# Phase 3: Basic Inventory (Quantity-Based) - COMPLETE ✅

## Completion Date
December 16, 2024

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## Overview

Phase 3 implements quantity-based inventory tracking (Layer 1 of the dual inventory model). This provides the foundation for inventory management, stock adjustments, and low stock alerts.

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## ✅ Completed Deliverables

### 1. Inventory Service (`server/modules/inventory/services/index.js`)
- ✅ `getQuantity()` - Get current inventory quantity
- ✅ `checkAvailability()` - Check if product is available in required quantity
- ✅ `adjustQuantity()` - Adjust inventory (increase/decrease) with movement tracking
- ✅ `setQuantity()` - Set absolute quantity with movement tracking
- ✅ `setReorderLevel()` - Set reorder level threshold
- ✅ `getInventory()` - Get inventory record with product/variant details
- ✅ `listInventory()` - List inventory with filters and pagination
- ✅ `getLowStockItems()` - Get items below reorder level
- ✅ `getInventoryMovements()` - Get movement history

### 2. Inventory Controllers (`server/modules/inventory/controllers/index.js`)
- ✅ All CRUD operations implemented
- ✅ Stock checks and availability
- ✅ Movement history retrieval
- ✅ System logging integration
- ✅ Proper error handling

### 3. Inventory Validations (`server/modules/inventory/validations/index.js`)
- ✅ Validation rules for all endpoints
- ✅ Query parameter validation
- ✅ Request body validation
- ✅ Proper error messages

### 4. Inventory Routes (`server/modules/inventory/routes/index.js`)
- ✅ RESTful endpoints with Swagger documentation
- ✅ Role-based authorization (manager/admin for adjustments)
- ✅ All routes integrated into main routes

### 5. Low Stock Alerts
- ✅ Implemented via `getLowStockItems()` function
- ✅ Accessible via `/api/inventory?low_stock=true` query parameter
- ✅ Returns items where `quantity <= reorder_level`

### 6. Inventory Movement Tracking
- ✅ All inventory changes recorded in `inventory_movements` table
- ✅ Movement history with pagination
- ✅ Support for multiple movement reasons:
  - GRN (Goods Receipt Note)
  - SALE
  - SALE_RETURN
  - PRODUCTION_CONSUME
  - PRODUCTION_OUTPUT
  - ADJUSTMENT

### 7. Inventory Seeder (`server/scripts/seeders/seedInventory.js`)
- ✅ Creates inventory records for existing products
- ✅ Handles products with and without variants
- ✅ Sets random quantities and reorder levels
- ✅ Added to main seeder script

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## 📡 API Endpoints

### Get Inventory Quantity
- **Endpoint:** `GET /api/inventory/quantity?product_id=1&variant_id=2`
- **Auth:** Required
- **Returns:** Current inventory quantity

### Check Availability
- **Endpoint:** `GET /api/inventory/check-availability?product_id=1&quantity=10&variant_id=2`
- **Auth:** Required
- **Returns:** Availability status (true/false)

### Get Inventory Record
- **Endpoint:** `GET /api/inventory/:productId?variant_id=2`
- **Auth:** Required
- **Returns:** Inventory record with product/variant details

### List Inventory
- **Endpoint:** `GET /api/inventory?page=1&limit=10&product_id=1&low_stock=true`
- **Auth:** Required
- **Returns:** Paginated inventory list with filters

### Get Inventory Movements
- **Endpoint:** `GET /api/inventory/:productId/movements?variant_id=2&page=1&limit=20`
- **Auth:** Required
- **Returns:** Paginated movement history

### Adjust Inventory
- **Endpoint:** `POST /api/inventory/adjust`
- **Auth:** Required (Manager/Admin only)
- **Body:**
  ```json
  {
    "product_id": 1,
    "variant_id": 2,
    "quantity_change": 10,
    "reason": "ADJUSTMENT",
    "reference_id": null
  }
  ```
- **Returns:** Updated inventory record

### Set Inventory Quantity
- **Endpoint:** `PUT /api/inventory/set-quantity`
- **Auth:** Required (Manager/Admin only)
- **Body:**
  ```json
  {
    "product_id": 1,
    "variant_id": 2,
    "quantity": 50,
    "notes": "Manual stock correction"
  }
  ```
- **Returns:** Updated inventory record

### Set Reorder Level
- **Endpoint:** `PUT /api/inventory/reorder-level`
- **Auth:** Required (Manager/Admin only)
- **Body:**
  ```json
  {
    "product_id": 1,
    "variant_id": 2,
    "reorder_level": 15
  }
  ```
- **Returns:** Updated inventory record

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## 🔑 Key Features

### Quantity-Based Tracking
- Tracks inventory quantities for products and variants
- Supports fractional quantities (DECIMAL 12,3)
- Prevents negative quantities

### Inventory Adjustments
- Increase or decrease inventory quantities
- Automatic movement record creation
- Validation to prevent negative stock

### Low Stock Alerts
- Configurable reorder levels per product/variant
- Easy filtering for low stock items
- Helps with inventory management

### Audit Trail
- All inventory changes logged
- Movement history with reasons
- Reference to source transactions

### Product & Variant Support
- Separate inventory tracking per variant
- Support for products without variants
- Flexible inventory management

### Role-Based Access Control
- Read operations: Authenticated users
- Write operations: Manager/Admin only
- Proper authorization checks

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## 📊 Database Schema

### Inventory Table
- `id` - Primary key
- `product_id` - Foreign key to products
- `variant_id` - Foreign key to product_variants (nullable)
- `quantity` - Current quantity (DECIMAL 12,3)
- `reorder_level` - Reorder threshold (DECIMAL 12,3)
- Unique constraint on (product_id, variant_id)

### Inventory Movement Table
- `id` - Primary key
- `product_id` - Foreign key to products
- `variant_id` - Foreign key to product_variants (nullable)
- `inventory_item_id` - Foreign key to inventory_items (nullable)
- `quantity_change` - Quantity change amount
- `reason` - Movement reason (ENUM)
- `reference_id` - Reference to source transaction (nullable)
- Immutable records (no updated_at)

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## 🔄 Integration Points

### With Phase 2 (Products)
- Uses Product and ProductVariant models
- Respects `track_inventory` flag
- Auto-creates inventory records when accessed

### With Future Phases
- **Phase 4 (Sales):** Will use inventory adjustments on sale creation/cancellation
- **Phase 5 (Procurement):** Will use GRN reason for inventory increases
- **Phase 6 (Production):** Will use PRODUCTION_CONSUME and PRODUCTION_OUTPUT reasons

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## 📝 Notes

- Inventory records are auto-created on first access (default quantity: 0)
- Movement history is immutable (no updates/deletes)
- Low stock filtering uses SQL literal for column comparison
- All operations logged to system_logs for audit trail
- Variant support allows separate inventory tracking per variant

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## ✅ Acceptance Criteria Met

- ✅ Can check product inventory quantity
- ✅ Inventory adjustments work correctly
- ✅ Inventory movements created on changes
- ✅ Reorder alerts trigger correctly
- ✅ Only authorized users can adjust inventory
- ✅ Product and variant support working
- ✅ Low stock filtering working
- ✅ Movement history accessible

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## 🚀 Next Steps

Phase 4: Basic Sales & POS (Core POS Functionality)
- Create POS sale
- Add/remove items from sale
- Calculate totals
- Cancel sale (before payment)
- Inventory reservation/release
- Invoice number generation

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**Phase 3 Status: COMPLETE ✅**

