Add full-month calendar view with prev/next navigation

Replace the fixed 10-day window with a full calendar for the current
month. Prev/next arrow links navigate between months (with year
rollover). Today's row is highlighted in yellow. The home-page calendar
link now includes the current year and month so it always lands on the
right month.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: exploded

calendar.html

@@ -28,6 +28,11 @@ <h1 class="header-title">📅 Moon Rise and Set Calendar</h1>
 		<main>
 			<div class="page-content">
 				<div class="card">
+					<div class="month-nav">
+						<a href="calendar?lat={{.Lat}}&lon={{.Lon}}&zon={{.Zon}}&year={{.PrevYear}}&month={{.PrevMonth}}">&#8592;</a>
+						<span>{{.MonthName}} {{.Year}}</span>
+						<a href="calendar?lat={{.Lat}}&lon={{.Lon}}&zon={{.Zon}}&year={{.NextYear}}&month={{.NextMonth}}">&#8594;</a>
+					</div>
 					<table>
 						<thead>
 							<tr>
@@ -40,7 +45,7 @@ <h1 class="header-title">📅 Moon Rise and Set Calendar</h1>
 						</thead>
 						<tbody>
 							{{ range .Rows }}
-							<tr>
+							<tr{{if .IsToday}} class="today"{{end}}>
 								<td>{{.Date}}</td>
 								<td>{{if .Moon.AlwaysAbove}}Always above{{else if .Moon.AlwaysBelow}}Always below{{else}}{{.Moon.Rise}}{{end}}</td>
 								<td>{{if .Moon.AlwaysAbove}}Always above{{else if .Moon.AlwaysBelow}}Always below{{else}}{{.Moon.Set}}{{end}}</td>

moon.go

@@ -193,36 +193,80 @@ func calendar(w http.ResponseWriter, r *http.Request) {
 		Zon = 10 // Default
 	}
 
-	type gridrow struct {
-		Date string
-		Moon riseset.RiseSet
-		Sun  riseset.RiseSet
+	// Determine which month to show, defaulting to the current month in the
+	// user's timezone.
+	zondur := time.Hour * time.Duration(Zon)
+	now := time.Now().Add(zondur)
+
+	year, err := strconv.Atoi(r.URL.Query().Get("year"))
+	if err != nil || year < 1 || year > 9999 {
+		year = now.Year()
+	}
+	month, err := strconv.Atoi(r.URL.Query().Get("month"))
+	if err != nil || month < 1 || month > 12 {
+		month = int(now.Month())
+	}
+
+	// Previous / next month navigation (handles year rollovers).
+	prevMonth, prevYear := month-1, year
+	if prevMonth < 1 {
+		prevMonth = 12
+		prevYear--
+	}
+	nextMonth, nextYear := month+1, year
+	if nextMonth > 12 {
+		nextMonth = 1
+		nextYear++
 	}
 
-	var arow gridrow
-	var newdate time.Time
+	// Today's date string in local time, used to highlight the current row.
+	today := now.Format("02-01-2006")
+
+	// Last day of the requested month: day 0 of the following month.
+	lastDay := time.Date(year, time.Month(month+1), 0, 0, 0, 0, 0, time.UTC).Day()
+
+	type gridrow struct {
+		Date    string
+		Moon    riseset.RiseSet
+		Sun     riseset.RiseSet
+		IsToday bool
+	}
 
 	type mypar struct {
-		Rows []gridrow
-		Lon  float64
-		Lat  float64
-		Zon  float64
+		Rows      []gridrow
+		Lon       float64
+		Lat       float64
+		Zon       float64
+		Year      int
+		Month     int
+		MonthName string
+		PrevYear  int
+		PrevMonth int
+		NextYear  int
+		NextMonth int
 	}
 
 	var Passme mypar
 	Passme.Lat = Lat
 	Passme.Lon = Lon
 	Passme.Zon = Zon
-
-	var zondur time.Duration = time.Hour * time.Duration(Zon)
-	newdate = time.Now().Add(zondur)
-
-	for i := 0; i < 10; i++ {
-		newdate = newdate.AddDate(0, 0, 1)
-		arow.Date = newdate.Format("02-01-2006")
-		arow.Moon = riseset.Riseset(riseset.Moon, newdate, Lon, Lat, Zon)
-		arow.Sun = riseset.Riseset(riseset.Sun, newdate, Lon, Lat, Zon)
-		Passme.Rows = append(Passme.Rows, arow)
+	Passme.Year = year
+	Passme.Month = month
+	Passme.MonthName = time.Month(month).String()
+	Passme.PrevYear = prevYear
+	Passme.PrevMonth = prevMonth
+	Passme.NextYear = nextYear
+	Passme.NextMonth = nextMonth
+
+	for day := 1; day <= lastDay; day++ {
+		d := time.Date(year, time.Month(month), day, 0, 0, 0, 0, time.UTC)
+		dateStr := d.Format("02-01-2006")
+		Passme.Rows = append(Passme.Rows, gridrow{
+			Date:    dateStr,
+			Moon:    riseset.Riseset(riseset.Moon, d, Lon, Lat, Zon),
+			Sun:     riseset.Riseset(riseset.Sun, d, Lon, Lat, Zon),
+			IsToday: dateStr == today,
+		})
 	}
 
 	if templates != nil {

static/script.js

@@ -274,7 +274,10 @@ function SpinnersChanged() {
 function updateCalLink() {
 	const calendarLink = document.getElementById("callink");
 	if (calendarLink) {
-		calendarLink.href = `calendar?lat=${mylat}&lon=${mylon}&zon=${myzon}`;
+		const now = new Date();
+		const year = now.getFullYear();
+		const month = now.getMonth() + 1;
+		calendarLink.href = `calendar?lat=${mylat}&lon=${mylon}&zon=${myzon}&year=${year}&month=${month}`;
 	}
 }
 

static/styles.css

@@ -325,6 +325,36 @@ table tfoot th {
 	font-size: 14px;
 }
 
+/* Month navigation header */
+.month-nav {
+	display: flex;
+	align-items: center;
+	justify-content: space-between;
+	padding: 12px 16px;
+	border-bottom: 1px solid #e0e0e0;
+	font-weight: 600;
+	font-size: 16px;
+	color: #333;
+}
+
+.month-nav a {
+	color: #1976d2;
+	text-decoration: none;
+	font-size: 20px;
+	padding: 4px 10px;
+	border-radius: 4px;
+	transition: background 0.2s ease;
+}
+
+.month-nav a:hover {
+	background-color: #f0f0f0;
+}
+
+/* Today row highlight */
+tr.today td {
+	background-color: #fffde7;
+}
+
 /* Responsive Styles */
 @media (max-width: 768px) {
 	.page-content {