Use a function to generate a UID2

import CryptoES from 'crypto-es'

activate(async ({ visitor, visit, helper }) => {  

  const genHash = (data) => {
    return CryptoES.SHA256(data).toString(CryptoES.enc.Base64)
    }
  const validateEmail = (email) => {
    return String(email)
      .toLowerCase()
      .match(
        /^(([^<>()[\]\\.,;:\s@"]+(\.[^<>()[\]\\.,;:\s@"]+)*)|.(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/
      );
    };

  let tealium_config = {
      tealium_account: 'CURRENT', 
      tealium_profile: 'CURRENT',
      tealium_datasource: 'DATA_SOURCE_KEY', // TODO: Change DATA_SOURCE_KEY to your Tealium Data Source key.
      email_hashed: false // TODO: If your email is already hashed, set this to true.
    };

  if(tealium_config.tealium_account == 'CURRENT') {
    tealium_config.tealium_account = visitor.properties.account
  }
  if(tealium_config.tealium_profile == 'CURRENT') {
    tealium_config.tealium_profile = visitor.properties.profile
  }

  // TODO: Change the attribute_number to point to the populated attribute with the visitor's email
  const email = visitor.getAttributeValueById('ATTRIBUTE_ID')
  let hashed_email = '';

  console.log(email)
  const tealium_vid = visitor.properties.visitor_id
  
  if(!tealium_config.email_hashed) {
    if(!validateEmail(email)) {
       throw new Error(`Email Attribute is not a valid email`);
      return false
    }
    hashed_email = genHash(email)
  } else {
    hashed_email = email
  }
  console.log(hashed_email)

  // TODO: Update the following variables with your TTD UID2 credentials
  const api_key = 'TTD_API_KEY' // TODO: Change TTD_API_KEY to your TTD API Key.
  const secret = 'UID2_SECRET' // TODO: Change UID2_SECRET to your TTD UID2 secret.

  const url = 'https://prod.uidapi.com/v2/identity/map'
  const key = CryptoES.enc.Base64.parse(secret)
  const hexRef = "0123456789abcdef"

  const randomBytes = (bytes) => {
    let buf = ''
    for (let i = 0; i < bytes * 2; i++)
      buf += hexRef.charAt(Math.floor(Math.random() * hexRef.length))
    return buf
  }

  const writeBigUint64BE = (num, bytes = 8) => {
    let buf = num.toString(16)
    let padding = ''
    for (let i = 0; i < bytes * 2 - buf.length; i++)
      padding += '0'
    return padding + buf
  }

  const encrypt = (data) => {
    const iv = randomBytes(12)
    const nonce = randomBytes(8)
    const millisec = Date.now()
    const timestamp = writeBigUint64BE(millisec)
    const payload = CryptoES.enc.Utf8.parse(JSON.stringify(data))
    const body = timestamp + nonce + payload 
    const ivBuf = CryptoES.enc.Hex.parse(iv)
    const encryptedBody = CryptoES.AES.encrypt(
      CryptoES.enc.Hex.parse(body),
      key,
      {
        iv: ivBuf,
        mode: CryptoES.mode.GCM,
        padding: CryptoES.pad.NoPadding
      }
    )
    const ciphertext = encryptedBody.ciphertext
    const authTag = CryptoES.mode.GCM.mac(CryptoES.algo.AES, key, ivBuf, null, ciphertext).toString()
    const enveloped = '01' + iv + ciphertext.toString() + authTag

    return {
      timestamp: parseInt(timestamp, 16),
      nonce: parseInt(nonce, 16),
      enveloped: CryptoES.enc.Hex.parse(enveloped).toString(CryptoES.enc.Base64)
    }
  }

  const decrypt = (data) => {
    const buf = CryptoES.enc.Base64.parse(data).toString(CryptoES.enc.Hex)
    const iv = CryptoES.enc.Hex.parse(buf.substring(0, 24))
    const ciphertext = CryptoES.enc.Hex.parse(buf.substring(24, buf.length - 32))
    const tag = buf.substring(buf.length - 32)
    const encryptedBody = new CryptoES.lib.CipherParams({ ciphertext: ciphertext })
    const decrypted = CryptoES.AES.decrypt(encryptedBody,key, 
      {
        iv: iv, 
        mode: CryptoES.mode.GCM, 
        padding: CryptoES.pad.NoPadding
      }
    ).toString()

    const timestamp = decrypted.substring(0, 16)
    const nonce = decrypted.substring(16, 32)
    const developed = decrypted.substring(32)
  
    return {
      timestamp: parseInt(timestamp, 16),
      nonce: parseInt(nonce, 16),
      developed: JSON.parse(CryptoES.enc.Hex.parse(developed).toString(CryptoES.enc.Utf8))
    }
  }

  const payload = {
    email_hash: [genHash(email)]
    }
  const {timestamp, nonce, enveloped} = encrypt(payload)

  console.log('\n********** encypted **********')
  console.log('timestamp:', timestamp)
  console.log('nonce:', nonce)
  console.log('enveloped:', enveloped)
  
  const response = await fetch(url, {
    method: 'POST',
    body: enveloped,
    headers: {
      'Authorization': `Bearer ${api_key}`
    }
  })

  if (response.status == 200) {
    const body = await response.text()
    console.log('\n********** response **********')
    console.log(body)
    const data = decrypt(body)
    console.log('\n********** decrypted **********')
    console.log('timeStamp:', data.timestamp)
    console.log('nonce:', data.nonce)
    console.log('response:', JSON.stringify(data.developed))
    console.log('\n')

// TODO: This event spec is sent to Tealium at the end of the Function. Make sure that the attributes in the event spec you created match the attributes in event_data.
 let event_data ={
      tealium_event: "UID2_event_data",
      tealium_visitor_id: tealium_vid,
      uid: data.developed.body.mapped[0].advertising_id,
      uid_timestamp : JSON.stringify(data.timestamp)
    };

// This is the step that sends the event_data object to Tealium for processing.
  console.log(JSON.stringify(event_data))
    if(event_data.uid) {
      track(event_data, tealium_config)
          .then(response => {
              if (!response.ok) {
                  throw new Error(`Network response was not ok. Status code: ${response.status}.`);
              }
              console.log('Status code:', response.status);
              return response.text();
          })
          .catch(error => console.error('Error:', error.message));
    } 
    else {
      console.error("Couldn't generate advertising ID")
      }
  } 
  else {
    console.log('\nxxxxx  failed  xxxxx\n')
    console.log(JSON.stringify(response))
    }
  })