# WooCommerce Composable Products - AI Context Document

**Author:** Marco Graetsch

## Project Overview

This plugin implements a custom WooCommerce product type where customers select a limited number of products from a configurable set of simple or variable products. The limit is configurable globally and per-product. The selectable products are defined by category, tag, or SKU. Pricing is either fixed or the sum of selected products. Think of a sticker pack where each package contains N stickers chosen by the customer.

This project is 100% AI-generated ("vibe-coded") using Claude.AI.

## Technical Stack

- **Language:** PHP 8.3+
- **Framework:** WordPress Plugin API
- **E-commerce:** WooCommerce 10.0+
- **Template Engine:** Twig 3.0 (via Composer)
- **Frontend:** Vanilla JavaScript + jQuery
- **Styling:** Custom CSS
- **Dependencies:** Composer
- **i18n:** WordPress i18n (.pot/.po/.mo), text domain: `wc-composable-product`
- **CI/CD:** Gitea Actions (`.gitea/workflows/release.yml`)

## Project Structure

```txt
wc-composable-product/
├── .gitea/workflows/
│   └── release.yml            # CI/CD release workflow
├── assets/
│   ├── css/
│   │   ├── admin.css          # Admin panel styling
│   │   └── frontend.css       # Customer-facing styles (with stock indicators)
│   └── js/
│       ├── admin.js           # Product edit interface logic
│       └── frontend.js        # AJAX cart & selection UI
├── cache/                     # Twig template cache (writable, gitignored)
├── includes/
│   ├── Admin/
│   │   ├── ProductData.php    # Product data tab & meta boxes
│   │   └── Settings.php       # WooCommerce settings integration
│   ├── CartHandler.php        # Add-to-cart & cart display logic (with stock validation)
│   ├── Plugin.php             # Main plugin class (Singleton)
│   ├── ProductSelector.php    # Frontend product selector renderer (with stock info)
│   ├── ProductType.php        # Custom WC_Product extension
│   └── StockManager.php       # Stock management & inventory tracking
├── languages/                 # Translation files (.pot, .po, .mo)
├── releases/                  # Release packages (gitignored)
├── templates/
│   └── product-selector.twig  # Frontend selection interface
├── vendor/                    # Composer dependencies (gitignored, included in releases)
├── composer.json
└── wc-composable-product.php  # Main plugin file
```

## Architecture

### Core Classes

1. **Plugin.php** — Main singleton class
   - Initializes Twig with WordPress functions registered as both Twig functions AND filters
   - Registers hooks, manages asset enqueuing, provides template rendering API
   - Settings.php is lazy-loaded via `woocommerce_get_settings_pages` filter (not in `includes()`) to avoid "Class WC_Settings_Page not found" errors

2. **ProductType.php** — Custom WooCommerce product type (`composable`)
   - Extends `WC_Product`
   - Queries available products via `get_available_products()` using `WP_Query`
   - **Critical**: Uses `tax_query` with `product_type` taxonomy to exclude composable products (NOT `meta_query` — WooCommerce stores product types as taxonomy terms)
   - Handles variable products by expanding them into individual variations via `get_children()`
   - Products are filtered by `is_purchasable()` only (not `is_in_stock()` — stock is shown visually and validated at add-to-cart)

3. **CartHandler.php** — Cart integration
   - Validates selections, stores selected products in cart meta, calculates pricing
   - Uses `woocommerce_is_purchasable` filter to hide default add-to-cart button for composable products
   - Price recalculation uses a static `$already_calculated` flag per request (no persistent session flags — `set_price()` is in-memory only)

4. **ProductSelector.php** — Frontend renderer
   - Renders Twig template with product data, stock info, and pre-formatted price HTML via `wc_price()`

5. **Admin/ProductData.php** — Product edit interface
   - Adds "Composable Options" tab with category/tag/SKU selection fields
   - Saved meta: `_composable_selection_limit`, `_composable_pricing_mode`, `_composable_criteria_type`, `_composable_categories`, `_composable_tags`, `_composable_skus`

6. **Admin/Settings.php** — Global settings (extends `WC_Settings_Page`)
   - Default selection limit, pricing mode, display preferences

7. **StockManager.php** — Inventory management
   - Stock validation, automatic deduction on order completion, restoration on cancellation
   - Prevents WooCommerce double-deduction via `woocommerce_can_reduce_order_stock`

### Data Flow

**Product Creation:** Admin selects "Composable product" type → configures criteria/limits/pricing → metadata saved as `_composable_*` fields

**Frontend Display:** `CartHandler::render_product_selector()` → `ProductType::get_available_products()` queries products via taxonomy/SKU → `ProductSelector::render()` passes data to Twig template → JavaScript handles selection UI

**Add to Cart:** Customer selects products → JS validates limit → AJAX request with `composable_products[]` → server-side validation (selection + stock) → selections stored in cart item data → price calculated per pricing mode

**Order Processing:** Order completed → `StockManager` deducts inventory → order notes added for audit → on cancellation/refund: stock restored

### Key Hooks

- `woocommerce_add_to_cart_validation` — validate selections
- `woocommerce_add_cart_item_data` — store selections
- `woocommerce_before_calculate_totals` — update prices
- `woocommerce_get_item_data` — display in cart
- `woocommerce_order_status_completed/processing` — deduct stock
- `woocommerce_order_status_cancelled/refunded` — restore stock

### Security

- Input: `absint()` for IDs/limits, `sanitize_text_field()` for modes, `sanitize_textarea_field()` for SKUs
- Output: `esc_html()`, `esc_attr()`, `esc_url()` (registered as both Twig functions and filters)
- Nonce verification via WooCommerce

### Developer API

```php
$product = wc_get_product($product_id);
if ($product->get_type() === 'composable') {
    $products = $product->get_available_products();
    $limit = $product->get_selection_limit();
    $price = $product->calculate_composed_price($selected_ids);
}
```

## Translations

All strings use text domain `wc-composable-product`. Available locales:

- `en_US` (base), `de_DE`, `de_DE_informal`, `de_CH`, `de_CH_informal`, `fr_CH`, `it_CH`

Compile .po to .mo: `for po in languages/*.po; do msgfmt -o "${po%.po}.mo" "$po"; done`

WordPress requires compiled .mo files — .po files alone are insufficient.

## Release Workflow

### Automated (Gitea CI/CD)

Push an annotated tag (`v*`) to trigger the workflow. It installs PHP 8.3, production Composer deps, compiles translations, verifies version matches tag, creates ZIP with checksums, and publishes a Gitea release.

### Manual

```bash
# From project root
zip -r releases/wc-composable-product-vX.X.X.zip . \
  -x "*.git*" "*.vscode*" "*.claude*" "CLAUDE.md" \
  "wp-core/*" "wp-plugins/*" "*.log" "composer.lock" \
  "cache/*" "releases/*" "*.zip" "logs/*"
```

The `vendor/` directory MUST be included in releases (Twig dependency required at runtime).

### Git Workflow

- Develop on `dev` branch, merge to `main` for releases
- Tags: annotated, format `vX.X.X` (e.g., `v1.2.0`)
- Commit messages include `Co-Authored-By: Claude` attribution

## Critical Lessons Learned

1. **WooCommerce stores product types as taxonomy terms** (`product_type` taxonomy), NOT as postmeta. Using `meta_query` on `_product_type` silently returns zero results because the meta key doesn't exist.

2. **`WC_Product::set_price()` is in-memory only** — changes are lost between HTTP requests. Never persist a "price already calculated" flag to cart session; use a static per-request flag instead.

3. **Settings.php must be lazy-loaded** — `require_once` in `Plugin::includes()` causes "Class WC_Settings_Page not found" because WooCommerce hasn't loaded that class yet. Load it inside the `woocommerce_get_settings_pages` filter callback instead.

4. **Register WordPress functions as both Twig functions AND filters** — other plugins may bundle their own Twig instance that parses our templates. Both `{{ esc_attr(value) }}` and `{{ value|esc_attr }}` syntax must work.

5. **HPOS compatibility declaration is required** — without it, WooCommerce shows incompatibility warnings.

6. **WordPress i18n requires compiled .mo files** — .po files are source only; WordPress cannot use them directly.

7. **Don't filter by `is_in_stock()` during product retrieval** — it's too strict (excludes backorder-enabled products, products without stock management). Show all purchasable products; let the frontend display stock status and validate at add-to-cart time.

## For AI Assistants

When starting a new session:

1. Read this CLAUDE.md first
2. Check git log for recent changes
3. Verify you're on the `dev` branch before making changes
4. Run `composer install` if vendor/ is missing
5. Test changes before committing
6. Follow commit message format with Claude Code attribution
7. Always use `tax_query` (not `meta_query`) for product type filtering