var trumpet = require('trumpet')
var { through, duplex, concat, pipe } = require('mississippi')

var mimeTypes = {
  'application/atom': 'atom',
  'application/atom+xml': 'atom',
  'text/atom': 'atom',
  'text/atom+xml': 'atom',
  'application/rss': 'rss',
  'application/rss+xml': 'rss',
  'text/rss': 'rss',
  'text/rss+xml': 'rss',
  'application/rdf': 'rdf',
  'application/rdf+xml': 'rdf',
  'text/rdf': 'rdf',
  'text/rdf+xml': 'rdf',
  'application/feed+json': 'json-feed',
  'application/json': 'json-feed'
}

module.exports = function find (f) {
  var tr = trumpet()
  var snk = through.obj((data, _, done) => {
    try {
      done(null, f(data))
    } catch (error) {
      done(error)
    }
  })
  var i = 0
  var mid = through.obj()
  mid.setMaxListeners(0)
  mid.on('pipe', () => (i += 1))
  mid.on('unpipe', () => {
    if ((i -= 1) === 0 && tr._readableState.ended) mid.end()
  })
  tr.once('end', () => {
    if (i === 0 && !mid._readableState.ended) mid.end()
  })

  pipe(
    mid,
    through.obj((data, _, done) => {
      if (mimeTypes[data.type] == null) return done()
      done(null, data)
    }),
    concat(list => snk.end(list)),
    error => (error != null) && snk.emit('error', error)
  )

  tr.selectAll('link', link => {
    var data = {}
    var src = through.obj()
    link.getAttribute('href', href => (data.href = href))
    link.getAttribute('rel', rel => (data.rel = rel))
    link.getAttribute('type', type => (data.type = type))
    link.getAttribute('title', title => (data.title = title))

    pipe(
      link.createReadStream(),
      concat(() => src.end(data)),
      error => {
        if (error != null) mid.emit('error', error)
        // else src.end(data)
      }
    )

    src.pipe(mid, { end: false })
  })

  return duplex.obj(tr, snk)
}