feature: add initial openusercss handshake

content/install-hook-openusercss.js

@@ -0,0 +1,58 @@
+'use strict';
+
+(() => {
+  const manifest = chrome.runtime.getManifest();
+
+  // Tell the page that we exist and that it should send the handshake
+  window.postMessage({
+    'type': 'ouc-begin-handshake'
+  }, '*');
+
+  // Wait for the handshake
+  window.addEventListener('message', event => {
+    if (event.data && event.data.type === 'ouc-handshake-question') {
+      // This is a representation of features that Stylus is capable of
+      const implementedFeatures = [
+        'install-usercss',
+        'configure-after-install',
+        'builtin-editor',
+        'create-usercss',
+        'edit-usercss',
+        'import-moz-export',
+        'export-moz-export',
+        'update-manual',
+        'update-auto',
+        'export-json-backups',
+        'import-json-backups',
+        'manage-local'
+      ];
+      const reportedFeatures = [];
+
+      // The handshake question includes a list of required and optional features
+      // we match them with features we have implemented, and build a union array.
+      event.data.featuresList.required.forEach(feature => {
+        if (implementedFeatures.includes(feature)) {
+          reportedFeatures.push(feature);
+        }
+      });
+
+      event.data.featuresList.optional.forEach(feature => {
+        if (implementedFeatures.includes(feature)) {
+          reportedFeatures.push(feature);
+        }
+      });
+
+      // We send the handshake response, which includes the key we got, plus some
+      // additional metadata
+      window.postMessage({
+        'type':      'ouc-handshake-response',
+        'key':       event.data.key,
+        'extension': {
+          'name':         manifest.name,
+          'version':      manifest.version,
+          'capabilities': reportedFeatures
+        }
+      }, '*');
+    }
+  });
+})();

manifest.json

@@ -60,6 +60,12 @@
       "all_frames": false,
       "js": ["content/install-hook-userstyles.js"]
     },
+    {
+      "matches": ["https://openusercss.org/*", "https://openusercss.com/*"],
+      "run_at": "document_start",
+      "all_frames": false,
+      "js": ["content/install-hook-openusercss.js"]
+    },
     {
       "matches": ["<all_urls>"],
       "include_globs": ["*.user.css", "*.user.styl"],