[WIP] Add token-efficiency techniques across AI generation pipeline

services/llmCache.ts

@@ -0,0 +1,196 @@
+/**
+ * llmCache.ts
+ *
+ * IndexedDB-backed response cache for Gemini calls.
+ *
+ * Cache key is a deterministic hash of (model, compacted prompt, schema
+ * fingerprint, temperature).  Entries expire after `TTL_MS` (default 24 h)
+ * so stale data is never served indefinitely.
+ *
+ * All operations are async and safe to call concurrently.
+ */
+
+const DB_NAME = 'LlmCacheDB';
+const STORE_NAME = 'responses';
+const DB_VERSION = 1;
+const TTL_MS = 24 * 60 * 60 * 1000; // 24 hours
+
+// ── DB helpers ────────────────────────────────────────────────────────────────
+
+let _db: IDBDatabase | null = null;
+
+function openDb(): Promise<IDBDatabase> {
+  if (_db) return Promise.resolve(_db);
+  return new Promise((resolve, reject) => {
+    const req = indexedDB.open(DB_NAME, DB_VERSION);
+    req.onerror = () => reject(req.error);
+    req.onupgradeneeded = (e) => {
+      const db = (e.target as IDBOpenDBRequest).result;
+      if (!db.objectStoreNames.contains(STORE_NAME)) {
+        const store = db.createObjectStore(STORE_NAME, { keyPath: 'key' });
+        store.createIndex('expiresAt', 'expiresAt', { unique: false });
+      }
+    };
+    req.onsuccess = (e) => {
+      _db = (e.target as IDBOpenDBRequest).result;
+      resolve(_db);
+    };
+  });
+}
+
+// ── Key generation ────────────────────────────────────────────────────────────
+
+/**
+ * Simple, deterministic string hash (djb2).
+ * Not cryptographic – only needs to be collision-resistant within a cache.
+ */
+function hashString(s: string): string {
+  let h = 5381;
+  for (let i = 0; i < s.length; i++) {
+    h = ((h << 5) + h) ^ s.charCodeAt(i);
+    h = h >>> 0; // keep 32-bit unsigned
+  }
+  return h.toString(16);
+}
+
+export interface CacheKeyParams {
+  model: string;
+  prompt: string;
+  /** Pass the schema object; it will be JSON-stringified for fingerprinting. */
+  schema?: unknown;
+  temperature?: number;
+}
+
+export function buildCacheKey(params: CacheKeyParams): string {
+  const raw = [
+    params.model,
+    params.prompt,
+    params.schema ? JSON.stringify(params.schema) : '',
+    String(params.temperature ?? 1),
+  ].join('\x00');
+  return hashString(raw);
+}
+
+// ── Cache entry ───────────────────────────────────────────────────────────────
+
+interface CacheEntry {
+  key: string;
+  response: string;
+  createdAt: number;
+  expiresAt: number;
+}
+
+// ── Public API ────────────────────────────────────────────────────────────────
+
+export async function cacheGet(key: string): Promise<string | null> {
+  try {
+    const db = await openDb();
+    return new Promise((resolve, reject) => {
+      const tx = db.transaction(STORE_NAME, 'readonly');
+      const store = tx.objectStore(STORE_NAME);
+      const req = store.get(key);
+      req.onerror = () => reject(req.error);
+      req.onsuccess = () => {
+        const entry = req.result as CacheEntry | undefined;
+        if (!entry) { resolve(null); return; }
+        if (Date.now() > entry.expiresAt) {
+          // Expired – delete async, return null
+          cacheDelete(key).catch(() => {});
+          resolve(null);
+          return;
+        }
+        resolve(entry.response);
+      };
+    });
+  } catch {
+    return null; // Never let cache errors break the main flow
+  }
+}
+
+export async function cacheSet(key: string, response: string): Promise<void> {
+  try {
+    const db = await openDb();
+    const entry: CacheEntry = {
+      key,
+      response,
+      createdAt: Date.now(),
+      expiresAt: Date.now() + TTL_MS,
+    };
+    return new Promise((resolve, reject) => {
+      const tx = db.transaction(STORE_NAME, 'readwrite');
+      const store = tx.objectStore(STORE_NAME);
+      const req = store.put(entry);
+      req.onerror = () => reject(req.error);
+      req.onsuccess = () => resolve();
+    });
+  } catch {
+    // Cache write failures are non-fatal
+  }
+}
+
+export async function cacheDelete(key: string): Promise<void> {
+  try {
+    const db = await openDb();
+    return new Promise((resolve, reject) => {
+      const tx = db.transaction(STORE_NAME, 'readwrite');
+      const store = tx.objectStore(STORE_NAME);
+      const req = store.delete(key);
+      req.onerror = () => reject(req.error);
+      req.onsuccess = () => resolve();
+    });
+  } catch {}
+}
+
+/** Remove all expired entries.  Call this on app startup to prevent DB bloat. */
+export async function evictExpired(): Promise<void> {
+  try {
+    const db = await openDb();
+    return new Promise((resolve, reject) => {
+      const tx = db.transaction(STORE_NAME, 'readwrite');
+      const store = tx.objectStore(STORE_NAME);
+      const idx = store.index('expiresAt');
+      const range = IDBKeyRange.upperBound(Date.now());
+      const req = idx.openCursor(range);
+      req.onerror = () => reject(req.error);
+      req.onsuccess = (e) => {
+        const cursor = (e.target as IDBRequest<IDBCursorWithValue>).result;
+        if (cursor) {
+          cursor.delete();
+          cursor.continue();
+        } else {
+          resolve();
+        }
+      };
+    });
+  } catch {}
+}
+
+/** Return approximate number of entries in the cache (for UI stats). */
+export async function cacheCount(): Promise<number> {
+  try {
+    const db = await openDb();
+    return new Promise((resolve, reject) => {
+      const tx = db.transaction(STORE_NAME, 'readonly');
+      const store = tx.objectStore(STORE_NAME);
+      const req = store.count();
+      req.onerror = () => reject(req.error);
+      req.onsuccess = () => resolve(req.result);
+    });
+  } catch {
+    return 0;
+  }
+}
+
+/** Clear all cache entries (e.g., user action). */
+export async function cacheClear(): Promise<void> {
+  try {
+    const db = await openDb();
+    return new Promise((resolve, reject) => {
+      const tx = db.transaction(STORE_NAME, 'readwrite');
+      const store = tx.objectStore(STORE_NAME);
+      const req = store.clear();
+      req.onerror = () => reject(req.error);
+      req.onsuccess = () => resolve();
+    });
+  } catch {}
+}