Transaction.js

/** @license MIT License (c) copyright 2010-2014 original author or authors */

/**
 * Licensed under the MIT License at:
 * http://www.opensource.org/licenses/mit-license.php
 * @author: Brian Cavalier
 */
var when = require('when');

function Transaction(runTransaction) {
	this.runTransaction = runTransaction;
}

Transaction.prototype = {
	map: function(f) {
		var runTransaction = this.runTransaction;
		return new Transaction(function(transactionState) {
			var result = runTransaction(transactionState);
			return [when(result[0], f), result[1]];
		});
	},

	flatMap: function(f) {
		var runTransaction = this.runTransaction;
		return new Transaction(function(transactionState) {
			var result = runTransaction(transactionState);
			var value = when(result[0], f).then(function(transaction) {
				return transaction.runTransaction(result[1])[0];
			});
			return [value, result[1]];
		});
	},

	commit: function(datasource) {
		var result = this.runTransaction(datasource);
		return when.all([when.join(result[0], result[1].diff).spread(function(data, diff) {
			return when(datasource.update(diff(data))).yield(data);
		}), datasource]);
	}
};

Transaction.begin = function() {
	return new Transaction(function(datasource) {
		var data = datasource.fetch();

		return [data, {
			datasource: datasource,
			diff: when(data, datasource.metadata.diff.bind(datasource.metadata))
		}];
	});
};

Transaction.of = function(x) {
	return new Transaction(function(transactionState) {
		return [x, transactionState];
	});
};