import { createMiddleware } from 'hono/factory'

export function metaValidateWebhookSignature() {
  return createMiddleware(async (c, next) => {
    const requestBody = await c.req.arrayBuffer()
    const payloadSignature = c.req.header('X-Hub-Signature-256')

    const validRequest = await verifySignature(c.env.META_API_SECRET, requestBody, payloadSignature)
    console.log('Meta Valid Request?', validRequest)

    if (!validRequest) { return c.json({ error: 'Invalid signature' }, 403) }

    await next()
  })
}

/*
Meta Docs
https://developers.facebook.com/docs/messenger-platform/webhooks/
https://developers.facebook.com/docs/whatsapp/cloud-api/webhooks/components
https://developers.facebook.com/docs/graph-api/webhooks/getting-started#create-endpoint
https://developers.facebook.com/docs/whatsapp/cloud-api/guides/set-up-webhooks
https://developers.facebook.com/docs/whatsapp/cloud-api/webhooks/payload-examples/

Research
https://developers.facebook.com/docs/whatsapp/sample-app-endpoints
https://stackoverflow.com/questions/72813196/how-to-register-whatsapp-webhooks-in-nodejs
https://glitch.com/edit/#!/whatsapp-cloud-api-echo-bot
https://www.linkedin.com/pulse/facebook-webhook-payload-signature-verification-aspnet-rehman-tw8xf/
*/
async function verifySignature(secret, payload, signatureHeader) {
  if (!signatureHeader || signatureHeader.length == 0) {
    return false;
  }
  const signature = signatureHeader.split('sha256=')[1]

  if (!signature || signature.length == 0) {
    return false;
  }

  // Encode the secret and the order
  const encoder = new TextEncoder();
  const encodedSecret = encoder.encode(secret);
  const encodedPayload = new Uint8Array(payload).buffer;

  // Import the secret key
  const key = await crypto.subtle.importKey(
    'raw',
    encodedSecret,
    { name: 'HMAC', hash: 'SHA-256' },
    false,
    ['sign']
  );

  // Create the HMAC signature
  const signatureArrayBuffer = await crypto.subtle.sign(
    'HMAC',
    key,
    encodedPayload
  );

  // Convert the ArrayBuffer to a hexadecimal string
  const calculatedSignature = Array.from(new Uint8Array(signatureArrayBuffer))
    .map(byte => byte.toString(16).padStart(2, '0'))
    .join('');

  return signature === calculatedSignature;
}