feat(frontend): complete next.js 15 frontend application with ai-centric travel planning ui

[BjornMelin]

Overview

Complete implementation of the TripSage frontend application using Next.js 15, React 19, and modern AI-centric design patterns. This issue consolidates the massive frontend development scope outlined in TODO.md into a comprehensive implementation plan.

Background

The frontend represents a critical component of the TripSage MVP, requiring modern technologies and AI-first design patterns to support the refactored backend architecture (LangGraph agents, direct SDK integrations, Mem0 memory system).

Technology Stack

• Framework: Next.js 15.3+ with App Router
• React: React 19+ with Server Components
• TypeScript: 5.5+ with strict mode
• Styling: Tailwind CSS v4 with OKLCH colors
• Components: shadcn/ui v3 (latest)
• State: Zustand v5 for client state
• Data Fetching: TanStack Query v5 for server state
• AI Integration: Vercel AI SDK v5 for streaming
• Testing: Vitest + React Testing Library + Playwright
• Performance: Turbopack for development

Implementation Phases

Phase 1: Foundation & Core Setup (Weeks 1-2)

• Project Initialization

  • Initialize Next.js 15.3+ project with App Router
  • Configure TypeScript 5.5+ with strict mode
  • Set up ESLint 9 with modern configurations
  • Configure Biome for formatting and linting
  • Set up Turbopack for development

• Styling & Component System

  • Configure Tailwind CSS v4 with OKLCH color system
  • Install and configure shadcn/ui v3 components
  • Create enhanced design system with CVA (class-variance-authority)
  • Implement dark/light theme support
  • Create travel-specific component library

• State Management Architecture

  • Configure Zustand v5 stores (User, Trip, Chat, Agent Status, Search, Budget, Currency, Deals, API Keys)
  • Set up TanStack Query v5 for server state management
  • Create type-safe API client with proper error handling
  • Implement optimistic updates and cache management

Phase 2: Authentication & Security (BYOK) (Weeks 3-4)

• API Key Management (BYOK)

  • Build secure API key input components with auto-clear functionality
  • Implement client-side key validation patterns
  • Create comprehensive key status display (without revealing keys)
  • Add key rotation dialogs with expiration warnings
  • Implement secure session management with timeouts
  • Create CSP headers for sensitive pages
  • Build audit log visualization components

• Authentication System

  • Integrate with backend authentication endpoints
  • Implement secure session handling
  • Create authentication flow components
  • Add multi-factor authentication support
  • Build user profile management interface

Phase 3: AI Chat Interface (Weeks 5-6)

• Core Chat Implementation

  • Integrate Vercel AI SDK v5 for streaming responses
  • Build chat interface with Vercel AI SDK patterns
  • Implement streaming responses with typing indicators
  • Create rich content rendering (markdown, code blocks)
  • Add message history with search capabilities
  • Build conversation management system

• Agent Status & Visualization

  • Create agent status monitoring components
  • Build real-time task tracking and progress display
  • Implement resource usage monitoring
  • Add activity logging capabilities
  • Create session management for agents
  • Build agent handoff visualization

• Advanced Chat Features

  • File and image upload capabilities
  • Voice input/output support (scheduled for integration)
  • Chat export functionality
  • Message attachments handling
  • Context preservation across sessions

Phase 4: Error Boundaries & Loading States (Weeks 7-8)

• Next.js 15 Error Handling

  • Implement App Router error boundaries (error.tsx, global-error.tsx)
  • Create production-ready error reporting with errorService
  • Build comprehensive error fallback components with recovery options
  • Integrate enhanced error tracking and user feedback

• Advanced Loading States

  • Build comprehensive loading states using CVA
  • Develop travel-specific skeleton components (flights, hotels, trips)
  • Add route-level loading states (loading.tsx files)
  • Create enhanced loading animations and transitions
  • Implement progressive loading patterns

Phase 5: Travel Planning Features (Weeks 9-12)

• Search & Discovery

  • Build accommodation search interface
  • Create flight search forms with advanced filtering
  • Implement destination search with recommendations
  • Add activity search and booking interface
  • Integrate weather display for destinations

• Trip Planning Workflow

  • Create itinerary timeline component with drag-and-drop
  • Build trip planning wizard with step-by-step guidance
  • Implement collaborative trip planning features
  • Add trip comparison and analysis tools
  • Create trip sharing and export functionality

• Visual Integration

  • Integrate Mapbox GL for trip visualization
  • Add interactive maps with route planning
  • Create location-based recommendations
  • Build photo galleries and media management
  • Implement virtual tour integration

Phase 6: Budget & Financial Features (Weeks 13-16)

• Budget Management

  • Create comprehensive budget tracking dashboard
  • Build expense management with receipt capture
  • Implement currency conversion with real-time rates
  • Add cost splitting functionality for group travel
  • Create budget alerts and spending notifications

• Financial Analysis

  • Build budget overview and reporting
  • Create spending pattern analysis
  • Add price comparison tools
  • Implement fare alerts and price tracking
  • Build financial goal setting and tracking

Phase 7: State & API Integration (Weeks 17-18)

• Backend Integration

  • Connect all components to refactored backend APIs
  • Integrate with LangGraph agent endpoints
  • Connect to Mem0 memory system for personalization
  • Integrate with direct SDK services
  • Handle real-time updates and synchronization

• Data Management

  • Implement comprehensive error handling patterns
  • Add retry logic with exponential backoff
  • Create offline support strategies
  • Build data synchronization mechanisms
  • Implement caching strategies with React Query

Phase 8: Performance Optimization (Weeks 19-20)

• Core Web Vitals Optimization

  • Implement code splitting and lazy loading
  • Configure Next.js Image optimization
  • Set up advanced caching with React Query
  • Optimize bundle size with tree shaking
  • Ensure Core Web Vitals compliance

• Advanced Performance

  • Implement service worker for offline functionality
  • Add performance monitoring and analytics
  • Create bundle analysis and optimization
  • Implement memory leak prevention
  • Add performance budgets and monitoring

Phase 9: Testing & Quality (Weeks 21-22)

• Comprehensive Testing

  • Unit tests with Vitest and React Testing Library
  • Integration tests for all major workflows
  • E2E tests with Playwright for critical paths
  • Visual regression testing setup
  • Accessibility testing with axe-core

• Quality Assurance

  • Performance testing and optimization
  • Browser compatibility testing
  • Mobile responsive testing
  • Security testing and validation
  • User experience testing and feedback

Phase 10: Deployment & Monitoring (Weeks 23-24)

• Production Deployment

  • Configure Vercel deployment with optimal settings
  • Set up environment-specific configurations
  • Implement monitoring dashboards
  • Add error tracking with Sentry
  • Create performance monitoring

• Analytics & Insights

  • Integrate PostHog analytics
  • Set up user behavior tracking
  • Create conversion funnel analysis
  • Implement A/B testing framework
  • Add business metrics dashboards

Key Features Implementation

AI-Centric Design

// Enhanced chat interface with AI SDK v5
import { useChat } from 'ai/react'
import { AgentStatusPanel } from '@/components/agent-status-panel'

export function ChatInterface() {
  const { messages, input, handleInputChange, handleSubmit, isLoading } = useChat({
    api: '/api/chat',
    streamMode: 'stream-data'
  })
  
  return (
    <div className="flex h-screen">
      <ChatMessages messages={messages} />
      <AgentStatusPanel />
      <ChatInput 
        input={input}
        onChange={handleInputChange}
        onSubmit={handleSubmit}
        isLoading={isLoading}
      />
    </div>
  )
}

State Management Architecture

// Zustand store with TypeScript
import { create } from 'zustand'
import { TripState, ChatState, AgentState } from '@/types'

interface AppState {
  trip: TripState
  chat: ChatState
  agents: AgentState
  updateTrip: (trip: Partial<TripState>) => void
  addMessage: (message: ChatMessage) => void
  updateAgentStatus: (status: AgentStatus) => void
}

export const useAppStore = create<AppState>((set) => ({
  // State implementation
}))

Travel-Specific Components

// Enhanced trip timeline with agent integration
export function TripTimeline({ tripId }: { tripId: string }) {
  const { data: trip } = useTripQuery(tripId)
  const agentStatus = useAgentStatus()
  
  return (
    <div className="space-y-4">
      <TripTimelineHeader trip={trip} />
      <AgentRecommendations tripId={tripId} />
      <TripItinerary items={trip.itinerary} />
      <BudgetTracker budget={trip.budget} />
    </div>
  )
}

Performance Targets

Core Web Vitals

• First Contentful Paint (FCP): <1.2s
• Largest Contentful Paint (LCP): <2.5s
• Cumulative Layout Shift (CLS): <0.1
• First Input Delay (FID): <100ms
• Time to Interactive (TTI): <3.5s

Bundle Optimization

• Initial Bundle Size: <250KB gzipped
• Route Chunks: <100KB gzipped per route
• Image Optimization: WebP/AVIF with Next.js Image
• Code Splitting: Automatic route-based + manual component-based

Testing Strategy

Coverage Targets

• Unit Tests: 90%+ coverage (Vitest + Testing Library)
• Integration Tests: All major user flows
• E2E Tests: Critical paths with Playwright
• Performance Tests: Core Web Vitals validation
• Accessibility: WCAG 2.1 AA compliance

Test Architecture

// Example test structure
describe('TripPlanningWorkflow', () => {
  it('should create trip with agent assistance', async () => {
    // Test agent-assisted trip creation
  })
  
  it('should handle memory-based personalization', async () => {
    // Test Mem0 integration
  })
  
  it('should recover from errors gracefully', async () => {
    // Test error boundaries and recovery
  })
})

Acceptance Criteria

Functional

• All 8 phases implemented and tested
• Integration with all refactored backend services
• AI-centric travel planning workflow complete
• BYOK security implementation working
• Real-time agent status monitoring functional
• Comprehensive error handling and recovery

Performance

• Core Web Vitals targets met
• Bundle size optimized
• 90%+ test coverage achieved
• Accessibility compliance verified
• Mobile responsive design complete

Business

• Travel planning workflow intuitive and efficient
• AI features enhance user experience
• Budget management fully functional
• Collaboration features working
• Analytics and monitoring operational

Timeline

24 weeks - Comprehensive frontend development with parallel backend integration

Dependencies

• Backend refactoring completion (Issues feat(agents): migrate to LangGraph for 70% complexity reduction and 2-5x performance #161, [UPDATED] Complete MCP to SDK Migration - 6 Services Remaining #159, feat(database): consolidate to supabase with pgvector for superior performance #146, feat: implement crawl4ai direct SDK integration to replace firecrawl #139)
• API endpoints stable and documented
• Authentication system implemented
• Design system and branding guidelines

References

• TODO.md Frontend Implementation section
• Backend API documentation
• Design system requirements
• Performance optimization guidelines
• Testing strategy documentation