/**
 * View model for the changes list.
 *
 * @class mw.rcfilters.dm.ChangesListViewModel
 * @ignore
 * @mixes OO.EventEmitter
 *
 * @param {jQuery} $initialFieldset The initial server-generated legacy form content
 */
const ChangesListViewModel = function MwRcfiltersDmChangesListViewModel( $initialFieldset ) {
	// Mixin constructor
	OO.EventEmitter.call( this );

	this.valid = true;
	this.newChangesExist = false;
	this.liveUpdate = false;
	this.unseenWatchedChanges = false;

	this.extractNextFrom( $initialFieldset );
};

/* Initialization */
OO.initClass( ChangesListViewModel );
OO.mixinClass( ChangesListViewModel, OO.EventEmitter );

/* Events */

/**
 * The list of changes is now invalid (out of date).
 *
 * @event invalidate
 * @ignore
 */

/**
 * The list of changes has been updated.
 *
 * @event update
 * @ignore
 * @param {jQuery|string} $changesListContent List of changes
 * @param {jQuery} $fieldset Server-generated form
 * @param {string} noResultsDetails Type of no result error
 * @param {boolean} isInitialDOM Whether the previous dom variables are from the initial page load
 * @param {boolean} fromLiveUpdate These are new changes fetched via Live Update
 */

/**
 * The existence of changes newer than those currently displayed has changed.
 *
 * @event newChangesExist
 * @param {boolean} newChangesExist
 * @ignore
 */

/**
 * The state of the 'live update' feature has changed.
 *
 * @event liveUpdateChange
 * @param {boolean} enable
 * @ignore
 */

/* Methods */

/**
 * Invalidate the list of changes
 *
 * @fires invalidate
 * @ignore
 */
ChangesListViewModel.prototype.invalidate = function () {
	if ( this.valid ) {
		this.valid = false;
		this.emit( 'invalidate' );
	}
};

/**
 * Update the model with an updated list of changes
 *
 * @param {jQuery|string} changesListContent
 * @param {jQuery} $fieldset
 * @param {string} noResultsDetails Type of no result error
 * @param {boolean} [isInitialDOM] Using the initial (already attached) DOM elements
 * @param {boolean} [separateOldAndNew] Whether a logical separation between old and new changes is needed
 * @fires update
 */
ChangesListViewModel.prototype.update = function ( changesListContent, $fieldset, noResultsDetails, isInitialDOM, separateOldAndNew ) {
	const from = this.nextFrom;
	this.valid = true;
	this.extractNextFrom( $fieldset );
	this.checkForUnseenWatchedChanges( changesListContent );
	this.emit( 'update', changesListContent, $fieldset, noResultsDetails, isInitialDOM, separateOldAndNew ? from : null );
};

/**
 * Specify whether new changes exist
 *
 * @param {boolean} newChangesExist
 * @fires newChangesExist
 */
ChangesListViewModel.prototype.setNewChangesExist = function ( newChangesExist ) {
	if ( newChangesExist !== this.newChangesExist ) {
		this.newChangesExist = newChangesExist;
		this.emit( 'newChangesExist', newChangesExist );
	}
};

/**
 * @return {boolean} Whether new changes exist
 */
ChangesListViewModel.prototype.getNewChangesExist = function () {
	return this.newChangesExist;
};

/**
 * Extract the value of the 'from' parameter from a link in the field set
 *
 * @param {jQuery} $fieldset
 */
ChangesListViewModel.prototype.extractNextFrom = function ( $fieldset ) {
	const data = $fieldset.find( '.rclistfrom > a, .wlinfo' ).data( 'params' );
	if ( data && data.from ) {
		this.nextFrom = data.from;
		this.nextFromFormatted = data.fromFormatted;
	}
};

/**
 * @return {string} The 'from' parameter that can be used to query new changes
 */
ChangesListViewModel.prototype.getNextFrom = function () {
	return this.nextFrom;
};

/**
 * @return {string} The 'from' parameter formatted per the user's datetime format preference
 */
ChangesListViewModel.prototype.getNextFromFormatted = function () {
	return this.nextFromFormatted;
};

/**
 * Toggle the 'live update' feature on/off
 *
 * @param {boolean} enable
 */
ChangesListViewModel.prototype.toggleLiveUpdate = function ( enable ) {
	enable = enable === undefined ? !this.liveUpdate : enable;
	if ( enable !== this.liveUpdate ) {
		this.liveUpdate = enable;
		this.emit( 'liveUpdateChange', this.liveUpdate );
	}
};

/**
 * @return {boolean} The 'live update' feature is enabled
 */
ChangesListViewModel.prototype.getLiveUpdate = function () {
	return this.liveUpdate;
};

/**
 * Check if some of the given changes watched and unseen
 *
 * @param {jQuery|string} changeslistContent
 */
ChangesListViewModel.prototype.checkForUnseenWatchedChanges = function ( changeslistContent ) {
	this.unseenWatchedChanges = changeslistContent !== 'NO_RESULTS' &&
		changeslistContent.find( '.mw-changeslist-line-watched' ).length > 0;
};

/**
 * @return {boolean} Whether some of the current changes are watched and unseen
 */
ChangesListViewModel.prototype.hasUnseenWatchedChanges = function () {
	return this.unseenWatchedChanges;
};

module.exports = ChangesListViewModel;
