From af41c6a15533baa3bfe222078510500d9dca2388 Mon Sep 17 00:00:00 2001
From: Matt Holt <mholt@users.noreply.github.com>
Date: Thu, 8 Aug 2024 07:35:16 -0600
Subject: [PATCH] DateTime function to convert to time.Time value (close #115)
 (#116)

---
 types.go      | 19 ++++++++++++++++++
 types_test.go | 55 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+)

diff --git a/types.go b/types.go
index 7d04dd2..c600aa4 100644
--- a/types.go
+++ b/types.go
@@ -9,6 +9,7 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+	"time"
 	"unicode"
 )
 
@@ -384,6 +385,24 @@ func ParseDate(ddmmyy string) (Date, error) {
 	return Date{true, dd, mm, yy}, nil
 }
 
+// DateTime converts the provided Date and Time values to a standard UTC time.Time.
+// The referenceYear parameter is used to determine the offset (century) for the two-digit year in Date.
+// For example, if the referenceYear is 2024, the offset used is 2000; and the input date's year is prepended with 20.
+// If referenceYear is 0, the current UTC year is used.
+// If either Date or Time is not valid, DateTime returns the zero time.Time.
+func DateTime(referenceYear int, d Date, t Time) time.Time {
+	if !d.Valid || !t.Valid {
+		return time.Time{}
+	}
+	if referenceYear == 0 {
+		referenceYear = time.Now().UTC().Year()
+	}
+	century := referenceYear / 100 * 100 // truncate the last two digits (year within century); keep first two digits of the full year
+	return time.Date(century+d.YY, time.Month(d.MM), d.DD,
+		t.Hour, t.Minute, t.Second, t.Millisecond*1e6,
+		time.UTC)
+}
+
 // LatDir returns the latitude direction symbol
 func LatDir(l float64) string {
 	if l < 0.0 {
diff --git a/types_test.go b/types_test.go
index e261462..da630a1 100644
--- a/types_test.go
+++ b/types_test.go
@@ -3,6 +3,7 @@ package nmea
 import (
 	"fmt"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/assert"
 )
@@ -220,6 +221,60 @@ func TestDateString(t *testing.T) {
 	}
 }
 
+func TestDateTime(t *testing.T) {
+	for i, testCase := range []struct {
+		refYear int
+		date    Date
+		time    Time
+		expect  time.Time
+	}{
+		{
+			refYear: 2024,
+			date:    Date{DD: 1, MM: 2, YY: 3, Valid: true},
+			time:    Time{Hour: 1, Minute: 2, Second: 3, Millisecond: 4, Valid: true},
+			expect:  time.Date(2003, time.February, 1, 1, 2, 3, 4e6, time.UTC),
+		},
+		{
+			refYear: 1999,
+			date:    Date{DD: 1, MM: 2, YY: 3, Valid: true},
+			time:    Time{Hour: 1, Minute: 2, Second: 3, Millisecond: 4, Valid: true},
+			expect:  time.Date(1903, time.February, 1, 1, 2, 3, 4e6, time.UTC),
+		},
+		{
+			refYear: 2025,
+			date:    Date{DD: 23, MM: 7, YY: 24, Valid: true},
+			time:    Time{Hour: 18, Minute: 5, Second: 12, Millisecond: 1, Valid: true},
+			expect:  time.Date(2024, time.July, 23, 18, 5, 12, 1e6, time.UTC),
+		},
+		// zero reference year; this test will fail starting in the year 3000
+		{
+			refYear: 0,
+			date:    Date{DD: 1, MM: 2, YY: 3, Valid: true},
+			time:    Time{Hour: 1, Minute: 2, Second: 3, Millisecond: 4, Valid: true},
+			expect:  time.Date(2003, time.February, 1, 1, 2, 3, 4e6, time.UTC),
+		},
+		// invalid date
+		{
+			refYear: 2024,
+			date:    Date{DD: 1, MM: 2, YY: 3},
+			time:    Time{Hour: 1, Minute: 2, Second: 3, Millisecond: 4, Valid: true},
+			expect:  time.Time{},
+		},
+		// invalid time
+		{
+			refYear: 2024,
+			date:    Date{DD: 1, MM: 2, YY: 3, Valid: true},
+			time:    Time{Hour: 1, Minute: 2, Second: 3, Millisecond: 4},
+			expect:  time.Time{},
+		},
+	} {
+		actual := DateTime(testCase.refYear, testCase.date, testCase.time)
+		if !actual.Equal(testCase.expect) {
+			t.Fatalf("Test %d (refYear=%d date=%s time=%s): Expected %s but got %s", i, testCase.refYear, testCase.date, testCase.time, testCase.expect, actual)
+		}
+	}
+}
+
 func TestLatDir(t *testing.T) {
 	tests := []struct {
 		value    float64