Redux Middleware

Middleware in MistWarp extends Redux functionality by intercepting actions before they reach reducers. This enables features like VM synchronization, persistence, logging, and async operations.

Store Configuration

Basic Setup

import { createStore, applyMiddleware, compose } from 'redux';
import thunk from 'redux-thunk';
import rootReducer from './reducers';

// Configure store
const configureStore = (initialState) => {
  const composeEnhancers = 
    window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ || compose;
  
  return createStore(
    rootReducer,
    initialState,
    composeEnhancers(applyMiddleware(thunk))
  );
};

export default configureStore;

Development Tools

Redux DevTools configuration for development:

// Redux DevTools configuration
const devToolsConfig = {
  // Limit action history
  maxAge: 50,
  
  // Trace actions
  trace: true,
  
  // Serialize state
  serialize: {
    options: {
      undefined: true,
      function: true
    }
  },
  
  // Action sanitizer
  actionSanitizer: (action) => ({
    ...action,
    // Remove large payloads from dev tools
    payload: action.type.includes('ASSET_') ? 
      '[Asset Data]' : action.payload
  }),
  
  // State sanitizer
  stateSanitizer: (state) => ({
    ...state,
    // Hide sensitive data
    assets: '[Assets Hidden]'
  })
};

Custom Middleware

VM Middleware

Synchronizes Redux actions with the Virtual Machine:

// src/middleware/vm-middleware.js
const vmMiddleware = (vm) => (store) => (next) => (action) => {
  const result = next(action);
  
  // Sync certain actions with VM
  switch (action.type) {
    case 'SET_EDITING_TARGET':
      vm.setEditingTarget(action.targetId);
      break;
      
    case 'SET_TURBO_MODE':
      vm.setTurboMode(action.turboMode);
      break;
      
    case 'SET_COMPATIBLE_MODE':
      vm.setCompatibilityMode(action.compatibilityMode);
      break;
  }
  
  return result;
};

export default vmMiddleware;

Persistence Middleware

Automatically saves certain state changes to localStorage:

// src/middleware/persistence-middleware.js
const persistenceMiddleware = (store) => (next) => (action) => {
  const result = next(action);
  
  // Persist certain state changes
  const persistActions = [
    'SET_THEME',
    'SET_STAGE_SIZE',
    'SET_ADDON_ENABLED',
    'SET_ADDON_SETTINGS'
  ];
  
  if (persistActions.includes(action.type)) {
    const state = store.getState();
    localStorage.setItem('mistwarp-settings', JSON.stringify({
      theme: state.gui.theme,
      stageSize: state.gui.stage.stageSize,
      addons: state.addons
    }));
  }
  
  return result;
};

export default persistenceMiddleware;

State Synchronization

VM Listener

Handles bidirectional communication between Redux store and VM:

// src/lib/vm-listener.js
class VMListener {
  constructor(store) {
    this.store = store;
    this.vm = null;
  }
  
  attachVM(vm) {
    this.vm = vm;
    this.setupVMListeners();
  }
  
  setupVMListeners() {
    this.vm.on('targetsUpdate', this.handleTargetsUpdate.bind(this));
    this.vm.on('MONITORS_UPDATE', this.handleMonitorsUpdate.bind(this));
    this.vm.on('PROJECT_LOADED', this.handleProjectLoaded.bind(this));
    this.vm.on('PROJECT_CHANGED', this.handleProjectChanged.bind(this));
  }
  
  handleTargetsUpdate(data) {
    this.store.dispatch({
      type: 'UPDATE_TARGETS',
      targets: data.targetList,
      editingTarget: data.editingTarget
    });
  }
  
  handleMonitorsUpdate(monitors) {
    this.store.dispatch({
      type: 'UPDATE_MONITORS',
      monitors: monitors
    });
  }
  
  handleProjectLoaded() {
    this.store.dispatch({
      type: 'SET_PROJECT_LOADING',
      isLoading: false
    });
    
    this.store.dispatch({
      type: 'SET_SAVE_STATE',
      saveState: 'SAVED'
    });
  }
  
  handleProjectChanged() {
    this.store.dispatch({
      type: 'SET_SAVE_STATE',
      saveState: 'NOT_SAVED'
    });
  }
}

export default VMListener;

Asset Loading Middleware

Handles asynchronous asset loading:

// src/middleware/asset-middleware.js
const assetMiddleware = (assetManager) => (store) => (next) => (action) => {
  if (action.type === 'LOAD_ASSET_REQUEST') {
    // Dispatch loading state
    store.dispatch({
      type: 'SET_ASSET_LOADING',
      assetId: action.assetId,
      isLoading: true
    });
    
    // Load asset asynchronously
    assetManager.loadAsset(action.assetId)
      .then(assetData => {
        store.dispatch({
          type: 'LOAD_ASSET_SUCCESS',
          assetId: action.assetId,
          data: assetData
        });
      })
      .catch(error => {
        store.dispatch({
          type: 'LOAD_ASSET_ERROR',
          assetId: action.assetId,
          error: error.message
        });
      });
  }
  
  return next(action);
};

export default assetMiddleware;

Development Middleware

Action Logger

Logs all actions in development mode:

// Development middleware for action logging
const actionLogger = (store) => (next) => (action) => {
  if (process.env.NODE_ENV === 'development') {
    console.group(`Action: ${action.type}`);
    console.log('Payload:', action);
    console.log('Previous State:', store.getState());
    
    const result = next(action);
    
    console.log('New State:', store.getState());
    console.groupEnd();
    
    return result;
  }
  
  return next(action);
};

export default actionLogger;

Performance Monitor

Tracks action performance:

const performanceMiddleware = (store) => (next) => (action) => {
  const start = performance.now();
  
  const result = next(action);
  
  const end = performance.now();
  const duration = end - start;
  
  if (duration > 10) { // Log slow actions
    console.warn(`Slow action: ${action.type} took ${duration.toFixed(2)}ms`);
  }
  
  return result;
};

Error Handling

Error Boundary Middleware

Catches and handles errors in actions:

const errorMiddleware = (store) => (next) => (action) => {
  try {
    return next(action);
  } catch (error) {
    console.error('Redux action error:', error);
    
    // Dispatch error action
    store.dispatch({
      type: 'GLOBAL_ERROR',
      error: {
        message: error.message,
        stack: error.stack,
        action: action.type
      }
    });
    
    // Prevent state corruption
    return { type: 'ERROR_HANDLED' };
  }
};

Async Operations

Thunk Actions

Using redux-thunk for async operations:

// src/actions/project-actions.js
export const loadProject = (projectId) => {
  return async (dispatch, getState) => {
    dispatch({ type: 'SET_PROJECT_LOADING', isLoading: true });
    
    try {
      const projectData = await fetch(`/api/projects/${projectId}`).then(r => r.json());
      
      dispatch({
        type: 'SET_PROJECT',
        project: projectData
      });
      
      dispatch({ type: 'SET_PROJECT_LOADING', isLoading: false });
      
    } catch (error) {
      dispatch({
        type: 'SET_PROJECT_ERROR',
        error: error.message
      });
    }
  };
};

Saga Pattern

For complex async workflows:

// src/middleware/saga-middleware.js
const sagaMiddleware = (store) => (next) => (action) => {
  const result = next(action);
  
  // Handle saga actions
  if (action.meta && action.meta.saga) {
    const saga = action.meta.saga;
    runSaga(saga, action, store);
  }
  
  return result;
};

const runSaga = async (saga, action, store) => {
  try {
    const generator = saga(action);
    let next = generator.next();
    
    while (!next.done) {
      const effect = next.value;
      
      if (effect.type === 'CALL') {
        const result = await effect.fn(...effect.args);
        next = generator.next(result);
      } else if (effect.type === 'PUT') {
        store.dispatch(effect.action);
        next = generator.next();
      }
    }
  } catch (error) {
    store.dispatch({
      type: 'SAGA_ERROR',
      error: error.message,
      saga: saga.name
    });
  }
};

Testing Middleware

Middleware Testing

import vmMiddleware from '../middleware/vm-middleware';

describe('VM Middleware', () => {
  let mockVM, store, next, middleware;
  
  beforeEach(() => {
    mockVM = {
      setEditingTarget: jest.fn(),
      setTurboMode: jest.fn()
    };
    
    store = { getState: jest.fn() };
    next = jest.fn();
    middleware = vmMiddleware(mockVM)(store)(next);
  });
  
  test('should call VM methods for relevant actions', () => {
    const action = { type: 'SET_EDITING_TARGET', targetId: 'sprite1' };
    
    middleware(action);
    
    expect(next).toHaveBeenCalledWith(action);
    expect(mockVM.setEditingTarget).toHaveBeenCalledWith('sprite1');
  });
  
  test('should pass through unrelated actions', () => {
    const action = { type: 'UNRELATED_ACTION' };
    
    middleware(action);
    
    expect(next).toHaveBeenCalledWith(action);
    expect(mockVM.setEditingTarget).not.toHaveBeenCalled();
  });
});

Best Practices

Middleware Order

The order of middleware matters:

const store = createStore(
  rootReducer,
  applyMiddleware(
    errorMiddleware,      // First: catch all errors
    actionLogger,        // Second: log actions
    persistenceMiddleware, // Third: handle persistence
    vmMiddleware(vm),    // Fourth: sync with VM
    thunk               // Last: handle async actions
  )
);

Performance Considerations

• Keep middleware lightweight
• Avoid expensive operations in middleware
• Use debouncing for frequent actions:

const debounceMiddleware = (store) => (next) => {
  const debounced = new Map();
  
  return (action) => {
    if (action.meta && action.meta.debounce) {
      const key = `${action.type}_${action.meta.key || 'default'}`;
      
      if (debounced.has(key)) {
        clearTimeout(debounced.get(key));
      }
      
      debounced.set(key, setTimeout(() => {
        next(action);
        debounced.delete(key);
      }, action.meta.debounce));
      
      return action;
    }
    
    return next(action);
  };
};

Middleware provides powerful hooks into Redux's action flow, enabling cross-cutting concerns like logging, persistence, and VM synchronization while keeping reducers pure and focused.