Implement plugin

.gitignore

@@ -7,4 +7,5 @@ bundle.js
 target
 lib
 *.tar.gz
-.eslintcache
+.eslintcache
+.tmp

scripts/postcss/css-url-processor.js

@@ -0,0 +1,81 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+const valueParser = require("postcss-value-parser");
+const  resolve = require("path").resolve;
+
+function colorsFromURL(url, colorVariables) {
+    const params = new URL(`file://${url}`).searchParams;
+    const primary = params.get("primary");
+    if (!primary) {
+        return null;
+    }
+    const secondary = params.get("secondary");
+    const primaryColor = colorVariables[primary];
+    const secondaryColor = colorVariables[secondary];
+    if (!primaryColor) {
+        throw new Error(`Variable ${primary} not found in resolved color variables!`);
+    }
+    if (!secondaryColor) {
+        throw new Error(`Variable ${secondary} not found in resolved color variables!`);
+    }
+    return [primaryColor, secondaryColor];
+}
+
+function processURL(decl, replacer, colorVariables) {
+    const value = decl.value;
+    const parsed = valueParser(value);
+    parsed.walk(async node => {
+        if (node.type !== "function" || node.value !== "url") {
+            return;
+        }
+        const urlStringNode = node.nodes[0];
+        const oldURL = urlStringNode.value;
+        const cssPath = decl.source?.input.file.replace(/[^/]*$/, "");
+        const oldURLAbsolute = resolve(cssPath, oldURL);
+        const colors  = colorsFromURL(oldURLAbsolute, colorVariables);
+        if (!colors) {
+            // If no primary color is provided via url params, then this url need not be handled.
+            return;
+        }
+        const newURL = replacer(oldURLAbsolute.replace(/\?.+/, ""), ...colors);
+        if (!newURL) {
+            throw new Error("Replacer failed to produce a replacement URL!");
+        }
+        urlStringNode.value = newURL;
+    });
+    decl.assign({prop: decl.prop, value: parsed.toString()})
+}
+
+/* *
+ * @type {import('postcss').PluginCreator}
+ */
+module.exports = (opts = {}) => {
+    return {
+        postcssPlugin: "postcss-url-to-variable",
+
+        Once(root) {
+            /*
+            Go through each declaration and if it contains an URL, replace the url with the result
+            of running replacer(url)
+            */
+            root.walkDecls(decl => processURL(decl, opts.replacer, opts.colors));
+        },
+    };
+};
+
+module.exports.postcss = true;
+

scripts/postcss/svg-colorizer.js

@@ -0,0 +1,42 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+const fs = require("fs");
+const path = require("path");
+/**
+ * Builds a new svg with the colors replaced and returns its location.
+ * @param {string} svgLocation The location of the input svg file
+ * @param {string} primaryColor Primary color for the new svg
+ * @param {string} secondaryColor Secondary color for the new svg
+ */
+module.exports.buildColorizedSVG = function (svgLocation, primaryColor, secondaryColor) {
+    const svgCode = fs.readFileSync(svgLocation, { encoding: "utf-8"});
+    let coloredSVGCode = svgCode.replaceAll("#ff00ff", primaryColor);
+    coloredSVGCode = coloredSVGCode.replaceAll("#00ffff", secondaryColor);
+    const fileName = svgLocation.match(/.+\/(.+\.svg)/)[1];
+    const outputPath = path.resolve(__dirname, "../../.tmp");
+    try {
+       fs.mkdirSync(outputPath);
+    }
+    catch (e) {
+        if (e.code !== "EEXIST") {
+            throw e;
+        }
+    }
+    const outputFile = `${outputPath}/${fileName}`;
+    fs.writeFileSync(outputFile, coloredSVGCode);
+    return outputFile;
+}