swagger-api/swagger-codegen ? reverse-engineered prompt

Build me a tool that takes an OpenAPI or Swagger file and turns it into usable code and docs. I want it to generate API client libraries, server stubs, and simple HTML documentation from one spec file, with support for a bunch of common languages like Java, Python, PHP, JavaScript, Go, C Sharp, Ruby, and TypeScript. It should be easy to run from the command line, work with either a local file or a URL, and let me choose the target language and output folder.

Please also make it able to validate the spec first, and include a few sample commands for common use cases like generating a client for the Petstore example. If it helps, add Docker friendly support too. Keep it practical and make sure the templates are easy to customize, since this is meant to be a code generator people can actually extend.