# Design Document

## Overview

The Shopify Price Updater is a Node.js command-line script that uses Shopify's GraphQL Admin API to bulk update product prices based on tag filtering. The script will be built using the `@shopify/shopify-api` package and will implement proper error handling, rate limiting, and progress tracking.

## Architecture

The application follows a modular architecture with clear separation of concerns:

```
shopify-price-updater/
├── src/
│   ├── config/
│   │   └── environment.js     # Environment variable loading and validation
│   ├── services/
│   │   ├── shopify.js         # Shopify API client and authentication
│   │   ├── product.js         # Product querying and updating logic
│   │   └── progress.js        # Progress logging functionality
│   ├── utils/
│   │   ├── price.js           # Price calculation utilities
│   │   └── logger.js          # Console and file logging utilities
│   └── index.js               # Main application entry point
├── .env.example               # Environment variable template
├── package.json
└── Progress.md                # Generated progress log file
```

## Compare At Price Workflow

The Compare At price functionality works as follows:

1. **Price Capture**: When a product variant is processed, the current price is captured as the "original price"
2. **Price Calculation**: The new price is calculated by applying the percentage adjustment to the original price
3. **Compare At Assignment**: The original price (before adjustment) is set as the Compare At price
4. **Simultaneous Update**: Both the new price and Compare At price are updated in a single GraphQL mutation
5. **Progress Tracking**: All three values (original, new, and Compare At) are logged for transparency

This creates a promotional pricing display where customers can see both the current discounted price and the original price for comparison.

## Components and Interfaces

### Environment Configuration (`config/environment.js`)

- Loads and validates environment variables from `.env` file
- Required variables: `SHOPIFY_SHOP_DOMAIN`, `SHOPIFY_ACCESS_TOKEN`, `TARGET_TAG`, `PRICE_ADJUSTMENT_PERCENTAGE`
- Validates that percentage is a valid number and tag is not empty
- Exports configuration object with validated values

### Shopify Service (`services/shopify.js`)

- Initializes Shopify GraphQL client using `@shopify/shopify-api`
- Handles authentication and session management
- Provides methods for executing GraphQL queries and mutations
- Implements retry logic for rate limiting (HTTP 429 responses)

### Product Service (`services/product.js`)

- Implements GraphQL queries to fetch products by tag
- Handles pagination for large product sets using cursor-based pagination
- Implements GraphQL mutations for price and Compare At price updates
- Manages product variant price updates (products can have multiple variants)
- Sets Compare At price to the original price before applying percentage adjustment
- Automatically formats tag queries with "tag:" prefix if not already present

### Progress Service (`services/progress.js`)

- Creates and manages Progress.md file
- Logs operation start, product updates, errors, and completion summary
- Appends to existing file with timestamps for multiple runs
- Formats progress entries in markdown for readability

### Price Utilities (`utils/price.js`)

- Calculates new prices based on percentage adjustment
- Handles rounding to appropriate decimal places for currency
- Validates price ranges and handles edge cases (negative prices, zero prices)
- Provides functions to prepare price update objects with both price and Compare At price values

### Logger Utilities (`utils/logger.js`)

- Provides consistent logging to console and progress file
- Implements different log levels (info, warning, error)
- Formats output for both human readability and progress tracking

## Data Models

### Product Query Response

```graphql
query getProductsByTag($query: String!, $first: Int!, $after: String) {
	products(first: $first, after: $after, query: $query) {
		edges {
			node {
				id
				title
				tags
				variants(first: 100) {
					edges {
						node {
							id
							price
							compareAtPrice
						}
					}
				}
			}
			cursor
		}
		pageInfo {
			hasNextPage
			endCursor
		}
	}
}
```

### Product Update Mutation

```graphql
mutation productVariantUpdate($input: ProductVariantInput!) {
	productVariantUpdate(input: $input) {
		productVariant {
			id
			price
			compareAtPrice
		}
		userErrors {
			field
			message
		}
	}
}
```

### Configuration Object

```javascript
{
  shopDomain: string,
  accessToken: string,
  targetTag: string,
  priceAdjustmentPercentage: number
}
```

### Progress Entry

```javascript
{
  timestamp: Date,
  productId: string,
  productTitle: string,
  variantId: string,
  oldPrice: number,
  newPrice: number,
  compareAtPrice: number,
  status: 'success' | 'error',
  errorMessage?: string
}
```

## Error Handling

### Rate Limiting

- Implement exponential backoff for HTTP 429 responses
- Use Shopify's rate limit headers to determine retry timing
- Maximum retry attempts: 3 with increasing delays (1s, 2s, 4s)

### API Errors

- Parse GraphQL userErrors from mutation responses
- Log specific error messages for debugging
- Continue processing remaining products when individual updates fail

### Network Errors

- Catch and handle network connectivity issues
- Implement retry logic for transient network failures
- Graceful degradation when API is temporarily unavailable

### Data Validation

- Validate product data before attempting updates
- Skip products with invalid price data
- Handle edge cases like products without variants

### Progress Tracking Errors

- Continue script execution even if progress logging fails
- Fallback to console-only logging if file writing fails
- Ensure critical operations aren't blocked by logging issues

## Testing Strategy

### Unit Tests

- Test price calculation utilities with various percentage values
- Test environment configuration loading and validation
- Test GraphQL query and mutation builders
- Test error handling scenarios with mocked API responses

### Integration Tests

- Test Shopify API authentication with test credentials
- Test product querying with known test data
- Test price update operations in Shopify development store
- Test progress logging functionality

### End-to-End Tests

- Test complete workflow with development store
- Verify price updates are applied correctly
- Test error recovery and continuation scenarios
- Validate progress logging accuracy

### Manual Testing Checklist

- Test with various percentage values (positive, negative, decimal)
- Test with products having multiple variants
- Test with large product sets requiring pagination
- Test error scenarios (invalid credentials, network issues)
- Verify Progress.md file generation and formatting