var React = require('react');
var classSet = require('classnames');

function isLeftClickEvent(event) {
  return event.button === 0;
}

function isModifiedEvent(event) {
  return !!(event.metaKey || event.altKey || event.ctrlKey || event.shiftKey);
}

module.exports = {
  propTypes: {
    activeClassName: React.PropTypes.string.isRequired,
    to: React.PropTypes.string.isRequired,
    params: React.PropTypes.object,
    query: React.PropTypes.object,
    onClick: React.PropTypes.func
  },
  contextTypes: {
    router: React.PropTypes.func.isRequired
  },


  getDefaultProps: function () {
    return {
      activeClassName: 'active'
    };
  },

  /**
   * Returns the value of the "href" attribute to use on the DOM element.
   */
  getHref: function () {
    return this.context.router.makeHref(this.props.to, this.props.params, this.props.query);
  },

  /**
   * Returns the value of the "class" attribute to use on the DOM element, which contains
   * the value of the activeClassName property when this <Link> is active.
   */
  getClassName: function () {
    var classNames = {};

    if (this.props.className) {
      classNames[this.props.className] = true;
    }

    if (this.context.router.isActive(this.props.to, this.props.params, this.props.query)) {
      classNames[this.props.activeClassName] = true;
    }

    return classSet(classNames);
  },

  handleRouteTo: function (event) {
    var allowTransition = true;
    var clickResult;

    if (this.props.onClick) {
      clickResult = this.props.onClick(event);
    }

    if (isModifiedEvent(event) || !isLeftClickEvent(event)) {
      return;
    }

    if (clickResult === false || event.defaultPrevented === true) {
      allowTransition = false;
    }

    event.preventDefault();

    if (allowTransition) {
      this.context.router.transitionTo(this.props.to, this.props.params, this.props.query);
    }
  }
};