export const BOARD_SESSION_KEY = "matrix-board-session-v1";

function validContext(context) {
  return context === null || (
    context && ["template", "animation"].includes(context.type)
    && ["id", "name", "revision", "baseline"].every((key) => typeof context[key] === "string" && context[key])
    && typeof context.readOnly === "boolean"
    && (context.type !== "animation" || context.readOnly)
  );
}

export function readBoardSession(storage, draft, bootId) {
  const raw = storage?.getItem(BOARD_SESSION_KEY);
  if (!raw) return { bootId: null, context: null };
  try {
    const value = JSON.parse(raw);
    if (value.version !== 1 || typeof value.bootId !== "string" || !validContext(value.context)) {
      throw new Error("invalid session");
    }
    return {
      bootId: value.bootId,
      context: value.bootId === bootId && value.draft === draft ? value.context : null,
    };
  } catch {
    throw new Error("画板保存绑定损坏或来自未来版本；原值已保留，请另存当前内容后处理浏览器存储。");
  }
}

export function writeBoardSession(storage, bootId, draft, context) {
  storage.setItem(BOARD_SESSION_KEY, JSON.stringify({ version: 1, bootId, draft, context }));
}

// Resolve only editable static defaults and the read-only demo animation.
// Ordinary animations retain their existing explicit frame editing workflow.
export async function loadDefaultBoard(apiJson) {
  const reference = await apiJson("/api/display/default-content");
  if (reference.type === "template") {
    return { ...await apiJson(`/api/templates/${reference.id}`), type: "template" };
  }
  if (reference.type !== "animation" || !reference.is_demo) return null;
  const animation = await apiJson(`/api/animations/${reference.id}/frames`);
  const first = animation.frames[0];
  if (!first) throw new Error("默认演示动图没有帧");
  const frame = await apiJson(`/api/animations/${reference.id}/frames/${first.id}`);
  return { ...animation, type: "animation", read_only: true, scene: frame.scene };
}

export async function initializeDefaultBoard({ canLoad, load, apply, retain }) {
  if (!canLoad()) return false;
  const content = await load();
  if (!canLoad()) {
    retain();
    return false;
  }
  if (content) apply(content);
  else retain();
  return Boolean(content);
}