# QR Code Storage Location System Design

## Overview
Implement a hierarchical storage location system with QR code generation and scanning capabilities to enable quick component location entry and filtering.

## Database Schema

### 1. Storage Locations Table
```sql
CREATE TABLE storage_locations (
  id SERIAL PRIMARY KEY,
  name VARCHAR(255) NOT NULL,
  description TEXT,
  qr_code VARCHAR(100) UNIQUE NOT NULL,
  parent_id INTEGER REFERENCES storage_locations(id),
  level INTEGER NOT NULL DEFAULT 0,
  path TEXT NOT NULL, -- Materialized path: "shelf1/drawer2/box3"
  is_active BOOLEAN DEFAULT TRUE,
  created_at TIMESTAMP DEFAULT NOW(),
  updated_at TIMESTAMP DEFAULT NOW()
);

CREATE INDEX idx_storage_locations_parent_id ON storage_locations(parent_id);
CREATE INDEX idx_storage_locations_qr_code ON storage_locations(qr_code);
CREATE INDEX idx_storage_locations_path ON storage_locations USING gin(path gin_trgm_ops);
CREATE UNIQUE INDEX idx_storage_locations_name_parent ON storage_locations(name, parent_id);
```

### 2. Modified Components Table
```sql
-- Migration to add storage_location_id to components
ALTER TABLE components 
ADD COLUMN storage_location_id INTEGER REFERENCES storage_locations(id),
ADD COLUMN legacy_position VARCHAR(255); -- Keep old position data for migration

-- Move existing position data to legacy_position
UPDATE components SET legacy_position = position;
```

## QR Code Format Design

### Hierarchical QR Code Strategy
To avoid confusion with multiple QR codes in the same image, use a hierarchical encoding strategy:

```
Format: SL:{level}:{unique_id}:{parent_path_hash}
Examples:
- Shelf: "SL:1:ABC123:ROOT"
- Drawer: "SL:2:DEF456:ABC123"  
- Box: "SL:3:GHI789:DEF456"
```

### QR Code Components:
- **SL**: Storage Location prefix
- **Level**: Hierarchy level (1=shelf, 2=drawer, 3=box, etc.)
- **Unique ID**: Short alphanumeric code (6-8 chars)
- **Parent Hash**: Reference to parent location

## Multi-QR Code Detection Strategy

### 1. Spatial Filtering
```
When multiple QR codes detected:
1. Calculate distance between codes
2. If distance < threshold:
   - Prefer higher hierarchy level (lower number)
   - Present disambiguation UI
3. If distance > threshold:
   - Allow user to tap/select desired code
```

### 2. Context-Aware Selection
```
Selection Priority:
1. Exact level match (if user scanning for specific level)
2. Deepest level in hierarchy (most specific location)
3. Recently used locations (user preference learning)
4. Manual disambiguation prompt
```

### 3. Visual Feedback
```
Camera Overlay:
- Draw bounding boxes around each detected QR code
- Color-code by hierarchy level
- Show location path preview on hover/tap
- Highlight "best match" with different color
```

## Implementation Components

### 1. Elixir Modules

#### Storage Location Schema
```elixir
defmodule ComponentsElixir.Inventory.StorageLocation do
  use Ecto.Schema
  import Ecto.Changeset
  
  schema "storage_locations" do
    field :name, :string
    field :description, :string
    field :qr_code, :string
    field :level, :integer, default: 0
    field :path, :string
    field :is_active, :boolean, default: true
    
    belongs_to :parent, __MODULE__
    has_many :children, __MODULE__, foreign_key: :parent_id
    has_many :components, Component
    
    timestamps()
  end
end
```

#### QR Code Generation
```elixir
defmodule ComponentsElixir.QRCode do
  def generate_storage_qr(location) do
    qr_data = "SL:#{location.level}:#{location.qr_code}:#{parent_hash(location)}"
    
    # Use :qr_code library to generate QR image
    :qr_code.encode(qr_data)
    |> :qr_code.png()
  end
  
  def parse_storage_qr(qr_string) do
    case String.split(qr_string, ":") do
      ["SL", level, code, parent] ->
        {:ok, %{level: level, code: code, parent: parent}}
      _ ->
        {:error, :invalid_format}
    end
  end
end
```

### 2. Phoenix LiveView Components

#### QR Scanner Component
```elixir
defmodule ComponentsElixirWeb.QRScannerLive do
  use ComponentsElixirWeb, :live_view
  
  def mount(_params, _session, socket) do
    socket = 
      socket
      |> assign(:scanning, false)
      |> assign(:detected_codes, [])
      |> assign(:selected_location, nil)
      |> allow_upload(:qr_scan, 
          accept: ~w(.jpg .jpeg .png), 
          max_entries: 1,
          auto_upload: true)
    
    {:ok, socket}
  end
  
  def handle_event("start_scan", _, socket) do
    {:noreply, assign(socket, :scanning, true)}
  end
  
  def handle_event("qr_detected", %{"codes" => codes}, socket) do
    parsed_codes = Enum.map(codes, &parse_and_resolve_location/1)
    
    socket = 
      socket
      |> assign(:detected_codes, parsed_codes)
      |> maybe_auto_select_location(parsed_codes)
    
    {:noreply, socket}
  end
  
  defp maybe_auto_select_location(socket, [single_code]) do
    assign(socket, :selected_location, single_code)
  end
  
  defp maybe_auto_select_location(socket, multiple_codes) do
    # Show disambiguation UI
    assign(socket, :selected_location, nil)
  end
end
```

### 3. JavaScript QR Detection

#### Camera Integration
```javascript
// assets/js/qr_scanner.js
import jsQR from "jsqr";

export const QRScanner = {
  mounted() {
    this.video = this.el.querySelector('video');
    this.canvas = this.el.querySelector('canvas');
    this.context = this.canvas.getContext('2d');
    
    this.startCamera();
    this.scanLoop();
  },
  
  async startCamera() {
    try {
      const stream = await navigator.mediaDevices.getUserMedia({
        video: { 
          facingMode: 'environment', // Use back camera
          width: { ideal: 1280 },
          height: { ideal: 720 }
        }
      });
      this.video.srcObject = stream;
    } catch (err) {
      console.error('Camera access denied:', err);
    }
  },
  
  scanLoop() {
    if (this.video.readyState === this.video.HAVE_ENOUGH_DATA) {
      this.canvas.width = this.video.videoWidth;
      this.canvas.height = this.video.videoHeight;
      
      this.context.drawImage(this.video, 0, 0);
      const imageData = this.context.getImageData(0, 0, this.canvas.width, this.canvas.height);
      
      // Detect multiple QR codes
      const codes = this.detectMultipleQRCodes(imageData);
      
      if (codes.length > 0) {
        this.pushEvent("qr_detected", { codes: codes });
      }
    }
    
    requestAnimationFrame(() => this.scanLoop());
  },
  
  detectMultipleQRCodes(imageData) {
    // Implementation for detecting multiple QR codes
    // This is a simplified version - you'd need a more robust library
    const detected = [];
    
    // Scan in grid pattern to find multiple codes
    const gridSize = 4;
    const width = imageData.width / gridSize;
    const height = imageData.height / gridSize;
    
    for (let x = 0; x < gridSize; x++) {
      for (let y = 0; y < gridSize; y++) {
        const subImageData = this.getSubImageData(
          imageData, 
          x * width, 
          y * height, 
          width, 
          height
        );
        
        const code = jsQR(subImageData.data, subImageData.width, subImageData.height);
        if (code && this.isStorageLocationQR(code.data)) {
          detected.push({
            data: code.data,
            location: { x: x * width, y: y * height },
            corners: code.location
          });
        }
      }
    }
    
    return this.filterDuplicates(detected);
  },
  
  isStorageLocationQR(data) {
    return data.startsWith('SL:');
  }
};
```

## User Experience Flow

### 1. Adding Components with QR Scan
```
1. User clicks "Add Component" 
2. Position field shows camera icon
3. Click camera → QR scanner opens
4. Scan storage location QR code
5. If multiple codes detected:
   - Show overlay with detected locations
   - User taps to select specific location
6. Location path auto-filled: "Shelf A → Drawer 2 → Box 5"
7. Component saved with storage_location_id
```

### 2. Filtering by Storage Location
```
1. Component list shows location filter dropdown
2. Filter options show hierarchical tree:
   ├── Shelf A
   │   ├── Drawer 1
   │   │   ├── Box 1
   │   │   └── Box 2
   │   └── Drawer 2
   └── Shelf B
3. Select any level to filter components
4. Breadcrumb shows: "Shelf A → Drawer 2" (23 components)
```

### 3. Location Management
```
1. New "Storage Locations" section in admin
2. Add/edit locations with auto QR generation
3. Print QR labels with location hierarchy
4. Bulk QR code generation for initial setup
```

## Handling Multiple QR Codes in Same Image

### Strategy 1: Spatial Separation
- Calculate euclidean distance between QR code centers
- If distance < 100px → show disambiguation
- If distance > 100px → allow selection by tap

### Strategy 2: Hierarchy Preference
- Always prefer deepest level (most specific)
- If same level → show all options
- Color-code by hierarchy level in UI

### Strategy 3: Machine Learning (Future)
- Learn user selection patterns
- Predict most likely intended QR code
- Still allow manual override

## Migration Strategy

### Phase 1: Add Storage Locations
1. Create migration for storage_locations table
2. Add storage_location_id to components
3. Create admin interface for location management

### Phase 2: QR Code Generation
1. Add QR code generation to location creation
2. Implement QR code printing/export functionality
3. Generate codes for existing locations

### Phase 3: QR Code Scanning
1. Add camera permissions and JavaScript QR scanner
2. Implement single QR code detection first
3. Add multi-QR detection and disambiguation

### Phase 4: Advanced Features
1. Location-based filtering and search
2. Bulk operations by location
3. Location analytics and optimization

## Technical Dependencies

### Elixir Dependencies
```elixir
# mix.exs
{:qr_code, "~> 3.1"},              # QR code generation
{:image, "~> 0.37"},               # Image processing
{:ex_image_info, "~> 0.2.4"}      # Image metadata
```

### JavaScript Dependencies
???

## Database Indexes for Performance
```sql
-- Fast location lookups
CREATE INDEX idx_components_storage_location_id ON components(storage_location_id);

-- Hierarchical queries
CREATE INDEX idx_storage_locations_path_gin ON storage_locations USING gin(path gin_trgm_ops);

-- QR code uniqueness and fast lookup
CREATE UNIQUE INDEX idx_storage_locations_qr_code ON storage_locations(qr_code);
```

This design provides a robust foundation for QR code-based storage management while handling the complexity of multiple codes in the same image through spatial analysis and user interaction patterns.