/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
 * You can obtain one at http://mozilla.org/MPL/2.0/. */

/* global XPCOMUtils, Services, PlacesUtils, EventEmitter */
/* global gLinks */
/* exported PlacesProvider */

"use strict";

this.EXPORTED_SYMBOLS = ["PlacesProvider"];

const {interfaces: Ci, utils: Cu} = Components;
Cu.import("resource://gre/modules/Services.jsm");
Cu.import("resource://gre/modules/XPCOMUtils.jsm");

XPCOMUtils.defineLazyModuleGetter(this, "PlacesUtils",
  "resource://gre/modules/PlacesUtils.jsm");

XPCOMUtils.defineLazyGetter(this, "EventEmitter", function() {
  const {EventEmitter} = Cu.import("resource://devtools/shared/event-emitter.js", {});
  return EventEmitter;
});

XPCOMUtils.defineLazyModuleGetter(this, "Task",
                                  "resource://gre/modules/Task.jsm");
XPCOMUtils.defineLazyModuleGetter(this, "NewTabUtils",
                                  "resource://gre/modules/NewTabUtils.jsm");

// The maximum number of results PlacesProvider retrieves from history.
const HISTORY_RESULTS_LIMIT = 100;

/* Queries history to retrieve the most visited sites. Emits events when the
 * history changes.
 * Implements the EventEmitter interface.
 */
let Links = function Links() {
  EventEmitter.decorate(this);
};

Links.prototype = {
  /**
   * Set this to change the maximum number of links the provider will provide.
   */
  get maxNumLinks() {
    // getter, so it can't be replaced dynamically
    return HISTORY_RESULTS_LIMIT;
  },

  /**
   * A set of functions called by @mozilla.org/browser/nav-historyservice
   * All history events are emitted from this object.
   */
  historyObserver: {
    _batchProcessingDepth: 0,
    _batchCalledFrecencyChanged: false,

    /**
     * Called by the history service.
     */
    onBeginUpdateBatch() {
      this._batchProcessingDepth += 1;
    },

    onEndUpdateBatch() {
      this._batchProcessingDepth -= 1;
      if (this._batchProcessingDepth == 0 && this._batchCalledFrecencyChanged) {
        this.onManyFrecenciesChanged();
        this._batchCalledFrecencyChanged = false;
      }
    },

    onDeleteURI: function historyObserver_onDeleteURI(aURI) {
      // let observers remove sensetive data associated with deleted visit
      gLinks.emit("deleteURI", {
        url: aURI.spec,
      });
    },

    onClearHistory: function historyObserver_onClearHistory() {
      gLinks.emit("clearHistory");
    },

    onFrecencyChanged: function historyObserver_onFrecencyChanged(aURI,
                           aNewFrecency, aGUID, aHidden, aLastVisitDate) { // jshint ignore:line

      // If something is doing a batch update of history entries we don't want
      // to do lots of work for each record. So we just track the fact we need
      // to call onManyFrecenciesChanged() once the batch is complete.
      if (this._batchProcessingDepth > 0) {
        this._batchCalledFrecencyChanged = true;
        return;
      }

      // The implementation of the query in getLinks excludes hidden and
      // unvisited pages, so it's important to exclude them here, too.
      if (!aHidden && aLastVisitDate &&
          NewTabUtils.linkChecker.checkLoadURI(aURI.spec)) {
        gLinks.emit("linkChanged", {
          url: aURI.spec,
          frecency: aNewFrecency,
          lastVisitDate: aLastVisitDate,
          type: "history",
        });
      }
    },

    onManyFrecenciesChanged: function historyObserver_onManyFrecenciesChanged() {
      // Called when frecencies are invalidated and also when clearHistory is called
      // See toolkit/components/places/tests/unit/test_frecency_observers.js
      gLinks.emit("manyLinksChanged");
    },

    onVisit(aURI, aVisitId, aTime, aSessionId, aReferrerVisitId, aTransitionType,
            aGuid, aHidden, aVisitCount, aTyped, aLastKnownTitle) {
      // For new visits, if we're not batch processing, notify for a title update
      if (!this._batchProcessingDepth && aVisitCount == 1 && aLastKnownTitle) {
        this.onTitleChanged(aURI, aLastKnownTitle, aGuid);
      }
    },

    onTitleChanged: function historyObserver_onTitleChanged(aURI, aNewTitle) {
      if (NewTabUtils.linkChecker.checkLoadURI(aURI.spec)) {
        gLinks.emit("linkChanged", {
          url: aURI.spec,
          title: aNewTitle
        });
      }
    },

    QueryInterface: XPCOMUtils.generateQI([Ci.nsINavHistoryObserver,
                                           Ci.nsISupportsWeakReference])
  },

  /**
   * Must be called before the provider is used.
   * Makes it easy to disable under pref
   */
  init: function PlacesProvider_init() {
    try {
      PlacesUtils.history.addObserver(this.historyObserver, true);
    } catch (e) {
      Cu.reportError(e);
    }
  },

  /**
   * Gets the current set of links delivered by this provider.
   *
   * @returns {Promise} Returns a promise with the array of links as payload.
   */
  getLinks: Task.async(function*() {
    // Select a single page per host with highest frecency, highest recency.
    // Choose N top such pages. Note +rev_host, to turn off optimizer per :mak
    // suggestion.
    let sqlQuery = `SELECT url, title, frecency,
                          last_visit_date as lastVisitDate,
                          "history" as type
                   FROM moz_places
                   WHERE frecency in (
                     SELECT MAX(frecency) as frecency
                     FROM moz_places
                     WHERE hidden = 0 AND last_visit_date NOTNULL
                     GROUP BY +rev_host
                     ORDER BY frecency DESC
                     LIMIT :limit
                   )
                   GROUP BY rev_host HAVING MAX(lastVisitDate)
                   ORDER BY frecency DESC, lastVisitDate DESC, url`;

    let links = yield this.executePlacesQuery(sqlQuery, {
                  columns: ["url", "title", "lastVisitDate", "frecency", "type"],
                  params: {limit: this.maxNumLinks}
                });

    return links.filter(link => NewTabUtils.linkChecker.checkLoadURI(link.url));
  }),

  /**
   * Executes arbitrary query against places database
   *
   * @param {String} aSql
   *        SQL query to execute
   * @param {Object} [optional] aOptions
   *        aOptions.columns - an array of column names. if supplied the returned
   *        items will consist of objects keyed on column names. Otherwise
   *        an array of raw values is returned in the select order
   *        aOptions.param - an object of SQL binding parameters
   *        aOptions.callback - a callback to handle query rows
   *
   * @returns {Promise} Returns a promise with the array of retrieved items
   */
  executePlacesQuery: Task.async(function*(aSql, aOptions = {}) {
    let {columns, params, callback} = aOptions;
    let items = [];
    let queryError = null;
    let conn = yield PlacesUtils.promiseDBConnection();
    yield conn.executeCached(aSql, params, aRow => {
      try {
        // check if caller wants to handle query raws
        if (callback) {
          callback(aRow);
        } else {
          // otherwise fill in the item and add items array
          let item = null;
          // if columns array is given construct an object
          if (columns && Array.isArray(columns)) {
            item = {};
            columns.forEach(column => {
              item[column] = aRow.getResultByName(column);
            });
          } else {
            // if no columns - make an array of raw values
            item = [];
            for (let i = 0; i < aRow.numEntries; i++) {
              item.push(aRow.getResultByIndex(i));
            }
          }
          items.push(item);
        }
      } catch (e) {
        queryError = e;
        throw StopIteration;
      }
    });
    if (queryError) {
      throw new Error(queryError);
    }
    return items;
  }),
};

/**
 * Singleton that serves as the default link provider for the grid.
 */
const gLinks = new Links(); // jshint ignore:line

let PlacesProvider = {
  links: gLinks,
};

// Kept only for backwards-compatibility
XPCOMUtils.defineLazyGetter(PlacesProvider, "LinkChecker",
  () => NewTabUtils.linkChecker);