snow_task_messages.js

var TaskMessages = Class.create();
TaskMessages.prototype = {
    initialize: function(sysId) {
		this.sysId = sysId;
		this.exclude = [
			'calendar_stc', 'sys_class_name', 'calendar_duration', 'sys_domain,location',
			'business_duration', 'reassignment_count', 'upon_reject',			
		];
		this._generateHistory();
    },
	_generateHistory: function() {
		var ghs = new GlideHistorySet('task', this.sysId);

		try {
			if(ghs.getSummaryRecord() !== null) {
				ghs.refresh();
			} else {
				ghs.generate();
			}
		} catch (e) {
			gs.log(e);
			throw new Error("Unexpected error when attempting to generate history for: ", this.sysId);
		}
	},
	_getMessages: function(types, notTypes, updatesOnly) {
		var hs = new GlideRecord('sys_history_set');
		var hsId = null;

		hs.orderByDesc('sys_created_on');
		hs.addQuery('id', this.sysId);
		hs.setLimit(1);		
		hs.query();

		if(hs.next()) {
			hsId = hs.getValue('sys_id');
		} else {
			throw new Error("No HistorySet for: ", this.sysId);
		}

		// Query history line by set id and filter out non-used fields.
		var hl = new GlideRecord('sys_history_line');
		hl.addQuery('set', hsId);
		if(updatesOnly === true) {
			hl.addQuery('update', '!=', 0);
		}
		
		hl.addQuery('field', 'NOT IN', this.exclude.join(','));

		if(notTypes) {
			hl.addQuery('field', 'NOT IN', notTypes);
		}

		if(types) {
			hl.addQuery('field', 'IN', types);
		}

		hl.orderByDesc('update_time');
		hl.query();
		
		var lines = [];

		while(hl.next()) {
			var line = {};
			line.sys_id = hl.getValue('sys_id');
			line.new_value = hl.getValue('new');
			line.old_value = hl.getValue('old');
			line.user_name = hl.getValue('user_name');
			line.user_company = hl.user.company.getDisplayValue('name');
			line.update = hl.getValue('update');
			line.label = hl.getValue('label');
			line.created_on = hl.getValue('update_time');
			line.field = hl.getValue('field');
			lines.push(line);
		}
		
		return lines;
	},
	get events() {
		return this._getMessages([], ['work_notes', 'comments'], true);
	},
	get workNotes() {
		return this._getMessages(['work_notes'], [], false);
	},	
	get comments() {
		return this._getMessages(['comments'], [], false);
	},
    type: 'TaskMessages'
};