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| 'use strict';
/**
* Twostep - a simple flow-control library for node.js.
*
* Steppy - even more simple in usage tool covering majority
* of the everyday routine use-cases.
*/
var slice = Array.prototype.slice;
/**
* Group represents one step in Step's execution flow.
* Makes a decision when the execution should jump to the next step.
*
* @param {function(err, args...)} callback
* Callback to be called when all data is collected or an error occured.
*/
function Group(callback) {
this.slots = [null];
this.reservedSlots = 0;
this.callback = callback;
this.isDone = false;
}
Group.prototype.done = function done(err) {
if (this.isDone) return;
this.isDone = true;
this.slots[0] = err;
this.callback.apply(null, this.slots);
};
Group.prototype.error = function error(err) {
this.done(err);
};
/**
* Reserve space for one argument in the `slots` array.
* @return {Number} index of the reserved slot
*/
Group.prototype._reserveSlot = function() {
this.reservedSlots++;
return this.slots.push(undefined) - 1;
};
/**
* Fill the reserved slot addressed by `index` with the given `value`.
*/
Group.prototype._fillSlot = function(index, data) {
this.slots[index] = data;
if (!--this.reservedSlots) {
this.done();
}
};
/**
* Reserve one slot in the arguments array to be passed
* to the group's callback. Group's callback will not be called until
* all reserved slots are filled with data or the error occures.
*
* @return {function(err, data)} callback to fill the slot with data
*/
Group.prototype.slot = function slot() {
var self = this;
var index = self._reserveSlot();
return function(err, data) {
process.nextTick(function() {
if (err) {
return self.error(err);
}
self._fillSlot(index, data);
});
};
};
/**
* Creates a nested group, all results of which will be passed into the reserved
* slot as a single array
*/
Group.prototype.makeGroup = function makeGroup() {
var callback = this.slot();
var newGroup = new Group(function (err) {
// omit first 2 elements because of fake element
var data = slice.call(arguments, 2);
callback(err, data);
});
newGroup.slot()(null, null);
return newGroup;
};
/**
* Wrapper for passing synchronous values to the next step
*/
Group.prototype.pass = function pass(/*values*/) {
var values = slice.call(arguments);
for (var i = 0, l = values.length; i < l; i++) {
this.slot()(null, values[i]);
}
};
/**
* TwoStep section
*/
/**
* Chaining together all passed functions.
* The results of the step call are passed to the following step
* in the form of stepN(err, args...).
* The execution result of the whole chain is passed
* via the callback call: callback(err, result).
*
* @return {function(args..., callback)} the resulting chain of steps
*/
function chainSteps(/*fun1, fun2, ..., funN*/) {
var steps = slice.call(arguments);
return function(/*arg1, ... argN, callback*/) {
var initArgs = slice.call(arguments);
var callback = initArgs.pop();
if (!callback) {
throw new Error('Callback is missing');
}
iterateSteps(steps, initArgs, callback);
};
};
/**
* Similar to `makeSteps` but the chaining continues only on
* successful execution of the previous step and breaks after
* the first error occured.
*/
function chainStepsNoError() {
var steps = slice.call(arguments).map(function(step) {
return notHandlingError(step);
});
return chainSteps.apply(null, steps);
};
/**
* The heart of the TwoStep, function executing and chaining all given steps
*/
function iterateSteps(steps, initArgs, callback) {
var pos = 0;
function next(/*err, args...*/) {
if (pos >= steps.length) {
return callback.apply(null, arguments);
}
var step = steps[pos++];
var group = new Group(next);
try {
step.apply(group, arguments);
} catch (e) {
return group.error(e);
}
};
next.apply(null, initArgs);
}
function notHandlingError(func) {
return function(err, args) {
if (err) throw err;
return func.apply(this, arguments);
};
}
function identity(arg) {
return arg;
}
/**
* Chain and execute given steps immediately. The last step in chain
* will be the error- and result-handling callback.
*/
function chainAndCall(chainer) {
return function(/*step1, step2, ...*/) {
var steps = slice.call(arguments);
var callback = steps.pop();
chainer.apply(null, steps)(callback);
};
}
exports.Step = chainAndCall(chainSteps);
exports.Step.fn = chainSteps;
exports.Step.simple = identity;
exports.Step.throwIfError = notHandlingError;
exports.Steppy = chainAndCall(chainStepsNoError);
exports.Steppy.fn = chainStepsNoError;
exports.Group = Group;
|