const ed = require('@noble/ed25519');

/**
 * Represents an ECC key manager that can generate and sign messages using Ed25519 keys.
 */
export class ECCManager {
  /**
   * Initializes a new ECC key manager with a new random private key and its corresponding public key.
   * @returns {Promise<ECCManager>} A Promise that resolves to the new ECCManager object.
   */
  static async create() {
    const eccManager = new ECCManager();
    eccManager.CSK = ed.utils.randomPrivateKey();
    eccManager.CVK = await ed.getPublicKey(eccManager.CSK);
    return eccManager;
  }

  /**
   * Creates a new ECC key manager instance with the given private and public keys.
   * @param {Uint8Array} privateKey - The private key for the ECC key manager.
   * @param {Uint8Array} publicKey - The public key for the ECC key manager.
   */
  constructor(privateKey, publicKey) {
    this.CSK = privateKey;
    this.CVK = publicKey;
  }

  /**
   * Creates a digital signature for the specified message using the client's private key.
   * @param {string} msg - The message to sign.
   * @returns {Promise<string>} A Promise that resolves to the digital signature as a string.
   */
  async signMsg(msg) {
    return ed.sign(msg, this.CSK);
  }

  /**
   * Adds a header with the digital signature of a given payload to a set of HTTP headers.
   * @async
   * @param {Headers} currentHeaders - The current set of HTTP headers to add the signature header to.
   * @param {Object} payload - The payload object to sign and add to the headers.
   * @returns {Promise<Headers>} A Promise that resolves to the updated set of HTTP headers.
   */
  async addPayloadSignatureHeader(currentHeaders, payload) {
    // Convert the payload to a Uint8Array using JSON encoding
    const encoder = new TextEncoder();
    const payloadBytes = encoder.encode(JSON.stringify(payload));

    // Sign the payload using the ed25519 algorithm and the client's private key
    const signature = await ed.sign(payloadBytes, this.CSK);

    //FIXME depricated function | Encode the signature using base64
    const base64Signature = btoa(String.fromCharCode.apply(null, signature));

    // Append the X-Payload-Signature header to the given set of HTTP headers, with the value set to the base64-encoded signature
    currentHeaders.append("X-Payload-Signature", base64Signature);

    // Return the updated set of HTTP headers as a Promise
    return currentHeaders;
  }
}