feat(plugins): add PluginLoader with manifest discovery and validation

Amit Haridas

src/plugins/plugin-loader.js

@@ -0,0 +1,75 @@
+const fs = require('fs');
+const path = require('path');
+
+class PluginLoader {
+  /**
+   * @param {string[]} searchDirs - Directories to scan for plugin folders
+   */
+  constructor(searchDirs = []) {
+    this.searchDirs = searchDirs;
+    this.loadedIds = new Set();
+  }
+
+  /**
+   * Discover plugins by scanning searchDirs for manifest.json files.
+   * Returns array of { id, name, version, description, manifest, PluginClass, dir }
+   */
+  discoverPlugins() {
+    const plugins = [];
+    for (const dir of this.searchDirs) {
+      if (!fs.existsSync(dir)) continue;
+      const entries = fs.readdirSync(dir, { withFileTypes: true });
+      for (const entry of entries) {
+        if (!entry.isDirectory()) continue;
+        const pluginDir = path.join(dir, entry.name);
+        const manifestPath = path.join(pluginDir, 'manifest.json');
+        if (!fs.existsSync(manifestPath)) continue;
+        try {
+          const raw = fs.readFileSync(manifestPath, 'utf-8');
+          const manifest = JSON.parse(raw);
+          this.validateManifest(manifest);
+          let PluginClass = null;
+          const indexPath = path.join(pluginDir, 'index.js');
+          if (fs.existsSync(indexPath)) {
+            try {
+              const loaded = require(indexPath);
+              PluginClass = loaded.Plugin || loaded.default || null;
+            } catch (err) {
+              console.error(`[PluginLoader] Failed to load index.js for "${manifest.id}":`, err.message);
+              continue;
+            }
+          }
+          plugins.push({
+            id: manifest.id,
+            name: manifest.name,
+            version: manifest.version,
+            description: manifest.description,
+            manifest,
+            PluginClass,
+            dir: pluginDir
+          });
+          this.loadedIds.add(manifest.id);
+        } catch (err) {
+          console.error(`[PluginLoader] Skipping plugin in ${pluginDir}:`, err.message);
+        }
+      }
+    }
+    return plugins;
+  }
+
+  /**
+   * Validate a manifest object. Throws on invalid.
+   */
+  validateManifest(manifest) {
+    if (!manifest.id) throw new Error('Manifest missing required field: id');
+    if (!manifest.name) throw new Error('Manifest missing required field: name');
+    if (!manifest.version) throw new Error('Manifest missing required field: version');
+    if (!manifest.description) throw new Error('Manifest missing required field: description');
+    if (this.loadedIds.has(manifest.id)) {
+      throw new Error(`Duplicate plugin id: "${manifest.id}"`);
+    }
+    return true;
+  }
+}
+
+module.exports = { PluginLoader };