'use strict';
define(function(require) {

/**
 * Class to handle form input navigation.
 *
 * If 'Enter' is hit, next input element will be focused,
 * and if the input element is the last one, trigger 'onLast' callback.
 *
 * options:
 *   {
 *     formElem: element,             // The form element
 *     checkFormValidity: function    // Function to check form validity
 *     onLast: function               // Callback when 'Enter' in the last input
 *   }
 */
function FormNavigation(options) {
  function extend(destination, source) {
    for (var property in source) {
      destination[property] = source[property];
    }
    return destination;
  }

  if (!options.formElem) {
    throw new Error('The form element should be defined.');
  }

  var self = this;
  this.options = extend({
    formElem: null,
    checkFormValidity: function checkFormValidity() {
      return self.options.formElem.checkValidity();
    },
    onLast: function() {}
  }, options);

  this.options.formElem.addEventListener('keypress',
    this.onKeyPress.bind(this));
  this.options.formElem.addEventListener('click',
    this.onClick.bind(this));
}

FormNavigation.prototype = {
  onKeyPress: function formNav_onKeyPress(event) {
    if (event.keyCode === 13) {
      // If the user hit enter, focus the next form element, or, if the current
      // element is the last one and the form is valid, submit the form.
      var nextInput = this.focusNextInput(event);
      if (!nextInput && this.options.checkFormValidity()) {
        this.options.onLast(event);
      }
    }
  },

  onClick: function formNav_onClick(event) {
    if (event.target.type === 'reset') {
      var formValidity = this.options.checkFormValidity();
      var buttonElems = this.options.formElem.getElementsByTagName('button');
      for (var i = 0; i < buttonElems.length; i++) {
        var button = buttonElems[i];
        if (button.type !== 'reset') {
            button.disabled = !formValidity;
        }
      }
    }
  },

  focusNextInput: function formNav_focusNextInput(event) {
    var currentInput = event.target;
    var inputElems = this.options.formElem.getElementsByTagName('input');
    var currentInputFound = false;

    for (var i = 0; i < inputElems.length; i++) {
      var input = inputElems[i];
      if (currentInput === input) {
        currentInputFound = true;
        continue;
      } else if (!currentInputFound) {
        continue;
      }

      if (input.type === 'hidden' || input.type === 'button') {
        continue;
      }

      input.focus();
      if (document.activeElement !== input) {
        // We couldn't focus the element we wanted.  Try with the next one.
        continue;
      }
      return input;
    }

    // If we couldn't find anything to focus, just blur the initial element.
    currentInput.blur();
    return null;
  }
};

return FormNavigation;

});