From 0d12c6a8833ba4d3acbce03b9fca4f8911a23664 Mon Sep 17 00:00:00 2001
From: Mitchell Austin <mr.fye@oneandthesame.net>
Date: Thu, 2 Sep 2021 08:23:07 -0700
Subject: [PATCH] Update roundClamp to match HTML number input stepping
 behavior

- Rounds to steps starting from min
- Uses rounding precision determined by the greater of min or step
- If max is not on a step, uses the closest step less than max
---
 packages/components/src/utils/math.js      | 18 +++++++++--
 packages/components/src/utils/test/math.js | 35 ++++++++++++++++------
 2 files changed, 41 insertions(+), 12 deletions(-)

diff --git a/packages/components/src/utils/math.js b/packages/components/src/utils/math.js
index 76a3d66ed88ec..5a3b4b7debfe3 100644
--- a/packages/components/src/utils/math.js
+++ b/packages/components/src/utils/math.js
@@ -79,9 +79,21 @@ export function roundClamp(
 ) {
 	const baseValue = getNumber( value );
 	const stepValue = getNumber( step );
-	const precision = getPrecision( step );
-	const rounded = Math.round( baseValue / stepValue ) * stepValue;
-	const clampedValue = clamp( rounded, min, max );
+	const precision = Math.max( getPrecision( step ), getPrecision( min ) );
+	const realMin = min === Infinity ? 0 : min;
+
+	let tare = 0;
+	if ( realMin % stepValue ) {
+		tare = realMin;
+	}
+
+	let maxOnStep = max;
+	if ( max % stepValue || Math.abs( tare ) ) {
+		maxOnStep = Math.floor( ( max - tare ) / stepValue ) * stepValue + tare;
+	}
+
+	const rounded = Math.round( ( baseValue - tare ) / stepValue ) * stepValue;
+	const clampedValue = clamp( rounded + tare, min, maxOnStep );
 
 	return precision
 		? getNumber( clampedValue.toFixed( precision ) )
diff --git a/packages/components/src/utils/test/math.js b/packages/components/src/utils/test/math.js
index 42d4bd5abc56e..5ca36115da0b6 100644
--- a/packages/components/src/utils/test/math.js
+++ b/packages/components/src/utils/test/math.js
@@ -59,15 +59,15 @@ describe( 'roundClamp', () => {
 	} );
 
 	it( 'should clamp with step', () => {
-		expect( roundClamp( 40, 1, 100, 10 ) ).toBe( 40 );
-		expect( roundClamp( 42, 1, 100, 10 ) ).toBe( 40 );
-		expect( roundClamp( 45, 1, 100, 10 ) ).toBe( 50 );
-		expect( roundClamp( 49, 1, 100, 10 ) ).toBe( 50 );
-		expect( roundClamp( 50, 1, 100, 10 ) ).toBe( 50 );
-
-		expect( roundClamp( 50, 1, 100, 15 ) ).toBe( 45 );
-		expect( roundClamp( 50, 1, 100, '15' ) ).toBe( 45 );
-		expect( roundClamp( 50, 1, 100, 11 ) ).toBe( 55 );
+		expect( roundClamp( 40, 0, 100, 10 ) ).toBe( 40 );
+		expect( roundClamp( 42, 0, 100, 10 ) ).toBe( 40 );
+		expect( roundClamp( 45, 0, 100, 10 ) ).toBe( 50 );
+		expect( roundClamp( 49, 0, 100, 10 ) ).toBe( 50 );
+		expect( roundClamp( 50, 0, 100, 10 ) ).toBe( 50 );
+
+		expect( roundClamp( 50, 0, 100, 15 ) ).toBe( 45 );
+		expect( roundClamp( 50, 0, 100, '15' ) ).toBe( 45 );
+		expect( roundClamp( 50, 0, 100, 11 ) ).toBe( 55 );
 	} );
 
 	it( 'should clamp with float in step', () => {
@@ -77,4 +77,21 @@ describe( 'roundClamp', () => {
 		expect( roundClamp( 40.06, 1, 100, 0.1 ) ).toBe( 40.1 );
 		expect( roundClamp( 40.123005, 1, 100, 0.001 ) ).toBe( 40.123 );
 	} );
+
+	it( 'should round to steps starting from min', () => {
+		expect( roundClamp( 10, 0.25, 100, 1 ) ).toBe( 10.25 );
+		expect( roundClamp( 10, -20.25, 100, 1 ) ).toBe( 9.75 );
+		expect( roundClamp( 10.5, 0.05, 100, 0.1 ) ).toBe( 10.45 );
+		expect( roundClamp( 10.51, 0.05, 100, 0.1 ) ).toBe( 10.55 );
+	} );
+
+	it( 'should restrain max to a value that is a multiple of step starting from min', () => {
+		expect( roundClamp( 10, 1, 10, 2 ) ).toBe( 9 );
+		expect( roundClamp( 10.125, 0.1, 10, 0.125 ) ).toBe( 9.975 );
+	} );
+
+	it( 'should round with a precision that’s the greater of min and step', () => {
+		expect( roundClamp( 10.061, 0.01, 20, 0.1 ) ).toBe( 10.11 );
+		expect( roundClamp( 10.105, 0.1, 20, 0.01 ) ).toBe( 10.11 );
+	} );
 } );