var readSaveStateMachine = function()

in JSLib/src/cache.js [1189:1280]
58 lines of code
16 McCabe index (conditional complexity)

        var readSaveStateMachine = function (operation, opTargetState, cacheState, data, isPrefetch) {
            /// <summary>State machine describing the behavior for reading and saving data into the cache.</summary>
            /// <param name="operation" type="DataCacheOperation">Operation being run.</param>
            /// <param name="opTargetState" type="Object">Operation state to transition to.</param>
            /// <param name="cacheState" type="Object">Current cache state.</param>
            /// <param name="data" type="Object" optional="true">Additional data passed to the state.</param>
            /// <param name="isPrefetch" type="Boolean">Flag indicating whether a read (false) or prefetch (true) operation is running.
            /// <remarks>
            /// This state machine contains behavior common to read and prefetch operations.
            /// </remarks>

            var error = operation.error;
            var transition = operation.transition;
            var wait = operation.wait;
            var request;

            switch (opTargetState) {
                case OPERATION_STATE_END:
                    // State that signals the operation is done.
                    fireOnIdle();
                    break;

                case READ_STATE_LOCAL:
                    // State that requests for a page from the local store.
                    // Data is expected to be the index of the page to request.
                    request = readPage(data).then(function (found, page) {
                        // Signal the cache that a read operation is running.
                        if (!operation.canceled) {
                            if (found) {
                                // The page is in the local store, check if the operation can be resolved.
                                transition(READ_STATE_DONE, page);
                            } else {
                                // The page is not in the local store, request it from the source.
                                transition(READ_STATE_SOURCE, data);
                            }
                        }
                    });
                    break;

                case READ_STATE_SOURCE:
                    // State that requests for a page from the cache source.
                    // Data is expected to be the index of the page to request.
                    request = fetchPage(data).then(function (page) {
                        // Signal the cache that a read operation is running.
                        if (!operation.canceled) {
                            // Update the stats and save the page to the local store.
                            if (isPrefetch) {
                                stats.prefetches++;
                            } else {
                                stats.netReads++;
                            }
                            transition(READ_STATE_SAVE, page);
                        }
                    }, error);
                    break;

                case READ_STATE_SAVE:
                    // State that saves a  page to the local store.
                    // Data is expected to be the page to save.
                    // Write access to the store is exclusive.
                    if (cacheState !== CACHE_STATE_WRITE) {
                        changeState(CACHE_STATE_WRITE);
                        request = savePage(data.i, data).then(function (saved) {
                            if (!operation.canceled) {
                                if (!saved && isPrefetch) {
                                    operation.pending = 0;
                                }
                                // Check if the operation can be resolved.
                                transition(READ_STATE_DONE, data);
                            }
                            changeState(CACHE_STATE_IDLE);
                        });
                    }
                    break;

                default:
                    // Unknown state that can't be handled by this state machine.
                    return false;
            }

            if (request) {
                // The operation might have been canceled between stack frames do to the async calls.
                if (operation.canceled) {
                    request.cancel();
                } else if (operation.s === opTargetState) {
                    // Wait for the request to complete.
                    wait(request);
                }
            }

            return true;
        };