From a170fd8344da7ca70108b34367d58aee62591876 Mon Sep 17 00:00:00 2001
From: Gabriel Arazas <foodogsquared@foodogsquared.one>
Date: Sat, 15 Jun 2024 13:38:42 +0800
Subject: [PATCH] bahaghari/lib: add math.mod' function

---
 subprojects/bahaghari/lib/math.nix       | 38 ++++++++++++++++
 subprojects/bahaghari/tests/lib/math.nix | 55 ++++++++++++++++++++++++
 2 files changed, 93 insertions(+)

diff --git a/subprojects/bahaghari/lib/math.nix b/subprojects/bahaghari/lib/math.nix
index 63184775..8c7b5d1b 100644
--- a/subprojects/bahaghari/lib/math.nix
+++ b/subprojects/bahaghari/lib/math.nix
@@ -238,6 +238,44 @@ rec {
     in
       floor (difference + 0.5) * nearest;
 
+  /* Similar to the nixpkgs' `trivial.mod` but retain the decimal values. This
+     is just an approximation from ECMAScript's implementation of the modulo
+     operator (%).
+
+     Type: mod' :: Number -> Number -> Number
+
+     Example:
+       mod' 4.25 2
+       => 0.25
+
+       mod' 1.5 2
+       => 1.5
+
+       mod' 65 5
+       => 0
+
+       mod' (-54) 4
+       => -2
+
+       mod' (-54) (-4)
+       => -2
+  */
+  mod' = base: number:
+    let
+      base' = abs base;
+      number' = abs number;
+      difference = number' * ((floor base' / (floor number')) + 1);
+
+      result = number' - (difference - base');
+    in
+      if number' > base' then
+        base
+      else
+        if base < 0 then
+          -(result)
+        else
+          result;
+
   /* Adds all of the given items on the list starting from a sum of zero.
 
      Type: summate :: List[Number] -> Number
diff --git a/subprojects/bahaghari/tests/lib/math.nix b/subprojects/bahaghari/tests/lib/math.nix
index 50cf1f07..f3710deb 100644
--- a/subprojects/bahaghari/tests/lib/math.nix
+++ b/subprojects/bahaghari/tests/lib/math.nix
@@ -212,6 +212,61 @@ lib.runTests {
     expected = 1.4142135624;
   };
 
+  testMathMod = {
+    expr = self.math.mod' 65.5 3;
+    expected = 2.5;
+  };
+
+  testMathMod2 = {
+    expr = self.math.mod' 1.5 3;
+    expected = 1.5;
+  };
+
+  testMathMod3 = {
+    expr = self.math.mod' 4.25 2;
+    expected = 0.25;
+  };
+
+  testMathMod4 = {
+    expr = self.math.mod' 6 6;
+    expected = 0;
+  };
+
+  testMathMod5 = {
+    expr = self.math.mod' 6.5 6;
+    expected = 0.5;
+  };
+
+  testMathMod6 = {
+    expr = self.math.mod' 7856.5 20;
+    expected = 16.5;
+  };
+
+  testMathMod7 = {
+    expr = self.math.mod' 7568639.2 45633;
+    expected = 39194.200000000186;
+  };
+
+  testMathModBothPositive = {
+    expr = self.math.mod' 54.5 20.5;
+    expected = 13.5;
+  };
+
+  testMathModNegativeBase = {
+    expr = self.math.mod' (-54.5) 20.5;
+    expected = -13.5;
+  };
+
+  testMathModNegativeNumber = {
+    expr = self.math.mod' 54.5 (-20.5);
+    expected = 13.5;
+  };
+
+  testMathModBothNegatives = {
+    expr = self.math.mod' (-54.5) (-20.5);
+    expected = -13.5;
+  };
+
   testMathExp = {
     expr = self.math.exp 1;
     expected = 2.7182818284590452353602874713527;