# CLAUDE.md

This file provides guidance to Claude Code (claude.ai/code) when working with code in this repository.

## Project Overview

jrunner is a Java CLI tool for migrating data between databases. It reads data from a source database using SQL queries and writes it to a destination table, batching inserts for performance. The tool supports multiple database types via JDBC drivers including PostgreSQL, IBM AS/400, and Microsoft SQL Server.

## Build and Test Commands

Build the project:
```bash
gradle build
# or use wrapper
./gradlew build
```

Run tests:
```bash
gradle test
# or use wrapper
./gradlew test
```

Build distribution package:
```bash
gradle build
# Creates jrunner/build/distributions/jrunner.zip
```

Deploy to /opt (as documented in readme.md):
```bash
sudo unzip jrunner/build/distributions/jrunner.zip -d /opt/
sudo ln -sf /opt/jrunner/bin/jrunner /usr/local/bin/jrunner
```

## Architecture

### Single-File Design
The entire application logic resides in `jrunner/src/main/java/jrunner/jrunner.java`. This is a monolithic command-line tool with no abstraction layers or separate modules.

### Data Flow
1. Parse command-line arguments (-scu, -scn, -scp for source; -dcu, -dcn, -dcp for destination)
2. Read SQL query from file specified by -sq flag
3. Connect to source and destination databases via JDBC
4. Execute source query and fetch results (fetch size: 10,000 rows)
5. Build batched INSERT statements (250 rows per batch)
6. Execute batches against destination table specified by -dt flag
7. Optionally clear target table before insert if -c flag is set

### Type Handling
The tool includes explicit handling for different SQL data types in a switch statement (lines 229-312). Supported types include VARCHAR, TEXT, CHAR, CLOB, DATE, TIME, TIMESTAMP, and BIGINT. String types get quote escaping and optional trimming.

### Database Drivers
JDBC drivers are configured in `jrunner/build.gradle`:
- PostgreSQL: org.postgresql:postgresql:42.5.0
- IBM AS/400 (JT400): net.sf.jt400:jt400:11.0
- Microsoft SQL Server: com.microsoft.sqlserver:mssql-jdbc:9.2.0.jre8
- SQL Server Integrated Auth: com.microsoft.sqlserver:mssql-jdbc_auth:9.2.0.x64

The AS/400 driver requires explicit Class.forName() registration (line 144).

## Configuration

The project uses a YAML configuration format (run.yml) to specify database connections, SQL script paths, and runtime options. However, the main application currently uses command-line arguments instead of parsing this YAML file.

Command-line flags:
- `-scu` - source JDBC URL
- `-scn` - source username
- `-scp` - source password
- `-dcu` - destination JDBC URL
- `-dcn` - destination username
- `-dcp` - destination password
- `-sq` - path to source SQL query file
- `-dt` - fully qualified destination table name
- `-t` - trim text fields (default: true)
- `-c` - clear target table before insert (default: true)

## Key Implementation Details

### Batch Size
INSERT statements are batched at 250 rows (hardcoded at line 324). When the batch threshold is reached, sql is prepended with "INSERT INTO {table} VALUES" and executed.

### Error Handling
SQLException handling prints stack trace and exits immediately with System.exit(0). There is no transaction rollback or partial failure recovery.

### Performance Considerations
- Result set fetch size is set to 10,000 rows (line 173)
- Progress counter prints with carriage return for real-time updates
- Timestamps captured at start (line 174) and end (line 368) for duration tracking