forerunnerdb/js/lib/Overload.js

A NoSQL document store database for browsers and Node.js.

"use strict";

/**
 * Allows a method to accept overloaded calls with different parameters controlling
 * which passed overload function is called.
 * @param {Object} def
 * @returns {Function}
 * @constructor
 */
var Overload = function (def) {
	if (def) {
		var self = this,
			index,
			count,
			tmpDef,
			defNewKey,
			sigIndex,
			signatures;

		if (!(def instanceof Array)) {
			tmpDef = {};

			// Def is an object, make sure all prop names are devoid of spaces
			for (index in def) {
				if (def.hasOwnProperty(index)) {
					defNewKey = index.replace(/ /g, '');

					// Check if the definition array has a * string in it
					if (defNewKey.indexOf('*') === -1) {
						// No * found
						tmpDef[defNewKey] = def[index];
					} else {
						// A * was found, generate the different signatures that this
						// definition could represent
						signatures = this.generateSignaturePermutations(defNewKey);

						for (sigIndex = 0; sigIndex < signatures.length; sigIndex++) {
							if (!tmpDef[signatures[sigIndex]]) {
								tmpDef[signatures[sigIndex]] = def[index];
							}
						}
					}
				}
			}

			def = tmpDef;
		}

		return function () {
			var arr = [],
				lookup,
				type,
				name;

			// Check if we are being passed a key/function object or an array of functions
			if (def instanceof Array) {
				// We were passed an array of functions
				count = def.length;
				for (index = 0; index < count; index++) {
					if (def[index].length === arguments.length) {
						return self.callExtend(this, '$main', def, def[index], arguments);
					}
				}
			} else {
				// Generate lookup key from arguments
				// Copy arguments to an array
				for (index = 0; index < arguments.length; index++) {
					type = typeof arguments[index];

					// Handle detecting arrays
					if (type === 'object' && arguments[index] instanceof Array) {
						type = 'array';
					}

					// Handle been presented with a single undefined argument
					if (arguments.length === 1 && type === 'undefined') {
						break;
					}

					// Add the type to the argument types array
					arr.push(type);
				}

				lookup = arr.join(',');

				// Check for an exact lookup match
				if (def[lookup]) {
					return self.callExtend(this, '$main', def, def[lookup], arguments);
				} else {
					for (index = arr.length; index >= 0; index--) {
						// Get the closest match
						lookup = arr.slice(0, index).join(',');

						if (def[lookup + ',...']) {
							// Matched against arguments + "any other"
							return self.callExtend(this, '$main', def, def[lookup + ',...'], arguments);
						}
					}
				}
			}

			name = typeof this.name === 'function' ? this.name() : 'Unknown';
			throw('ForerunnerDB.Overload "' + name + '": Overloaded method does not have a matching signature for the passed arguments: ' + this.jStringify(arr));
		};
	}

	return function () {};
};

/**
 * Generates an array of all the different definition signatures that can be
 * created from the passed string with a catch-all wildcard *. E.g. it will
 * convert the signature: string,*,string to all potentials:
 * string,string,string
 * string,number,string
 * string,object,string,
 * string,function,string,
 * string,undefined,string
 *
 * @param {String} str Signature string with a wildcard in it.
 * @returns {Array} An array of signature strings that are generated.
 */
Overload.prototype.generateSignaturePermutations = function (str) {
	var signatures = [],
		newSignature,
		types = ['string', 'object', 'number', 'function', 'undefined'],
		index;

	if (str.indexOf('*') > -1) {
		// There is at least one "any" type, break out into multiple keys
		// We could do this at query time with regular expressions but
		// would be significantly slower
		for (index = 0; index < types.length; index++) {
			newSignature = str.replace('*', types[index]);
			signatures = signatures.concat(this.generateSignaturePermutations(newSignature));
		}
	} else {
		signatures.push(str);
	}

	return signatures;
};

Overload.prototype.callExtend = function (context, prop, propContext, func, args) {
	var tmp,
		ret;

	if (context && propContext[prop]) {
		tmp = context[prop];

		context[prop] = propContext[prop];
		ret = func.apply(context, args);
		context[prop] = tmp;

		return ret;
	} else {
		return func.apply(context, args);
	}
};

module.exports = Overload;