This document explains the technical decisions behind choosing TypeScript and a monorepo architecture for this project.

Why TypeScript: Self-Documenting Code with IDE Integration

TypeScript transforms your codebase into living documentation. When developers work with your project, their IDE becomes a powerful guide that shows exactly what each function expects, what it returns, and how different parts of the system connect.

Concrete Examples from Our Project

// packages/kafka/src/types.ts - Database events are fully typed
export type DatabaseEvent<T> = {
  before: T | null;
  after: T;
  source: {
    version: string;
    connector: string;
    name: string;
    ts_ms: number;
    // ... 15+ more typed fields
  };
  op: "c" | "r" | "u" | "d"; // Only valid operations allowed
};

IDE Benefits

• Autocomplete: Developers immediately see all available fields and methods
• Error Prevention: Typos and incorrect usage are caught before runtime
• Refactoring Confidence: Renaming properties updates everywhere automatically
• Documentation at Point of Use: Hover over any function to see its signature, parameters, and return type

Why Monorepo: Eliminating Duplication Through Shared Types

The monorepo structure prevents the classic problem of duplicated interfaces between services. Instead of each service defining its own version of User, Organization, or KafkaMessage, you define them once and share them everywhere.

Shared Type Definitions

// packages/service-discovery/src/types.ts
export type Service = (typeof [utils.SERVICES](<http://utils.SERVICES>))[number];
export type ServiceMap = Record<Service, string>;

// apps/internal/analytics/src/types.ts  
export interface AnalyticsEvent {
  id: string;
  type: string;
  userId: string;
  timestamp: Date;
  metadata?: Record<string, any>;
}

export interface KafkaMessage {
  topic: string;
  partition: number;
  offset: string;
  value: AnalyticsEvent;
}

Usage Across Services

// Frontend consuming shared types
import type { Organization, Member } from "@repo/auth";

// Analytics service using the same Kafka types
import type { KafkaMessage, AnalyticsEvent } from "@repo/analytics";

// Service discovery used everywhere
import type { ServiceMap } from "@repo/service-discovery";

Monorepo Benefits

1. Single Source of Truth

Your AnalyticsEvent interface is defined once in apps/internal/analytics/src/types.ts and used by both producers and consumers.

2. Atomic Changes