modular-saas-architecture

Build SAAS platforms with pluggable business modules (Advanced Inventory, Restaurant, Pharmacy, etc.) that can be enabled/disabled per tenant without breaking the system. Use when designing modular SAAS features, implementing module toggles, ensuring module independence, and building scalable multi-tenant platforms with optional features.

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Install skill "modular-saas-architecture" with this command: npx skills add peterbamuhigire/skills-web-dev/peterbamuhigire-skills-web-dev-modular-saas-architecture

Required Plugins

Superpowers plugin: MUST be active for all work using this skill. Use throughout the entire build pipeline — design decisions, code generation, debugging, quality checks, and any task where it offers enhanced capabilities. If superpowers provides a better way to accomplish something, prefer it over the default approach.

Modular SAAS Architecture

Overview

Architecture pattern for building SAAS platforms where business modules (Advanced Inventory, Restaurant, Pharmacy, Retail, etc.) can be independently enabled, disabled, or added without affecting other parts of the system.

Core Principles:

  • Module Independence: Each module is self-contained with minimal dependencies
  • Graceful Degradation: Disabling a module doesn't break dependent features
  • Per-Tenant Control: Each tenant can enable only the modules they need
  • Zero Breaking Changes: Adding/removing modules preserves existing functionality
  • Clean Interfaces: Modules communicate through well-defined contracts

Security Baseline (Required): Always load and apply the Vibe Security Skill for any web app, API, or module implementation work.

Key Benefits:

  • Customers pay only for modules they use
  • Faster feature development (independent teams per module)
  • Easier testing (modules tested in isolation)
  • Better scaling (resource-intensive modules can scale independently)
  • Reduced complexity (tenants see only their enabled modules)

When to Use

✅ Use for:

  • Multi-tenant SAAS platforms with diverse customer needs
  • Systems serving different industries (retail, healthcare, hospitality, etc.)
  • Platforms with optional premium features
  • Applications requiring vertical-specific functionality
  • Systems with varying compliance requirements per industry

❌ Don't use for:

  • Single-tenant applications
  • Simple CRUD apps without feature variations
  • Tightly coupled monolithic systems
  • Systems where all features are always required

Module Architecture Pattern

System Structure

┌────────────────────────────────────────────────────────────┐
│                  SAAS Platform (Maduuka)                   │
├────────────────────────────────────────────────────────────┤
│                     CORE SYSTEM                            │
│  ┌──────────────────────────────────────────────────┐     │
│  │ • Authentication & Authorization                  │     │
│  │ • Multi-tenant Isolation                         │     │
│  │ • User Management                                │     │
│  │ • Billing & Subscriptions                        │     │
│  │ • Audit Logs                                     │     │
│  │ • Module Registry & Feature Flags                │     │
│  └──────────────────────────────────────────────────┘     │
│                           ▲                                │
│                           │                                │
│          ┌────────────────┴────────────────┐              │
│          │                                  │              │
├──────────▼──────────┬──────────▼────────────┬─────────────┤
│  BUSINESS MODULES   │   BUSINESS MODULES    │   MODULES   │
├─────────────────────┼───────────────────────┼─────────────┤
│ 🏪 Retail Module    │ 🍽️  Restaurant Module │ 💊 Pharmacy │
│   • POS Sales       │   • Table Management  │   • Rx Mgmt │
│   • Inventory       │   • Order Management  │   • Drug DB │
│   • Invoicing       │   • Kitchen Display   │   • Scripts │
│                     │   • Reservations      │             │
├─────────────────────┼───────────────────────┼─────────────┤
│ 📦 Adv. Inventory   │ 🏨 Hospitality Module │ 📚 Library  │
│   • Stock Items     │   • Room Booking      │   • Catalog │
│   • UOM Conversion  │   • Housekeeping      │   • Lending │
│   • Multi-location  │   • Guest Management  │   • Fines   │
│   • Transfers       │                       │             │
└─────────────────────┴───────────────────────┴─────────────┘

Per-Tenant Configuration:
Tenant A: Retail + Adv. Inventory (enabled)
Tenant B: Restaurant + Hospitality (enabled)
Tenant C: Pharmacy only (enabled)

Module Anatomy

Each module consists of:

modules/
├── advanced-inventory/
│   ├── module.config.php         # Module metadata
│   ├── permissions.php           # Module-specific permissions
│   ├── routes.php               # API endpoints
│   ├── database/
│   │   ├── schema.sql           # Module tables (tenant-scoped)
│   │   └── migrations/          # Database changes
│   ├── api/                     # Module API handlers
│   ├── views/                   # UI pages (optional)
│   ├── services/                # Business logic
│   ├── models/                  # Data models
│   └── tests/                   # Module tests

Module Definition Pattern

1. Module Configuration

// modules/advanced-inventory/module.config.php
return [
    'module_code' => 'ADV_INV',
    'name' => 'Advanced Inventory',
    'description' => 'Multi-location inventory with UOM conversions and transfers',
    'version' => '1.0.0',
    'icon' => 'bi-boxes',

    // Module dependencies (optional)
    'requires' => [],  // Empty = no dependencies
    // 'requires' => ['CORE', 'RETAIL'],  // Requires these modules

    // Module provides these features
    'features' => [
        'stock_items',
        'uom_conversions',
        'stock_transfers',
        'multi_location_inventory',
        'stock_adjustments',
    ],

    // Permissions defined by this module
    'permissions' => [
        'VIEW_INVENTORY',
        'MANAGE_STOCK',
        'APPROVE_TRANSFERS',
        'VIEW_REPORTS',
    ],

    // Database tables owned by this module
    'tables' => [
        'tbl_stock_items',
        'tbl_stock_item_uoms',
        'tbl_stock_transfers',
        'tbl_stock_adjustments',
        'tbl_inventory_transactions',
    ],

    // Navigation menu items
    'menu' => [
        [
            'label' => 'Inventory',
            'icon' => 'bi-boxes',
            'items' => [
                ['label' => 'Stock Items', 'url' => '/stock-items-catalog.php'],
                ['label' => 'UOM Conversions', 'url' => '/advanced-inventory-uom.php'],
                ['label' => 'Stock Transfers', 'url' => '/stock-transfers.php'],
            ]
        ]
    ],

    // Billing information
    'pricing' => [
        'type' => 'addon',  // 'core', 'addon', 'enterprise'
        'price_monthly' => 29.99,
        'trial_days' => 14,
    ]
];

2. Module Registry

// src/ModuleRegistry.php
class ModuleRegistry {
    private $db;
    private $cacheFile = __DIR__ . '/../cache/modules.json';

    public function getAvailableModules(): array {
        // Scan modules directory
        $modules = [];
        $moduleDirs = glob(__DIR__ . '/../modules/*', GLOB_ONLYDIR);

        foreach ($moduleDirs as $dir) {
            $configFile = $dir . '/module.config.php';
            if (file_exists($configFile)) {
                $config = require $configFile;
                $modules[$config['module_code']] = $config;
            }
        }

        return $modules;
    }

    public function getEnabledModules(int $franchiseId): array {
        $stmt = $this->db->prepare('
            SELECT module_code, config
            FROM tbl_franchise_modules
            WHERE franchise_id = ? AND is_enabled = 1
        ');
        $stmt->execute([$franchiseId]);
        return $stmt->fetchAll(PDO::FETCH_ASSOC);
    }

    public function isModuleEnabled(int $franchiseId, string $moduleCode): bool {
        $stmt = $this->db->prepare('
            SELECT is_enabled
            FROM tbl_franchise_modules
            WHERE franchise_id = ? AND module_code = ?
        ');
        $stmt->execute([$franchiseId, $moduleCode]);
        return (bool) $stmt->fetchColumn();
    }
}

3. Module Access Control

// src/config/auth.php

/**
 * Require module access (fails gracefully if module disabled)
 */
function requireModuleAccess(string $moduleCode): void {
    if (!isLoggedIn()) {
        header('Location: ./sign-in.php');
        exit();
    }

    $franchiseId = (int) $_SESSION['franchise_id'];

    $db = (new \App\Config\Database())->getConnection();
    $stmt = $db->prepare('
        SELECT is_enabled
        FROM tbl_franchise_modules
        WHERE franchise_id = ? AND module_code = ?
    ');
    $stmt->execute([$franchiseId, $moduleCode]);
    $enabled = $stmt->fetchColumn();

    if (!$enabled) {
        // Module not enabled for this tenant
        header('Location: ./module-not-available.php?module=' . urlencode($moduleCode));
        exit();
    }
}

/**
 * Check if module is enabled (non-blocking)
 */
function hasModuleAccess(string $moduleCode): bool {
    if (!isLoggedIn()) {
        return false;
    }

    $franchiseId = (int) $_SESSION['franchise_id'];

    $db = (new \App\Config\Database())->getConnection();
    $stmt = $db->prepare('
        SELECT is_enabled
        FROM tbl_franchise_modules
        WHERE franchise_id = ? AND module_code = ?
    ');
    $stmt->execute([$franchiseId, $moduleCode]);
    return (bool) $stmt->fetchColumn();
}

4. Page-Level Module Protection

// advanced-inventory-uom.php
<?php
require_once 'src/config/auth.php';

if (!isLoggedIn()) {
    header('Location: ./sign-in.php');
    exit();
}

// CRITICAL: Require module access
requireModuleAccess('ADV_INV');
requirePermissionGlobal('VIEW_INVENTORY');

// Page continues only if module is enabled
?>

Minimal Module Registry Stub (Template Mode)

Use this when scaffolding a template so UI and menu logic are already module-aware, even before real module tables exist.

// src/Modules/ModuleRegistry.php
class ModuleRegistry {
    public function getAvailableModules(): array {
        return [
            'INVENTORY' => ['label' => 'Inventory', 'menu' => '/inventory.php'],
            'SALES' => ['label' => 'Sales', 'menu' => '/sales.php'],
        ];
    }
}

// src/config/modules.php
function hasModuleAccess(string $moduleCode, int $tenantId): bool {
    return true;
}

function requireModuleAccess(string $moduleCode, int $tenantId): void {
    if (!hasModuleAccess($moduleCode, $tenantId)) {
        header('Location: /module-not-available.php');
        exit();
    }
}

Module Independence Patterns

1. Optional Dependencies

Problem: Module A wants to use Module B, but Module B might be disabled.

Solution: Check module availability before using.

// In Restaurant Module
class OrderService {
    public function createOrder(array $data) {
        // Core order creation (always works)
        $order = $this->saveOrder($data);

        // Optional: Use Advanced Inventory if enabled
        if (hasModuleAccess('ADV_INV')) {
            $this->updateInventory($order);
        } else {
            // Fallback: Use simple inventory
            $this->updateBasicStock($order);
        }

        // Optional: Send to Kitchen Display if enabled
        if (hasModuleAccess('KITCHEN_DISPLAY')) {
            $this->sendToKitchen($order);
        }

        return $order;
    }
}

2. Interface-Based Integration

Problem: Module A needs functionality that might come from different modules.

Solution: Define interfaces, modules implement them.

// Core interface
interface InventoryProvider {
    public function checkStock(int $itemId, float $quantity): bool;
    public function decrementStock(int $itemId, float $quantity): void;
}

// Basic implementation (always available)
class BasicInventory implements InventoryProvider {
    public function checkStock(int $itemId, float $quantity): bool {
        // Simple stock check
    }

    public function decrementStock(int $itemId, float $quantity): void {
        // Simple decrement
    }
}

// Advanced module implementation (optional)
class AdvancedInventory implements InventoryProvider {
    public function checkStock(int $itemId, float $quantity): bool {
        // Multi-location, UOM-aware check
    }

    public function decrementStock(int $itemId, float $quantity): void {
        // Multi-location, UOM-aware decrement with audit trail
    }
}

// Factory selects implementation based on enabled modules
class InventoryFactory {
    public static function create(): InventoryProvider {
        if (hasModuleAccess('ADV_INV')) {
            return new AdvancedInventory();
        }
        return new BasicInventory();
    }
}

3. Event-Driven Communication

Problem: Module A wants to notify Module B when something happens, but Module B might not exist.

Solution: Use event system with optional listeners.

// Event system (core)
class EventDispatcher {
    private static $listeners = [];

    public static function listen(string $event, callable $handler): void {
        self::$listeners[$event][] = $handler;
    }

    public static function dispatch(string $event, array $data = []): void {
        if (!isset(self::$listeners[$event])) {
            return; // No listeners, no problem
        }

        foreach (self::$listeners[$event] as $handler) {
            try {
                $handler($data);
            } catch (\Exception $e) {
                // Log error but don't break other listeners
                error_log("Event handler failed: " . $e->getMessage());
            }
        }
    }
}

// Module A (always enabled)
class SalesModule {
    public function completeSale(Sale $sale) {
        // Complete sale logic
        $this->saveSale($sale);

        // Notify anyone listening (optional)
        EventDispatcher::dispatch('sale.completed', ['sale' => $sale]);
    }
}

// Module B (optional - Advanced Inventory)
// modules/advanced-inventory/bootstrap.php
if (hasModuleAccess('ADV_INV')) {
    EventDispatcher::listen('sale.completed', function($data) {
        $inventoryService = new InventoryService();
        $inventoryService->decrementStock($data['sale']);
    });
}

// Module C (optional - Loyalty)
// modules/loyalty/bootstrap.php
if (hasModuleAccess('LOYALTY')) {
    EventDispatcher::listen('sale.completed', function($data) {
        $loyaltyService = new LoyaltyService();
        $loyaltyService->awardPoints($data['sale']);
    });
}

Database Design for Modular SAAS

1. Module Tables

Each module owns its tables:

-- Core tables (always present)
CREATE TABLE tbl_users (...);
CREATE TABLE tbl_franchises (...);
CREATE TABLE tbl_permissions (...);

-- Advanced Inventory module tables
CREATE TABLE tbl_stock_items (
    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    franchise_id BIGINT NOT NULL,  -- Tenant isolation
    name VARCHAR(255) NOT NULL,
    -- ... other fields
    FOREIGN KEY (franchise_id) REFERENCES tbl_franchises(id)
);

CREATE TABLE tbl_stock_item_uoms (
    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    stock_item_id BIGINT NOT NULL,
    -- ... other fields
    FOREIGN KEY (stock_item_id) REFERENCES tbl_stock_items(id) ON DELETE CASCADE
);

-- Restaurant module tables
CREATE TABLE tbl_restaurant_tables (
    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    franchise_id BIGINT NOT NULL,
    table_number VARCHAR(50) NOT NULL,
    -- ... other fields
    FOREIGN KEY (franchise_id) REFERENCES tbl_franchises(id)
);

2. Module Registry Table

-- Track available modules
CREATE TABLE tbl_modules (
    module_code VARCHAR(50) PRIMARY KEY,
    name VARCHAR(255) NOT NULL,
    description TEXT,
    version VARCHAR(20),
    is_core BOOLEAN DEFAULT 0,  -- Core modules cannot be disabled
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

-- Track which modules are enabled per tenant
CREATE TABLE tbl_franchise_modules (
    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    franchise_id BIGINT NOT NULL,
    module_code VARCHAR(50) NOT NULL,
    is_enabled BOOLEAN DEFAULT 1,
    enabled_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    disabled_at TIMESTAMP NULL,
    config JSON,  -- Module-specific settings
    UNIQUE KEY (franchise_id, module_code),
    FOREIGN KEY (franchise_id) REFERENCES tbl_franchises(id),
    FOREIGN KEY (module_code) REFERENCES tbl_modules(module_code)
);

-- Billing for modules
CREATE TABLE tbl_franchise_module_subscriptions (
    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    franchise_id BIGINT NOT NULL,
    module_code VARCHAR(50) NOT NULL,
    status ENUM('trial', 'active', 'cancelled', 'expired') DEFAULT 'trial',
    trial_ends_at TIMESTAMP NULL,
    next_billing_date DATE,
    price_monthly DECIMAL(10, 2),
    created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (franchise_id) REFERENCES tbl_franchises(id),
    FOREIGN KEY (module_code) REFERENCES tbl_modules(module_code)
);

3. Cross-Module References (Safe Pattern)

Problem: Module A table references Module B table, but Module B might be disabled.

Solution: Use nullable foreign keys with soft references.

-- Sales table (core/retail module)
CREATE TABLE tbl_sales (
    id BIGINT PRIMARY KEY AUTO_INCREMENT,
    franchise_id BIGINT NOT NULL,

    -- Safe reference to optional module
    restaurant_table_id BIGINT NULL,  -- Nullable!

    -- Don't use FK if target module is optional
    -- FOREIGN KEY (restaurant_table_id) REFERENCES tbl_restaurant_tables(id)

    -- Instead, check at application level:
    -- if (hasModuleAccess('RESTAURANT') && $tableId) { validate($tableId); }
);

UI/UX for Modular Systems

1. Dynamic Navigation

Menu constraints (Required):

  • Keep navigation minimal and job-focused.
  • Each menu may have max 5 submenus.
  • Each submenu may have max 6 items.
  • If more items are needed, add one extra submenu level (no deeper).
  • Use Bootstrap Icons on all headings and entries (bi-*).
  • Prefer fewer pages: group related features into one screen with permissioned sections.
// includes/topbar.php
<?php
$enabledModules = getEnabledModules($_SESSION['franchise_id']);
?>

<nav>
    <!-- Core navigation always visible -->
    <a href="/dashboard.php">Dashboard</a>
    <a href="/settings.php">Settings</a>

    <!-- Module-specific navigation -->
    <?php if (hasModuleAccess('RETAIL')): ?>
        <a href="/pos-sales.php">POS</a>
        <a href="/invoices.php">Invoices</a>
    <?php endif; ?>

    <?php if (hasModuleAccess('ADV_INV')): ?>
        <div class="dropdown">
            <a href="#">Inventory</a>
            <ul>
                <li><a href="/stock-items-catalog.php">Stock Items</a></li>
                <li><a href="/advanced-inventory-uom.php">UOM Conversions</a></li>
                <li><a href="/stock-transfers.php">Transfers</a></li>
            </ul>
        </div>
    <?php endif; ?>

    <?php if (hasModuleAccess('RESTAURANT')): ?>
        <a href="/restaurant-orders.php">Orders</a>
        <a href="/tables.php">Tables</a>
    <?php endif; ?>
</nav>

2. Module Marketplace UI

// modules-marketplace.php
<?php
requirePermissionGlobal('MANAGE_BILLING');  // Only owners can enable modules

$availableModules = getAvailableModules();
$enabledModules = getEnabledModules($_SESSION['franchise_id']);
?>

<h2>Available Modules</h2>

<?php foreach ($availableModules as $code => $module): ?>
    <?php $isEnabled = in_array($code, array_column($enabledModules, 'module_code')); ?>

    <div class="module-card <?= $isEnabled ? 'enabled' : '' ?>">
        <i class="<?= $module['icon'] ?>"></i>
        <h3><?= $module['name'] ?></h3>
        <p><?= $module['description'] ?></p>

        <?php if ($module['pricing']['type'] === 'core'): ?>
            <span class="badge bg-blue">Included</span>
        <?php else: ?>
            <p class="price">$<?= $module['pricing']['price_monthly'] ?>/month</p>
        <?php endif; ?>

        <?php if (!$isEnabled): ?>
            <button onclick="enableModule('<?= $code ?>')">
                Enable (<?= $module['pricing']['trial_days'] ?> day trial)
            </button>
        <?php else: ?>
            <button disabled>Enabled</button>
            <button onclick="disableModule('<?= $code ?>')" class="btn-danger">
                Disable
            </button>
        <?php endif; ?>
    </div>
<?php endforeach; ?>

3. Feature Not Available Page

// module-not-available.php
<?php
$moduleCode = $_GET['module'] ?? 'UNKNOWN';
$moduleName = getModuleName($moduleCode);
?>

<div class="text-center py-5">
    <i class="bi bi-lock-fill" style="font-size: 4rem; color: #ccc;"></i>
    <h2>Module Not Available</h2>
    <p>The <strong><?= $moduleName ?></strong> module is not enabled for your account.</p>

    <a href="/modules-marketplace.php" class="btn btn-primary">
        View Available Modules
    </a>
    <a href="/dashboard.php" class="btn btn-secondary">
        Back to Dashboard
    </a>
</div>

Module Lifecycle Management

1. Enabling a Module

// api/modules.php?action=enable
public function enableModule(int $franchiseId, string $moduleCode): array {
    // 1. Validate module exists
    $moduleConfig = $this->moduleRegistry->getModule($moduleCode);
    if (!$moduleConfig) {
        return ['success' => false, 'message' => 'Module not found'];
    }

    // 2. Check dependencies
    foreach ($moduleConfig['requires'] as $requiredModule) {
        if (!$this->isModuleEnabled($franchiseId, $requiredModule)) {
            return [
                'success' => false,
                'message' => "Requires {$requiredModule} module to be enabled first"
            ];
        }
    }

    // 3. Run module migrations (create tables)
    $this->runModuleMigrations($moduleCode);

    // 4. Enable module
    $stmt = $this->db->prepare('
        INSERT INTO tbl_franchise_modules
        (franchise_id, module_code, is_enabled)
        VALUES (?, ?, 1)
        ON DUPLICATE KEY UPDATE
            is_enabled = 1,
            enabled_at = CURRENT_TIMESTAMP
    ');
    $stmt->execute([$franchiseId, $moduleCode]);

    // 5. Create trial subscription
    $this->createTrialSubscription($franchiseId, $moduleCode);

    // 6. Audit log
    auditLog('MODULE_ENABLED', [
        'franchise_id' => $franchiseId,
        'module_code' => $moduleCode
    ]);

    return ['success' => true, 'message' => 'Module enabled'];
}

2. Disabling a Module

public function disableModule(int $franchiseId, string $moduleCode): array {
    // 1. Check if other modules depend on this
    $dependentModules = $this->getDependentModules($franchiseId, $moduleCode);
    if (!empty($dependentModules)) {
        return [
            'success' => false,
            'message' => 'Cannot disable. Required by: ' . implode(', ', $dependentModules)
        ];
    }

    // 2. Don't delete data, just disable access
    $stmt = $this->db->prepare('
        UPDATE tbl_franchise_modules
        SET is_enabled = 0, disabled_at = CURRENT_TIMESTAMP
        WHERE franchise_id = ? AND module_code = ?
    ');
    $stmt->execute([$franchiseId, $moduleCode]);

    // 3. Cancel subscription
    $this->cancelSubscription($franchiseId, $moduleCode);

    // 4. Audit log
    auditLog('MODULE_DISABLED', [
        'franchise_id' => $franchiseId,
        'module_code' => $moduleCode
    ]);

    return ['success' => true, 'message' => 'Module disabled'];
}

3. Data Retention After Disable

Important: Never delete module data when module is disabled!

// When module is disabled:
// ✅ GOOD: Keep data, disable access
UPDATE tbl_franchise_modules SET is_enabled = 0 WHERE ...;
// User can re-enable and data is still there

// ❌ BAD: Delete data
DELETE FROM tbl_stock_items WHERE franchise_id = ?;
// User loses all data if they re-enable!

Testing Modular Systems

1. Module Isolation Tests

class AdvancedInventoryModuleTest extends TestCase {
    public function testModuleWorksIndependently() {
        // Enable only Advanced Inventory
        $this->enableModule('ADV_INV');
        $this->disableModule('RESTAURANT');
        $this->disableModule('PHARMACY');

        // Should work without other modules
        $stockItem = $this->createStockItem(['name' => 'Test Item']);
        $this->assertNotNull($stockItem);

        $uom = $this->createUOMConversion($stockItem->id, 'Gram', 0.001);
        $this->assertNotNull($uom);
    }

    public function testModuleAccessControl() {
        // Disable module
        $this->disableModule('ADV_INV');

        // Accessing module page should redirect
        $response = $this->get('/advanced-inventory-uom.php');
        $this->assertRedirect('/module-not-available.php');
    }
}

2. Cross-Module Integration Tests

public function testRestaurantWithInventoryIntegration() {
    // Enable both modules
    $this->enableModule('RESTAURANT');
    $this->enableModule('ADV_INV');

    // Create stock item
    $stockItem = $this->createStockItem(['name' => 'Tomato']);

    // Create restaurant order using stock item
    $order = $this->createRestaurantOrder([
        'items' => [['stock_item_id' => $stockItem->id, 'qty' => 2]]
    ]);

    // Verify inventory was decremented
    $this->assertEquals($stockItem->quantity - 2, $this->getStockQuantity($stockItem->id));
}

public function testRestaurantWithoutInventory() {
    // Enable only Restaurant
    $this->enableModule('RESTAURANT');
    $this->disableModule('ADV_INV');

    // Create order (should use basic inventory)
    $order = $this->createRestaurantOrder([
        'items' => [['product_id' => 1, 'qty' => 2]]
    ]);

    // Should work without Advanced Inventory
    $this->assertNotNull($order);
}

Best Practices

DO ✅

Module Design:

  • Keep modules self-contained (own tables, own logic)
  • Use feature flags for module checks (hasModuleAccess())
  • Provide fallback when optional modules are disabled
  • Version module APIs for backward compatibility
  • Document module dependencies clearly

Database:

  • Always include franchise_id for tenant isolation
  • Use migrations for module schema changes
  • Keep data when module is disabled (soft delete)
  • Use nullable FKs for cross-module references

Testing:

  • Test module works independently
  • Test graceful degradation when dependencies missing
  • Test re-enabling after disable (data preserved)
  • Test billing/subscription flow

DON'T ❌

Module Design:

  • Don't hard-code module dependencies (check at runtime)
  • Don't break core features when module disabled
  • Don't expose module internals to other modules
  • Don't assume module is always enabled

Database:

  • Don't delete module data on disable (user may re-enable)
  • Don't use hard FK constraints for optional modules
  • Don't share tables between modules (coupling)
  • Don't skip tenant_id in module tables

UI/UX:

  • Don't show disabled module navigation
  • Don't let users access disabled module pages
  • Don't display cryptic errors (show upgrade CTA)

Anti-Patterns

❌ Hard Dependencies

// BAD: Assumes Advanced Inventory is always enabled
class RestaurantOrderService {
    public function createOrder($data) {
        $inventory = new AdvancedInventoryService();  // Crashes if disabled!
        $inventory->decrementStock($data['items']);
    }
}

// GOOD: Check if module is enabled
class RestaurantOrderService {
    public function createOrder($data) {
        if (hasModuleAccess('ADV_INV')) {
            $inventory = new AdvancedInventoryService();
            $inventory->decrementStock($data['items']);
        } else {
            $this->decrementBasicStock($data['items']);
        }
    }
}

❌ Circular Dependencies

// BAD: Restaurant depends on Inventory, Inventory depends on Restaurant
// Restaurant Module
class OrderService {
    public function createOrder() {
        $inventory = new InventoryService();  // Restaurant → Inventory
    }
}

// Inventory Module
class InventoryService {
    public function transferStock() {
        $orders = new OrderService();  // Inventory → Restaurant
    }
}

// GOOD: Use events to decouple
// Restaurant Module
class OrderService {
    public function createOrder() {
        EventDispatcher::dispatch('order.created', $order);
    }
}

// Inventory Module (listens to event)
EventDispatcher::listen('order.created', function($order) {
    $inventory = new InventoryService();
    $inventory->decrementStock($order);
});

❌ Deleting Data on Disable

// BAD: User loses data if they disable and re-enable
public function disableModule($franchiseId, $moduleCode) {
    if ($moduleCode === 'ADV_INV') {
        $this->db->exec("DELETE FROM tbl_stock_items WHERE franchise_id = $franchiseId");
    }
}

// GOOD: Keep data, just disable access
public function disableModule($franchiseId, $moduleCode) {
    $this->db->prepare('
        UPDATE tbl_franchise_modules
        SET is_enabled = 0
        WHERE franchise_id = ? AND module_code = ?
    ')->execute([$franchiseId, $moduleCode]);
}

Summary

Core Principles:

  1. Module Independence: Each module is self-contained and optional
  2. Graceful Degradation: System works when modules are disabled
  3. Per-Tenant Control: Each tenant enables only needed modules
  4. Zero Breaking Changes: Adding/removing modules preserves functionality
  5. Clean Interfaces: Modules communicate through contracts

Implementation Checklist:

  • Module config file with metadata
  • Module access control (requireModuleAccess())
  • Optional dependency checks (hasModuleAccess())
  • Module registry in database
  • Per-tenant module subscriptions
  • Dynamic navigation based on enabled modules
  • Fallback logic when modules disabled
  • Migration system for module schemas
  • Billing integration for module pricing
  • Tests for module isolation and integration

Key Insight: Build modules like Lego blocks—each piece works independently, but they snap together perfectly to create more powerful features.

Source Transparency

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