From 96fffcf2a67269e3f0c320edcf7e2c4f02878ca5 Mon Sep 17 00:00:00 2001
From: Don Cross <cosinekitty@gmail.com>
Date: Sun, 2 Oct 2022 11:33:04 -0400
Subject: [PATCH] JavaScript: better forward/reverse moon phase tests.

In the unit tests for searching forward and backward
for moon phases, in addition to new moons, also test
first quarter, full moon, and third quarter.

Verify that forward and backward searches work for
100 start times between a single pair of consecutive events.
---
 generate/test.js | 70 +++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 57 insertions(+), 13 deletions(-)

diff --git a/generate/test.js b/generate/test.js
index 1921e4eb..b728abe8 100644
--- a/generate/test.js
+++ b/generate/test.js
@@ -244,20 +244,29 @@ function MoonPhase() {
     return 0;
 }
 
-function MoonReverse() {
+function MoonReverse(longitude) {
+    return (
+        MoonReversePhase(0) ||
+        MoonReversePhase(90) ||
+        MoonReversePhase(180) ||
+        MoonReversePhase(270)
+    );
+}
+
+function MoonReversePhase(longitude) {
     // Verify that SearchMoonPhase works both forward and backward in time.
 
     const numNewMoons = 5000;
     let utList = [];
-    let i, result;
+    let i, result, diff;
 
     let dtMin = +1000;
     let dtMax = -1000;
     let time = Astronomy.MakeTime(new Date('1800-01-01T00:00:00Z'));
     for (i = 0; i < numNewMoons; ++i) {
-        result = Astronomy.SearchMoonPhase(0, time, +40);
+        result = Astronomy.SearchMoonPhase(longitude, time, +40);
         if (result === null) {
-            console.error(`JS MoonReverse(i=${i}): failed to find new moon after ${time}`);
+            console.error(`JS MoonReverse(i=${i}): failed to find phase ${longitude} after ${time}`);
             return 1;
         }
         utList.push(result.ut);
@@ -270,9 +279,9 @@ function MoonReverse() {
         time = result.AddDays(+0.1);
     }
 
-    Debug(`JS MoonReverse: dtMin=${dtMin.toFixed(3)} days, dtMax=${dtMax.toFixed(3)} days.`);
-    if (dtMin < 29.273 || dtMax > 29.832) {
-        console.error(`JS MoonReverse: Time between consecutive new moons is suspicious.`);
+    Debug(`JS MoonReverse(${longitude}): dtMin=${dtMin.toFixed(3)} days, dtMax=${dtMax.toFixed(3)} days.`);
+    if (dtMin < 29.175 || dtMax > 29.926) {
+        console.error(`JS MoonReverse(${longitude}): Time between consecutive phases is suspicious.`);
         return 1;
     }
 
@@ -280,21 +289,56 @@ function MoonReverse() {
     time = time.AddDays(20);
     let maxDiff = 0;
     for (i = numNewMoons-1; i >= 0; --i) {
-        result = Astronomy.SearchMoonPhase(0, time, -40);
+        result = Astronomy.SearchMoonPhase(longitude, time, -40);
         if (result === null) {
-            console.error(`JS MoonReverse(i=${i}): failed to find new moon before ${time}`);
+            console.error(`JS MoonReverse(i=${i}): failed to find phase ${longitude} before ${time}`);
             return 1;
         }
-        const diff = SECONDS_PER_DAY * abs(result.ut - utList[i]);
+        diff = SECONDS_PER_DAY * abs(result.ut - utList[i]);
         if (diff > maxDiff) maxDiff = diff;
         time = result.AddDays(-0.1);
     }
 
-    console.log(`JS MoonReverse: Maximum discrepancy in reverse search = ${maxDiff.toFixed(3)} seconds.`);
-    if (maxDiff > 0.128) {
-        console.error(`JS MoonReverse: EXCESSIVE DISCREPANCY in reverse search.`);
+    Debug(`JS MoonReverse(${longitude}): Maximum discrepancy in reverse search = ${maxDiff.toFixed(3)} seconds.`);
+    if (maxDiff > 0.165) {
+        console.error(`JS MoonReverse(${longitude}): EXCESSIVE DISCREPANCY in reverse search.`);
         return 1;
     }
+
+    // Pick a pair of consecutive events from the middle of the list.
+    // Verify forward and backward searches work correctly from many intermediate times.
+    const nslots = 100;
+    const k = Math.floor(nslots / 2);
+    const ut1 = utList[k];
+    const ut2 = utList[k+1];
+    for (i = 1; i < nslots; ++i) {
+        const ut = ut1 + (i/nslots)*(ut2 - ut1)
+        time = Astronomy.MakeTime(ut);
+
+        const before = Astronomy.SearchMoonPhase(longitude, time, -40);
+        if (!before) {
+            console.error(`JS MoonReverse(${longitude}): backward search failed from ${time}`);
+            return 1;
+        }
+        diff = SECONDS_PER_DAY * abs(before.ut - ut1);
+        if (diff > 0.07) {
+            console.error(`JS MoonPhase(${longitude}): backward search from ${time} has error = ${diff.toExponential(4)} seconds.`);
+            return 1;
+        }
+
+        const after = Astronomy.SearchMoonPhase(longitude, time, +40);
+        if (!after) {
+            console.error(`JS MoonReverse(${longitude}): forward search failed from ${time}`);
+            return 1;
+        }
+        diff = SECONDS_PER_DAY * abs(after.ut - ut2);
+        if (diff > 0.07) {
+            console.error(`JS MoonPhase(${longitude}): forward search from ${time} has error = ${diff.toExponential(4)} seconds.`);
+            return 1;
+        }
+    }
+
+    console.log(`JS MoonReverse(${longitude}): PASS`);
     return 0;
 }