var bel = require('bel') // turns template tag into DOM elements
var morphdom = require('@arve.knudsen/morphdom') // efficiently diffs + morphs two DOM elements
var defaultEvents = require('./update-events.js') // default events to be copied when dom elements update

module.exports = bel

// TODO move this + defaultEvents to a new module once we receive more feedback
module.exports.update = function (fromNode, toNode, opts) {
  if (!opts) opts = {}
  if (opts.events !== false) {
    if (!opts.onBeforeElUpdated) opts.onBeforeElUpdated = copier
  }

  return morphdom(fromNode, toNode, opts)

  // morphdom only copies attributes. we decided we also wanted to copy events
  // that can be set via attributes
  function copier (f, t) {
    // copy events:
    var events = opts.events || defaultEvents
    for (var i = 0; i < events.length; i++) {
      var ev = events[i]
      if (t[ev]) { // if new element has a whitelisted attribute
        f[ev] = t[ev] // update existing element
      } else if (f[ev]) { // if existing element has it and new one doesnt
        f[ev] = undefined // remove it from existing element
      }
    }
    // copy values for form elements
    if (f.nodeName === 'INPUT') {
      if (f.type !== 'file') {
        // Keep value if not set on mutating element
        if (t.getAttribute('value') === null) t.value = f.value
      }
    } else if (f.nodeName === 'TEXTAREA') {
      if (t.getAttribute('value') === null) f.value = t.value
    }
  }
}