/**
 * IndexedDB backing for PdfByteStore — survives page reloads.
 *
 * Keys are scoped by session so multi-session demos don't share bytes.
 * Failures are logged and ignored so a broken IDB never blocks upload.
 */

import type { DocumentId } from "@citation-evidence/engine/shared";

const DB_NAME = "citation-evidence-pdf-bytes";
const DB_VERSION = 1;
const STORE_NAME = "bytes";

export interface PersistedByteEntry {
  readonly key: string;
  readonly sessionId: string;
  readonly documentId: string;
  readonly contentType: string;
  readonly bytes: ArrayBuffer;
}

function entryKey(sessionId: string, documentId: string): string {
  return `${sessionId}::${documentId}`;
}

function openDb(): Promise<IDBDatabase> {
  return new Promise((resolve, reject) => {
    if (typeof indexedDB === "undefined") {
      reject(new Error("indexedDB not available"));
      return;
    }
    const req = indexedDB.open(DB_NAME, DB_VERSION);
    req.onerror = () => reject(req.error ?? new Error("indexedDB open failed"));
    req.onsuccess = () => resolve(req.result);
    req.onupgradeneeded = () => {
      const db = req.result;
      if (!db.objectStoreNames.contains(STORE_NAME)) {
        const store = db.createObjectStore(STORE_NAME, { keyPath: "key" });
        store.createIndex("sessionId", "sessionId", { unique: false });
      }
    };
  });
}

function idbReq<T>(request: IDBRequest<T>): Promise<T> {
  return new Promise((resolve, reject) => {
    request.onsuccess = () => resolve(request.result);
    request.onerror = () => reject(request.error ?? new Error("idb request failed"));
  });
}

function txDone(tx: IDBTransaction): Promise<void> {
  return new Promise((resolve, reject) => {
    tx.oncomplete = () => resolve();
    tx.onerror = () => reject(tx.error ?? new Error("idb tx failed"));
    tx.onabort = () => reject(tx.error ?? new Error("idb tx aborted"));
  });
}

export async function idbPutBytes(
  sessionId: string,
  documentId: DocumentId,
  bytes: Uint8Array,
  contentType: string,
): Promise<void> {
  try {
    const db = await openDb();
    try {
      const copy = bytes.buffer.slice(
        bytes.byteOffset,
        bytes.byteOffset + bytes.byteLength,
      ) as ArrayBuffer;
      const entry: PersistedByteEntry = {
        key: entryKey(sessionId, documentId),
        sessionId,
        documentId,
        contentType,
        bytes: copy,
      };
      const tx = db.transaction(STORE_NAME, "readwrite");
      tx.objectStore(STORE_NAME).put(entry);
      await txDone(tx);
    } finally {
      db.close();
    }
  } catch (err) {
    console.warn("idbPutBytes failed", err);
  }
}

export async function idbDeleteBytes(
  sessionId: string,
  documentId: DocumentId,
): Promise<void> {
  try {
    const db = await openDb();
    try {
      const tx = db.transaction(STORE_NAME, "readwrite");
      tx.objectStore(STORE_NAME).delete(entryKey(sessionId, documentId));
      await txDone(tx);
    } finally {
      db.close();
    }
  } catch (err) {
    console.warn("idbDeleteBytes failed", err);
  }
}

export async function idbClearSession(sessionId: string): Promise<void> {
  try {
    const db = await openDb();
    try {
      const tx = db.transaction(STORE_NAME, "readwrite");
      const store = tx.objectStore(STORE_NAME);
      const index = store.index("sessionId");
      const keys = await idbReq(index.getAllKeys(IDBKeyRange.only(sessionId)));
      for (const key of keys) {
        store.delete(key);
      }
      await txDone(tx);
    } finally {
      db.close();
    }
  } catch (err) {
    console.warn("idbClearSession failed", err);
  }
}

export async function idbListSession(
  sessionId: string,
): Promise<readonly PersistedByteEntry[]> {
  try {
    const db = await openDb();
    try {
      const tx = db.transaction(STORE_NAME, "readonly");
      const index = tx.objectStore(STORE_NAME).index("sessionId");
      const rows = await idbReq(index.getAll(IDBKeyRange.only(sessionId)));
      await txDone(tx);
      return rows as PersistedByteEntry[];
    } finally {
      db.close();
    }
  } catch (err) {
    console.warn("idbListSession failed", err);
    return [];
  }
}