feat: import ekey from Android db (#20)

src/util/DatabaseKeyExtractor.ts

@@ -0,0 +1,44 @@
+import { SQLDatabase, SQLStatic, loadSQL } from './sqlite';
+
+export interface QMAndroidKeyEntry {
+  name: string;
+  key: string;
+}
+
+export class DatabaseKeyExtractor {
+  private static _instance: DatabaseKeyExtractor;
+
+  static async getInstance() {
+    if (!DatabaseKeyExtractor._instance) {
+      DatabaseKeyExtractor._instance = new DatabaseKeyExtractor(await loadSQL());
+    }
+    return DatabaseKeyExtractor._instance;
+  }
+
+  constructor(private SQL: SQLStatic) {}
+
+  private hasTable(db: SQLDatabase, name: string): boolean {
+    const tables = db.exec('SELECT name FROM sqlite_master WHERE type="table"')[0].values.map((x) => x[0]);
+    return tables.includes(name);
+  }
+
+  extractQmAndroidDbKeys(buffer: ArrayBuffer): null | QMAndroidKeyEntry[] {
+    let db: SQLDatabase | null = null;
+
+    try {
+      db = new this.SQL.Database(new Uint8Array(buffer));
+      if (!this.hasTable(db, 'audio_file_ekey_table')) {
+        return null;
+      }
+
+      const keys = db.exec('select file_path, ekey from `audio_file_ekey_table`')[0].values;
+      return keys.map(([path, key]) => ({
+        // strip dir name
+        name: String(path).replace(/.+\//, ''),
+        key: String(key),
+      }));
+    } finally {
+      db?.close();
+    }
+  }
+}