bbc/flashheart

"use strict";
/**
 * @fileOverview allows you to bind a change watcher that looks for get and set operations on an arbitrary
 * property of an object at at any depth. This allows you to look for changes or intercept values asynchronously or otherwise.
 * @module documents/binder
 * @requires async
 * @requires documents/probe
 * @requires lodash
 * @requires promise
 */
var Promise = require( 'promise' );
var async = require( "async" );
var probe = require( "./probe" );
var sys = require( "lodash" );

/**
 * Identifies the properties that the binder expects
 * @type {{getter: null, getterAsync: boolean, setter: null, validator: null, validatorAsync: boolean, setterAsync: boolean}}
 * @private
 */
var dataBinderOptions = exports.dataBinderOptions = {
    getter         : null,
    getterAsync    : false,
    setter         : null,
    validator      : null,
    validatorAsync : false,
    setterAsync    : false
};

/**
 * You can unbind previously bound objects from here.
 *
 * @param {string} path The path that was bound using {@link module:documents/binder.bind}
 * @param {*} record The object that was bound
 */
exports.unbind = function ( path, record ) {
    var context = record;
    var lastParent = context;
    var parts = path.split( probe.delimiter );
    var lastPartName = path;
    var lastParentName;
    sys.each( parts, function ( part ) {
        lastParentName = part;
        lastParent = context;
        context = context[part];
        lastPartName = part;
        if ( sys.isNull( context ) || sys.isUndefined( context ) ) {
            context = {};
        }
    } );

    if ( lastParent === context ) {
        deleteBindings( record, lastPartName );
    } else {
        deleteBindings( lastParent, lastPartName );
    }

    function deleteBindings( mountPoint, mountName ) {
        mountPoint[mountName] = mountPoint["__" + mountName + "__"];
        delete mountPoint["__" + mountName + "__"];
    }
};

/**
 * Bind to a property somewhere in an object. The property is found using dot notation and can be arbitrarily deep.
 * @param {string} path The path into the object to locate the property. For instance this could be `"_id"`, `"name.last"`.
 * or `"some.really.really.long.path.including.an.array.2.name"`
 * @param {object} record Anything you can hang a property off of
 * @param {options} options What you wanna do with the doohicky when yoyu bind it.
 * @param {function(*):Promise|*=} options.getter This is the method to run when getting the value. When it runs, you will receive
 * a single parameter which is the current value as the object understands it. You can return the value directly, just raise an event or
 * whatever your little heart demands. However, if you are asynchronous, this will turn your return value into a promise, one of the
 * few places this system will embrace promises over node-like error passing and that is mainly because this is a getter so a return value
 * is particularly important. *
 * @param {*} options.getter.value The current value of the record
 * @param {function(err, value)=} options.getter.callback When asynchronous, return you value through this method using node style
 * error passing (the promise is handled for you by this method).
 * @param {boolean=} options.getterAsync When true (not truthy) the getter is treated asynchronously and returns a promise with your value.
 * @param {function(*, *, *)=} options.setter A setter method
 * @param {*} options.setter.newVal The new value
 * @param {*} options.setter.oldVal The old value
 * @param {*} options.setter.record The record hosting the change
 * @param {function(*, *, *, function=)=} options.validator If you want a validator to run before settings values, pass this guy in
 * @param {*} options.validator.newVal The new value
 * @param {*} options.validator.oldVal The old value
 * @param {*} options.validator.record The record hosting the change
 * @param {function(err)=} options.validator.callback If the validator is asynchronous, then pass your value back here, otherwise pass it back as a return value.
 * When you use an asynchronous instance, pass the error in the first value and then the rest of the parameters are yours to play with
 * @param {boolean=} options.validatorAsync When true (not truthy) the validator is treated asynchornously and returns a promise with your value.
 * @returns {*}
 */
exports.bind = function ( path, record, options ) {
    options = sys.extend( {}, dataBinderOptions, options );
    var context = record;
    var lastParent = context;
    var parts = path.split( probe.delimiter );
    var lastPartName = path;
    var lastParentName;

    sys.each( parts, function ( part ) {
        lastParentName = part;
        lastParent = context;
        context = context[part];
        lastPartName = part;
        if ( sys.isNull( context ) || sys.isUndefined( context ) ) {
            context = {};
        }
    } );

    if ( lastParent === context ) {
        setUpBindings( record, lastPartName );
    } else {
        setUpBindings( lastParent, lastPartName );
    }

    function setUpBindings( mountPoint, mountName ) {
        mountPoint["__" + mountName + "__"] = mountPoint[mountName];
        Object.defineProperty( mountPoint, mountName, {
            get : function () {
                if ( sys.isFunction( options.getter ) ) {
                    var promise;
                    if ( options.getterAsync === true ) {
                        promise = Promise.denodeify( options.getter );
                    }

                    if ( promise ) {
                        return promise( mountPoint["__" + mountName + "__"] ).then( function ( val ) {
                            mountPoint["__" + mountName + "__"] = val;
                        } );
                    } else {
                        mountPoint["__" + mountName + "__"] = options.getter( mountPoint["__" + mountName + "__"] );
                        return mountPoint["__" + mountName + "__"];
                    }

                } else {
                    return mountPoint["__" + mountName + "__"];
                }
            },
            set : function ( val ) {
                async.waterfall( [
                    function ( done ) {
                        if ( sys.isFunction( options.validator ) ) {
                            if ( options.validatorAsync ) {
                                options.validator( val, mountPoint["__" + mountName + "__"], record, done );
                            } else {
                                var res = options.validator( val, mountPoint["__" + mountName + "__"], record );
                                if ( res === true ) {
                                    done();
                                } else {
                                    done( res );
                                }
                            }
                        } else {
                            done();
                        }
                    },
                    function ( done ) {
                        if ( sys.isFunction( options.setter ) ) {
                            if ( options.setterAsync === true ) {
                                options.setter( val, mountPoint["__" + mountName + "__"], record, done );
                            } else {
                                done( null, options.setter( val, mountPoint["__" + mountName + "__"], record ) );
                            }
                        } else {
                            done( null, val );
                        }
                    }
                ], function ( err, newVal ) {
                    if ( err ) { throw new Error( err ); }
                    mountPoint["__" + mountName + "__"] = newVal;
                } );

            }
        } );
    }

    return context;
};