const crypto = require('crypto')

const BLOCK_SIZE = 256
const MAX_CHUNK_SIZE = BLOCK_SIZE - 11 // 11 is the PCKS1 padding

function encrypt(key, txt) {
  try {
    const buf = Buffer.from(txt)
    let finalBuf = Buffer.from([])
    const n = Math.ceil(buf.length / MAX_CHUNK_SIZE)
    const arr = Array(n).fill(0)
    const pubc = cert.pub(key)
    arr.forEach((_, i) => {
      const f = crypto.publicEncrypt(
        {
          key: pubc,
          padding: crypto.constants.RSA_PKCS1_PADDING, // RSA_PKCS1_OAEP_PADDING
        },
        buf.subarray(i * MAX_CHUNK_SIZE, i * MAX_CHUNK_SIZE + MAX_CHUNK_SIZE)
      )
      finalBuf = Buffer.concat([finalBuf, f])
    })
    return finalBuf.toString('base64')
  } catch (e) {
    console.log('encrypt ERROR', e)
    return ''
  }
}

function decrypt(privateKey, enc) {
  try {
    const buf = Buffer.from(enc, 'base64')
    let finalDec = ''
    const n = Math.ceil(buf.length / BLOCK_SIZE)
    const arr = Array(n).fill(0)
    const privc = cert.priv(privateKey)
    arr.forEach((_, i) => {
      const b = crypto.privateDecrypt(
        {
          key: privc,
          padding: crypto.constants.RSA_PKCS1_PADDING,
        },
        buf.subarray(i * BLOCK_SIZE, i * BLOCK_SIZE + BLOCK_SIZE)
      )
      finalDec += b.toString('utf-8')
    })
    return finalDec
  } catch (e) {
    console.log('RSA decrypt ERROR', e)
    return ''
  }
}

function genKeys() {
  return new Promise((resolve, reject) => {
    crypto.generateKeyPair(
      'rsa',
      {
        modulusLength: 2048,
      },
      (err, publicKey, privKey) => {
        const pubPEM = publicKey.export({
          type: 'pkcs1',
          format: 'pem',
        })
        const pubBase64 = cert.unpub(pubPEM)
        const privPEM = privKey.export({
          type: 'pkcs1',
          format: 'pem',
        })
        const privBase64 = cert.unpriv(privPEM)
        resolve({
          public: pubBase64,
          private: privBase64,
        })
      }
    )
  })
}

const cert = {
  unpub: function (key) {
    let s = key
    s = s.replace('-----BEGIN RSA PUBLIC KEY-----', '')
    s = s.replace('-----END RSA PUBLIC KEY-----', '')
    return s.replace(/[\r\n]+/gm, '')
  },
  unpriv: function (key) {
    let s = key
    s = s.replace('-----BEGIN RSA PRIVATE KEY-----', '')
    s = s.replace('-----END RSA PRIVATE KEY-----', '')
    return s.replace(/[\r\n]+/gm, '')
  },
  pub: function (key) {
    return (
      '-----BEGIN RSA PUBLIC KEY-----\n' +
      key +
      '\n' +
      '-----END RSA PUBLIC KEY-----'
    )
  },
  priv: function (key) {
    return (
      '-----BEGIN RSA PRIVATE KEY-----\n' +
      key +
      '\n' +
      '-----END RSA PRIVATE KEY-----'
    )
  },
}

module.exports = { encrypt, decrypt, genKeys }