KRED-2946: This PR adds support for the Midtrans Partner Update Merchant Notification API and improves project documentation.

CLAUDE.md

@@ -0,0 +1,112 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+This is a Ruby gem that provides a client library for the Midtrans Payment Gateway API. The gem wraps various Midtrans API endpoints (payment transactions, virtual accounts, disbursements, merchant management, etc.) with a clean Ruby interface.
+
+## Development Commands
+
+### Running Tests
+```bash
+rake spec                              # Run all tests
+bundle exec rspec spec/path/to/file_spec.rb  # Run specific test file
+bundle exec rspec spec/path/to/file_spec.rb:LINE  # Run specific test at line
+```
+
+### Interactive Console
+```bash
+bin/console    # IRB console with the gem loaded
+```
+
+### Build and Install
+```bash
+bundle exec rake install   # Install gem locally
+bundle exec rake release   # Release new version (tags, pushes to rubygems)
+```
+
+## Architecture
+
+### Client Architecture
+The gem follows a layered architecture pattern:
+
+1. **Client Layer** (`lib/midtrans_api/client.rb`)
+   - Main entry point that users interact with
+   - Manages Faraday HTTP connection with Basic Auth
+   - Provides convenience methods that return API instances (e.g., `client.gopay_charge`, `client.merchant`)
+   - Supports three API environments via configuration: production, sandbox, and partner API
+   - HTTP methods: `get()`, `post()`, `patch()`
+
+2. **API Layer** (`lib/midtrans_api/api/*`)
+   - Each API endpoint has its own class that inherits from `MidtransApi::Api::Base`
+   - Organized by feature domain (e.g., `Merchant::Create`, `Gopay::Charge`, `Transaction::Expire`)
+   - API classes define the endpoint `PATH` constant and HTTP method (e.g., `post()`, `patch()`)
+   - Responsible for making HTTP requests via the client and returning Model instances
+
+3. **Model Layer** (`lib/midtrans_api/model/*`)
+   - Each API response is mapped to a Model class that inherits from `MidtransApi::Model::Base`
+   - Models use `resource_attributes` macro to define accessible response fields
+   - Base class handles initialization from API response hash via `assign_attributes`
+   - Models implement `resolve_params_attr()` for key transformation (typically identity transform)
+
+4. **Configuration** (`lib/midtrans_api/configure.rb`)
+   - Manages API credentials (client_key, server_key)
+   - Environment selection (sandbox vs production vs partner API)
+   - Optional features: notification URL override, logging, timeout settings
+
+### Adding New API Endpoints
+
+To add a new Midtrans API endpoint:
+
+1. **Create API class** at `lib/midtrans_api/api/{domain}/{action}.rb`:
+   ```ruby
+   class MyApi < MidtransApi::Api::Base
+     PATH = 'endpoint/path'
+
+     def post(params, additional_headers_params)
+       response = client.post(PATH, params, {
+         'X-CUSTOM-HEADER': additional_headers_params
+       })
+       MidtransApi::Model::Domain::MyApi.new(response)
+     end
+   end
+   ```
+
+2. **Create Model class** at `lib/midtrans_api/model/{domain}/{action}.rb`:
+   ```ruby
+   class MyApi < MidtransApi::Model::Base
+     resource_attributes :field1, :field2, :field3
+
+     def resolve_params_attr(attr)
+       attr.to_s  # or custom transformation
+     end
+   end
+   ```
+
+3. **Register in Client** (`lib/midtrans_api/client.rb`):
+   - Add `require` statements at the top for both API and Model files
+   - Add convenience method to instantiate the API class:
+     ```ruby
+     def my_api
+       @my_api ||= MidtransApi::Api::Domain::MyApi.new(self)
+     end
+     ```
+   - If using new HTTP verb, add method (e.g., `put()`, `delete()`)
+
+4. **Create test file** at `spec/lib/midtrans_api/api/{domain}/{action}_spec.rb`:
+   - Use WebMock to stub HTTP requests
+   - Test that correct model instance is returned
+   - Test that proper headers are sent
+   - Follow pattern from existing specs (e.g., `merchant/create_spec.rb`)
+
+### Error Handling
+- Custom errors defined in `lib/midtrans_api/errors.rb`
+- Middleware `HandleResponseException` intercepts HTTP errors and raises appropriate exceptions
+- See Midtrans API documentation for status codes
+
+### Logging and Security
+- Uses Faraday middleware for logging
+- `FaradayLogFormatter` provides custom log formatting
+- `JsonMasker` and `UrlMasker` utilities mask sensitive data in logs
+- Configure via `filtered_logs` and `mask_params` client options