# Healthcare Dev — Code Examples

## Example 1

```typescript
import express, { Request, Response, NextFunction } from 'express';
import { v4 as uuidv4 } from 'uuid';
import crypto from 'crypto';
import jwt from 'jsonwebtoken';
import { Pool } from 'pg';
import Redis from 'ioredis';
import winston from 'winston';
import { z } from 'zod';
import hl7 from 'hl7-standard';
import dicom from 'dicom-parser';

/**
 * FHIR R4 Compliant Electronic Health Record System
 * HIPAA-compliant implementation with comprehensive security and audit logging
 */

// FHIR Resource Types
enum ResourceType {
    Patient = 'Patient',
    Practitioner = 'Practitioner',
    Encounter = 'Encounter',
    Observation = 'Observation',
    Medication = 'Medication',
    MedicationRequest = 'MedicationRequest',
    Condition = 'Condition',
    Procedure = 'Procedure',
    DiagnosticReport = 'DiagnosticReport',
    AllergyIntolerance = 'AllergyIntolerance',
    Immunization = 'Immunization',
    CarePlan = 'CarePlan',
}

// HIPAA Audit Event Types
enum AuditEventType {
    CREATE = 'C',
    READ = 'R',
    UPDATE = 'U',
    DELETE = 'D',
    EXECUTE = 'E',
    LOGIN = 'LOGIN',
    LOGOUT = 'LOGOUT',
    EMERGENCY_ACCESS = 'EMERGENCY',
}

// Configuration
const config = {
    hipaa: {
        encryptionAlgorithm: 'aes-256-gcm',
        keyRotationDays: 90,
        sessionTimeout: 900000, // 15 minutes
        passwordComplexity: /^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{12,}$/,
        maxLoginAttempts: 3,
        auditRetentionYears: 7,
    },
    fhir: {
        version: 'R4',
        baseUrl: process.env.FHIR_BASE_URL || 'https://api.healthcare.org/fhir',
        supportedFormats: ['application/fhir+json', 'application/fhir+xml'],
    },
    security: {
        jwtSecret: process.env.JWT_SECRET!,
        jwtExpiry: '1h',
        mfaRequired: true,
        breakGlassEnabled: true,
    },
};

// Database with encryption at rest
const db = new Pool({
    host: process.env.DB_HOST,
    port: parseInt(process.env.DB_PORT || '5432'),
    database: process.env.DB_NAME,
    user: process.env.DB_USER,
    password: process.env.DB_PASSWORD,
    ssl: {
        rejectUnauthorized: true,
        ca: process.env.DB_CA_CERT,
    },
    max: 20,
    idleTimeoutMillis: 30000,
});

// Redis for caching and session management
const redis = new Redis({
    host: process.env.REDIS_HOST,
    port: parseInt(process.env.REDIS_PORT || '6379'),
    password: process.env.REDIS_PASSWORD,
    tls: {
        rejectUnauthorized: true,
    },
});

// HIPAA-compliant audit logger
const auditLogger = winston.createLogger({
    level: 'info',
    format: winston.format.combine(
        winston.format.timestamp(),
        winston.format.json()
    ),
    transports: [
        new winston.transports.File({ 
            filename: 'hipaa-audit.log',
            maxsize: 10485760, // 10MB
            maxFiles: 100,
            options: { flags: 'a' }
        }),
        new winston.transports.Console({
            format: winston.format.simple()
        })
    ],
});

// FHIR Resource Interfaces
interface FHIRResource {
    resourceType: ResourceType;
    id?: string;
    meta?: {
        versionId: string;
        lastUpdated: string;
        profile?: string[];
        security?: Coding[];
        tag?: Coding[];
    };
}

interface Patient extends FHIRResource {
    resourceType: ResourceType.Patient;
    identifier?: Identifier[];
    active?: boolean;
    name?: HumanName[];
    telecom?: ContactPoint[];
    gender?: 'male' | 'female' | 'other' | 'unknown';
    birthDate?: string;
    deceasedBoolean?: boolean;
    deceasedDateTime?: string;
    address?: Address[];
    maritalStatus?: CodeableConcept;
    multipleBirthBoolean?: boolean;
    multipleBirthInteger?: number;
    photo?: Attachment[];
    contact?: PatientContact[];
    communication?: PatientCommunication[];
    generalPractitioner?: Reference[];
    managingOrganization?: Reference;
}

interface Observation extends FHIRResource {
    resourceType: ResourceType.Observation;
    status: 'registered' | 'preliminary' | 'final' | 'amended' | 'corrected' | 'cancelled' | 'entered-in-error';
    category?: CodeableConcept[];
    code: CodeableConcept;
    subject?: Reference;
    encounter?: Reference;
    effectiveDateTime?: string;
    effectivePeriod?: Period;
    issued?: string;
    performer?: Reference[];
    valueQuantity?: Quantity;
    valueCodeableConcept?: CodeableConcept;
    valueString?: string;
    valueBoolean?: boolean;
    valueInteger?: number;
    valueRange?: Range;
    interpretation?: CodeableConcept[];
    note?: Annotation[];
    referenceRange?: ObservationReferenceRange[];
}

// HIPAA Security Service
class HIPAASecurityService {
    private encryptionKey: Buffer;
    
    constructor() {
        this.encryptionKey = this.deriveKey();
        this.scheduleKeyRotation();
    }
    
    private deriveKey(): Buffer {
        const masterKey = process.env.MASTER_KEY!;
        const salt = process.env.KEY_SALT!;
        return crypto.pbkdf2Sync(masterKey, salt, 100000, 32, 'sha256');
    }
    
    private scheduleKeyRotation() {
        setInterval(() => {
            this.rotateEncryptionKey();
        }, config.hipaa.keyRotationDays * 24 * 60 * 60 * 1000);
    }
    
    private async rotateEncryptionKey() {
        // Generate new key
        const newKey = crypto.randomBytes(32);
        
        // Re-encrypt all sensitive data with new key
        await this.reencryptData(newKey);
        
        // Update key in secure key management system
        this.encryptionKey = newKey;
        
        auditLogger.info('Encryption key rotated', {
            timestamp: new Date().toISOString(),
            keyVersion: crypto.createHash('sha256').update(newKey).digest('hex').substring(0, 8),
        });
    }
    
    encryptPHI(data: string): { encrypted: string; iv: string; tag: string } {
        const iv = crypto.randomBytes(16);
        const cipher = crypto.createCipheriv(config.hipaa.encryptionAlgorithm, this.encryptionKey, iv);
        
        let encrypted = cipher.update(data, 'utf8', 'hex');
        encrypted += cipher.final('hex');
        
        const tag = (cipher as any).getAuthTag();
        
        return {
            encrypted,
            iv: iv.toString('hex'),
            tag: tag.toString('hex'),
        };
    }
    
    decryptPHI(encrypted: string, iv: string, tag: string): string {
        const decipher = crypto.createDecipheriv(
            config.hipaa.encryptionAlgorithm,
            this.encryptionKey,
            Buffer.from(iv, 'hex')
        );
        
        (decipher as any).setAuthTag(Buffer.from(tag, 'hex'));
        
        let decrypted = decipher.update(encrypted, 'hex', 'utf8');
        decrypted += decipher.final('utf8');
        
        return decrypted;
    }
    
    async reencryptData(newKey: Buffer) {
        // Implementation for re-encrypting existing data
        const client = await db.connect();
        try {
            await client.query('BEGIN');
            
            // Re-encrypt patient data
            const patients = await client.query('SELECT * FROM patients WHERE encrypted = true');
            for (const patient of patients.rows) {
                const decrypted = this.decryptPHI(
                    patient.encrypted_data,
                    patient.encryption_iv,
                    patient.encryption_tag
                );
                
                const reencrypted = this.encryptWithKey(decrypted, newKey);
                
                await client.query(
                    'UPDATE patients SET encrypted_data = $1, encryption_iv = $2, encryption_tag = $3 WHERE id = $4',
                    [reencrypted.encrypted, reencrypted.iv, reencrypted.tag, patient.id]
                );
            }
            
            await client.query('COMMIT');
        } catch (error) {
            await client.query('ROLLBACK');
            throw error;
        } finally {
            client.release();
        }
    }
    
    private encryptWithKey(data: string, key: Buffer) {
        const iv = crypto.randomBytes(16);
        const cipher = crypto.createCipheriv(config.hipaa.encryptionAlgorithm, key, iv);
        
        let encrypted = cipher.update(data, 'utf8', 'hex');
        encrypted += cipher.final('hex');
        
        const tag = (cipher as any).getAuthTag();
        
        return {
            encrypted,
            iv: iv.toString('hex'),
            tag: tag.toString('hex'),
        };
    }
    
    hashPassword(password: string): string {
        const salt = crypto.randomBytes(16).toString('hex');
        const hash = crypto.pbkdf2Sync(password, salt, 100000, 64, 'sha512').toString('hex');
        return `${salt}:${hash}`;
    }
    
    verifyPassword(password: string, hashedPassword: string): boolean {
        const [salt, hash] = hashedPassword.split(':');
        const verifyHash = crypto.pbkdf2Sync(password, salt, 100000, 64, 'sha512').toString('hex');
        return hash === verifyHash;
    }
    
    generateSessionToken(userId: string, role: string): string {
        return jwt.sign(
            {
                userId,
                role,
                sessionId: uuidv4(),
                iat: Math.floor(Date.now() / 1000),
            },
            config.security.jwtSecret,
            { expiresIn: config.security.jwtExpiry }
        );
    }
    
    verifySessionToken(token: string): any {
        try {
            return jwt.verify(token, config.security.jwtSecret);
        } catch (error) {
            return null;
        }
    }
}

// HIPAA Audit Service
class HIPAAAuditService {
    async logAccess(
        userId: string,
        patientId: string,
        resourceType: string,
        action: AuditEventType,
        outcome: 'success' | 'failure',
        reason?: string
    ) {
        const auditEntry = {
            timestamp: new Date().toISOString(),
            userId,
            patientId,
            resourceType,
            action,
            outcome,
            reason,
            ipAddress: this.getClientIp(),
            userAgent: this.getUserAgent(),
            sessionId: this.getSessionId(),
        };
        
        // Log to audit log
        auditLogger.info('PHI Access', auditEntry);
        
        // Store in database for long-term retention
        await db.query(
            `INSERT INTO audit_log 
             (timestamp, user_id, patient_id, resource_type, action, outcome, reason, ip_address, user_agent, session_id)
             VALUES ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)`,
            [
                auditEntry.timestamp,
                auditEntry.userId,
                auditEntry.patientId,
                auditEntry.resourceType,
                auditEntry.action,
                auditEntry.outcome,
                auditEntry.reason,
                auditEntry.ipAddress,
                auditEntry.userAgent,
                auditEntry.sessionId,
            ]
        );
        
        // Real-time alerting for suspicious activity
        if (outcome === 'failure') {
            await this.checkSuspiciousActivity(userId);
        }
    }
    
    async checkSuspiciousActivity(userId: string) {
        const recentFailures = await db.query(
            `SELECT COUNT(*) as count 
             FROM audit_log 
             WHERE user_id = $1 
             AND outcome = 'failure' 
             AND timestamp > NOW() - INTERVAL '15 minutes'`,
            [userId]
        );
        
        if (recentFailures.rows[0].count >= 5) {
            // Alert security team
            await this.sendSecurityAlert({
                type: 'SUSPICIOUS_ACTIVITY',
                userId,
                message: 'Multiple failed access attempts detected',
                severity: 'HIGH',
            });
            
            // Temporarily lock account
            await this.lockUserAccount(userId);
        }
    }
    
    async sendSecurityAlert(alert: any) {
        // Send to security monitoring system
        // Implementation would integrate with SIEM
        auditLogger.warn('Security Alert', alert);
    }
    
    async lockUserAccount(userId: string) {
        await db.query(
            'UPDATE users SET locked = true, lock_reason = $1, locked_at = NOW() WHERE id = $2',
            ['Suspicious activity detected', userId]
        );
    }
    
    private getClientIp(): string {
        // Get from request context
        return '127.0.0.1'; // Placeholder
    }
    
    private getUserAgent(): string {
        // Get from request headers
        return 'Mozilla/5.0'; // Placeholder
    }
    
    private getSessionId(): string {
        // Get from session context
        return uuidv4(); // Placeholder
    }
}

// FHIR Resource Repository
class FHIRRepository {
    private security = new HIPAASecurityService();
    private audit = new HIPAAAuditService();
    
    async createResource(
        resource: FHIRResource,
        userId: string,
        reason?: string
    ): Promise<FHIRResource> {
        const client = await db.connect();
        
        try {
            await client.query('BEGIN');
            
            // Generate resource ID and metadata
            resource.id = resource.id || uuidv4();
            resource.meta = {
                versionId: '1',
                lastUpdated: new Date().toISOString(),
                profile: this.getResourceProfiles(resource.resourceType),
            };
            
            // Encrypt sensitive data
            const encryptedData = this.security.encryptPHI(JSON.stringify(resource));
            
            // Store resource
            await client.query(
                `INSERT INTO fhir_resources 
                 (id, resource_type, version, data, encrypted_data, encryption_iv, encryption_tag, created_at, created_by)
                 VALUES ($1, $2, $3, $4, $5, $6, $7, NOW(), $8)`,
                [
                    resource.id,
                    resource.resourceType,
                    1,
                    null, // Store encrypted only
                    encryptedData.encrypted,
                    encryptedData.iv,
                    encryptedData.tag,
                    userId,
                ]
            );
            
            // Create audit log
            await this.audit.logAccess(
                userId,
                this.getPatientId(resource),
                resource.resourceType,
                AuditEventType.CREATE,
                'success',
                reason
            );
            
            await client.query('COMMIT');
            
            return resource;
        } catch (error) {
            await client.query('ROLLBACK');
            
            await this.audit.logAccess(
                userId,
                this.getPatientId(resource),
                resource.resourceType,
                AuditEventType.CREATE,
                'failure',
                error.message
            );
            
            throw error;
        } finally {
            client.release();
        }
    }
    
    async readResource(
        resourceType: ResourceType,
        id: string,
        userId: string,
        reason?: string
    ): Promise<FHIRResource | null> {
        try {
            // Check access permissions
            const hasAccess = await this.checkAccess(userId, resourceType, id);
            if (!hasAccess) {
                await this.audit.logAccess(
                    userId,
                    id,
                    resourceType,
                    AuditEventType.READ,
                    'failure',
                    'Access denied'
                );
                throw new Error('Access denied');
            }
            
            // Retrieve resource
            const result = await db.query(
                'SELECT * FROM fhir_resources WHERE id = $1 AND resource_type = $2',
                [id, resourceType]
            );
            
            if (result.rows.length === 0) {
                return null;
            }
            
            const row = result.rows[0];
            
            // Decrypt resource
            const decrypted = this.security.decryptPHI(
                row.encrypted_data,
                row.encryption_iv,
                row.encryption_tag
            );
            
            const resource = JSON.parse(decrypted);
            
            // Log access
            await this.audit.logAccess(
                userId,
                this.getPatientId(resource),
                resourceType,
                AuditEventType.READ,
                'success',
                reason
            );
            
            return resource;
        } catch (error) {
            await this.audit.logAccess(
                userId,
                id,
                resourceType,
                AuditEventType.READ,
                'failure',
                error.message
            );
            throw error;
        }
    }
    
    async updateResource(
        resource: FHIRResource,
        userId: string,
        reason?: string
    ): Promise<FHIRResource> {
        const client = await db.connect();
        
        try {
            await client.query('BEGIN');
            
            // Get current version
            const current = await this.readResource(
                resource.resourceType,
                resource.id!,
                userId,
                'Update operation'
            );
            
            if (!current) {
                throw new Error('Resource not found');
            }
            
            // Update metadata
            const newVersion = parseInt(current.meta!.versionId) + 1;
            resource.meta = {
                ...resource.meta,
                versionId: newVersion.toString(),
                lastUpdated: new Date().toISOString(),
            };
            
            // Archive current version
            await client.query(
                `INSERT INTO fhir_resource_history 
                 SELECT * FROM fhir_resources WHERE id = $1`,
                [resource.id]
            );
            
            // Encrypt and update
            const encryptedData = this.security.encryptPHI(JSON.stringify(resource));
            
            await client.query(
                `UPDATE fhir_resources 
                 SET version = $1, encrypted_data = $2, encryption_iv = $3, 
                     encryption_tag = $4, updated_at = NOW(), updated_by = $5
                 WHERE id = $6`,
                [
                    newVersion,
                    encryptedData.encrypted,
                    encryptedData.iv,
                    encryptedData.tag,
                    userId,
                    resource.id,
                ]
            );
            
            // Audit log
            await this.audit.logAccess(
                userId,
                this.getPatientId(resource),
                resource.resourceType,
                AuditEventType.UPDATE,
                'success',
                reason
            );
            
            await client.query('COMMIT');
            
            return resource;
        } catch (error) {
            await client.query('ROLLBACK');
            
            await this.audit.logAccess(
                userId,
                resource.id!,
                resource.resourceType,
                AuditEventType.UPDATE,
                'failure',
                error.message
            );
            
            throw error;
        } finally {
            client.release();
        }
    }
    
    async searchResources(
        resourceType: ResourceType,
        params: any,
        userId: string
    ): Promise<Bundle> {
        // Implement FHIR search with proper access control
        const searchResults: FHIRResource[] = [];
        
        // Build search query based on FHIR search parameters
        let query = `SELECT * FROM fhir_resources WHERE resource_type = $1`;
        const queryParams = [resourceType];
        
        // Add search parameters
        if (params.patient) {
            query += ` AND data->>'subject'->>'reference' = $${queryParams.length + 1}`;
            queryParams.push(`Patient/${params.patient}`);
        }
        
        if (params.date) {
            // Handle date search
        }
        
        // Execute search
        const results = await db.query(query, queryParams);
        
        // Decrypt and filter based on access
        for (const row of results.rows) {
            if (await this.checkAccess(userId, resourceType, row.id)) {
                const decrypted = this.security.decryptPHI(
                    row.encrypted_data,
                    row.encryption_iv,
                    row.encryption_tag
                );
                searchResults.push(JSON.parse(decrypted));
            }
        }
        
        // Create FHIR Bundle
        return {
            resourceType: 'Bundle',
            type: 'searchset',
            total: searchResults.length,
            entry: searchResults.map(resource => ({
                fullUrl: `${config.fhir.baseUrl}/${resource.resourceType}/${resource.id}`,
                resource,
            })),
        };
    }
    
    private async checkAccess(userId: string, resourceType: string, resourceId: string): Promise<boolean> {
        // Implement role-based access control
        const user = await db.query('SELECT role, department FROM users WHERE id = $1', [userId]);
        
        if (user.rows.length === 0) {
            return false;
        }
        
        const { role, department } = user.rows[0];
        
        // Check role-based permissions
        if (role === 'admin') {
            return true;
        }
        
        if (role === 'physician') {
            // Check if physician has relationship with patient
            return await this.checkPhysicianPatientRelationship(userId, resourceId);
        }
        
        if (role === 'nurse') {
            // Check department and shift
            return await this.checkNurseAccess(userId, resourceId, department);
        }
        
        return false;
    }
    
    private async checkPhysicianPatientRelationship(physicianId: string, patientId: string): Promise<boolean> {
        const result = await db.query(
            `SELECT COUNT(*) as count 
             FROM patient_physician_relationships 
             WHERE physician_id = $1 AND patient_id = $2 AND active = true`,
            [physicianId, patientId]
        );
        
        return result.rows[0].count > 0;
    }
    
    private async checkNurseAccess(nurseId: string, patientId: string, department: string): Promise<boolean> {
        // Check if patient is in nurse's department
        const result = await db.query(
            `SELECT COUNT(*) as count 
             FROM patient_admissions 
             WHERE patient_id = $1 AND department = $2 AND discharged_at IS NULL`,
            [patientId, department]
        );
        
        return result.rows[0].count > 0;
    }
    
    private getResourceProfiles(resourceType: ResourceType): string[] {
        // Return US Core profiles
        const profiles: { [key: string]: string[] } = {
            [ResourceType.Patient]: ['http://hl7.org/fhir/us/core/StructureDefinition/us-core-patient'],
            [ResourceType.Observation]: ['http://hl7.org/fhir/us/core/StructureDefinition/us-core-observation'],
            [ResourceType.Condition]: ['http://hl7.org/fhir/us/core/StructureDefinition/us-core-condition'],
        };
        
        return profiles[resourceType] || [];
    }
    
    private getPatientId(resource: FHIRResource): string {
        if (resource.resourceType === ResourceType.Patient) {
            return resource.id!;
        }
        
        // Extract patient reference from other resources
        const resourceWithSubject = resource as any;
        if (resourceWithSubject.subject?.reference) {
            return resourceWithSubject.subject.reference.replace('Patient/', '');
        }
        
        return 'unknown';
    }
}

// Clinical Decision Support
class ClinicalDecisionSupport {
    async checkDrugInteractions(medications: Medication[]): Promise<Alert[]> {
        const alerts: Alert[] = [];
        
        // Check for drug-drug interactions
        for (let i = 0; i < medications.length; i++) {
            for (let j = i + 1; j < medications.length; j++) {
                const interaction = await this.checkInteraction(
                    medications[i],
                    medications[j]
                );
                
                if (interaction) {
                    alerts.push({
                        severity: interaction.severity,
                        type: 'drug-interaction',
                        message: interaction.message,
                        medications: [medications[i].id!, medications[j].id!],
                    });
                }
            }
        }
        
        return alerts;
    }
    
    async checkAllergies(patient: Patient, medication: Medication): Promise<Alert[]> {
        const alerts: Alert[] = [];
        
        // Get patient allergies
        const allergies = await this.getPatientAllergies(patient.id!);
        
        for (const allergy of allergies) {
            if (this.medicationContainsAllergen(medication, allergy)) {
                alerts.push({
                    severity: 'high',
                    type: 'allergy',
                    message: `Patient is allergic to ${allergy.substance}`,
                    allergyId: allergy.id,
                    medicationId: medication.id!,
                });
            }
        }
        
        return alerts;
    }
    
    async checkDosing(
        medication: Medication,
        patient: Patient,
        renalFunction?: number,
        hepaticFunction?: number
    ): Promise<Alert[]> {
        const alerts: Alert[] = [];
        
        // Calculate age
        const age = this.calculateAge(patient.birthDate!);
        
        // Check pediatric dosing
        if (age < 18) {
            const pediatricDose = await this.getPediatricDosing(medication, age, patient);
            if (pediatricDose) {
                alerts.push({
                    severity: 'medium',
                    type: 'dosing',
                    message: `Recommended pediatric dose: ${pediatricDose}`,
                });
            }
        }
        
        // Check geriatric dosing
        if (age > 65) {
            const geriatricDose = await this.getGeriatricDosing(medication, age);
            if (geriatricDose) {
                alerts.push({
                    severity: 'medium',
                    type: 'dosing',
                    message: `Consider dose adjustment for geriatric patient: ${geriatricDose}`,
                });
            }
        }
        
        // Check renal dosing
        if (renalFunction && renalFunction < 60) {
            const renalDose = await this.getRenalDosing(medication, renalFunction);
            if (renalDose) {
                alerts.push({
                    severity: 'high',
                    type: 'dosing',
                    message: `Renal dose adjustment needed: ${renalDose}`,
                });
            }
        }
        
        // Check hepatic dosing
        if (hepaticFunction && hepaticFunction < 70) {
            const hepaticDose = await this.getHepaticDosing(medication, hepaticFunction);
            if (hepaticDose) {
                alerts.push({
                    severity: 'high',
                    type: 'dosing',
                    message: `Hepatic dose adjustment needed: ${hepaticDose}`,
                });
            }
        }
        
        return alerts;
    }
    
    private async checkInteraction(med1: Medication, med2: Medication) {
        // Query drug interaction database
        // This would integrate with a service like First Databank or Micromedex
        return null; // Placeholder
    }
    
    private async getPatientAllergies(patientId: string) {
        const result = await db.query(
            'SELECT * FROM allergies WHERE patient_id = $1 AND active = true',
            [patientId]
        );
        return result.rows;
    }
    
    private medicationContainsAllergen(medication: Medication, allergy: any): boolean {
        // Check if medication contains allergen
        return false; // Placeholder
    }
    
    private calculateAge(birthDate: string): number {
        const birth = new Date(birthDate);
        const today = new Date();
        let age = today.getFullYear() - birth.getFullYear();
        const monthDiff = today.getMonth() - birth.getMonth();
        
        if (monthDiff < 0 || (monthDiff === 0 && today.getDate() < birth.getDate())) {
            age--;
        }
        
        return age;
    }
    
    private async getPediatricDosing(medication: Medication, age: number, patient: Patient) {
        // Calculate pediatric dosing based on age and weight
        return null; // Placeholder
    }
    
    private async getGeriatricDosing(medication: Medication, age: number) {
        // Get geriatric dosing recommendations
        return null; // Placeholder
    }
    
    private async getRenalDosing(medication: Medication, gfr: number) {
        // Calculate renal dosing adjustment
        return null; // Placeholder
    }
    
    private async getHepaticDosing(medication: Medication, liverFunction: number) {
        // Calculate hepatic dosing adjustment
        return null; // Placeholder
    }
}

// HL7 Message Processing
class HL7Processor {
    async processMessage(message: string): Promise<void> {
        try {
            // Parse HL7 message
            const parsed = hl7.parse(message);
            
            // Extract message type
            const messageType = parsed.MSH[9][0]; // Message type
            
            // Process based on message type
            switch (messageType) {
                case 'ADT': // Admission, Discharge, Transfer
                    await this.processADT(parsed);
                    break;
                case 'ORM': // Order Message
                    await this.processORM(parsed);
                    break;
                case 'ORU': // Observation Result
                    await this.processORU(parsed);
                    break;
                case 'SIU': // Scheduling
                    await this.processSIU(parsed);
                    break;
                default:
                    throw new Error(`Unsupported message type: ${messageType}`);
            }
            
            // Send acknowledgment
            await this.sendACK(parsed);
            
        } catch (error) {
            auditLogger.error('HL7 processing error', {
                error: error.message,
                message: message.substring(0, 100),
            });
            
            // Send NACK
            await this.sendNACK(error.message);
        }
    }
    
    private async processADT(message: any) {
        const eventType = message.MSH[9][1]; // Event type (A01, A02, etc.)
        
        switch (eventType) {
            case 'A01': // Admission
                await this.handleAdmission(message);
                break;
            case 'A03': // Discharge
                await this.handleDischarge(message);
                break;
            case 'A02': // Transfer
                await this.handleTransfer(message);
                break;
        }
    }
    
    private async processORM(message: any) {
        // Process order message
        const order = {
            patientId: message.PID[3][0],
            orderNumber: message.ORC[2][0],
            orderDate: message.ORC[9][0],
            orderingProvider: message.ORC[12][0],
            orderType: message.OBR[4][0],
        };
        
        // Store order in database
        await db.query(
            `INSERT INTO orders (patient_id, order_number, order_date, provider_id, order_type)
             VALUES ($1, $2, $3, $4, $5)`,
            [order.patientId, order.orderNumber, order.orderDate, order.orderingProvider, order.orderType]
        );
    }
    
    private async processORU(message: any) {
        // Process observation result
        const observation = {
            patientId: message.PID[3][0],
            observationId: message.OBR[3][0],
            observationDate: message.OBR[7][0],
            results: [],
        };
        
        // Extract results from OBX segments
        for (const obx of message.OBX || []) {
            observation.results.push({
                type: obx[3][0],
                value: obx[5][0],
                units: obx[6][0],
                referenceRange: obx[7][0],
                abnormalFlag: obx[8][0],
            });
        }
        
        // Convert to FHIR Observation and store
        const fhirObservation = await this.convertToFHIRObservation(observation);
        // Store observation
    }
    
    private async processSIU(message: any) {
        // Process scheduling message
        const appointment = {
            patientId: message.PID[3][0],
            appointmentId: message.SCH[1][0],
            startTime: message.SCH[11][0],
            duration: message.SCH[9][0],
            providerId: message.AIP[3][0],
            location: message.AIL[3][0],
        };
        
        // Store appointment
        await db.query(
            `INSERT INTO appointments 
             (patient_id, appointment_id, start_time, duration, provider_id, location)
             VALUES ($1, $2, $3, $4, $5, $6)`,
            [
                appointment.patientId,
                appointment.appointmentId,
                appointment.startTime,
                appointment.duration,
                appointment.providerId,
                appointment.location,
            ]
        );
    }
    
    private async handleAdmission(message: any) {
        // Handle patient admission
        const admission = {
            patientId: message.PID[3][0],
            admissionDate: message.PV1[44][0],
            department: message.PV1[3][0],
            room: message.PV1[3][2],
            bed: message.PV1[3][3],
            attendingPhysician: message.PV1[7][0],
        };
        
        await db.query(
            `INSERT INTO admissions 
             (patient_id, admission_date, department, room, bed, attending_physician)
             VALUES ($1, $2, $3, $4, $5, $6)`,
            Object.values(admission)
        );
    }
    
    private async handleDischarge(message: any) {
        // Handle patient discharge
        const discharge = {
            patientId: message.PID[3][0],
            dischargeDate: message.PV1[45][0],
            dischargeDisposition: message.PV1[36][0],
        };
        
        await db.query(
            `UPDATE admissions 
             SET discharge_date = $1, discharge_disposition = $2
             WHERE patient_id = $3 AND discharge_date IS NULL`,
            [discharge.dischargeDate, discharge.dischargeDisposition, discharge.patientId]
        );
    }
    
    private async handleTransfer(message: any) {
        // Handle patient transfer
        const transfer = {
            patientId: message.PID[3][0],
            fromDepartment: message.PV1[6][0],
            toDepartment: message.PV1[3][0],
            transferDate: message.EVN[6][0],
        };
        
        await db.query(
            `INSERT INTO transfers 
             (patient_id, from_department, to_department, transfer_date)
             VALUES ($1, $2, $3, $4)`,
            Object.values(transfer)
        );
    }
    
    private async convertToFHIRObservation(hl7Observation: any): Promise<Observation> {
        // Convert HL7 observation to FHIR format
        return {
            resourceType: ResourceType.Observation,
            status: 'final',
            code: {
                coding: [{
                    system: 'http://loinc.org',
                    code: hl7Observation.type,
                }],
            },
            effectiveDateTime: hl7Observation.observationDate,
            valueQuantity: {
                value: parseFloat(hl7Observation.results[0]?.value),
                unit: hl7Observation.results[0]?.units,
            },
        };
    }
    
    private async sendACK(originalMessage: any) {
        // Send HL7 acknowledgment
        const ack = {
            MSH: {
                ...originalMessage.MSH,
                9: ['ACK'],
            },
            MSA: {
                1: 'AA', // Application Accept
                2: originalMessage.MSH[10], // Message control ID
            },
        };
        
        // Send ACK message
    }
    
    private async sendNACK(error: string) {
        // Send negative acknowledgment
        const nack = {
            MSA: {
                1: 'AE', // Application Error
                3: error,
            },
        };
        
        // Send NACK message
    }
}

// DICOM Image Processing
class DICOMProcessor {
    async processImage(buffer: Buffer): Promise<void> {
        try {
            // Parse DICOM file
            const dataSet = dicom.parseDicom(buffer);
            
            // Extract metadata
            const metadata = {
                patientId: dataSet.string('x00100020'),
                patientName: dataSet.string('x00100010'),
                studyInstanceUID: dataSet.string('x0020000d'),
                seriesInstanceUID: dataSet.string('x0020000e'),
                sopInstanceUID: dataSet.string('x00080018'),
                modality: dataSet.string('x00080060'),
                studyDate: dataSet.string('x00080020'),
                studyDescription: dataSet.string('x00081030'),
            };
            
            // Store metadata in database
            await this.storeDICOMMetadata(metadata);
            
            // Store image in PACS
            await this.storeInPACS(buffer, metadata);
            
            // Apply de-identification if needed
            if (process.env.DEIDENTIFY_IMAGES === 'true') {
                await this.deidentifyImage(dataSet);
            }
            
        } catch (error) {
            auditLogger.error('DICOM processing error', {
                error: error.message,
            });
            throw error;
        }
    }
    
    private async storeDICOMMetadata(metadata: any) {
        await db.query(
            `INSERT INTO dicom_studies 
             (patient_id, study_uid, series_uid, sop_uid, modality, study_date, description)
             VALUES ($1, $2, $3, $4, $5, $6, $7)`,
            [
                metadata.patientId,
                metadata.studyInstanceUID,
                metadata.seriesInstanceUID,
                metadata.sopInstanceUID,
                metadata.modality,
                metadata.studyDate,
                metadata.studyDescription,
            ]
        );
    }
    
    private async storeInPACS(buffer: Buffer, metadata: any) {
        // Store image in Picture Archiving and Communication System
        // This would integrate with a PACS server
    }
    
    private async deidentifyImage(dataSet: any) {
        // Remove patient identifying information
        const tagsToRemove = [
            'x00100010', // Patient Name
            'x00100020', // Patient ID
            'x00100030', // Patient Birth Date
            'x00100040', // Patient Sex
            'x00101010', // Patient Age
        ];
        
        for (const tag of tagsToRemove) {
            delete dataSet.elements[tag];
        }
    }
}

// Telemedicine Platform
class TelemedicineService {
    async createVideoConsultation(
        patientId: string,
        providerId: string,
        scheduledTime: Date
    ): Promise<VideoConsultation> {
        // Generate secure room
        const roomId = uuidv4();
        const roomToken = this.generateSecureToken();
        
        // Create consultation record
        const consultation = {
            id: uuidv4(),
            patientId,
            providerId,
            roomId,
            scheduledTime,
            status: 'scheduled',
            patientToken: this.generatePatientToken(roomId, patientId),
            providerToken: this.generateProviderToken(roomId, providerId),
        };
        
        // Store consultation
        await db.query(
            `INSERT INTO video_consultations 
             (id, patient_id, provider_id, room_id, scheduled_time, status, created_at)
             VALUES ($1, $2, $3, $4, $5, $6, NOW())`,
            [
                consultation.id,
                consultation.patientId,
                consultation.providerId,
                consultation.roomId,
                consultation.scheduledTime,
                consultation.status,
            ]
        );
        
        // Send notifications
        await this.sendConsultationNotifications(consultation);
        
        return consultation;
    }
    
    async startConsultation(consultationId: string, userId: string): Promise<void> {
        // Update consultation status
        await db.query(
            'UPDATE video_consultations SET status = $1, started_at = NOW() WHERE id = $2',
            ['in_progress', consultationId]
        );
        
        // Start recording if required for documentation
        if (process.env.RECORD_CONSULTATIONS === 'true') {
            await this.startRecording(consultationId);
        }
        
        // Log for audit
        auditLogger.info('Video consultation started', {
            consultationId,
            userId,
            timestamp: new Date().toISOString(),
        });
    }
    
    async endConsultation(
        consultationId: string,
        userId: string,
        notes?: string
    ): Promise<void> {
        // Update consultation status
        await db.query(
            `UPDATE video_consultations 
             SET status = $1, ended_at = NOW(), clinical_notes = $2 
             WHERE id = $3`,
            ['completed', notes, consultationId]
        );
        
        // Stop recording
        await this.stopRecording(consultationId);
        
        // Generate consultation summary
        await this.generateConsultationSummary(consultationId);
        
        // Create billing record
        await this.createBillingRecord(consultationId);
    }
    
    private generateSecureToken(): string {
        return crypto.randomBytes(32).toString('base64url');
    }
    
    private generatePatientToken(roomId: string, patientId: string): string {
        return jwt.sign(
            {
                roomId,
                patientId,
                role: 'patient',
                permissions: ['join', 'video', 'audio', 'chat'],
            },
            config.security.jwtSecret,
            { expiresIn: '2h' }
        );
    }
    
    private generateProviderToken(roomId: string, providerId: string): string {
        return jwt.sign(
            {
                roomId,
                providerId,
                role: 'provider',
                permissions: ['join', 'video', 'audio', 'chat', 'record', 'screenshare'],
            },
            config.security.jwtSecret,
            { expiresIn: '2h' }
        );
    }
    
    private async sendConsultationNotifications(consultation: any) {
        // Send email/SMS notifications to patient and provider
    }
    
    private async startRecording(consultationId: string) {
        // Start video recording for documentation
        // Must comply with consent and privacy regulations
    }
    
    private async stopRecording(consultationId: string) {
        // Stop and securely store recording
    }
    
    private async generateConsultationSummary(consultationId: string) {
        // Generate clinical summary document
    }
    
    private async createBillingRecord(consultationId: string) {
        // Create billing record for telemedicine consultation
        // Include appropriate CPT codes for telehealth
    }
}

// Type definitions
interface Identifier {
    system?: string;
    value: string;
}

interface HumanName {
    family: string;
    given: string[];
}

interface ContactPoint {
    system: 'phone' | 'email';
    value: string;
}

interface Address {
    line: string[];
    city: string;
    state: string;
    postalCode: string;
    country: string;
}

interface CodeableConcept {
    coding?: Coding[];
    text?: string;
}

interface Coding {
    system: string;
    code: string;
    display?: string;
}

interface Reference {
    reference: string;
    display?: string;
}

interface Period {
    start: string;
    end?: string;
}

interface Quantity {
    value: number;
    unit: string;
    system?: string;
    code?: string;
}

interface Range {
    low: Quantity;
    high: Quantity;
}

interface Annotation {
    text: string;
    time?: string;
}

interface ObservationReferenceRange {
    low?: Quantity;
    high?: Quantity;
    text?: string;
}

interface Attachment {
    contentType: string;
    data?: string;
    url?: string;
}

interface PatientContact {
    relationship?: CodeableConcept[];
    name?: HumanName;
    telecom?: ContactPoint[];
}

interface PatientCommunication {
    language: CodeableConcept;
    preferred?: boolean;
}

interface Bundle {
    resourceType: 'Bundle';
    type: 'searchset' | 'document' | 'message' | 'transaction' | 'batch';
    total?: number;
    entry?: BundleEntry[];
}

interface BundleEntry {
    fullUrl?: string;
    resource: FHIRResource;
}

interface Medication extends FHIRResource {
    resourceType: ResourceType.Medication;
    code: CodeableConcept;
}

interface Alert {
    severity: 'low' | 'medium' | 'high';
    type: string;
    message: string;
    [key: string]: any;
}

interface VideoConsultation {
    id: string;
    patientId: string;
    providerId: string;
    roomId: string;
    scheduledTime: Date;
    status: string;
    patientToken: string;
    providerToken: string;
}

// Export services
export {
    HIPAASecurityService,
    HIPAAAuditService,
    FHIRRepository,
    ClinicalDecisionSupport,
    HL7Processor,
    DICOMProcessor,
    TelemedicineService,
};
```