Case Study

Payday Chat

A real-time, members-only network for online business founders.

The Problem

Founders needed a private, high-signal place to network, build teams, and scale revenue — not another noisy public feed. Payday Chat is invite-only and built around real-time collaboration.

My Role

Built solo with AI-assisted development — Flutter client, NestJS API, data model, real-time layer, and deployment.

Visit Platform ↗

Highlights

Real-time messaging with presence and live events over WebSockets
One NestJS API powering both a Flutter mobile app and a web client
PostgreSQL domain model with Redis for caching and pub/sub fan-out
NGINX gateway, Stripe payments, and OAuth authentication

Stack

FlutterDartNestJSPostgreSQLRedisNGINXStripe

Constraints

Invite-only product — auth and access control had to be correct from day one.
One backend, two clients (Flutter + web) — schema and contracts had to be shared, not duplicated.
Realtime is a feature, not a nice-to-have — presence and live events must survive reconnects.

System Architecture

Clients

Flutter Mobile App

Web App

Gateway

NGINX

API

NestJS REST

WebSocket Gateway

Data

PostgreSQL

Redis (cache + pub/sub)

External

Stripe

OAuth

Key Trade-offs

The decisions worth defending — what I chose, what I turned down, and why.

Realtime transport

Chose

WebSockets with Redis pub/sub fan-out

Rejected

Long-polling or third-party realtime SaaS

Predictable latency, no per-message vendor cost, and Redis already in the stack for caching — one fewer moving part.

Mobile client framework

Chose

Flutter (single codebase for iOS + Android)

Rejected

Native Swift + Kotlin clients

Solo build — two native clients would have doubled the surface area and slowed iteration on the API.

API style

Chose

REST + dedicated WebSocket gateway

Rejected

GraphQL subscriptions

Simpler operational story, easier to cache at the NGINX layer, and the realtime channel stays an explicit, observable component.

What I'd Do Differently

An honest retrospective — the stuff I'd change with more time, more users, or a second pass.

1Introduce contract tests between the NestJS API and the Flutter client earlier — a few breakages were caught only at runtime.
2Move long-lived sockets to a dedicated process so API deploys don't drop client connections.
3Add structured event versioning from day one instead of retrofitting it once the schema started moving.

Technical Deep-Dive

Architecture, specifications, and implementation details.

Naming Conventions

Consistent naming makes the codebase predictable and Copilot suggestions accurate. Follow these rules everywhere without exception.

#Files & Directories

Type	Convention	Example
All files	`kebab-case.type.ts`	`member-profile.entity.ts`
Module folder	`kebab-case/`	`src/members/`
Entity	`feature-name.entity.ts`	`member-profile.entity.ts`
Service	`feature-name.service.ts`	`members.service.ts`
Controller	`feature-name.controller.ts`	`members.controller.ts`
Module	`feature-name.module.ts`	`members.module.ts`
DTO	`action-feature.dto.ts`	`create-post.dto.ts`
Guard	`guard-name.guard.ts`	`jwt-auth.guard.ts`
Strategy	`strategy-name.strategy.ts`	`jwt.strategy.ts`
Decorator	`decorator-name.decorator.ts`	`current-user.decorator.ts`
Filter	`filter-name.filter.ts`	`http-exception.filter.ts`
Interceptor	`name.interceptor.ts`	`transform.interceptor.ts`
Processor	`queue-name.processor.ts`	`email.processor.ts`
Interface	`interface-name.interface.ts`	`jwt-payload.interface.ts`
Test	same as source + `.spec.ts`	`members.service.spec.ts`

#TypeScript Classes

Type	Convention	Example
Class (all types)	`PascalCase`	`MembersService`
Interface	`PascalCase` (no `I` prefix)	`JwtPayload`
Enum	`PascalCase`	`MembershipTier`
Type alias	`PascalCase`	`AuthProvider`
Decorator	`PascalCase`	`@CurrentUser()`

#Variables & Methods

Type	Convention	Example
Variables	`camelCase`	`const userId = ...`
Methods	`camelCase`	`async findOneOrFail()`
Constants (module-level)	`SCREAMING_SNAKE`	`export const REDIS_CLIENT = 'REDIS_CLIENT'`
Private class properties	`camelCase` (no `_` prefix)	`private readonly repo`

#Database

Type	Convention	Example
Table names	`snake_case` (plural)	`member_profiles`, `conversation_participants`
Column names	`snake_case`	`display_name`, `created_at`
Primary key	`id`	always UUID, always `id`
Foreign keys	`{table_singular}_id`	`user_id`, `conversation_id`
Boolean columns	`is_{adjective}`	`is_verified`, `is_admin`, `is_featured`
Timestamp columns	`{verb}_{preposition}_at`	`created_at`, `updated_at`, `deleted_at`, `last_login_at`
Enum columns	`{noun}` (no `_type` unless ambiguous)	`status`, `tier` — but `post_type`, `event_type` where needed
Junction tables	`{table1}_{table2}` alphabetically	`conversation_participants`, `event_attendees`
Indexes	`idx_{table}_{columns}`	`idx_posts_author`, `idx_profiles_skills`

#Redis Keys

Pattern: {resource}:{identifier}:{field?}

Key	Example	TTL
User profile cache	`profile:{userId}`	5 min
Match suggestions	`matches:{userId}`	24 hours
Presence status	`presence:{userId}`	5 min (300s) with heartbeat
Rate limit counter	`throttle:{userId}:{route}`	Per window
Leaderboard	`leaderboard:week`, `leaderboard:month`, `leaderboard:all`	1 hour
Conversation cache	`conversation:{convId}:messages`	2 min
Feed cache	`feed:{userId}:home`	30 sec

#Socket.io Room Names

Pattern: {resource}:{identifier}

Room	Members	Purpose
`user:{userId}`	Single user	Personal notifications
`conversation:{convId}`	Conversation participants	Messaging
`feed:{channelId}`	Channel subscribers	Live feed updates
`feed:home`	All connected members	Global feed updates
`event:{eventId}`	RSVPed attendees	Live event + chat

#BullMQ Queue & Job Names

Queue	Jobs
`email`	`welcome`, `verify-email`, `password-reset`, `notification`, `event-confirmation`, `event-reminder`
`notifications`	`dispatch`
`embeddings`	`generate`, `refresh-all`
`media`	`process-image`, `process-video`, `combine-hls`
`cleanup`	`expire-opportunities`, `archive-events`, `purge-deleted-messages`

#API Routes

Pattern: /{resource} (plural, kebab-case for multi-word)

Resource	Route Prefix
Auth	`/auth`
Members	`/members`
Feed	`/feed`
Conversations	`/conversations`
Opportunities	`/opportunities`
Events	`/events`
Resources	`/resources`
Notifications	`/notifications`
Payments	`/payments`
Admin	`/admin`
Health	`/health`

Sub-resources follow REST conventions:

GET  /opportunities/:id/applications       List applications
POST /opportunities/:id/applications       Apply
PATCH /opportunities/:id/applications/:appId  Update status

#TypeORM Column Mapping

Always explicitly map TypeScript camelCase to database snake_case:

// ✅ Always explicit
@Column({ name: 'display_name', length: 100 })
displayName: string;

@CreateDateColumn({ name: 'created_at' })
createdAt: Date;

// ❌ Never rely on automatic naming (it breaks cross-platform)
@Column()
displayName: string;

#Environment Variables

All environment variables: SCREAMING_SNAKE_CASE

Grouped by prefix:

DB_* — database
REDIS_* — Redis
JWT_* — JWT tokens
MAIL_* — email
STRIPE_* — payments
AWS_* — S3 storage
GOOGLE_* — Google OAuth
APPLE_* — Apple Sign-In
THROTTLE_* — rate limiting
BULL_* — job queue
SWAGGER_* — API docs

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