/*
 * Copyright (C) Sapphirecode - All Rights Reserved
 * This file is part of Auth-Server-Helper which is released under MIT.
 * See file 'LICENSE' for full license details.
 * Created by Timo Hocker <timo@scode.ovh>, December 2020
 */

import { generate_keypair } from '@sapphirecode/crypto-helper';

interface Keypair {
  private_key: string;
  public_key: string;
}

interface Key {
  key: Keypair;
  valid_until: number;
  timeout: NodeJS.Timeout;
}

function get_index (iat: number): string {
  return Math.floor (iat / 60)
    .toFixed (0);
}

class KeyStore {
  private _keys: Record<string, Key> = {};

  private set_timeout (index: string, valid_for: number): NodeJS.Timeout {
    return setTimeout (() => {
      delete this._keys[index];
    }, (valid_for + 5) * 1000);
  }

  public async get_sign_key (iat: number, valid_for: number): Promise<string> {
    const index = get_index (iat);

    if (valid_for <= 0)
      throw new Error ('cannot create infinitely valid key');

    if ((iat + 1) * 1000 < (new Date)
      .getTime ())
      throw new Error ('cannot access already expired keys');

    const valid_until = (new Date)
      .getTime () + (valid_for * 1000);

    if (typeof this._keys[index] !== 'undefined') {
      const key = this._keys[index];
      if (key.valid_until < valid_until) {
        clearTimeout (key.timeout);
        key.timeout = this.set_timeout (index, valid_for);
        key.valid_until = valid_until;
      }
      return key.key.private_key;
    }

    this._keys[index] = {
      key:     await generate_keypair (),
      timeout: this.set_timeout (index, valid_for),
      valid_until
    };

    return this._keys[index].key.private_key;
  }

  public get_key (iat: number): string {
    const index = get_index (iat);

    if (typeof this._keys[index] === 'undefined')
      throw new Error ('key could not be found');

    const key = this._keys[index];
    return key.key.public_key;
  }
}

const ks: KeyStore = (new KeyStore);
export default ks;
export { KeyStore };