data-cursor/lib/getCursor.js

Javascript Library to traverse nested structures and modify in place without mutating data

'use strict';

Object.defineProperty(exports, "__esModule", {
    value: true
});
exports.default = getCursor;

var _Operations = require('./Operations');

var CURSOR_SYMBOL = '@@IS_CURSOR' + Math.random();

var isOperationInProcess = false;
var currentOperationName = '';
var operationPath = null;
var initialOperationArgs = null;

function _getCursor(currentValue, operations, changeParentProperty, transactionDescriptor, currentPathKey, isRoot) {
    var mutableValue = null;
    var mutableValueCreated = false;
    var isSetMutableValueToParent = false;

    function checkTransactionState() {
        if (transactionDescriptor.isClosed) {
            throw new Error('Cursor is closed becauze transaction ended');
        }
    }

    var childChangeParentProperty = function childChangeParentProperty(key, newValue, prevValue) {
        if (cursor.get(key).value() === prevValue) {
            cursor.set(key, newValue);
        }
    };

    function getMutableValue() {
        if (!mutableValueCreated) {
            mutableValue = operations.getMutableVersionForValue(currentValue);
            mutableValueCreated = true;
        }

        return mutableValue;
    }

    var lastSetValue = currentValue;

    var operators = operations.getOperatorsForValue(currentValue);

    function getNestedCursor(keyPath, value) {
        return _getCursor(value, operations, childChangeParentProperty, transactionDescriptor, keyPath, false);
    }

    function updateMutableValue(newValue) {
        mutableValue = operations.getMutableVersionForValue(newValue);
        mutableValueCreated = true;

        return mutableValue;
    }

    function changeThisInParent(newValue) {
        if (isRoot) {
            changeParentProperty(newValue, lastSetValue, operationPath, currentOperationName, initialOperationArgs);
        } else {
            changeParentProperty(currentPathKey, newValue, lastSetValue, operationPath, currentOperationName, initialOperationArgs);
        }
    }

    var cursor = operators.reduce(function (accum, _ref) {
        var key = _ref.key;
        var value = _ref.value;

        accum[key] = function () {
            for (var _len = arguments.length, args = Array(_len), _key = 0; _key < _len; _key++) {
                args[_key] = arguments[_key];
            }

            if (!isOperationInProcess) {
                checkTransactionState();

                isOperationInProcess = true;

                initialOperationArgs = args;
                currentOperationName = key;

                operationPath = [];
            }

            if (!isRoot) {
                operationPath.push(currentPathKey);
            }

            var result = value({
                cursor: cursor,
                args: args,

                getNestedCursor: getNestedCursor,
                getMutableValue: getMutableValue,
                updateMutableValue: updateMutableValue,
                changeThisInParent: changeThisInParent,

                getValue: function getValue() {
                    return mutableValueCreated ? mutableValue : currentValue;
                }
            });

            isOperationInProcess = false;
            initialOperationArgs = null;
            operationPath = null;
            currentOperationName = '';

            return result;
        };

        return accum;
    }, {});

    Object.defineProperty(cursor, CURSOR_SYMBOL, {
        value: true,
        writable: false,
        enumerable: false
    });

    return cursor;
}

function getCursor(currentValue) {
    var operations = arguments.length <= 1 || arguments[1] === undefined ? _Operations.defaultOperations : arguments[1];
    var changeParentProperty = arguments.length <= 2 || arguments[2] === undefined ? function () {} : arguments[2];
    var transactionDescriptor = arguments.length <= 3 || arguments[3] === undefined ? { isClosed: false } : arguments[3];

    return _getCursor(currentValue, operations, changeParentProperty, transactionDescriptor, '', true);
}