let ensureIndexesPromise = null;

async function ensureApplicableDiagnosisIndexes(db) {
  if (!ensureIndexesPromise) {
    ensureIndexesPromise = Promise.all([
      db.collection("drug-info").createIndex({ applicableDiagnosisCodes: 1 }),
      db.collection("online-drug-info").createIndex({ applicableDiagnosisCodes: 1 }),
    ]).catch((error) => {
      ensureIndexesPromise = null;
      throw error;
    });
  }
  await ensureIndexesPromise;
}

async function validateApplicableDiagnosisCodes(params, db) {
  if (!Object.prototype.hasOwnProperty.call(params, "applicableDiagnosisCodes")) {
    return { present: false, value: [] };
  }

  const rawCodes = params.applicableDiagnosisCodes;
  if (!Array.isArray(rawCodes)) {
    throw new Error("适应诊断格式错误");
  }

  const uniqueCodes = [];
  const seen = new Set();
  for (const rawCode of rawCodes) {
    if (typeof rawCode !== "string" || !rawCode.trim()) {
      throw new Error("适应诊断包含无效编码");
    }
    const code = rawCode.trim();
    if (!seen.has(code)) {
      seen.add(code);
      uniqueCodes.push(code);
    }
  }

  if (uniqueCodes.length) {
    const diagnoses = await db.collection("hlw-diagnosis").find(
      { code: { $in: uniqueCodes } },
      { projection: { _id: 0, code: 1 } }
    ).toArray();
    const existingCodes = new Set(diagnoses.map(item => item.code));
    if (uniqueCodes.some(code => !existingCodes.has(code))) {
      throw new Error("部分适应诊断不存在，请重新选择");
    }
  }

  await ensureApplicableDiagnosisIndexes(db);
  return { present: true, value: uniqueCodes };
}

module.exports = {
  ensureApplicableDiagnosisIndexes,
  validateApplicableDiagnosisCodes,
};