webshell/Writing Programs.md

Implement the sl ("steam locomotive") command from Linux in TypeScript. I want an exact replica of the original Linux command. Strictly follow the following APIs and concepts:

1. class SimpleStream
   • on(listener: (data: T) => any): void
     • Attaches a listener to the stream
     • param listener -> the function to call when data is streamed
   • once(listener: (data: T) => any): void
     • Attaches a one-time listener to the stream
     • param listener -> the function to call when data is streamed
   • wait(): Promise
     • Patiently waits until new data is streamed, then returns it
     • return a promise for a single chunk of streamed data
   • off(listener: Function): void
     • Removes a listener from the stream
     • param listener -> the function to remove
   • emit(data: T): void
     • Streams data
     • param data -> the data to stream
2. Escape codes
   • Escape codes can be formatted using one of the following syntaxes:
     • \{code letter} -> for short codes like \n or \f
     • \0{code id};{first parameter};{second parameter};{...parameters}\0 -> for longer codes with complex parameters like cursor movement codes
     • A semicolon right after or before a null terminator (\0) inside of an escape code is a syntax error
   • Supported escape codes:
     • Short codes ( -> )
       1. n -> line feed (new line)
       2. f -> form feed (new page)
     • Longer codes (,,<...parameters> -> )
       1. cmr,{delta x},{delta y} -> moves the cursor relative to its current position by the specified amounts
       2. cma,{absolute x},{absolute y} -> moves the cursor absolute in the terminal coordinate space
   • Example usage:
     • stdout.emit("\\cma;3;2\\") - sets the cursor position to the specified XY coordinates - x=3, y=2
3. stdout/stdin - SimpleStream instances
   • they function as input/output interfaces to send text between the shell and other programs
   • stdout allows for formatting using the above mentioned Escape codes
   • Example usage:
     • stdout.emit("Hello world!\n") - streams the text to the stdout stream, works like printf in C
     • stdin.once(data => stdout.emit(`Received data: ${data}`)) - creates a single use listener in the stdin stream and prints out the received data
4. abstract class Program
   • abstract Exec(stdin: SimpleStream, stdout: SimpleStream, workdir: Item, args: string[]): Promise
     • Entry point for a program
     • param stdin -> input stream
     • param stdout -> output stream
     • param workdir -> Working directory filesystem item
     • param args -> arguments array, including the executed program name from the shell
       • for example for echo command: [ "echo", "test", "one", "two", "three" ]
     • returns a posix-like exit code