var Operation = require('./operation');
var Value = require('./value');
var Field = require('./field');

/**
 * Objects to be used as an operands of @Sql.Filter. It represents a two
 * expressions basic operation composed by a table column, the operator and the
 * value extracted from the rendering paramerers.
 */
module.exports = new Class({
	Extends: Operation
	,Tag: 'sql-filter-item'
	,Properties: {
		/**
		 * The column name.
		 */
		field: {
			type: String,
			value: null
		},
		/**
		 * The source table name or its alias if it has been specified.
		 */
		target: {
			type: String,
			value: null
		},
		/**
		 * The parameter name.
		 */
		param: {
			type: String,
			value: null
		}
	}

	/**
	 * Checks if parameter name has been defined and if it has a value.
	 */
	,isReady: function(params) {
		return this.param != null && params != null && params[this.param] != null;
	}

	,render: function(params) {
		var newOp = new Operation({type: this.type});

		newOp.push(new Field({
			name: this.field,
			target: this.target
		}));

		var value = params[this.param];
		newOp.push(new Value({value: value}));
			
		return newOp.render(params);
	}

	,findHolders: function() {
		return this.param ? [this.param] : null;
	}
});