import { readFileSync, existsSync } from 'node:fs';
import { join } from 'node:path';

/** 源数据非法时抛出。第二准则：缺失/非法一律显式暴露，不兜底。 */
export class SourceError extends Error {
  constructor(message) { super(message); this.name = 'SourceError'; }
}

function readJson(dir, name) {
  const p = join(dir, name);
  if (!existsSync(p)) throw new SourceError(`缺少源数据文件: ${p}`);
  try {
    return JSON.parse(readFileSync(p, 'utf8'));
  } catch (e) {
    throw new SourceError(`源数据 JSON 解析失败: ${p} — ${e.message}`);
  }
}

function readArray(dir, fileName, key) {
  const json = readJson(dir, fileName);
  const arr = json[key];
  if (!Array.isArray(arr)) {
    throw new SourceError(
      `源数据 ${fileName} 缺少顶层数组 "${key}"（实际为 ${typeof arr}）`,
    );
  }
  return arr;
}

/**
 * 读取并校验 gameabc 导出数据。
 * 源数组用 `{}` 占位空槽（下标即 ID），须跳过。
 */
export function loadSource(outputDir) {
  const objects = new Map();
  for (const entry of readArray(outputDir, 'gameabc_Object.json', 'ObjectList')) {
    if (!entry || !entry.Property) continue;
    const p = entry.Property;
    objects.set(p.ObjectID, { ...p, events: Object.keys(entry.Event ?? {}) });
  }

  const images = new Map();
  for (const i of readArray(outputDir, 'gameabc_Image.json', 'ImageFileList')) {
    if (!i || i.id === undefined) continue;
    if (i.w * i.h !== i.frame_all) {
      throw new SourceError(
        `图 ${i.bmp} 的网格与帧数不符: ${i.w}x${i.h}=${i.w * i.h} != frame_all=${i.frame_all}`,
      );
    }
    images.set(i.id, i);
  }

  const layers = readArray(outputDir, 'gameabc_Layer.json', 'LayerList')
    .filter((l) => l && l.Property)
    .map((l) => ({
      layerId: l.Property.LayerID,
      name: l.Property.LayerName,
      objectIds: l.ObjectList ?? [],
    }));

  const groups = readArray(outputDir, 'gameabc_GroupList.json', 'GroupList')
    .filter((g) => g && g.GroupID !== undefined)
    .map((g) => ({ groupId: g.GroupID, objectIds: g.ObjectList ?? [] }));

  return { objects, images, layers, groups };
}