Add CLAUDE.md with development guidance for Claude Code

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: velo

CLAUDE.md

@@ -0,0 +1,110 @@
+# CLAUDE.md
+
+This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.
+
+## Project Overview
+
+This is a multi-module Maven project for the Flink SQL Runner - a tool and library ecosystem for running Apache Flink SQL applications. The project is structured as a parent POM with multiple modules providing different functionality.
+
+## Module Structure
+
+- `flink-sql-runner/` - Main CLI application and Docker image
+- `connectors/` - Custom Flink connectors (kafka-safe, postgresql)
+- `formats/` - Custom data formats (flexible-csv, flexible-json)
+- `types/` - Custom data types (json-type, vector-type)
+- `stdlib/` - Standard library modules with system functions (json, math, text, vector, openai)
+- `testing/` - Testing utilities and sample UDF projects
+
+## Common Commands
+
+### Building and Testing
+```bash
+# Full build with all checks
+mvn clean install -Pci,flink-1.19
+
+# Fast build (skips tests, formatting, license checks)
+mvn clean install -Pfast
+
+# Run tests only
+mvn test
+
+# Run integration tests
+mvn verify
+
+# Code formatting check
+mvn spotless:check
+
+# Apply code formatting
+mvn spotless:apply
+
+# License header check
+mvn license:check
+
+# Apply license headers
+mvn license:format
+```
+
+### Running the Application
+```bash
+# Run SQL file
+java -jar flink-sql-runner/target/flink-sql-runner.jar --sqlfile script.sql
+
+# Run compiled plan
+java -jar flink-sql-runner/target/flink-sql-runner.jar --planfile plan.json
+
+# With custom configuration
+java -jar flink-sql-runner/target/flink-sql-runner.jar --sqlfile script.sql --config-dir config/
+
+# With UDF path
+java -jar flink-sql-runner/target/flink-sql-runner.jar --sqlfile script.sql --udfpath /path/to/udfs
+```
+
+## Technology Stack
+
+- **Java 11** - Base language version
+- **Apache Flink 1.19.2** - Stream processing framework (configurable via profiles)
+- **Maven** - Build system
+- **Lombok** - Code generation
+- **PicoCLI** - Command line interface
+- **JUnit 5** - Testing framework
+- **Testcontainers** - Integration testing
+- **Docker** - Containerization
+
+## Development Notes
+
+### Code Style
+- Uses Google Java Format for code formatting
+- Enforced via Spotless Maven plugin
+- License headers are automatically managed
+- Separate formatting rules for Flink-specific code (AOSP style)
+
+### Testing
+- Unit tests: `mvn test`
+- Integration tests: `mvn verify` (includes failsafe plugin)
+- Test coverage enforced at 70% minimum via JaCoCo
+
+### Flink Version Support
+Multiple Flink versions supported via Maven profiles:
+- `flink-1.19` (default)
+- `flink-1.20`
+- `flink-2.0`
+
+### Architecture
+The main application (`CliRunner`) processes command-line arguments and delegates to `BaseRunner` which:
+1. Initializes Flink configuration
+2. Resolves environment variables in SQL/JSON files
+3. Creates `SqlExecutor` to run SQL scripts or compiled plans
+4. Handles UDF loading and system function registration
+
+### Key Classes
+- `CliRunner` - Main entry point and CLI argument processing
+- `BaseRunner` - Core execution logic and configuration
+- `SqlExecutor` - Flink SQL script and plan execution
+- `EnvVarResolver` - Environment variable substitution in configs
+
+### Adding New Modules
+New modules should:
+1. Follow the existing directory structure
+2. Include proper Maven coordinates under `com.datasqrl.flinkrunner`
+3. Add to parent POM modules section
+4. Include common dependencies from parent (Lombok, JUnit, etc.)