcCompatible) {
+            // GPRMC date doesn't specify century. GPS came out in 1973 so if the year
+            // is less than 73, assume it's 20xx, otherwise assume it is 19xx.
+            let year = Number(yearString);
+
+            if (year < 73) {
+                year = 2000 + year;
+            }
+            else {
+                year = 1900 + year;
+            }
+
+            return year;
+        }
+        else {
+            return Number("20" + yearString);
+        }
+    }
+    else {
+        throw Error(`Unexpected year string: ${yearString}`);
+    }
+}
+
 /**
  * Parses a UTC time and optionally a date and returns a Date
  * object.
@@ -344,7 +371,7 @@ export function parseLongitude(lon: string, hemi: string): number {
  * @param {String=} date Optional date in format the ddmmyyyy or ddmmyy
  * @returns {Date}
  */
-export function parseTime(time: string, date?: string): Date {
+export function parseTime(time: string, date?: string, rmcCompatible = false): Date {
 
     if (time === "") {
         return new Date(0);
@@ -358,14 +385,7 @@ export function parseTime(time: string, date?: string): Date {
         const month = parseInt(date.slice(2, 4), 10) - 1;
         const day = date.slice(0, 2);
 
-        if (year.length === 4) {
-            ret.setUTCFullYear(Number(year), Number(month), Number(day));
-        } else {
-            // If we need to parse older GPRMC data, we should hack something like
-            // year < 73 ? 2000+year : 1900+year
-            // Since GPS appeared in 1973
-            ret.setUTCFullYear(Number("20" + year), Number(month), Number(day));
-        }
+        ret.setUTCFullYear(getYearFromString(year, rmcCompatible), Number(month), Number(day));
     }
 
     ret.setUTCHours(Number(time.slice(0, 2)));
@@ -383,32 +403,3 @@ export function parseTime(time: string, date?: string): Date {
 
     return ret;
 }
-
-
-/**
- * Parses a date in the format "yyMMdd" along with a time in the format
- * "hhmmss" or "hhmmss.ss" and returns a Date object.
- */
-export function parseDatetime(date: string, time: string): Date {
-    const day = parseInt(date.slice(0, 2), 10);
-    const month = parseInt(date.slice(2, 4), 10);
-    let year = parseInt(date.slice(4, 6), 10);
-    // GPRMC date doesn't specify century. GPS came out in 1973 so if the year
-    // is less than 73, assume it's 20xx, otherwise assume it is 19xx.
-    if (year < 73) {
-        year = year + 2000;
-    }
-    else {
-        year = year + 1900;
-    }
-
-    const hours = parseInt(time.slice(0, 2), 10);
-    const minutes = parseInt(time.slice(2, 4), 10);
-    const seconds = parseInt(time.slice(4, 6), 10);
-    let milliseconds = 0;
-    if (time.length === 9) {
-        milliseconds = parseInt(time.slice(7, 9), 10) * 10;
-    }
-
-    return new Date(Date.UTC(year, month - 1, day, hours, minutes, seconds, milliseconds));
-}
diff --git a/tests/RMCtest.ts b/tests/RMCtest.ts
index 48b3da2..10a3840 100644
--- a/tests/RMCtest.ts
+++ b/tests/RMCtest.ts
@@ -1,6 +1,6 @@
 import "should";
 
-import { parseNmeaSentence } from "../index";
+import { assertPacketIs, parseNmeaSentence } from "../index";
 
 
 describe("RMC", (): void => {
@@ -21,4 +21,13 @@ describe("RMC", (): void => {
     packet.should.have.property("variationPole", "W");
   });
 
+  it("miliseconds", (): void => {
+    const packet = parseNmeaSentence("$GNRMC,123411.200,A,4721.2973,N,01906.6971,E,16.19,142.59,040223,,,A,V*37");
+    assertPacketIs("RMC", packet);
+    packet.datetime.getMilliseconds().should.equal(200);
+
+    const packet2 = parseNmeaSentence("$GPRMC,123409.886,V,,,,,16.10,145.36,040223,,,N,V*08");
+    assertPacketIs("RMC", packet2);
+    packet2.datetime.getMilliseconds().should.equal(886);
+  });
 });