attribute/js/AttributeCore.js

/**
 * The attribute module provides an augmentable Attribute implementation, which
 * adds configurable attributes and attribute change events to the class being
 * augmented. It also provides a State class, which is used internally by Attribute,
 * but can also be used independently to provide a name/property/value data structure to
 * store state.
 *
 * @module attribute
 */

/**
 * The attribute-core submodule provides the lightest level of attribute handling support
 * without Attribute change events, or lesser used methods such as reset(), modifyAttrs(),
 * and removeAttr().
 *
 * @module attribute
 * @submodule attribute-core
 */
var O = Y.Object,
    Lang = Y.Lang,

    DOT = ".",

    // Externally configurable props
    GETTER = "getter",
    SETTER = "setter",
    READ_ONLY = "readOnly",
    WRITE_ONCE = "writeOnce",
    INIT_ONLY = "initOnly",
    VALIDATOR = "validator",
    VALUE = "value",
    VALUE_FN = "valueFn",
    LAZY_ADD = "lazyAdd",

    // Used for internal state management
    ADDED = "added",
    BYPASS_PROXY = "_bypassProxy",
    INITIALIZING = "initializing",
    INIT_VALUE = "initValue",
    LAZY = "lazy",
    IS_LAZY_ADD = "isLazyAdd",

    INVALID_VALUE;

/**
 * <p>
 * AttributeCore provides the lightest level of configurable attribute support. It is designed to be
 * augmented on to a host class, and provides the host with the ability to configure
 * attributes to store and retrieve state, <strong>but without support for attribute change events</strong>.
 * </p>
 * <p>For example, attributes added to the host can be configured:</p>
 * <ul>
 *     <li>As read only.</li>
 *     <li>As write once.</li>
 *     <li>With a setter function, which can be used to manipulate
 *     values passed to Attribute's <a href="#method_set">set</a> method, before they are stored.</li>
 *     <li>With a getter function, which can be used to manipulate stored values,
 *     before they are returned by Attribute's <a href="#method_get">get</a> method.</li>
 *     <li>With a validator function, to validate values before they are stored.</li>
 * </ul>
 *
 * <p>See the <a href="#method_addAttr">addAttr</a> method, for the complete set of configuration
 * options available for attributes.</p>
 *
 * <p>Object/Classes based on AttributeCore can augment <a href="AttributeEvents.html">AttributeEvents</a>
 * (with true for overwrite) and <a href="AttributeExtras.html">AttributeExtras</a> to add attribute event and
 * additional, less commonly used attribute methods, such as `modifyAttr`, `removeAttr` and `reset`.</p>
 *
 * @class AttributeCore
 * @param attrs {Object} The attributes to add during construction (passed through to <a href="#method_addAttrs">addAttrs</a>). These can also be defined on the constructor being augmented with Attribute by defining the ATTRS property on the constructor.
 * @param values {Object} The initial attribute values to apply (passed through to <a href="#method_addAttrs">addAttrs</a>). These are not merged/cloned. The caller is responsible for isolating user provided values if required.
 * @param lazy {boolean} Whether or not to add attributes lazily (passed through to <a href="#method_addAttrs">addAttrs</a>).
 */
function AttributeCore(attrs, values, lazy) {
    this._initAttrHost(attrs, values, lazy);
}

/**
 * <p>The value to return from an attribute setter in order to prevent the set from going through.</p>
 *
 * <p>You can return this value from your setter if you wish to combine validator and setter
 * functionality into a single setter function, which either returns the massaged value to be stored or
 * AttributeCore.INVALID_VALUE to prevent invalid values from being stored.</p>
 *
 * @property INVALID_VALUE
 * @type Object
 * @static
 * @final
 */
AttributeCore.INVALID_VALUE = {};
INVALID_VALUE = AttributeCore.INVALID_VALUE;

/**
 * The list of properties which can be configured for
 * each attribute (e.g. setter, getter, writeOnce etc.).
 *
 * This property is used internally as a whitelist for faster
 * Y.mix operations.
 *
 * @property _ATTR_CFG
 * @type Array
 * @static
 * @protected
 */
AttributeCore._ATTR_CFG = [SETTER, GETTER, VALIDATOR, VALUE, VALUE_FN, WRITE_ONCE, READ_ONLY, LAZY_ADD, BYPASS_PROXY];

AttributeCore.prototype = {

    /**
     * Constructor logic for attributes. Initializes the host state, and sets up the inital attributes passed to the
     * constructor.
     *
     * @method _initAttrHost
     * @param attrs {Object} The attributes to add during construction (passed through to <a href="#method_addAttrs">addAttrs</a>). These can also be defined on the constructor being augmented with Attribute by defining the ATTRS property on the constructor.
     * @param values {Object} The initial attribute values to apply (passed through to <a href="#method_addAttrs">addAttrs</a>). These are not merged/cloned. The caller is responsible for isolating user provided values if required.
     * @param lazy {boolean} Whether or not to add attributes lazily (passed through to <a href="#method_addAttrs">addAttrs</a>).
     * @private
     */
    _initAttrHost : function(attrs, values, lazy) {
        this._state = new Y.State();
        this._initAttrs(attrs, values, lazy);
    },

    /**
     * <p>
     * Adds an attribute with the provided configuration to the host object.
     * </p>
     * <p>
     * The config argument object supports the following properties:
     * </p>
     *
     * <dl>
     *    <dt>value &#60;Any&#62;</dt>
     *    <dd>The initial value to set on the attribute</dd>
     *
     *    <dt>valueFn &#60;Function | String&#62;</dt>
     *    <dd>
     *    <p>A function, which will return the initial value to set on the attribute. This is useful
     *    for cases where the attribute configuration is defined statically, but needs to
     *    reference the host instance ("this") to obtain an initial value. If both the value and valueFn properties are defined,
     *    the value returned by the valueFn has precedence over the value property, unless it returns undefined, in which
     *    case the value property is used.</p>
     *
     *    <p>valueFn can also be set to a string, representing the name of the instance method to be used to retrieve the value.</p>
     *    </dd>
     *
     *    <dt>readOnly &#60;boolean&#62;</dt>
     *    <dd>Whether or not the attribute is read only. Attributes having readOnly set to true
     *        cannot be modified by invoking the set method.</dd>
     *
     *    <dt>writeOnce &#60;boolean&#62; or &#60;string&#62;</dt>
     *    <dd>
     *        Whether or not the attribute is "write once". Attributes having writeOnce set to true,
     *        can only have their values set once, be it through the default configuration,
     *        constructor configuration arguments, or by invoking set.
     *        <p>The writeOnce attribute can also be set to the string "initOnly", in which case the attribute can only be set during initialization
     *        (when used with Base, this means it can only be set during construction)</p>
     *    </dd>
     *
     *    <dt>setter &#60;Function | String&#62;</dt>
     *    <dd>
     *    <p>The setter function used to massage or normalize the value passed to the set method for the attribute.
     *    The value returned by the setter will be the final stored value. Returning
     *    <a href="#property_Attribute.INVALID_VALUE">Attribute.INVALID_VALUE</a>, from the setter will prevent
     *    the value from being stored.
     *    </p>
     *
     *    <p>setter can also be set to a string, representing the name of the instance method to be used as the setter function.</p>
     *    </dd>
     *
     *    <dt>getter &#60;Function | String&#62;</dt>
     *    <dd>
     *    <p>
     *    The getter function used to massage or normalize the value returned by the get method for the attribute.
     *    The value returned by the getter function is the value which will be returned to the user when they
     *    invoke get.
     *    </p>
     *
     *    <p>getter can also be set to a string, representing the name of the instance method to be used as the getter function.</p>
     *    </dd>
     *
     *    <dt>validator &#60;Function | String&#62;</dt>
     *    <dd>
     *    <p>
     *    The validator function invoked prior to setting the stored value. Returning
     *    false from the validator function will prevent the value from being stored.
     *    </p>
     *
     *    <p>validator can also be set to a string, representing the name of the instance method to be used as the validator function.</p>
     *    </dd>
     *
     *    <dt>lazyAdd &#60;boolean&#62;</dt>
     *    <dd>Whether or not to delay initialization of the attribute until the first call to get/set it.
     *    This flag can be used to over-ride lazy initialization on a per attribute basis, when adding multiple attributes through
     *    the <a href="#method_addAttrs">addAttrs</a> method.</dd>
     *
     * </dl>
     *
     * <p>The setter, getter and validator are invoked with the value and name passed in as the first and second arguments, and with
     * the context ("this") set to the host object.</p>
     *
     * <p>Configuration properties outside of the list mentioned above are considered private properties used internally by attribute,
     * and are not intended for public use.</p>
     *
     * @method addAttr
     *
     * @param {String} name The name of the attribute.
     * @param {Object} config An object with attribute configuration property/value pairs, specifying the configuration for the attribute.
     *
     * <p>
     * <strong>NOTE:</strong> The configuration object is modified when adding an attribute, so if you need
     * to protect the original values, you will need to merge the object.
     * </p>
     *
     * @param {boolean} lazy (optional) Whether or not to add this attribute lazily (on the first call to get/set).
     *
     * @return {Object} A reference to the host object.
     *
     * @chainable
     */
    addAttr: function(name, config, lazy) {

        Y.log('Adding attribute: ' + name, 'info', 'attribute');

        var host = this, // help compression
            state = host._state,
            value,
            hasValue;

        config = config || {};

        lazy = (LAZY_ADD in config) ? config[LAZY_ADD] : lazy;

        if (lazy && !host.attrAdded(name)) {
            state.addAll(name, {
                lazy : config,
                added : true
            });
        } else {

            if (host.attrAdded(name) && !state.get(name, IS_LAZY_ADD)) { Y.log('Attribute: ' + name + ' already exists. Cannot add it again without removing it first', 'warn', 'attribute'); }

            if (!host.attrAdded(name) || state.get(name, IS_LAZY_ADD)) {

                hasValue = (VALUE in config);

                if (config.readOnly && !hasValue) { Y.log('readOnly attribute: ' + name + ', added without an initial value. Value will be set on initial call to set', 'warn', 'attribute');}

                if (hasValue) {
                    // We'll go through set, don't want to set value in config directly
                    value = config.value;
                    delete config.value;
                }

                config.added = true;
                config.initializing = true;

                state.addAll(name, config);

                if (hasValue) {
                    // Go through set, so that raw values get normalized/validated
                    host.set(name, value);
                }

                state.remove(name, INITIALIZING);
            }
        }

        return host;
    },

    /**
     * Checks if the given attribute has been added to the host
     *
     * @method attrAdded
     * @param {String} name The name of the attribute to check.
     * @return {boolean} true if an attribute with the given name has been added, false if it hasn't. This method will return true for lazily added attributes.
     */
    attrAdded: function(name) {
        return !!this._state.get(name, ADDED);
    },

    /**
     * Returns the current value of the attribute. If the attribute
     * has been configured with a 'getter' function, this method will delegate
     * to the 'getter' to obtain the value of the attribute.
     *
     * @method get
     *
     * @param {String} name The name of the attribute. If the value of the attribute is an Object,
     * dot notation can be used to obtain the value of a property of the object (e.g. <code>get("x.y.z")</code>)
     *
     * @return {Any} The value of the attribute
     */
    get : function(name) {
        return this._getAttr(name);
    },

    /**
     * Checks whether or not the attribute is one which has been
     * added lazily and still requires initialization.
     *
     * @method _isLazyAttr
     * @private
     * @param {String} name The name of the attribute
     * @return {boolean} true if it's a lazily added attribute, false otherwise.
     */
    _isLazyAttr: function(name) {
        return this._state.get(name, LAZY);
    },

    /**
     * Finishes initializing an attribute which has been lazily added.
     *
     * @method _addLazyAttr
     * @private
     * @param {Object} name The name of the attribute
     */
    _addLazyAttr: function(name, cfg) {
        var state = this._state,
            lazyCfg = state.get(name, LAZY);

        state.add(name, IS_LAZY_ADD, true);
        state.remove(name, LAZY);
        this.addAttr(name, lazyCfg);
    },

    /**
     * Sets the value of an attribute.
     *
     * @method set
     * @chainable
     *
     * @param {String} name The name of the attribute. If the
     * current value of the attribute is an Object, dot notation can be used
     * to set the value of a property within the object (e.g. <code>set("x.y.z", 5)</code>).
     *
     * @param {Any} value The value to set the attribute to.
     *
     * @return {Object} A reference to the host object.
     */
    set : function(name, val) {
        return this._setAttr(name, val);
    },

    /**
     * Allows setting of readOnly/writeOnce attributes. See <a href="#method_set">set</a> for argument details.
     *
     * @method _set
     * @protected
     * @chainable
     *
     * @param {String} name The name of the attribute.
     * @param {Any} val The value to set the attribute to.
     * @return {Object} A reference to the host object.
     */
    _set : function(name, val) {
        return this._setAttr(name, val, null, true);
    },

    /**
     * Provides the common implementation for the public set and protected _set methods.
     *
     * See <a href="#method_set">set</a> for argument details.
     *
     * @method _setAttr
     * @protected
     * @chainable
     *
     * @param {String} name The name of the attribute.
     * @param {Any} value The value to set the attribute to.
     * @param {Object} opts (Optional) Optional event data to be mixed into
     * the event facade passed to subscribers of the attribute's change event.
     * This is currently a hack. There's no real need for the AttributeCore implementation
     * to support this parameter, but breaking it out into AttributeEvents, results in
     * additional function hops for the critical path. May change in 3.5.0 PR3.
     * @param {boolean} force If true, allows the caller to set values for
     * readOnly or writeOnce attributes which have already been set.
     *
     * @return {Object} A reference to the host object.
     */
    _setAttr : function(name, val, opts, force)  {

        // HACK - no real reason core needs to know about opts, but
        // it adds fn hops if we want to break it out.
        // Not sure it's worth it for this critical path

        var allowSet = true,
            state = this._state,
            stateProxy = this._stateProxy,
            cfg,
            initialSet,
            strPath,
            path,
            currVal,
            writeOnce,
            initializing;

        if (name.indexOf(DOT) !== -1) {
            strPath = name;
            path = name.split(DOT);
            name = path.shift();
        }

        if (this._isLazyAttr(name)) {
            this._addLazyAttr(name);
        }

        cfg = state.getAll(name, true) || {};

        initialSet = (!(VALUE in cfg));

        if (stateProxy && name in stateProxy && !cfg._bypassProxy) {
            // TODO: Value is always set for proxy. Can we do any better? Maybe take a snapshot as the initial value for the first call to set?
            initialSet = false;
        }

        writeOnce = cfg.writeOnce;
        initializing = cfg.initializing;

        if (!initialSet && !force) {

            if (writeOnce) {
                Y.log('Set attribute:' + name + ', aborted; Attribute is writeOnce', 'warn', 'attribute');
                allowSet = false;
            }

            if (cfg.readOnly) {
                Y.log('Set attribute:' + name + ', aborted; Attribute is readOnly', 'warn', 'attribute');
                allowSet = false;
            }
        }

        if (!initializing && !force && writeOnce === INIT_ONLY) {
            Y.log('Set attribute:' + name + ', aborted; Attribute is writeOnce: "initOnly"', 'warn', 'attribute');
            allowSet = false;
        }

        if (allowSet) {
            // Don't need currVal if initialSet (might fail in custom getter if it always expects a non-undefined/non-null value)
            if (!initialSet) {
                currVal =  this.get(name);
            }

            if (path) {
               val = O.setValue(Y.clone(currVal), path, val);

               if (val === undefined) {
                   Y.log('Set attribute path:' + strPath + ', aborted; Path is invalid', 'warn', 'attribute');
                   allowSet = false;
               }
            }

            if (allowSet) {
                if (!this._fireAttrChange || initializing) {
                    this._setAttrVal(name, strPath, currVal, val);
                } else {
                    // HACK - no real reason core needs to know about _fireAttrChange, but
                    // it adds fn hops if we want to break it out. Not sure it's worth it for this critical path
                    this._fireAttrChange(name, strPath, currVal, val, opts);
                }
            }
        }

        return this;
    },

    /**
     * Provides the common implementation for the public get method,
     * allowing Attribute hosts to over-ride either method.
     *
     * See <a href="#method_get">get</a> for argument details.
     *
     * @method _getAttr
     * @protected
     * @chainable
     *
     * @param {String} name The name of the attribute.
     * @return {Any} The value of the attribute.
     */
    _getAttr : function(name) {
        var host = this, // help compression
            fullName = name,
            state = host._state,
            path,
            getter,
            val,
            cfg;

        if (name.indexOf(DOT) !== -1) {
            path = name.split(DOT);
            name = path.shift();
        }

        // On Demand - Should be rare - handles out of order valueFn references
        if (host._tCfgs && host._tCfgs[name]) {
            cfg = {};
            cfg[name] = host._tCfgs[name];
            delete host._tCfgs[name];
            host._addAttrs(cfg, host._tVals);
        }

        // Lazy Init
        if (host._isLazyAttr(name)) {
            host._addLazyAttr(name);
        }

        val = host._getStateVal(name);

        getter = state.get(name, GETTER);

        if (getter && !getter.call) {
            getter = this[getter];
        }

        val = (getter) ? getter.call(host, val, fullName) : val;
        val = (path) ? O.getValue(val, path) : val;

        return val;
    },

    /**
     * Gets the stored value for the attribute, from either the
     * internal state object, or the state proxy if it exits
     *
     * @method _getStateVal
     * @private
     * @param {String} name The name of the attribute
     * @return {Any} The stored value of the attribute
     */
    _getStateVal : function(name) {
        var stateProxy = this._stateProxy;
        return stateProxy && (name in stateProxy) && !this._state.get(name, BYPASS_PROXY) ? stateProxy[name] : this._state.get(name, VALUE);
    },

    /**
     * Sets the stored value for the attribute, in either the
     * internal state object, or the state proxy if it exits
     *
     * @method _setStateVal
     * @private
     * @param {String} name The name of the attribute
     * @param {Any} value The value of the attribute
     */
    _setStateVal : function(name, value) {
        var stateProxy = this._stateProxy;
        if (stateProxy && (name in stateProxy) && !this._state.get(name, BYPASS_PROXY)) {
            stateProxy[name] = value;
        } else {
            this._state.add(name, VALUE, value);
        }
    },

    /**
     * Updates the stored value of the attribute in the privately held State object,
     * if validation and setter passes.
     *
     * @method _setAttrVal
     * @private
     * @param {String} attrName The attribute name.
     * @param {String} subAttrName The sub-attribute name, if setting a sub-attribute property ("x.y.z").
     * @param {Any} prevVal The currently stored value of the attribute.
     * @param {Any} newVal The value which is going to be stored.
     *
     * @return {booolean} true if the new attribute value was stored, false if not.
     */
    _setAttrVal : function(attrName, subAttrName, prevVal, newVal) {

        var host = this,
            allowSet = true,
            cfg = this._state.getAll(attrName, true) || {},
            validator = cfg.validator,
            setter = cfg.setter,
            initializing = cfg.initializing,
            prevRawVal = this._getStateVal(attrName),
            name = subAttrName || attrName,
            retVal,
            valid;

        if (validator) {
            if (!validator.call) {
                // Assume string - trying to keep critical path tight, so avoiding Lang check
                validator = this[validator];
            }
            if (validator) {
                valid = validator.call(host, newVal, name);

                if (!valid && initializing) {
                    newVal = cfg.defaultValue;
                    valid = true; // Assume it's valid, for perf.
                }
            }
        }

        if (!validator || valid) {
            if (setter) {
                if (!setter.call) {
                    // Assume string - trying to keep critical path tight, so avoiding Lang check
                    setter = this[setter];
                }
                if (setter) {
                    retVal = setter.call(host, newVal, name);

                    if (retVal === INVALID_VALUE) {
                        Y.log('Attribute: ' + attrName + ', setter returned Attribute.INVALID_VALUE for value:' + newVal, 'warn', 'attribute');
                        allowSet = false;
                    } else if (retVal !== undefined){
                        Y.log('Attribute: ' + attrName + ', raw value: ' + newVal + ' modified by setter to:' + retVal, 'info', 'attribute');
                        newVal = retVal;
                    }
                }
            }

            if (allowSet) {
                if(!subAttrName && (newVal === prevRawVal) && !Lang.isObject(newVal)) {
                    Y.log('Attribute: ' + attrName + ', value unchanged:' + newVal, 'warn', 'attribute');
                    allowSet = false;
                } else {
                    // Store value
                    if (!(INIT_VALUE in cfg)) {
                        cfg.initValue = newVal;
                    }
                    host._setStateVal(attrName, newVal);
                }
            }

        } else {
            Y.log('Attribute:' + attrName + ', Validation failed for value:' + newVal, 'warn', 'attribute');
            allowSet = false;
        }

        return allowSet;
    },

    /**
     * Sets multiple attribute values.
     *
     * @method setAttrs
     * @param {Object} attrs  An object with attributes name/value pairs.
     * @return {Object} A reference to the host object.
     * @chainable
     */
    setAttrs : function(attrs) {
        return this._setAttrs(attrs);
    },

    /**
     * Implementation behind the public setAttrs method, to set multiple attribute values.
     *
     * @method _setAttrs
     * @protected
     * @param {Object} attrs  An object with attributes name/value pairs.
     * @return {Object} A reference to the host object.
     * @chainable
     */
    _setAttrs : function(attrs) {
        for (var attr in attrs) {
            if ( attrs.hasOwnProperty(attr) ) {
                this.set(attr, attrs[attr]);
            }
        }
        return this;
    },

    /**
     * Gets multiple attribute values.
     *
     * @method getAttrs
     * @param {Array | boolean} attrs Optional. An array of attribute names. If omitted, all attribute values are
     * returned. If set to true, all attributes modified from their initial values are returned.
     * @return {Object} An object with attribute name/value pairs.
     */
    getAttrs : function(attrs) {
        return this._getAttrs(attrs);
    },

    /**
     * Implementation behind the public getAttrs method, to get multiple attribute values.
     *
     * @method _getAttrs
     * @protected
     * @param {Array | boolean} attrs Optional. An array of attribute names. If omitted, all attribute values are
     * returned. If set to true, all attributes modified from their initial values are returned.
     * @return {Object} An object with attribute name/value pairs.
     */
    _getAttrs : function(attrs) {
        var host = this,
            o = {},
            i, l, attr, val,
            modifiedOnly = (attrs === true);

        // TODO - figure out how to get all "added"
        attrs = (attrs && !modifiedOnly) ? attrs : O.keys(host._state.data);

        for (i = 0, l = attrs.length; i < l; i++) {
            // Go through get, to honor cloning/normalization
            attr = attrs[i];
            val = host.get(attr);

            if (!modifiedOnly || host._getStateVal(attr) != host._state.get(attr, INIT_VALUE)) {
                o[attr] = host.get(attr);
            }
        }

        return o;
    },

    /**
     * Configures a group of attributes, and sets initial values.
     *
     * <p>
     * <strong>NOTE:</strong> This method does not isolate the configuration object by merging/cloning.
     * The caller is responsible for merging/cloning the configuration object if required.
     * </p>
     *
     * @method addAttrs
     * @chainable
     *
     * @param {Object} cfgs An object with attribute name/configuration pairs.
     * @param {Object} values An object with attribute name/value pairs, defining the initial values to apply.
     * Values defined in the cfgs argument will be over-written by values in this argument unless defined as read only.
     * @param {boolean} lazy Whether or not to delay the intialization of these attributes until the first call to get/set.
     * Individual attributes can over-ride this behavior by defining a lazyAdd configuration property in their configuration.
     * See <a href="#method_addAttr">addAttr</a>.
     *
     * @return {Object} A reference to the host object.
     */
    addAttrs : function(cfgs, values, lazy) {
        var host = this; // help compression
        if (cfgs) {
            host._tCfgs = cfgs;
            host._tVals = host._normAttrVals(values);
            host._addAttrs(cfgs, host._tVals, lazy);
            host._tCfgs = host._tVals = null;
        }

        return host;
    },

    /**
     * Implementation behind the public addAttrs method.
     *
     * This method is invoked directly by get if it encounters a scenario
     * in which an attribute's valueFn attempts to obtain the
     * value an attribute in the same group of attributes, which has not yet
     * been added (on demand initialization).
     *
     * @method _addAttrs
     * @private
     * @param {Object} cfgs An object with attribute name/configuration pairs.
     * @param {Object} values An object with attribute name/value pairs, defining the initial values to apply.
     * Values defined in the cfgs argument will be over-written by values in this argument unless defined as read only.
     * @param {boolean} lazy Whether or not to delay the intialization of these attributes until the first call to get/set.
     * Individual attributes can over-ride this behavior by defining a lazyAdd configuration property in their configuration.
     * See <a href="#method_addAttr">addAttr</a>.
     */
    _addAttrs : function(cfgs, values, lazy) {
        var host = this, // help compression
            attr,
            attrCfg,
            value;

        for (attr in cfgs) {
            if (cfgs.hasOwnProperty(attr)) {

                // Not Merging. Caller is responsible for isolating configs
                attrCfg = cfgs[attr];
                attrCfg.defaultValue = attrCfg.value;

                // Handle simple, complex and user values, accounting for read-only
                value = host._getAttrInitVal(attr, attrCfg, host._tVals);

                if (value !== undefined) {
                    attrCfg.value = value;
                }

                if (host._tCfgs[attr]) {
                    delete host._tCfgs[attr];
                }

                host.addAttr(attr, attrCfg, lazy);
            }
        }
    },

    /**
     * Utility method to protect an attribute configuration
     * hash, by merging the entire object and the individual
     * attr config objects.
     *
     * @method _protectAttrs
     * @protected
     * @param {Object} attrs A hash of attribute to configuration object pairs.
     * @return {Object} A protected version of the attrs argument.
     */
    _protectAttrs : function(attrs) {
        if (attrs) {
            attrs = Y.merge(attrs);
            for (var attr in attrs) {
                if (attrs.hasOwnProperty(attr)) {
                    attrs[attr] = Y.merge(attrs[attr]);
                }
            }
        }
        return attrs;
    },

    /**
     * Utility method to normalize attribute values. The base implementation
     * simply merges the hash to protect the original.
     *
     * @method _normAttrVals
     * @param {Object} valueHash An object with attribute name/value pairs
     *
     * @return {Object}
     *
     * @private
     */
    _normAttrVals : function(valueHash) {
        return (valueHash) ? Y.merge(valueHash) : null;
    },

    /**
     * Returns the initial value of the given attribute from
     * either the default configuration provided, or the
     * over-ridden value if it exists in the set of initValues
     * provided and the attribute is not read-only.
     *
     * @param {String} attr The name of the attribute
     * @param {Object} cfg The attribute configuration object
     * @param {Object} initValues The object with simple and complex attribute name/value pairs returned from _normAttrVals
     *
     * @return {Any} The initial value of the attribute.
     *
     * @method _getAttrInitVal
     * @private
     */
    _getAttrInitVal : function(attr, cfg, initValues) {
        var val, valFn;
        // init value is provided by the user if it exists, else, provided by the config
        if (!cfg.readOnly && initValues && initValues.hasOwnProperty(attr)) {
            val = initValues[attr];
        } else {
            val = cfg.value;
            valFn = cfg.valueFn;

            if (valFn) {
                if (!valFn.call) {
                    valFn = this[valFn];
                }
                if (valFn) {
                    val = valFn.call(this, attr);
                }
            }
        }

        Y.log('initValue for ' + attr + ':' + val, 'info', 'attribute');

        return val;
    },

    /**
     * Utility method to set up initial attributes defined during construction, either through the constructor.ATTRS property, or explicitly passed in.
     *
     * @method _initAttrs
     * @protected
     * @param attrs {Object} The attributes to add during construction (passed through to <a href="#method_addAttrs">addAttrs</a>). These can also be defined on the constructor being augmented with Attribute by defining the ATTRS property on the constructor.
     * @param values {Object} The initial attribute values to apply (passed through to <a href="#method_addAttrs">addAttrs</a>). These are not merged/cloned. The caller is responsible for isolating user provided values if required.
     * @param lazy {boolean} Whether or not to add attributes lazily (passed through to <a href="#method_addAttrs">addAttrs</a>).
     */
    _initAttrs : function(attrs, values, lazy) {
        // ATTRS support for Node, which is not Base based
        attrs = attrs || this.constructor.ATTRS;

        var Base = Y.Base,
            BaseCore = Y.BaseCore,
            baseInst = (Base && Y.instanceOf(this, Base)),
            baseCoreInst = (!baseInst && BaseCore && Y.instanceOf(this, BaseCore));

        if ( attrs && !baseInst && !baseCoreInst) {
            this.addAttrs(this._protectAttrs(attrs), values, lazy);
        }
    }
};

Y.AttributeCore = AttributeCore;