import {IonicRouter} from './router';
import * as util from '../util/util';


class UrlStateManager {

  constructor(window, router) {
    this.location = window.location;
    this.history = window.history;
    this.ls = window.localStorage;
    this.router = router;

    // overkill for location change listeners, but ensures we
    // know when the location has changed. Only 1 of the listeners
    // will actually do the work, the other will be skipped.
    window.addEventListener('popstate', () => {
      this.onLocationChange();
    });
    window.addEventListener('hashchange', () => {
      this.onLocationChange();
    });
  }

  load() {
    let paths = [this.getCurrentPath()];
    let savedPaths = this.paths();

    if (savedPaths[savedPaths.length - 1] == paths[0]) {
      // the last path in the saved paths is the same as the
      // current path, so use the saved paths to rebuild the history
      paths = savedPaths;

    } else {
      // the current path is not the same as the last path in the
      // saved history, so the saved history is no good, erase it
      this.paths([]);
    }

    return Promise.resolve({
      paths: paths,
      priority: 0
    });
  }

  stateChange(path, type, activeView) {
    let savedPaths = this.paths();

    // check if the given path is different than the current location
    let isDifferentPath = (this.getCurrentPath() !== path);

    if (type == 'pop') {
      // if the popstate came from the browser's back button (and not Ionic)
      // then we shouldn't force another browser history.back()
      // only do a history.back() if the URL hasn't been updated yet
      if (isDifferentPath) {
        this.history.back();
      }

      if (savedPaths.length && savedPaths[savedPaths.length - 1] != path) {
        // only if the last item in the saved paths
        // equals this path then it can be removed
        savedPaths.pop();
      }

    } else {

      if (this._hasInit) {
        if (isDifferentPath) {
          // push the new state to the history stack since the path
          // isn't already in the location hash
          this.history.pushState(path, '', '#' + path);
        }

      } else {
        // replace the very first load with the correct entering state info
        this.history.replaceState(path, '', '#' + path);
        this._hasInit = true;
      }

      if (savedPaths[savedPaths.length - 1] != path) {
        // only if the last item in the saved paths does
        // not equal this path then it can be added
        savedPaths.push(path);

        // don't allow the history to grow too large
        if (savedPaths.length > MAX_PATH_STORE) {
          savedPaths = savedPaths.slice( savedPaths.length - MAX_PATH_STORE );
        }
      }
    }

    // save the new path data
    this.paths(savedPaths);

    // ensure this resets
    this._currentPath = null;
  }

  stateClear() {
    this.paths([]);
  }

  onLocationChange() {
    let currentPath = this.getCurrentPath();

    if (currentPath == this._currentPath) {
      // absolutely no change since last onLocationChange
      return;
    }

    // keep in-memory the current path to quickly tell if things have changed
    this._currentPath = currentPath;

    // load up the saved paths
    let savedPaths = this.paths();

    if (currentPath === savedPaths[savedPaths.length - 1]) {
      // do nothing if the last saved path is
      // the same as the current path
      return;
    }

    if (currentPath === savedPaths[savedPaths.length - 2]) {
      // the user is moving back
      this.router.pop();

    } else {
      // the user is moving forward
      this.router.push(currentPath);
    }
  }

  paths(val) {
    if (arguments.length) {
      // set in-memory data
      this._paths = val;

      // set localStorage data
      try {
        this.ls.setItem(PATH_STORE_KEY, JSON.stringify(val));
      } catch(e) {}

    } else {

      if (!this._paths) {
        // we don't already have data in-memory

        // see if we have data in localStorage
        try {
          let strData = this.ls.getItem(PATH_STORE_KEY);
          if (strData) {
            this._paths = JSON.parse(strData);
          }
        } catch(e) {}

        // if not in localStorage yet then create new path data
        if (!this._paths) {
          this._paths = [];
        }
      }

      // return the in-memory data
      return this._paths;
    }
  }

  getCurrentPath() {
    // remove leading # to get the path
    return this.location.hash.slice(1);
  }

}

const PATH_STORE_KEY = 'ionic:history';
const MAX_PATH_STORE = 20;

IonicRouter.registerStateManager('url', UrlStateManager);