feat: Minify css

- Add dependency clean-css
- Add do_minifycss function as filter to eleventy
- Add workaround for demo mode with computed data file

.eleventy.js

@@ -1,6 +1,33 @@
+const CleanCSS = require("clean-css");
+// const is_production = typeof process.env.NODE_ENV === "string" && process.env.NODE_ENV === "production";
+const is_production = true;
+
+function do_minifycss(source, output_path) {
+	if(!output_path.endsWith(".css") || !is_production) return source;
+
+	const result = new CleanCSS({
+			level: 2
+	}).minify(source).styles.trim();
+	console.log(`MINIFY ${output_path}`, source.length, `→`, result.length, `(${((1 - (result.length / source.length)) * 100).toFixed(2)}% reduction)`);
+	return result;
+}
+
 module.exports = function (eleventyConfig) {
 	// eleventyConfig.addPlugin(EleventyHtmlBasePlugin);
 
+	eleventyConfig.addFilter("cssmin", function (code) {
+		return new CleanCSS({}).minify(code).styles;
+	});
+
+	eleventyConfig.addTransform("cssmin", do_minifycss);
+
+	eleventyConfig.addTransform("log", async function (content) {
+		console.log(this.page.inputPath);
+		console.log(this.page.outputPath);
+
+		return content; // no changes made.
+	});
+
 	eleventyConfig.setNunjucksEnvironmentOptions({
 		// throwOnUndefined: true,
 		trimBlocks: true