Calendar demo now includes seasons. Also goes for 10 years instead of 1.

Generate solstices and equinoxes in the calendar event enumerator.
Generate 10 years of data instead of 1, to better test the seasons.

demo/nodejs/calendar/calendar.ts

@@ -5,7 +5,7 @@
     interesting events for a calendar.
 */
 
-import { AstroTime, Observer, Body, SearchRiseSet, Search } from "./astronomy";
+import { AstroTime, Observer, Body, SearchRiseSet, Seasons, SeasonInfo } from "./astronomy";
 
 class AstroEvent {
     constructor(
@@ -85,6 +85,40 @@ class RiseSetEnumerator implements AstroEventEnumerator {
 }
 
 
+class SeasonEnumerator implements AstroEventEnumerator {
+    private slist: AstroEvent[];
+    private year: number;
+    private index: number;
+
+    FindFirst(startTime: AstroTime): AstroEvent {
+        this.year = startTime.date.getUTCFullYear();
+        this.LoadYear(this.year);
+        while (this.index < this.slist.length && this.slist[this.index].time.tt < startTime.tt) {
+            ++this.index;
+        }
+        return this.FindNext();
+    }
+
+    FindNext(): AstroEvent {
+        if (this.index === this.slist.length) {
+            this.LoadYear(++this.year);
+        }
+        return this.slist[this.index++];
+    }
+
+    private LoadYear(year: number): void {
+        const seasons = Seasons(year);
+        this.slist = [
+            new AstroEvent(seasons.mar_equinox,  'March equinox', this),
+            new AstroEvent(seasons.jun_solstice, 'June solstice', this),
+            new AstroEvent(seasons.sep_equinox,  'September equinox', this),
+            new AstroEvent(seasons.dec_solstice, 'December solstice', this),
+        ];
+        this.index = 0;
+    }
+}
+
+
 function RunTest(): void {
     const startTime = new AstroTime(new Date('2022-01-01T00:00:00Z'));
     const observer = new Observer(28.6, -81.2, 10.0);
@@ -92,15 +126,16 @@ function RunTest(): void {
         new RiseSetEnumerator(observer, Body.Sun, +1, 'sunrise'),
         new RiseSetEnumerator(observer, Body.Sun, -1, 'sunset'),
         new RiseSetEnumerator(observer, Body.Moon, +1, 'moonrise'),
-        new RiseSetEnumerator(observer, Body.Moon, -1, 'moonset')
+        new RiseSetEnumerator(observer, Body.Moon, -1, 'moonset'),
+        new SeasonEnumerator()
     ]);
 
+    const stopYear = startTime.date.getUTCFullYear() + 11;
     let evt:AstroEvent = collator.FindFirst(startTime);
-    while (evt !== null && evt.time.date.getUTCFullYear() === startTime.date.getUTCFullYear()) {
+    while (evt !== null && evt.time.date.getUTCFullYear() < stopYear) {
         console.log(`${evt.time} ${evt.title}`);
         evt = collator.FindNext();
     }
 }
 
-
 RunTest();