From f24111ea9f2bff0cc76d0a68a015ba905e28ef63 Mon Sep 17 00:00:00 2001
From: Zaid Abdulla <zaid@genieacs.com>
Date: Mon, 25 Oct 2021 13:42:59 -0700
Subject: [PATCH] Support modulo operator in expressions

---
 lib/common/expression-parser.ts |  7 ++++++-
 lib/common/expression.ts        | 18 +++++++++++++++---
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/lib/common/expression-parser.ts b/lib/common/expression-parser.ts
index ea6b294..9802f4d 100644
--- a/lib/common/expression-parser.ts
+++ b/lib/common/expression-parser.ts
@@ -285,7 +285,11 @@ const lang = parsimmon.createLanguage({
           .skip(parsimmon.optWhitespace),
         binaryLeft(
           parsimmon
-            .alt(parsimmon.string("*"), parsimmon.string("/"))
+            .alt(
+              parsimmon.string("*"),
+              parsimmon.string("/"),
+              parsimmon.string("%")
+            )
             .skip(parsimmon.optWhitespace),
           parsimmon.alt(
             r.Value,
@@ -384,6 +388,7 @@ export function stringify(exp: Expression, level = 0): string {
     "-": 31,
     "*": 32,
     "/": 32,
+    "%": 32,
   };
 
   const op = exp[0].toUpperCase();
diff --git a/lib/common/expression.ts b/lib/common/expression.ts
index 5b01eb6..8693ea1 100644
--- a/lib/common/expression.ts
+++ b/lib/common/expression.ts
@@ -244,9 +244,12 @@ export function evaluateCallback(exp: Expression): Expression {
   } else if (exp[0] === "/") {
     return reduce(exp, (a, b, i) => {
       if (a == null || b == null) return null;
-      if (!isArray(a) && !isArray(b))
-        return i === 0 ? toNumber(a) / toNumber(b) : toNumber(a) * toNumber(b);
-      return REDUCE_SKIP;
+      if (isArray(a) || isArray(b)) return REDUCE_SKIP;
+      const n1 = toNumber(a);
+      const n2 = toNumber(b);
+      if (i !== 0) return n1 * n2;
+      if (n2 === 0) return null;
+      return n1 / n2;
     });
   } else if (exp[0] === "+") {
     return reduce(exp, (a, b) => {
@@ -261,6 +264,15 @@ export function evaluateCallback(exp: Expression): Expression {
         return i === 0 ? toNumber(a) - toNumber(b) : toNumber(a) + toNumber(b);
       return REDUCE_SKIP;
     });
+  } else if (exp[0] === "%") {
+    return reduce(exp, (a, b, i) => {
+      if (a == null || b == null) return null;
+      if (isArray(a) || isArray(b) || i !== 0) return REDUCE_SKIP;
+      const n1 = toNumber(a);
+      const n2 = Math.trunc(toNumber(b));
+      if (n2 === 0) return null;
+      return n1 % n2;
+    });
   } else if (exp[0] === "||") {
     return reduce(exp, (a, b) => {
       if (a == null || b == null) return null;