  /* globals require, module */

  'use strict';

  /**
   * Module dependencies.
   */

  var pathtoRegexp = require('path-to-regexp');

  /**
   * Module exports.
   */

  module.exports = page;

  /**
   * Detect click event
   */
  var clickEvent = ('undefined' !== typeof document) && document.ontouchstart ? 'touchstart' : 'click';

  /**
   * To work properly with the URL
   * history.location generated polyfill in https://github.com/devote/HTML5-History-API
   */

  var location = ('undefined' !== typeof window) && (window.history.location || window.location);

  /**
   * Perform initial dispatch.
   */

  var dispatch = true;


  /**
   * Decode URL components (query string, pathname, hash).
   * Accommodates both regular percent encoding and x-www-form-urlencoded format.
   */
  var decodeURLComponents = true;

  /**
   * Base path.
   */

  var base = '';

  /**
   * Running flag.
   */

  var running;

  /**
   * HashBang option
   */

  var hashbang = false;

  /**
   * Previous context, for capturing
   * page exit events.
   */

  var prevContext;

  /**
   * Register `path` with callback `fn()`,
   * or route `path`, or redirection,
   * or `page.start()`.
   *
   *   page(fn);
   *   page('*', fn);
   *   page('/user/:id', load, user);
   *   page('/user/' + user.id, { some: 'thing' });
   *   page('/user/' + user.id);
   *   page('/from', '/to')
   *   page();
   *
   * @param {string|!Function|!Object} path
   * @param {Function=} fn
   * @api public
   */

  function page(path, fn) {
    // <callback>
    if ('function' === typeof path) {
      return page('*', path);
    }

    // route <path> to <callback ...>
    if ('function' === typeof fn) {
      var route = new Route(/** @type {string} */ (path));
      for (var i = 1; i < arguments.length; ++i) {
        page.callbacks.push(route.middleware(arguments[i]));
      }
      // show <path> with [state]
    } else if ('string' === typeof path) {
      page['string' === typeof fn ? 'redirect' : 'show'](path, fn);
      // start [options]
    } else {
      page.start(path);
    }
  }

  /**
   * Callback functions.
   */

  page.callbacks = [];
  page.exits = [];

  /**
   * Current path being processed
   * @type {string}
   */
  page.current = '';

  /**
   * Number of pages navigated to.
   * @type {number}
   *
   *     page.len == 0;
   *     page('/login');
   *     page.len == 1;
   */

  page.len = 0;

  /**
   * Get or set basepath to `path`.
   *
   * @param {string} path
   * @api public
   */

  page.base = function(path) {
    if (0 === arguments.length) return base;
    base = path;
  };

  /**
   * Bind with the given `options`.
   *
   * Options:
   *
   *    - `click` bind to click events [true]
   *    - `popstate` bind to popstate [true]
   *    - `dispatch` perform initial dispatch [true]
   *
   * @param {Object} options
   * @api public
   */

  page.start = function(options) {
    options = options || {};
    if (running) return;
    running = true;
    if (false === options.dispatch) dispatch = false;
    if (false === options.decodeURLComponents) decodeURLComponents = false;
    if (false !== options.popstate) window.addEventListener('popstate', onpopstate, false);
    if (false !== options.click) {
      document.addEventListener(clickEvent, onclick, false);
    }
    if (true === options.hashbang) hashbang = true;
    if (!dispatch) return;
    var url = (hashbang && ~location.hash.indexOf('#!')) ? location.hash.substr(2) + location.search : location.pathname + location.search + location.hash;
    page.replace(url, null, true, dispatch);
  };

  /**
   * Unbind click and popstate event handlers.
   *
   * @api public
   */

  page.stop = function() {
    if (!running) return;
    page.current = '';
    page.len = 0;
    running = false;
    document.removeEventListener(clickEvent, onclick, false);
    window.removeEventListener('popstate', onpopstate, false);
  };

  /**
   * Show `path` with optional `state` object.
   *
   * @param {string} path
   * @param {Object=} state
   * @param {boolean=} dispatch
   * @param {boolean=} push
   * @return {!Context}
   * @api public
   */

  page.show = function(path, state, dispatch, push) {
    var ctx = new Context(path, state);
    page.current = ctx.path;
    if (false !== dispatch) page.dispatch(ctx);
    if (false !== ctx.handled && false !== push) ctx.pushState();
    return ctx;
  };

  /**
   * Goes back in the history
   * Back should always let the current route push state and then go back.
   *
   * @param {string} path - fallback path to go back if no more history exists, if undefined defaults to page.base
   * @param {Object=} state
   * @api public
   */

  page.back = function(path, state) {
    if (page.len > 0) {
      // this may need more testing to see if all browsers
      // wait for the next tick to go back in history
      history.back();
      page.len--;
    } else if (path) {
      setTimeout(function() {
        page.show(path, state);
      });
    }else{
      setTimeout(function() {
        page.show(base, state);
      });
    }
  };


  /**
   * Register route to redirect from one path to other
   * or just redirect to another route
   *
   * @param {string} from - if param 'to' is undefined redirects to 'from'
   * @param {string=} to
   * @api public
   */
  page.redirect = function(from, to) {
    // Define route from a path to another
    if ('string' === typeof from && 'string' === typeof to) {
      page(from, function(e) {
        setTimeout(function() {
          page.replace(/** @type {!string} */ (to));
        }, 0);
      });
    }

    // Wait for the push state and replace it with another
    if ('string' === typeof from && 'undefined' === typeof to) {
      setTimeout(function() {
        page.replace(from);
      }, 0);
    }
  };

  /**
   * Replace `path` with optional `state` object.
   *
   * @param {string} path
   * @param {Object=} state
   * @param {boolean=} init
   * @param {boolean=} dispatch
   * @return {!Context}
   * @api public
   */


  page.replace = function(path, state, init, dispatch) {
    var ctx = new Context(path, state);
    page.current = ctx.path;
    ctx.init = init;
    ctx.save(); // save before dispatching, which may redirect
    if (false !== dispatch) page.dispatch(ctx);
    return ctx;
  };

  /**
   * Dispatch the given `ctx`.
   *
   * @param {Context} ctx
   * @api private
   */
  page.dispatch = function(ctx) {
    var prev = prevContext,
      i = 0,
      j = 0;

    prevContext = ctx;

    function nextExit() {
      var fn = page.exits[j++];
      if (!fn) return nextEnter();
      fn(prev, nextExit);
    }

    function nextEnter() {
      var fn = page.callbacks[i++];

      if (ctx.path !== page.current) {
        ctx.handled = false;
        return;
      }
      if (!fn) return unhandled(ctx);
      fn(ctx, nextEnter);
    }

    if (prev) {
      nextExit();
    } else {
      nextEnter();
    }
  };

  /**
   * Unhandled `ctx`. When it's not the initial
   * popstate then redirect. If you wish to handle
   * 404s on your own use `page('*', callback)`.
   *
   * @param {Context} ctx
   * @api private
   */
  function unhandled(ctx) {
    if (ctx.handled) return;
    var current;

    if (hashbang) {
      current = base + location.hash.replace('#!', '');
    } else {
      current = location.pathname + location.search;
    }

    if (current === ctx.canonicalPath) return;
    page.stop();
    ctx.handled = false;
    location.href = ctx.canonicalPath;
  }

  /**
   * Register an exit route on `path` with
   * callback `fn()`, which will be called
   * on the previous context when a new
   * page is visited.
   */
  page.exit = function(path, fn) {
    if (typeof path === 'function') {
      return page.exit('*', path);
    }

    var route = new Route(path);
    for (var i = 1; i < arguments.length; ++i) {
      page.exits.push(route.middleware(arguments[i]));
    }
  };

  /**
   * Remove URL encoding from the given `str`.
   * Accommodates whitespace in both x-www-form-urlencoded
   * and regular percent-encoded form.
   *
   * @param {string} val - URL component to decode
   */
  function decodeURLEncodedURIComponent(val) {
    if (typeof val !== 'string') { return val; }
    return decodeURLComponents ? decodeURIComponent(val.replace(/\+/g, ' ')) : val;
  }

  /**
   * Initialize a new "request" `Context`
   * with the given `path` and optional initial `state`.
   *
   * @constructor
   * @param {string} path
   * @param {Object=} state
   * @api public
   */

  function Context(path, state) {
    if ('/' === path[0] && 0 !== path.indexOf(base)) path = base + (hashbang ? '#!' : '') + path;
    var i = path.indexOf('?');

    this.canonicalPath = path;
    this.path = path.replace(base, '') || '/';
    if (hashbang) this.path = this.path.replace('#!', '') || '/';

    this.title = document.title;
    this.state = state || {};
    this.state.path = path;
    this.querystring = ~i ? decodeURLEncodedURIComponent(path.slice(i + 1)) : '';
    this.pathname = decodeURLEncodedURIComponent(~i ? path.slice(0, i) : path);
    this.params = {};

    // fragment
    this.hash = '';
    if (!hashbang) {
      if (!~this.path.indexOf('#')) return;
      var parts = this.path.split('#');
      this.path = parts[0];
      this.hash = decodeURLEncodedURIComponent(parts[1]) || '';
      this.querystring = this.querystring.split('#')[0];
    }
  }

  /**
   * Expose `Context`.
   */

  page.Context = Context;

  /**
   * Push state.
   *
   * @api private
   */

  Context.prototype.pushState = function() {
    page.len++;
    history.pushState(this.state, this.title, hashbang && this.path !== '/' ? '#!' + this.path : this.canonicalPath);
  };

  /**
   * Save the context state.
   *
   * @api public
   */

  Context.prototype.save = function() {
    history.replaceState(this.state, this.title, hashbang && this.path !== '/' ? '#!' + this.path : this.canonicalPath);
  };

  /**
   * Initialize `Route` with the given HTTP `path`,
   * and an array of `callbacks` and `options`.
   *
   * Options:
   *
   *   - `sensitive`    enable case-sensitive routes
   *   - `strict`       enable strict matching for trailing slashes
   *
   * @constructor
   * @param {string} path
   * @param {Object=} options
   * @api private
   */

  function Route(path, options) {
    options = options || {};
    this.path = (path === '*') ? '(.*)' : path;
    this.method = 'GET';
    this.regexp = pathtoRegexp(this.path,
      this.keys = [],
      options);
  }

  /**
   * Expose `Route`.
   */

  page.Route = Route;

  /**
   * Return route middleware with
   * the given callback `fn()`.
   *
   * @param {Function} fn
   * @return {Function}
   * @api public
   */

  Route.prototype.middleware = function(fn) {
    var self = this;
    return function(ctx, next) {
      if (self.match(ctx.path, ctx.params)) return fn(ctx, next);
      next();
    };
  };

  /**
   * Check if this route matches `path`, if so
   * populate `params`.
   *
   * @param {string} path
   * @param {Object} params
   * @return {boolean}
   * @api private
   */

  Route.prototype.match = function(path, params) {
    var keys = this.keys,
      qsIndex = path.indexOf('?'),
      pathname = ~qsIndex ? path.slice(0, qsIndex) : path,
      m = this.regexp.exec(decodeURIComponent(pathname));

    if (!m) return false;

    for (var i = 1, len = m.length; i < len; ++i) {
      var key = keys[i - 1];
      var val = decodeURLEncodedURIComponent(m[i]);
      if (val !== undefined || !(hasOwnProperty.call(params, key.name))) {
        params[key.name] = val;
      }
    }

    return true;
  };


  /**
   * Handle "populate" events.
   */

  var onpopstate = (function () {
    var loaded = false;
    if ('undefined' === typeof window) {
      return;
    }
    if (document.readyState === 'complete') {
      loaded = true;
    } else {
      window.addEventListener('load', function() {
        setTimeout(function() {
          loaded = true;
        }, 0);
      });
    }
    return function onpopstate(e) {
      if (!loaded) return;
      if (e.state) {
        var path = e.state.path;
        page.replace(path, e.state);
      } else {
        page.show(location.pathname + location.hash, undefined, undefined, false);
      }
    };
  })();
  /**
   * Handle "click" events.
   */

  function onclick(e) {

    if (1 !== which(e)) return;

    if (e.metaKey || e.ctrlKey || e.shiftKey) return;
    if (e.defaultPrevented) return;



    // ensure link
    var el = e.target;
    while (el && 'A' !== el.nodeName) el = el.parentNode;
    if (!el || 'A' !== el.nodeName) return;



    // Ignore if tag has
    // 1. "download" attribute
    // 2. rel="external" attribute
    if (el.hasAttribute('download') || el.getAttribute('rel') === 'external') return;

    // ensure non-hash for the same path
    var link = el.getAttribute('href');
    if (!hashbang && el.pathname === location.pathname && (el.hash || '#' === link)) return;



    // Check for mailto: in the href
    if (link && link.indexOf('mailto:') > -1) return;

    // check target
    if (el.target) return;

    // x-origin
    if (!sameOrigin(el.href)) return;



    // rebuild path
    var path = el.pathname + el.search + (el.hash || '');

    path = path[0] !== '/' ? '/' + path : path;

    // strip leading "/[drive letter]:" on NW.js on Windows
    if (typeof process !== 'undefined' && path.match(/^\/[a-zA-Z]:\//)) {
      path = path.replace(/^\/[a-zA-Z]:\//, '/');
    }

    // same page
    var orig = path;

    if (path.indexOf(base) === 0) {
      path = path.substr(base.length);
    }

    if (hashbang) path = path.replace('#!', '');

    if (base && orig === path) return;

    e.preventDefault();
    page.show(orig);
  }

  /**
   * Event button.
   */

  function which(e) {
    e = e || window.event;
    return null === e.which ? e.button : e.which;
  }

  /**
   * Check if `href` is the same origin.
   */

  function sameOrigin(href) {
    var origin = location.protocol + '//' + location.hostname;
    if (location.port) origin += ':' + location.port;
    return (href && (0 === href.indexOf(origin)));
  }

  page.sameOrigin = sameOrigin;
