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⚡ Developer Learning Path

Technical Integration, API Development & Blockchain Implementation


🎯 Learning Path Overview

This comprehensive technical path covers API integration, blockchain development, smart contract interaction, and custom application development with the CAU Checking App platform.

Prerequisites: Basic programming knowledge (JavaScript, Python, or similar) Estimated Time: 6-8 hours total Target Audience: Software developers, blockchain developers, system integrators Outcome: Full-stack integration capabilities with production-ready code examples


📚 Module 1: API Authentication & Setup

Duration: 60 minutes

What You'll Learn

Step-by-Step Guide

1.1 Understanding the API Architecture

The CAU Checking App exposes a comprehensive REST API with the following structure:

https://api.contracting.app/v1/
├── /auth/           # Authentication endpoints
├── /projects/       # Project management
├── /contracts/      # Smart contract operations
├── /payments/       # Payment processing
├── /users/          # User management
├── /organizations/  # Organization endpoints
├── /documents/      # File and document handling
├── /messaging/      # Communication systems
└── /blockchain/     # Blockchain operations

1.2 API Authentication Setup

Three authentication methods available:

  1. API Key Authentication (Recommended for server-to-server)
# Get your API key from Settings > API Keys
curl -H "Authorization: Bearer YOUR_API_KEY" \
     https://api.contracting.app/v1/projects
  1. OAuth 2.0 (For user-facing applications)
// OAuth flow example
const oauth = {
    client_id: 'your_client_id',
    redirect_uri: 'https://yourapp.com/callback',
    scope: 'read:projects write:payments',
    response_type: 'code'
};

window.location.href = `https://contracting.app/oauth/authorize?${new URLSearchParams(oauth)}`;
  1. JWT Tokens (For web applications)
// Login and get JWT
const response = await fetch('https://api.contracting.app/v1/auth/login', {
    method: 'POST',
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({
        email: 'your@email.com',
        password: 'your_password'
    })
});

const { access_token } = await response.json();
localStorage.setItem('token', access_token);

1.3 Development Environment Setup

Local development configuration:

# Clone starter template
git clone https://github.com/cau-checking/api-starter-kit.git
cd api-starter-kit

# Install dependencies
npm install  # or pip install -r requirements.txt for Python

# Environment configuration
cp .env.example .env

.env configuration:

# CAU Checking App API Configuration
API_BASE_URL=https://api.contracting.app/v1
API_KEY=your_api_key_here
CLIENT_ID=your_oauth_client_id
CLIENT_SECRET=your_oauth_client_secret

# Development settings
DEBUG=true
LOG_LEVEL=debug
RATE_LIMIT_REQUESTS=1000

Practice Exercise: Set up authentication and make your first API call to retrieve user profile information.


📚 Module 2: Core API Integration

Duration: 90 minutes

What You'll Learn

Step-by-Step Guide

2.1 Project Management API

Complete project lifecycle through API:

// Create a new project
async function createProject() {
    const projectData = {
        name: "Downtown Office Complex",
        description: "50-story commercial building",
        type: "commercial",
        budget: 25000000,
        phases: [
            { name: "Foundation", percentage: 25, duration_weeks: 8 },
            { name: "Structure", percentage: 35, duration_weeks: 16 },
            { name: "Systems", percentage: 25, duration_weeks: 12 },
            { name: "Finishing", percentage: 15, duration_weeks: 10 }
        ],
        team_members: [
            { email: "pm@contractor.com", role: "project_manager" },
            { email: "super@contractor.com", role: "supervisor" }
        ]
    };

    const response = await fetch(`${API_BASE_URL}/projects`, {
        method: 'POST',
        headers: {
            'Authorization': `Bearer ${API_KEY}`,
            'Content-Type': 'application/json'
        },
        body: JSON.stringify(projectData)
    });

    const project = await response.json();
    console.log('Project created:', project);
    return project;
}

// Update project progress
async function updateProjectProgress(projectId, phaseId, completionPercent) {
    const update = {
        phase_id: phaseId,
        completion_percentage: completionPercent,
        notes: "Progress update via API",
        updated_by: "system"
    };

    const response = await fetch(`${API_BASE_URL}/projects/${projectId}/progress`, {
        method: 'PUT',
        headers: {
            'Authorization': `Bearer ${API_KEY}`,
            'Content-Type': 'application/json'
        },
        body: JSON.stringify(update)
    });

    return response.json();
}

2.2 Payment Processing Integration

Handle payment workflows programmatically:

// Process electronic check payment
async function processECheckPayment(paymentData) {
    const payment = {
        recipient: {
            name: "ABC Subcontractors",
            account_number: "123456789",
            routing_number: "021000021",
            account_type: "checking"
        },
        amount: 15000.00,
        currency: "USD",
        description: "Foundation completion payment",
        project_id: "proj_123456",
        phase_id: "phase_001",
        payment_date: "2024-01-15"
    };

    const response = await fetch(`${API_BASE_URL}/payments/echeck`, {
        method: 'POST',
        headers: {
            'Authorization': `Bearer ${API_KEY}`,
            'Content-Type': 'application/json'
        },
        body: JSON.stringify(payment)
    });

    return response.json();
}

// Track payment status
async function trackPaymentStatus(paymentId) {
    const response = await fetch(`${API_BASE_URL}/payments/${paymentId}/status`, {
        headers: { 'Authorization': `Bearer ${API_KEY}` }
    });

    const status = await response.json();
    console.log('Payment Status:', status);

    // Status can be: scheduled, processing, completed, failed, cancelled
    return status;
}

2.3 Document Management API

Handle file uploads and document management:

// Upload project document
async function uploadProjectDocument(projectId, file, documentType) {
    const formData = new FormData();
    formData.append('file', file);
    formData.append('document_type', documentType);
    formData.append('project_id', projectId);

    const response = await fetch(`${API_BASE_URL}/documents/upload`, {
        method: 'POST',
        headers: {
            'Authorization': `Bearer ${API_KEY}`
            // Note: Don't set Content-Type for FormData
        },
        body: formData
    });

    return response.json();
}

// Get project documents
async function getProjectDocuments(projectId, filters = {}) {
    const params = new URLSearchParams({
        project_id: projectId,
        ...filters
    });

    const response = await fetch(`${API_BASE_URL}/documents?${params}`, {
        headers: { 'Authorization': `Bearer ${API_KEY}` }
    });

    return response.json();
}

2.4 Webhook Configuration

Set up real-time event notifications:

// Configure webhooks for project events
async function setupWebhooks() {
    const webhookConfig = {
        url: "https://yourapp.com/webhooks/cau-checking",
        events: [
            "project.updated",
            "payment.completed", 
            "payment.failed",
            "contract.signed",
            "document.uploaded"
        ],
        secret: "your_webhook_secret_key"
    };

    const response = await fetch(`${API_BASE_URL}/webhooks`, {
        method: 'POST',
        headers: {
            'Authorization': `Bearer ${API_KEY}`,
            'Content-Type': 'application/json'
        },
        body: JSON.stringify(webhookConfig)
    });

    return response.json();
}

// Webhook handler example (Express.js)
app.post('/webhooks/cau-checking', (req, res) => {
    const signature = req.headers['x-cau-signature'];
    const payload = JSON.stringify(req.body);

    // Verify webhook signature
    const expectedSignature = crypto
        .createHmac('sha256', WEBHOOK_SECRET)
        .update(payload)
        .digest('hex');

    if (signature === expectedSignature) {
        handleWebhookEvent(req.body);
        res.status(200).send('OK');
    } else {
        res.status(401).send('Unauthorized');
    }
});

Integration Exercise: Build a simple project dashboard that displays real-time project updates using webhooks.


📚 Module 3: Blockchain Integration & Smart Contracts

Duration: 120 minutes

What You'll Learn

Step-by-Step Guide

3.1 Web3 Setup and Wallet Integration

Connect to blockchain networks:

// Web3 initialization
import Web3 from 'web3';

class BlockchainManager {
    constructor() {
        this.web3 = null;
        this.account = null;
        this.networkId = null;
    }

    async connect() {
        if (typeof window.ethereum !== 'undefined') {
            this.web3 = new Web3(window.ethereum);

            try {
                // Request account access
                const accounts = await window.ethereum.request({
                    method: 'eth_requestAccounts'
                });

                this.account = accounts[0];
                this.networkId = await this.web3.eth.net.getId();

                console.log('Connected to:', this.account);
                return true;
            } catch (error) {
                console.error('User denied account access');
                return false;
            }
        } else {
            console.error('MetaMask not detected');
            return false;
        }
    }

    async switchNetwork(networkId) {
        const networks = {
            1: { // Ethereum Mainnet
                chainId: '0x1',
                chainName: 'Ethereum Mainnet',
                rpcUrls: ['https://mainnet.infura.io/v3/YOUR_PROJECT_ID']
            },
            1329: { // SEI Network
                chainId: '0x531',
                chainName: 'SEI Network',
                rpcUrls: ['https://evm-rpc.sei-apis.com'],
                nativeCurrency: {
                    name: 'SEI',
                    symbol: 'SEI',
                    decimals: 18
                }
            }
        };

        const network = networks[networkId];
        if (!network) throw new Error('Unsupported network');

        try {
            await window.ethereum.request({
                method: 'wallet_switchEthereumChain',
                params: [{ chainId: network.chainId }]
            });
        } catch (switchError) {
            // Add network if not exists
            if (switchError.code === 4902) {
                await window.ethereum.request({
                    method: 'wallet_addEthereumChain',
                    params: [network]
                });
            }
        }
    }
}

3.2 Smart Contract Interaction

Deploy and interact with construction contracts:

// Construction Contract ABI (simplified)
const CONSTRUCTION_CONTRACT_ABI = [
    {
        "inputs": [
            {"name": "projectName", "type": "string"},
            {"name": "totalValue", "type": "uint256"},
            {"name": "phases", "type": "uint256[]"},
            {"name": "participants", "type": "address[]"}
        ],
        "name": "createProject",
        "outputs": [{"name": "projectId", "type": "uint256"}],
        "type": "function"
    },
    {
        "inputs": [
            {"name": "projectId", "type": "uint256"},
            {"name": "phaseIndex", "type": "uint256"}
        ],
        "name": "approvePhase",
        "outputs": [],
        "type": "function"
    },
    {
        "inputs": [
            {"name": "projectId", "type": "uint256"},
            {"name": "phaseIndex", "type": "uint256"},
            {"name": "amount", "type": "uint256"}
        ],
        "name": "releasePayment",
        "outputs": [],
        "type": "function"
    }
];

class SmartContractManager {
    constructor(web3, contractAddress) {
        this.web3 = web3;
        this.contract = new web3.eth.Contract(CONSTRUCTION_CONTRACT_ABI, contractAddress);
    }

    async createProject(projectData) {
        const { name, totalValue, phases, participants } = projectData;

        try {
            const gasEstimate = await this.contract.methods
                .createProject(name, totalValue, phases, participants)
                .estimateGas({ from: this.web3.eth.defaultAccount });

            const result = await this.contract.methods
                .createProject(name, totalValue, phases, participants)
                .send({
                    from: this.web3.eth.defaultAccount,
                    gas: gasEstimate,
                    gasPrice: await this.web3.eth.getGasPrice()
                });

            console.log('Project created:', result);
            return result;
        } catch (error) {
            console.error('Error creating project:', error);
            throw error;
        }
    }

    async approvePhase(projectId, phaseIndex) {
        try {
            const result = await this.contract.methods
                .approvePhase(projectId, phaseIndex)
                .send({ from: this.web3.eth.defaultAccount });

            console.log('Phase approved:', result);
            return result;
        } catch (error) {
            console.error('Error approving phase:', error);
            throw error;
        }
    }

    // Listen for contract events
    setupEventListeners() {
        this.contract.events.ProjectCreated({
            filter: {},
            fromBlock: 'latest'
        })
        .on('data', (event) => {
            console.log('New project created:', event);
            this.handleProjectCreated(event);
        })
        .on('error', console.error);

        this.contract.events.PhaseApproved({
            filter: {},
            fromBlock: 'latest'
        })
        .on('data', (event) => {
            console.log('Phase approved:', event);
            this.handlePhaseApproved(event);
        });
    }

    handleProjectCreated(event) {
        // Sync with API backend
        const projectData = {
            blockchain_id: event.returnValues.projectId,
            transaction_hash: event.transactionHash,
            block_number: event.blockNumber
        };

        fetch(`${API_BASE_URL}/projects/sync-blockchain`, {
            method: 'POST',
            headers: {
                'Authorization': `Bearer ${API_KEY}`,
                'Content-Type': 'application/json'
            },
            body: JSON.stringify(projectData)
        });
    }
}

3.3 Contract Factory Integration

Use the contract factory for standardized deployments:

class ContractFactoryManager {
    constructor(web3, factoryAddress) {
        this.web3 = web3;
        this.factoryAddress = factoryAddress;
        this.factoryContract = new web3.eth.Contract(FACTORY_ABI, factoryAddress);
    }

    async deployProjectContract(projectConfig) {
        const {
            projectName,
            description,
            totalValue,
            participants,
            phasePercentages,
            ipfsHash
        } = projectConfig;

        try {
            // Estimate gas for deployment
            const gasEstimate = await this.factoryContract.methods
                .createProject(
                    projectName,
                    description,
                    this.web3.utils.toWei(totalValue.toString(), 'ether'),
                    participants,
                    phasePercentages,
                    ipfsHash || ""
                )
                .estimateGas({ from: this.web3.eth.defaultAccount });

            // Deploy contract
            const result = await this.factoryContract.methods
                .createProject(
                    projectName,
                    description,
                    this.web3.utils.toWei(totalValue.toString(), 'ether'),
                    participants,
                    phasePercentages,
                    ipfsHash || ""
                )
                .send({
                    from: this.web3.eth.defaultAccount,
                    gas: Math.floor(gasEstimate * 1.2), // Add 20% buffer
                    gasPrice: await this.web3.eth.getGasPrice()
                });

            console.log('Contract deployed:', result);
            return {
                transactionHash: result.transactionHash,
                contractAddress: result.events.ProjectCreated.returnValues.contractAddress,
                projectId: result.events.ProjectCreated.returnValues.projectId
            };

        } catch (error) {
            console.error('Deployment failed:', error);
            throw error;
        }
    }

    async getProjectContract(projectId) {
        const contractAddress = await this.factoryContract.methods
            .getProject(projectId)
            .call();

        return new this.web3.eth.Contract(CONSTRUCTION_CONTRACT_ABI, contractAddress);
    }
}

Blockchain Exercise: Deploy a test contract for a sample construction project and interact with it through both the smart contract and API.


📚 Module 4: Advanced Integration Patterns

Duration: 75 minutes

What You'll Learn

Step-by-Step Guide

4.1 WebSocket Integration for Real-time Updates

Set up real-time communication:

class RealtimeManager {
    constructor(apiKey) {
        this.apiKey = apiKey;
        this.socket = null;
        this.reconnectAttempts = 0;
        this.maxReconnectAttempts = 5;
    }

    connect() {
        const wsUrl = `wss://ws.contracting.app/v1?token=${this.apiKey}`;
        this.socket = new WebSocket(wsUrl);

        this.socket.onopen = () => {
            console.log('WebSocket connected');
            this.reconnectAttempts = 0;
            this.subscribe(['projects', 'payments', 'contracts']);
        };

        this.socket.onmessage = (event) => {
            const data = JSON.parse(event.data);
            this.handleMessage(data);
        };

        this.socket.onclose = () => {
            console.log('WebSocket disconnected');
            this.attemptReconnect();
        };

        this.socket.onerror = (error) => {
            console.error('WebSocket error:', error);
        };
    }

    subscribe(channels) {
        const subscription = {
            type: 'subscribe',
            channels: channels
        };

        this.send(subscription);
    }

    send(data) {
        if (this.socket && this.socket.readyState === WebSocket.OPEN) {
            this.socket.send(JSON.stringify(data));
        }
    }

    handleMessage(data) {
        switch (data.type) {
            case 'project_updated':
                this.onProjectUpdate(data.payload);
                break;
            case 'payment_completed':
                this.onPaymentComplete(data.payload);
                break;
            case 'contract_signed':
                this.onContractSigned(data.payload);
                break;
            default:
                console.log('Unknown message type:', data.type);
        }
    }

    onProjectUpdate(project) {
        // Update local state or trigger UI updates
        console.log('Project updated:', project);
        document.dispatchEvent(new CustomEvent('projectUpdate', { 
            detail: project 
        }));
    }

    attemptReconnect() {
        if (this.reconnectAttempts < this.maxReconnectAttempts) {
            this.reconnectAttempts++;
            const delay = Math.pow(2, this.reconnectAttempts) * 1000; // Exponential backoff

            setTimeout(() => {
                console.log(`Reconnecting... Attempt ${this.reconnectAttempts}`);
                this.connect();
            }, delay);
        }
    }
}

4.2 Advanced Error Handling and Retry Logic

Implement robust error handling:

class APIClient {
    constructor(baseURL, apiKey) {
        this.baseURL = baseURL;
        this.apiKey = apiKey;
        this.maxRetries = 3;
        this.retryDelay = 1000;
    }

    async request(endpoint, options = {}) {
        const url = `${this.baseURL}${endpoint}`;
        const defaultOptions = {
            headers: {
                'Authorization': `Bearer ${this.apiKey}`,
                'Content-Type': 'application/json',
                ...options.headers
            }
        };

        const requestOptions = { ...defaultOptions, ...options };

        for (let attempt = 0; attempt <= this.maxRetries; attempt++) {
            try {
                const response = await fetch(url, requestOptions);

                if (response.ok) {
                    return await response.json();
                }

                // Handle specific HTTP errors
                if (response.status === 429) {
                    // Rate limited - wait and retry
                    const retryAfter = response.headers.get('Retry-After') || 60;
                    await this.sleep(retryAfter * 1000);
                    continue;
                }

                if (response.status >= 500 && attempt < this.maxRetries) {
                    // Server error - retry with exponential backoff
                    await this.sleep(this.retryDelay * Math.pow(2, attempt));
                    continue;
                }

                // Client error or max retries exceeded
                const errorData = await response.json();
                throw new APIError(response.status, errorData.message, errorData);

            } catch (error) {
                if (attempt === this.maxRetries) {
                    throw error;
                }

                // Network error - retry
                await this.sleep(this.retryDelay * Math.pow(2, attempt));
            }
        }
    }

    sleep(ms) {
        return new Promise(resolve => setTimeout(resolve, ms));
    }

    // Convenience methods
    async get(endpoint) {
        return this.request(endpoint, { method: 'GET' });
    }

    async post(endpoint, data) {
        return this.request(endpoint, {
            method: 'POST',
            body: JSON.stringify(data)
        });
    }

    async put(endpoint, data) {
        return this.request(endpoint, {
            method: 'PUT',
            body: JSON.stringify(data)
        });
    }

    async delete(endpoint) {
        return this.request(endpoint, { method: 'DELETE' });
    }
}

class APIError extends Error {
    constructor(status, message, data = {}) {
        super(message);
        this.name = 'APIError';
        this.status = status;
        this.data = data;
    }
}

4.3 Batch Operations and Performance Optimization

Handle large datasets efficiently:

class BatchOperationManager {
    constructor(apiClient) {
        this.apiClient = apiClient;
        this.batchSize = 50;
    }

    async batchCreateProjects(projects) {
        const batches = this.createBatches(projects, this.batchSize);
        const results = [];

        for (let i = 0; i < batches.length; i++) {
            console.log(`Processing batch ${i + 1}/${batches.length}`);

            try {
                const batchResult = await this.apiClient.post('/projects/batch', {
                    projects: batches[i]
                });

                results.push(...batchResult.created);
            } catch (error) {
                console.error(`Batch ${i + 1} failed:`, error);

                // Fallback: Process individually
                for (const project of batches[i]) {
                    try {
                        const individual = await this.apiClient.post('/projects', project);
                        results.push(individual);
                    } catch (individualError) {
                        console.error('Individual project creation failed:', individualError);
                    }
                }
            }

            // Rate limiting protection
            if (i < batches.length - 1) {
                await this.sleep(500);
            }
        }

        return results;
    }

    async batchUpdatePayments(updates) {
        // Process updates in parallel with concurrency limit
        const concurrencyLimit = 5;
        const results = [];

        for (let i = 0; i < updates.length; i += concurrencyLimit) {
            const batch = updates.slice(i, i + concurrencyLimit);

            const promises = batch.map(async (update) => {
                try {
                    return await this.apiClient.put(`/payments/${update.id}`, update.data);
                } catch (error) {
                    console.error(`Payment update failed for ${update.id}:`, error);
                    return { error: error.message, id: update.id };
                }
            });

            const batchResults = await Promise.all(promises);
            results.push(...batchResults);
        }

        return results;
    }

    createBatches(array, batchSize) {
        const batches = [];
        for (let i = 0; i < array.length; i += batchSize) {
            batches.push(array.slice(i, i + batchSize));
        }
        return batches;
    }

    sleep(ms) {
        return new Promise(resolve => setTimeout(resolve, ms));
    }
}

Performance Exercise: Build a data synchronization system that efficiently handles large datasets and network issues.


📚 Module 5: Production Deployment & Monitoring

Duration: 60 minutes

What You'll Learn

Step-by-Step Guide

5.1 Production Environment Setup

Configure for production deployment:

// config/production.js
module.exports = {
    api: {
        baseURL: process.env.CAU_API_BASE_URL || 'https://api.contracting.app/v1',
        key: process.env.CAU_API_KEY,
        timeout: 30000,
        retries: 3
    },
    blockchain: {
        networkId: process.env.NETWORK_ID || 1329, // SEI Mainnet
        rpcUrl: process.env.RPC_URL,
        contractAddress: process.env.CONTRACT_ADDRESS
    },
    logging: {
        level: process.env.LOG_LEVEL || 'info',
        file: process.env.LOG_FILE || '/var/log/cau-integration.log'
    },
    monitoring: {
        enabled: true,
        errorTracking: process.env.SENTRY_DSN,
        metrics: process.env.METRICS_ENDPOINT
    }
};

5.2 Comprehensive Logging System

Implement structured logging:

const winston = require('winston');

class Logger {
    constructor() {
        this.logger = winston.createLogger({
            level: process.env.LOG_LEVEL || 'info',
            format: winston.format.combine(
                winston.format.timestamp(),
                winston.format.errors({ stack: true }),
                winston.format.json()
            ),
            defaultMeta: { service: 'cau-integration' },
            transports: [
                new winston.transports.File({ filename: 'logs/error.log', level: 'error' }),
                new winston.transports.File({ filename: 'logs/combined.log' }),
                new winston.transports.Console({
                    format: winston.format.simple()
                })
            ]
        });
    }

    logAPICall(endpoint, method, duration, statusCode) {
        this.logger.info('API Call', {
            endpoint,
            method,
            duration,
            statusCode,
            timestamp: new Date().toISOString()
        });
    }

    logBlockchainTransaction(txHash, operation, gasUsed) {
        this.logger.info('Blockchain Transaction', {
            txHash,
            operation,
            gasUsed,
            timestamp: new Date().toISOString()
        });
    }

    logError(error, context = {}) {
        this.logger.error('Application Error', {
            message: error.message,
            stack: error.stack,
            context,
            timestamp: new Date().toISOString()
        });
    }
}

// Usage example
const logger = new Logger();

// In API client
class MonitoredAPIClient extends APIClient {
    async request(endpoint, options = {}) {
        const startTime = Date.now();

        try {
            const result = await super.request(endpoint, options);
            const duration = Date.now() - startTime;

            logger.logAPICall(endpoint, options.method || 'GET', duration, 200);
            return result;

        } catch (error) {
            const duration = Date.now() - startTime;

            logger.logAPICall(endpoint, options.method || 'GET', duration, error.status || 0);
            logger.logError(error, { endpoint, options });

            throw error;
        }
    }
}

5.3 Health Monitoring and Alerting

Set up comprehensive health checks:

class HealthMonitor {
    constructor(apiClient, blockchainManager) {
        this.apiClient = apiClient;
        this.blockchainManager = blockchainManager;
        this.metrics = {
            apiResponseTimes: [],
            blockchainConnections: 0,
            errors: 0,
            uptime: process.uptime()
        };
    }

    async checkHealth() {
        const checks = await Promise.allSettled([
            this.checkAPIHealth(),
            this.checkBlockchainHealth(),
            this.checkDatabaseHealth()
        ]);

        const results = {
            timestamp: new Date().toISOString(),
            overall: 'healthy',
            services: {
                api: checks[0].status === 'fulfilled' ? checks[0].value : { status: 'unhealthy', error: checks[0].reason },
                blockchain: checks[1].status === 'fulfilled' ? checks[1].value : { status: 'unhealthy', error: checks[1].reason },
                database: checks[2].status === 'fulfilled' ? checks[2].value : { status: 'unhealthy', error: checks[2].reason }
            },
            metrics: this.getMetrics()
        };

        // Determine overall health
        const unhealthyServices = Object.values(results.services)
            .filter(service => service.status === 'unhealthy');

        if (unhealthyServices.length > 0) {
            results.overall = 'unhealthy';
            this.sendAlert(results);
        }

        return results;
    }

    async checkAPIHealth() {
        const start = Date.now();

        try {
            await this.apiClient.get('/health');
            const responseTime = Date.now() - start;

            this.metrics.apiResponseTimes.push(responseTime);
            if (this.metrics.apiResponseTimes.length > 100) {
                this.metrics.apiResponseTimes.shift();
            }

            return {
                status: 'healthy',
                responseTime,
                averageResponseTime: this.getAverageResponseTime()
            };
        } catch (error) {
            this.metrics.errors++;
            return {
                status: 'unhealthy',
                error: error.message,
                lastError: new Date().toISOString()
            };
        }
    }

    async checkBlockchainHealth() {
        try {
            if (!this.blockchainManager.web3) {
                return { status: 'unhealthy', error: 'Web3 not initialized' };
            }

            const blockNumber = await this.blockchainManager.web3.eth.getBlockNumber();
            const networkId = await this.blockchainManager.web3.eth.net.getId();

            return {
                status: 'healthy',
                blockNumber,
                networkId,
                connected: true
            };
        } catch (error) {
            return {
                status: 'unhealthy',
                error: error.message,
                connected: false
            };
        }
    }

    async checkDatabaseHealth() {
        // Implement database health check based on your setup
        return { status: 'healthy', connections: 'active' };
    }

    getAverageResponseTime() {
        if (this.metrics.apiResponseTimes.length === 0) return 0;
        return this.metrics.apiResponseTimes.reduce((a, b) => a + b, 0) / this.metrics.apiResponseTimes.length;
    }

    getMetrics() {
        return {
            uptime: process.uptime(),
            memoryUsage: process.memoryUsage(),
            errors: this.metrics.errors,
            averageApiResponseTime: this.getAverageResponseTime()
        };
    }

    async sendAlert(healthResults) {
        // Implement alerting (email, Slack, PagerDuty, etc.)
        console.log('ALERT: System unhealthy', healthResults);

        // Example: Send to monitoring service
        try {
            await fetch(process.env.ALERT_WEBHOOK, {
                method: 'POST',
                headers: { 'Content-Type': 'application/json' },
                body: JSON.stringify({
                    text: `CAU Integration Health Alert: ${healthResults.overall}`,
                    details: healthResults
                })
            });
        } catch (error) {
            console.error('Failed to send alert:', error);
        }
    }

    startPeriodicHealthChecks(intervalMinutes = 5) {
        setInterval(async () => {
            try {
                const health = await this.checkHealth();
                console.log('Health Check:', health.overall);
            } catch (error) {
                console.error('Health check failed:', error);
            }
        }, intervalMinutes * 60 * 1000);
    }
}

Production Exercise: Set up a complete monitoring system with health checks, alerting, and performance tracking.


🎓 Advanced Developer Mastery

Congratulations! 🚀

You've completed the Developer Learning Path and now have comprehensive skills for production-grade integration with the CAU Checking App platform.

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🛠️ Developer Resources & Tools

Official SDKs and Libraries

# JavaScript/Node.js SDK
npm install @cau-checking/sdk

# Python SDK  
pip install cau-checking-python

# Go SDK
go get github.com/cau-checking/go-sdk

# PHP Composer
composer require cau-checking/php-sdk

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