# Phase 6: Inventory Enhancements (UID-Based) - COMPLETE ✅

## Completion Date
December 16, 2024

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## Overview

Phase 6 implements UID-based inventory tracking (Layer 2) on top of the existing quantity-based inventory system. This enables tracking individual items with unique identifiers (UIDs/barcodes) while maintaining sync with quantity-based inventory.

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## ✅ Completed Deliverables

### 1. UID Generation Utilities (`utils/uidGenerator.js`)
- ✅ `generateUID()` - Generate unique UID (format: PREFIX-TIMESTAMP-RANDOM)
- ✅ `generateBarcode()` - Generate numeric barcode
- ✅ `isValidUID()` - Validate UID format
- ✅ `isValidBarcode()` - Validate barcode format

### 2. Barcode/QR Code Generator Utilities (`utils/barcodeGenerator.js`)
- ✅ `generateQRCodeDataURL()` - Generate QR code as data URL (base64)
- ✅ `generateQRCodeFile()` - Generate QR code file and save to disk
- ✅ `generateQRCodeBuffer()` - Generate QR code as buffer

### 3. Inventory Items Service (`modules/inventory/services/items.js`)
- ✅ `createInventoryItem()` - Create inventory item with UID/barcode, syncs with quantity layer
- ✅ `getInventoryItemByUID()` - Get inventory item by UID or barcode
- ✅ `updateInventoryItemStatus()` - Update item status, handles quantity sync
- ✅ `scanInventoryItem()` - Scan item with QR code generation
- ✅ `listInventoryItems()` - List items with filters and pagination

### 4. Inventory Items Controllers (`modules/inventory/controllers/items.js`)
- ✅ `createInventoryItem` - Create inventory item controller
- ✅ `getInventoryItemByUID` - Get inventory item controller
- ✅ `updateInventoryItemStatus` - Update status controller
- ✅ `scanInventoryItem` - Scan item controller
- ✅ `listInventoryItems` - List items controller

### 5. Inventory Items Validations (`modules/inventory/validations/items.js`)
- ✅ `validateCreateInventoryItem` - Validation for creating items
- ✅ `validateGetInventoryItemByUID` - Validation for getting item by UID
- ✅ `validateUpdateInventoryItemStatus` - Validation for status updates
- ✅ `validateScanInventoryItem` - Validation for scanning items
- ✅ `validateListInventoryItems` - Validation for listing items

### 6. Inventory Items Routes (`modules/inventory/routes/index.js`)
- ✅ POST /api/inventory/items - Create inventory item
- ✅ GET /api/inventory/items/:uid - Get inventory item by UID/barcode
- ✅ GET /api/inventory/items - List inventory items with filters
- ✅ GET /api/inventory/items/:uid/scan - Scan inventory item (includes QR code)
- ✅ PUT /api/inventory/items/:uid/status - Update inventory item status

### 7. Sales Service Integration
- ✅ Updated `createSale()` to support linking sale items to inventory items
- ✅ Optional `inventory_item_id` in sale items
- ✅ Inventory item status updated to RESERVED when linked to sale
- ✅ Quantity-based inventory reservation skipped when inventory_item_id provided
- ✅ Inventory movements recorded for UID-based items

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## 📡 API Endpoints

### Create Inventory Item
- **Endpoint:** `POST /api/inventory/items`
- **Auth:** Required (manager, system_admin)
- **Body:**
  ```json
  {
    "product_id": 1,
    "variant_id": 2,
    "source": "GRN",
    "uid": "UID-1234567890-ABCD", // Optional
    "barcode": "123456789012" // Optional
  }
  ```
- **Returns:** Created inventory item with UID and barcode

### Get Inventory Item by UID
- **Endpoint:** `GET /api/inventory/items/:uid`
- **Auth:** Required
- **Returns:** Inventory item with product and variant details

### List Inventory Items
- **Endpoint:** `GET /api/inventory/items?page=1&limit=10&product_id=1&status=IN_STOCK&source=GRN`
- **Auth:** Required
- **Filters:**
  - `product_id` - Filter by product ID
  - `variant_id` - Filter by variant ID
  - `status` - Filter by status (IN_STOCK, RESERVED, SOLD, RETURNED, DAMAGED, SCRAPPED)
  - `source` - Filter by source (GRN, PRODUCTION, RETURN)
- **Returns:** Paginated inventory items list

### Scan Inventory Item
- **Endpoint:** `GET /api/inventory/items/:uid/scan`
- **Auth:** Required
- **Returns:** Inventory item with QR code data URL

### Update Inventory Item Status
- **Endpoint:** `PUT /api/inventory/items/:uid/status`
- **Auth:** Required (manager, system_admin)
- **Body:**
  ```json
  {
    "status": "SOLD",
    "reason": "Item sold"
  }
  ```
- **Returns:** Updated inventory item

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## 🔑 Key Features

### UID Generation
- **Format:** `{PREFIX}-{TIMESTAMP}-{RANDOM}`
- **Example:** `XYZ-1734368400000-A1B2C3D4`
- **Configurable prefix** via `BARCODE_PREFIX` env variable
- **Unique identifiers** for each inventory item

### Barcode Generation
- **Numeric barcodes** for scanning
- **Configurable length** via `BARCODE_LENGTH` env variable
- **Unique barcodes** per item

### QR Code Generation
- **QR codes** for each inventory item UID
- **Data URL format** for easy embedding
- **File generation** for printing
- **Buffer format** for API responses

### Quantity/UID Layer Sync
- **Automatic sync** when creating inventory items
- **Quantity incremented** when item created
- **Quantity decremented** when item status changes to SOLD/SCRAPPED
- **Both layers stay in sync** automatically

### Inventory Item Status Transitions
- **IN_STOCK** - Item is available for sale
- **RESERVED** - Item is reserved (linked to sale)
- **SOLD** - Item has been sold
- **RETURNED** - Item has been returned
- **DAMAGED** - Item is damaged
- **SCRAPPED** - Item has been scrapped

### Sale Item Linking
- **Optional inventory_item_id** in sale items
- **Automatic status update** to RESERVED when linked
- **Validation** that item belongs to product/variant
- **Validation** that item is available (IN_STOCK)
- **Inventory movements** recorded for audit trail

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## 🔄 Integration Points

### With Phase 3 (Quantity-Based Inventory)
- **Automatic sync** between quantity and UID layers
- **Quantity incremented** when item created
- **Quantity decremented** when item sold/scrapped
- **Both layers** work together seamlessly

### With Phase 4 (Sales)
- **Sale items can link to inventory items** via `inventory_item_id`
- **Inventory item status** updated to RESERVED when linked
- **Quantity-based reservation** skipped when UID-based item provided
- **Full traceability** of which specific UID was sold

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## 📊 Database Schema

### InventoryItem Table
- `id` - Primary key
- `uid` - Unique identifier (unique, indexed)
- `product_id` - Foreign key to products (required)
- `variant_id` - Foreign key to product_variants (optional)
- `status` - ENUM (IN_STOCK, RESERVED, SOLD, RETURNED, DAMAGED, SCRAPPED)
- `source` - ENUM (GRN, PRODUCTION, RETURN)
- `barcode` - Barcode (optional, indexed)

### SaleItem Table (Updated)
- `inventory_item_id` - Foreign key to inventory_items (optional)
- Links sale items to specific UIDs when provided

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## 📝 Business Rules

1. **Inventory Item Creation:**
   - UID generated automatically if not provided
   - Barcode generated automatically if not provided
   - Quantity-based inventory incremented automatically
   - Initial status is IN_STOCK
   - Inventory movement recorded

2. **Status Transitions:**
   - IN_STOCK → RESERVED: When linked to sale
   - IN_STOCK → SOLD: When item sold directly
   - RESERVED → SOLD: When sale completed
   - SOLD/SCRAPPED → Quantity decremented

3. **Sale Item Linking:**
   - Optional `inventory_item_id` in sale items
   - Item must belong to product/variant
   - Item must be IN_STOCK
   - Status updated to RESERVED
   - Quantity-based reservation skipped

4. **Quantity/UID Sync:**
   - Item creation: Quantity +1
   - Item sold/scrapped: Quantity -1
   - Both layers maintained automatically

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## ✅ Acceptance Criteria Met

- ✅ Can create inventory items with UIDs
- ✅ Can scan item by UID/barcode
- ✅ Sale items linked to specific UIDs
- ✅ Quantity and UID layers stay in sync
- ✅ Status transitions work correctly
- ✅ QR code generation working
- ✅ Barcode generation working
- ✅ Inventory movements logged

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## 📦 Dependencies

- `qrcode` - For QR code generation (installed)

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## 🚀 Next Steps

Phase 7: Enterprise Features (Pricing, Taxes, Categories)
- Implement category management
- Implement pricing and price lists
- Implement tax management
- Enhance product categorization

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**Phase 6 Status: COMPLETE ✅**

