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'use strict'

/**
 * Module dependencies.
 */

const compressible = require('compressible')
const isJSON = require('koa-is-json')
const status = require('statuses')
const Stream = require('stream')
const bytes = require('bytes')

const Encodings = require('./encodings')

/**
* Regex to match no-transform directive in a cache-control header
*/
const NO_TRANSFORM_REGEX = /(?:^|,)\s*?no-transform\s*?(?:,|$)/

/**
 * Compress middleware.
 *
 * @param {Object} [options]
 * @return {Function}
 * @api public
 */

module.exports = (options = {}) => {
  let { filter = compressible, threshold = 1024, defaultEncoding = 'identity' } = options
  if (typeof threshold === 'string') threshold = bytes(threshold)

// `options.br = false` would remove it as a preferred encoding
  const preferredEncodings = Encodings.preferredEncodings.filter((encoding) => options[encoding] !== false && options[encoding] !== null)
  const encodingOptions = {}
  preferredEncodings.forEach((encoding) => {
    encodingOptions[encoding] = {
      ...Encodings.encodingMethodDefaultOptions[encoding],
      ...(options[encoding] || {})
    }
  })

Object.assign(compressMiddleware, {
    preferredEncodings,
    encodingOptions
  })

return compressMiddleware

async function compressMiddleware (ctx, next) {
    ctx.vary('Accept-Encoding')

await next()

// early exit if there's no content body or the body is already encoded
    let { body } = ctx
    if (!body) return
    if (ctx.res.headersSent || !ctx.writable) return
    if (ctx.compress === false) return
    if (ctx.request.method === 'HEAD') return
    if (status.empty[ctx.response.status]) return
    if (ctx.response.get('Content-Encoding')) return

// forced compression or implied
    if (!(ctx.compress === true || filter(ctx.response.type))) return

// don't compress for Cache-Control: no-transform
    // https://tools.ietf.org/html/rfc7234#section-5.2.1.6
    const cacheControl = ctx.response.get('Cache-Control')
    if (cacheControl && NO_TRANSFORM_REGEX.test(cacheControl)) return

// don't compress if the current response is below the threshold
    if (threshold && ctx.response.length < threshold) return

// get the preferred content encoding
    const encodings = new Encodings({
      preferredEncodings
    })
    encodings.parseAcceptEncoding(ctx.request.headers['accept-encoding'] || defaultEncoding)
    const encoding = encodings.getPreferredContentEncoding()

// identity === no compression
    if (encoding === 'identity') return

/** begin compression logic **/

// json
    if (isJSON(body)) body = ctx.body = JSON.stringify(body)

ctx.set('Content-Encoding', encoding)
    ctx.res.removeHeader('Content-Length')

const compress = Encodings.encodingMethods[encoding]
    const stream = ctx.body = compress(encodingOptions[encoding])

if (body instanceof Stream) {
      body.pipe(stream)
    } else {
      stream.end(body)
    }
  }
}