保存与恢复

import { readTextDiagram, serializeTextDiagram, type TextDiagramEmbed } from "@quirekit/text-diagram";
import type { DiagramSession } from "../shared/types";

/**
 * Creates a single-object host with compare-and-save semantics.
 * @param initial - Validated persisted object or new draft.
 * @param persist - Optional synchronous storage write; throwing leaves the baseline unchanged.
 * @returns A host whose requests cannot overwrite a newer accepted revision.
 */
export function createDiagramSession(initial: TextDiagramEmbed, persist?: (next: TextDiagramEmbed) => void): DiagramSession {
  let current = readTextDiagram(initial);
  return {
    /** @returns The immutable accepted revision. */
    read() { return current; },
    /** @returns A detached baseline with explicit commit and release callbacks. */
    capture() {
      const baseline = current, expected = serializeTextDiagram(baseline);
      let released = false;
      return {
        document: baseline,
        /** @param proposal - Source and preview proposed by the workbench. @returns Atomic host acceptance. */
        commit(proposal) {
          if (released) return "missing";
          if (serializeTextDiagram(current) !== expected) return "conflict";
          const next = readTextDiagram(proposal);
          if (next.id !== baseline.id || next.document.revision !== baseline.document.revision + 1 || !next.preview) {
            throw new TypeError("Invalid diagram save");
          }
          // Storage must succeed before publishing the new revision to the UI.
          persist?.(next);
          current = next;
          return "saved";
        },
        /** Closes this target without changing the accepted object. */
        release() { released = true; },
      };
    },
  };
}