citation-evidence/src/engine/session-snapshot.test.ts

/**
 * Per-session engine snapshot round-trip.
 *
 * The workplan (CE-WP-0005-T01) requires that two sessions persisted
 * under the per-session key scheme can each be restored independently
 * — proving the storage layout actually partitions data by session.
 */

import { describe, expect, it } from "vitest";

import type { Document, DocumentRepresentation } from "@shared/document";
import type { DocumentId, RepresentationId, SessionId } from "@shared/ids";

import {
  attachPersister,
  createEngine,
  engineSnapshotKey,
  restoreFromStorage,
  type Engine,
  type EngineSnapshot,
} from "./index";

function memoryStorage(): Pick<Storage, "getItem" | "setItem" | "removeItem"> {
  const map = new Map<string, string>();
  return {
    getItem: (k) => map.get(k) ?? null,
    setItem: (k, v) => void map.set(k, v),
    removeItem: (k) => void map.delete(k),
  };
}

function seedDoc(engine: Engine, label: string): { id: DocumentId } {
  const id = `doc_${label}` as DocumentId;
  const repId = `rep_${label}` as RepresentationId;
  const document: Document = {
    id,
    mediaType: "application/pdf",
    title: `Doc ${label}`,
    createdAt: "2026-05-25T00:00:00.000Z",
    updatedAt: "2026-05-25T00:00:00.000Z",
  };
  const representation: DocumentRepresentation = {
    id: repId,
    documentId: id,
    representationType: "pdf-text",
    contentHash: `hash-${label}`,
    canonicalText: `text for ${label}`,
    pageMap: [{ page: 1, width: 100, height: 100 }],
    offsetMap: [{ page: 1, globalStart: 0, globalEnd: 12, pageLength: 12 }],
    generatedAt: "2026-05-25T00:00:00.000Z",
  };
  engine.documents.register({ document, representation });
  return { id };
}

describe("per-session engine snapshot round-trip", () => {
  it("keeps two sessions' snapshots isolated under per-session storage keys", () => {
    const storage = memoryStorage();
    const sessA = "sess_aaa" as SessionId;
    const sessB = "sess_bbb" as SessionId;

    // Author session A.
    const engineA = createEngine();
    const offA = attachPersister(engineA, { key: engineSnapshotKey(sessA), storage });
    const a1 = seedDoc(engineA, "a1");
    const a2 = seedDoc(engineA, "a2");
    offA();

    // Author session B with completely different documents.
    const engineB = createEngine();
    const offB = attachPersister(engineB, { key: engineSnapshotKey(sessB), storage });
    const b1 = seedDoc(engineB, "b1");
    offB();

    // Restore each into its own fresh engine; assert isolation.
    const restoredA = createEngine();
    const resA = restoreFromStorage(restoredA, { key: engineSnapshotKey(sessA), storage });
    expect(resA.restored).toBe(true);
    const aIds = restoredA.documents.list().map((d) => d.id).sort();
    expect(aIds).toEqual([a1.id, a2.id].sort());

    const restoredB = createEngine();
    const resB = restoreFromStorage(restoredB, { key: engineSnapshotKey(sessB), storage });
    expect(resB.restored).toBe(true);
    const bIds = restoredB.documents.list().map((d) => d.id);
    expect(bIds).toEqual([b1.id]);

    // Sanity: each snapshot key really does hold a distinct snapshot.
    const rawA = storage.getItem(engineSnapshotKey(sessA));
    const rawB = storage.getItem(engineSnapshotKey(sessB));
    expect(rawA).not.toBeNull();
    expect(rawB).not.toBeNull();
    const snapA = JSON.parse(rawA!) as EngineSnapshot;
    const snapB = JSON.parse(rawB!) as EngineSnapshot;
    expect(snapA.documents).toHaveLength(2);
    expect(snapB.documents).toHaveLength(1);
  });
});