tweak service worker stuff

lib/templates.js

@@ -0,0 +1,43 @@
+const fs = require('fs');
+const glob = require('glob');
+
+const templates = glob.sync('*.html', { cwd: 'templates' })
+	.map(file => {
+		const template = fs.readFileSync(`templates/${file}`, 'utf-8');
+		const status = file.replace('.html', '').toLowerCase();
+
+		if (!/^[0-9x]{3}$/.test(status)) {
+			throw new Error(`Bad template — should be a valid status code like 404.html, or a wildcard like 2xx.html`);
+		}
+
+		const specificity = (
+			(status[0] === 'x' ? 0 : 4) +
+			(status[1] === 'x' ? 0 : 2) +
+			(status[2] === 'x' ? 0 : 1)
+		);
+
+		const pattern = new RegExp(`^${status.split('').map(d => d === 'x' ? '\\d' : d).join('')}$`);
+
+		return {
+			test: status => pattern.test(status),
+			specificity,
+			render(data) {
+				return template.replace(/%sapper\.(\w+)%/g, (match, key) => {
+					return key in data ? data[key] : '';
+				});
+			}
+		}
+	})
+	.sort((a, b) => b.specificity - a.specificity);
+
+exports.render = (status, data) => {
+	const template = templates.find(template => template.test(status));
+	if (template) return template.render(data);
+
+	return `Missing template for status code ${status}`;
+};
+
+exports.onchange = fn => {
+	// TODO in dev mode, keep this updated, and allow
+	// webpack compiler etc to hook into it
+};