var readSaveStateMachine = function()

in lib/cache.js [1291:1373]
58 lines of code
16 McCabe index (conditional complexity)

    var readSaveStateMachine = function (operation, opTargetState, cacheState, data, isPrefetch) {

        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;
    };