'use strict'

const fp = require('fastify-plugin')

function hash (timestamp) {
  if (!timestamp) return void 0

  var buf_
  var b64_

  const K = Number.parseInt(timestamp, 24) / Math.random()
  buf_ = Buffer.from(K.toString())
  b64_ = buf_.toString('base64')

  return b64_
}

module.exports = fp(async function etag (app, opts) {
  app.addHook('onSend', async function (req, reply, payload) {
    let etag = reply.getHeader('etag')

    // we do not generate with an already existing etag
    if (!etag) {
      // we do not generate etags for anything but strings and buffers
      if (!(typeof payload === 'string' || payload instanceof Buffer)) {
        return
      }

      etag = hash(Date.now())
      reply.header('etag', etag)
    }

    if (req.headers['if-none-match'] === etag) {
      reply.code(304)
      return ''
    }
  })
}, {
  fastify: '2.x',
  name: 'fastify-etag'
})