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const crypto = require("crypto");

exports.deterministicPartitionKey = (event) => {
  const TRIVIAL_PARTITION_KEY = "0";
  const MAX_PARTITION_KEY_LENGTH = 256;

  let candidate = event && event.partitionKey;

  if (!candidate) {
    const data = JSON.stringify(event);
    candidate = crypto.createHash("sha3-512").update(data).digest("hex");
  }

  if (typeof candidate !== "string") {
    candidate = JSON.stringify(candidate);
  }

  if (candidate.length > MAX_PARTITION_KEY_LENGTH) {
    candidate = crypto.createHash("sha3-512").update(candidate).digest("hex");
  }

  return candidate || TRIVIAL_PARTITION_KEY;
};