feat: TypeScript migration for high-impact areas

[devin-ai-integration]

feat: TypeScript migration for high-impact areas

Summary

This PR migrates the core Redux infrastructure and state management from JavaScript to TypeScript, focusing on high-impact areas as requested. The migration includes:

• Redux store configuration (configureStore.js → .ts) with proper typing for middleware, enhancers, and dynamic reducer injection
• Main app reducer (reducer.js → .ts) with typed actions and state interfaces
• Saga functions (saga.js → .ts) with Redux-Saga effect typing and API integration
• Global state type definitions (RootState.ts) with interfaces for the application state structure
• API type definitions (api.ts) for request/response structures
• TypeScript configuration (tsconfig.json) with incremental migration settings (strict: false)

The migration maintains existing functionality while adding type safety to the most critical parts of the application. TypeScript compilation passes successfully with npx tsc --noEmit.

Review & Testing Checklist for Human

• Verify API interfaces match actual responses - Check that the API types in app/types/api.ts accurately reflect real API responses, especially for login, currencies, messages, and notifications endpoints
• Test Redux state management - Confirm that all Redux actions, reducers, and selectors work correctly with the new typing, particularly state updates and action dispatching
• Test saga error handling - Verify that saga functions still handle errors properly after removing JSX syntax and replacing with direct message objects
• Build and run the application - Ensure the app builds and runs correctly in your environment (I encountered Node.js version compatibility issues that prevented full testing)
• Verify type accuracy - Check that the state interfaces in RootState.ts match your actual application state structure

Recommended test plan: Start the development server, log in, navigate through the dashboard, trigger some API calls (currencies, messages, notifications), and verify no runtime errors occur.

---

Diagram

%%{ init : { "theme" : "default" }}%%
graph TD
    tsconfig["tsconfig.json<br/>(TypeScript config)"]:::major-edit
    
    configureStore["app/utils/<br/>configureStore.ts"]:::major-edit
    reducers["app/utils/<br/>reducers.ts"]:::major-edit
    
    appReducer["app/containers/App/<br/>reducer.ts"]:::major-edit
    appSaga["app/containers/App/<br/>saga.ts"]:::major-edit
    
    rootState["app/types/<br/>RootState.ts"]:::major-edit
    apiTypes["app/types/<br/>api.ts"]:::major-edit
    moduleDeclarations["app/types/<br/>modules.d.ts"]:::major-edit
    
    appJs["app/app.js<br/>(entry point)"]:::context
    selectors["app/containers/App/<br/>selectors.js"]:::context
    
    configureStore --> reducers
    reducers --> appReducer
    configureStore --> appSaga
    appReducer --> rootState
    appSaga --> apiTypes
    appJs --> configureStore
    appReducer --> selectors
    
    tsconfig -.-> configureStore
    tsconfig -.-> reducers
    tsconfig -.-> appReducer
    tsconfig -.-> appSaga
    
    moduleDeclarations -.-> appSaga
    moduleDeclarations -.-> reducers
    
    subgraph Legend
        L1["Major Edit"]:::major-edit
        L2["Minor Edit"]:::minor-edit
        L3["Context/No Edit"]:::context
    end

classDef major-edit fill:#90EE90
classDef minor-edit fill:#87CEEB
classDef context fill:#FFFFFF

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Notes

• Incremental migration approach: Used "strict": false in tsconfig.json to allow gradual migration while maintaining compatibility with existing JavaScript modules
• Module declarations: Created modules.d.ts to handle imports from JavaScript files that haven't been converted yet, using any types where necessary
• JSX removal: Replaced JSX syntax in saga files with direct message object references to avoid TypeScript parsing issues
• Environment issues: Encountered Node.js/webpack compatibility issues during testing that appear to be pre-existing and unrelated to the TypeScript changes
• Type safety: All TypeScript compilation passes successfully, but some type assumptions should be verified against actual runtime data

Link to Devin run: https://app.devin.ai/sessions/6d160aeba1e14dad88df72258cf9744c
Requested by: @akkp-windsurf (Arthur Poon)

[devin-ai-integration]

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