From aa69c3ae915b720f20e88dbf37b08366ba7a01e9 Mon Sep 17 00:00:00 2001
From: Jeremy Ruston <jeremy@jermolene.com>
Date: Mon, 18 Nov 2024 18:15:20 +0000
Subject: [PATCH] Add colour-contrast operator

---
 core/modules/filters/colour-ops.js            | 32 ++++++++++++++++---
 .../data/operators/colour/ColourContrast.tid  | 17 ++++++++++
 2 files changed, 45 insertions(+), 4 deletions(-)
 create mode 100644 editions/test/tiddlers/tests/data/operators/colour/ColourContrast.tid

diff --git a/core/modules/filters/colour-ops.js b/core/modules/filters/colour-ops.js
index 6cf0f32ee..a004a1a1f 100644
--- a/core/modules/filters/colour-ops.js
+++ b/core/modules/filters/colour-ops.js
@@ -14,15 +14,15 @@ Filter operators for colour operations
 
 var Color = require("$:/core/modules/utils/dom/color.js").Color;
 
-exports["colour-lighten"] = makeColourOperator(function (c, operator, options) {
+exports["colour-lighten"] = makeSerialColourOperator(function (c, operator, options) {
 	return c.lighten($tw.utils.parseNumber(operator.operand));
 });
 
-exports["colour-darken"] = makeColourOperator(function (c, operator, options) {
+exports["colour-darken"] = makeSerialColourOperator(function (c, operator, options) {
 	return c.darken($tw.utils.parseNumber(operator.operand));
 });
 
-exports["colour-oklch"] = makeColourOperator(function (c, operator, options) {
+exports["colour-oklch"] = makeSerialColourOperator(function (c, operator, options) {
 	var prop = ((operator.suffixes || [])[0] || ["l"])[0];
 	if(["l","c","h"].indexOf(prop) !== -1) {
 		c.oklch[prop] = $tw.utils.parseNumber(operator.operand);
@@ -30,7 +30,21 @@ exports["colour-oklch"] = makeColourOperator(function (c, operator, options) {
 	return c;
 });
 
-function makeColourOperator(fn) {
+exports["colour-contrast"] = makeParallelColourOperator(function (colours, operator, options) {
+	var colourContrasts = [];
+	$tw.utils.each(colours,function(colour,index) {
+		if(!colour) {
+			colour = $tw.utils.parseCSSColorObject("white");
+			colours[index] = colour;
+		}
+		if(index > 0) {
+			colourContrasts.push(colour.contrast(colours[index - 1],"DeltaPhi").toString());
+		}
+	});
+	return colourContrasts;
+});
+
+function makeSerialColourOperator(fn) {
 	return function (source, operator, options) {
 		var results = [];
 		source(function (tiddler, title) {
@@ -46,4 +60,14 @@ function makeColourOperator(fn) {
 	};
 }
 
+function makeParallelColourOperator(fn) {
+	return function (source, operator, options) {
+		var colours = [];
+		source(function (tiddler, title) {
+			colours.push($tw.utils.parseCSSColorObject(title));
+		});
+		return fn(colours, operator, options);
+	};
+}
+
 })();
diff --git a/editions/test/tiddlers/tests/data/operators/colour/ColourContrast.tid b/editions/test/tiddlers/tests/data/operators/colour/ColourContrast.tid
new file mode 100644
index 000000000..5aa5281b3
--- /dev/null
+++ b/editions/test/tiddlers/tests/data/operators/colour/ColourContrast.tid
@@ -0,0 +1,17 @@
+title: Operators/Colour/ColourContrast
+description: Contrast colour function
+type: text/vnd.tiddlywiki-multiple
+tags: [[$:/tags/wiki-test-spec]]
+
+title: Output
+
+\parsermode inline
+<$text text={{{ [subfilter{Filter}] }}}/>
++
+title: Filter
+
+[[black]] [[gray]] +[colour-contrast:DeltaPhi[]trunc[]]
++
+title: ExpectedResult
+
+35
\ No newline at end of file