/**
 * wp.media.selectionSync
 *
 * Sync an attachments selection in a state with another state.
 *
 * Allows for selecting multiple images in the Insert Media workflow, and then
 * switching to the Insert Gallery workflow while preserving the attachments selection.
 *
 * @mixin
 */
var selectionSync = {
	/**
	 * @since 3.5.0
	 */
	syncSelection: function() {
		var selection = this.get('selection'),
			manager = this.frame._selection;

		if ( ! this.get('syncSelection') || ! manager || ! selection ) {
			return;
		}

		// If the selection supports multiple items, validate the stored
		// attachments based on the new selection's conditions. Record
		// the attachments that are not included; we'll maintain a
		// reference to those. Other attachments are considered in flux.
		if ( selection.multiple ) {
			selection.reset( [], { silent: true });
			selection.validateAll( manager.attachments );
			manager.difference = _.difference( manager.attachments.models, selection.models );
		}

		// Sync the selection's single item with the master.
		selection.single( manager.single );
	},

	/**
	 * Record the currently active attachments, which is a combination
	 * of the selection's attachments and the set of selected
	 * attachments that this specific selection considered invalid.
	 * Reset the difference and record the single attachment.
	 *
	 * @since 3.5.0
	 */
	recordSelection: function() {
		var selection = this.get('selection'),
			manager = this.frame._selection;

		if ( ! this.get('syncSelection') || ! manager || ! selection ) {
			return;
		}

		if ( selection.multiple ) {
			manager.attachments.reset( selection.toArray().concat( manager.difference ) );
			manager.difference = [];
		} else {
			manager.attachments.add( selection.toArray() );
		}

		manager.single = selection._single;
	}
};

module.exports = selectionSync;
