High-Level Design (HLD)

Component-level view of the platform: main modules, integration points, and how they connect.

1. Module Overview

┌──────────────────────────────────────────────────────────────────────────┐
│                         PREM TRAVELS PLATFORM                              │
├──────────────────────────────────────────────────────────────────────────┤
│  APPLICATIONS (Layer 4)                                                    │
│  ┌────────────┐ ┌────────────┐ ┌────────────┐ ┌────────────┐ ┌─────────┐ │
│  │   Admin    │ │   Driver   │ │  Employee  │ │  Customer  │ │ Vendor  │ │
│  │   Portal   │ │   Portal   │ │   Portal   │ │   Portal   │ │ Portal  │ │
│  └─────┬──────┘ └─────┬──────┘ └─────┬──────┘ └─────┬──────┘ └────┬─────┘ │
│        └──────────────┼──────────────┼──────────────┼─────────────┘       │
│                       ▼              ▼              ▼                     │
│  CORE SERVICES (Layers 1–3)                                                │
│  ┌─────────────┐ ┌─────────────┐ ┌─────────────┐ ┌─────────────────────┐ │
│  │ Auth & RBAC │ │  Workflow   │ │ Notification│ │ Document Lifecycle   │ │
│  │   Engine    │ │   Engine    │ │   Engine    │ │ & Central Bin        │ │
│  └──────┬──────┘ └──────┬──────┘ └──────┬──────┘ └──────────┬──────────┘ │
│         └───────────────┼───────────────┼────────────────────┘             │
│                         ▼                 ▼                                │
│  OPERATIONAL MODULES                                                       │
│  ┌─────────────┐ ┌─────────────┐ ┌─────────────┐ ┌─────────────┐        │
│  │  Booking &  │ │ HR, Attend. │ │   Fleet &    │ │  Payroll &  │        │
│  │  Work Order │ │  & Leave    │ │  Maintenance │ │  Disbursement│        │
│  └──────┬──────┘ └──────┬──────┘ └──────┬──────┘ └──────┬──────┘        │
│         └───────────────┼───────────────┼───────────────┘                 │
│                         ▼                                                 │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────┐                        │
│  │  Database   │  │ Event Bus   │  │  External   │                        │
│  │  (Primary)  │  │ (e.g. AWS)  │  │  (SMS/Email)│                        │
│  └─────────────┘  └─────────────┘  └─────────────┘                        │
└──────────────────────────────────────────────────────────────────────────┘

2. Key Integration Points

Portals ↔ Backend: All portals consume the same REST API; auth and RBAC determine allowed actions.
Workflow Engine: Used by bookings, work orders, payroll, leave, and other entities that require approval chains.
Notification Engine: Triggered by events (e.g. approval requests, document expiry); sends in-app, SMS, and email.
Document Lifecycle: Tracks expiry (licenses, RC, insurance); triggers reminders and escalations via events.
Payroll ↔ Attendance & Leave: Payroll reads attendance and leave data; policies drive calculations and deductions.

3. Design Principles

Policy-driven: Business rules (approvals, deductions, compliance) are configurable rather than hard-coded.

Event-driven where appropriate: Notifications, reminders, and workflow steps are triggered by events to keep the main path fast and decoupled.

Single source of truth: Core entities (employees, vehicles, customers, etc.) are maintained once and referenced across modules.

Audit & recoverability: Critical actions are logged; soft delete (central bin) allows recovery and traceability.

4. Extensibility

The platform is structured so that new entity types, workflows, and integrations can be added with minimal disruption. Master data (shifts, vehicle types, designations, policies) is centralized and reused across operational modules.