"use strict";

/**
 * @module models/event-context
 */

/**
 * Construct a new EventContext
 *
 * An eventcontext is used for circumstances such as search results, when we
 * have a particular event of interest, and a bunch of events before and after
 * it.
 *
 * It also stores pagination tokens for going backwards and forwards in the
 * timeline.
 *
 * @param {MatrixEvent} ourEvent  the event at the centre of this context
 *
 * @constructor
 */
function EventContext(ourEvent) {
    this._timeline = [ourEvent];
    this._ourEventIndex = 0;
    this._paginateTokens = {b: null, f: null};

    // this is used by MatrixClient to keep track of active requests
    this._paginateRequests = {b: null, f: null};
}

/**
 * Get the main event of interest
 *
 * This is a convenience function for getTimeline()[getOurEventIndex()].
 *
 * @return {MatrixEvent} The event at the centre of this context.
 */
EventContext.prototype.getEvent = function() {
    return this._timeline[this._ourEventIndex];
};

/**
 * Get the list of events in this context
 *
 * @return {Array} An array of MatrixEvents
 */
EventContext.prototype.getTimeline = function() {
    return this._timeline;
};

/**
 * Get the index in the timeline of our event
 *
 * @return {Number}
 */
EventContext.prototype.getOurEventIndex = function() {
    return this._ourEventIndex;
};

/**
 * Get a pagination token.
 *
 * @param {boolean} backwards   true to get the pagination token for going
 *                                  backwards in time
 * @return {string}
 */
EventContext.prototype.getPaginateToken = function(backwards) {
    return this._paginateTokens[backwards ? 'b' : 'f'];
};

/**
 * Set a pagination token.
 *
 * Generally this will be used only by the matrix js sdk.
 *
 * @param {string} token        pagination token
 * @param {boolean} backwards   true to set the pagination token for going
 *                                   backwards in time
 */
EventContext.prototype.setPaginateToken = function(token, backwards) {
    this._paginateTokens[backwards ? 'b' : 'f'] = token;
};

/**
 * Add more events to the timeline
 *
 * @param {Array} events      new events, in timeline order
 * @param {boolean} atStart   true to insert new events at the start
 */
EventContext.prototype.addEvents = function(events, atStart) {
    // TODO: should we share logic with Room.addEventsToTimeline?
    // Should Room even use EventContext?

    if (atStart) {
        this._timeline = events.concat(this._timeline);
        this._ourEventIndex += events.length;
    } else {
        this._timeline = this._timeline.concat(events);
    }
};

/**
 * The EventContext class
 */
module.exports = EventContext;