keyed_container.js

'use strict';

var nestedProperty = require('./nested_property');

var SIMPLE_PROPERTY_REGEX = /^\w*$/;

// bitmask for deciding what's updated. Sometimes the name needs to be updated,
// sometimes the value needs to be updated, and sometimes both do. This is just
// a simple way to track what's updated such that it's a simple OR operation to
// assimilate new updates.
//
// The only exception is the UNSET bit that tracks when we need to explicitly
// unset and remove the property. This concrn arises because of the special
// way in which nestedProperty handles null/undefined. When you specify `null`,
// it prunes any unused items in the tree. I ran into some issues with it getting
// null vs undefined confused, so UNSET is just a bit that forces the property
// update to send `null`, removing the property explicitly rather than setting
// it to undefined.
var NONE = 0;
var NAME = 1;
var VALUE = 2;
var BOTH = 3;
var UNSET = 4;

module.exports = function keyedContainer(baseObj, path, keyName, valueName) {
    keyName = keyName || 'name';
    valueName = valueName || 'value';
    var i, arr, baseProp;
    var changeTypes = {};

    if(path && path.length) {
        baseProp = nestedProperty(baseObj, path);
        arr = baseProp.get();
    } else {
        arr = baseObj;
    }

    path = path || '';

    // Construct an index:
    var indexLookup = {};
    if(arr) {
        for(i = 0; i < arr.length; i++) {
            indexLookup[arr[i][keyName]] = i;
        }
    }

    var isSimpleValueProp = SIMPLE_PROPERTY_REGEX.test(valueName);

    var obj = {
        set: function(name, value) {
            var changeType = value === null ? UNSET : NONE;

            // create the base array if necessary
            if(!arr) {
                if(!baseProp || changeType === UNSET) return;

                arr = [];
                baseProp.set(arr);
            }

            var idx = indexLookup[name];
            if(idx === undefined) {
                if(changeType === UNSET) return;

                changeType = changeType | BOTH;
                idx = arr.length;
                indexLookup[name] = idx;
            } else if(value !== (isSimpleValueProp ? arr[idx][valueName] : nestedProperty(arr[idx], valueName).get())) {
                changeType = changeType | VALUE;
            }

            var newValue = arr[idx] = arr[idx] || {};
            newValue[keyName] = name;

            if(isSimpleValueProp) {
                newValue[valueName] = value;
            } else {
                nestedProperty(newValue, valueName).set(value);
            }

            // If it's not an unset, force that bit to be unset. This is all related to the fact
            // that undefined and null are a bit specially implemented in nestedProperties.
            if(value !== null) {
                changeType = changeType & ~UNSET;
            }

            changeTypes[idx] = changeTypes[idx] | changeType;

            return obj;
        },
        get: function(name) {
            if(!arr) return;

            var idx = indexLookup[name];

            if(idx === undefined) {
                return undefined;
            } else if(isSimpleValueProp) {
                return arr[idx][valueName];
            } else {
                return nestedProperty(arr[idx], valueName).get();
            }
        },
        rename: function(name, newName) {
            var idx = indexLookup[name];

            if(idx === undefined) return obj;
            changeTypes[idx] = changeTypes[idx] | NAME;

            indexLookup[newName] = idx;
            delete indexLookup[name];

            arr[idx][keyName] = newName;

            return obj;
        },
        remove: function(name) {
            var idx = indexLookup[name];

            if(idx === undefined) return obj;

            var object = arr[idx];
            if(Object.keys(object).length > 2) {
                // This object contains more than just the key/value, so unset
                // the value without modifying the entry otherwise:
                changeTypes[idx] = changeTypes[idx] | VALUE;
                return obj.set(name, null);
            }

            if(isSimpleValueProp) {
                for(i = idx; i < arr.length; i++) {
                    changeTypes[i] = changeTypes[i] | BOTH;
                }
                for(i = idx; i < arr.length; i++) {
                    indexLookup[arr[i][keyName]]--;
                }
                arr.splice(idx, 1);
                delete(indexLookup[name]);
            } else {
                // Perform this update *strictly* so we can check whether the result's
                // been pruned. If so, it's a removal. If not, it's a value unset only.
                nestedProperty(object, valueName).set(null);

                // Now check if the top level nested property has any keys left. If so,
                // the object still has values so we only want to unset the key. If not,
                // the entire object can be removed since there's no other data.
                // var topLevelKeys = Object.keys(object[valueName.split('.')[0]] || []);

                changeTypes[idx] = changeTypes[idx] | VALUE | UNSET;
            }

            return obj;
        },
        constructUpdate: function() {
            var astr, idx;
            var update = {};
            var changed = Object.keys(changeTypes);
            for(var i = 0; i < changed.length; i++) {
                idx = changed[i];
                astr = path + '[' + idx + ']';
                if(arr[idx]) {
                    if(changeTypes[idx] & NAME) {
                        update[astr + '.' + keyName] = arr[idx][keyName];
                    }
                    if(changeTypes[idx] & VALUE) {
                        if(isSimpleValueProp) {
                            update[astr + '.' + valueName] = (changeTypes[idx] & UNSET) ? null : arr[idx][valueName];
                        } else {
                            update[astr + '.' + valueName] = (changeTypes[idx] & UNSET) ? null : nestedProperty(arr[idx], valueName).get();
                        }
                    }
                } else {
                    update[astr] = null;
                }
            }

            return update;
        }
    };

    return obj;
};