use std::ffi::{OsString, OsStr};
use std::process::{Command};
use std::os::unix::process::CommandExt;

fn main() -> std::io::Result<()> {
  let args = std::env::args_os();
  let is_debug = std::env::var_os("DEBUG_E").is_some();
  let dbg = |msg| if is_debug { eprintln!("{}", msg); } else {};

  let mut cmd : Vec<OsString> = vec![];
  let mut depth = 0;
  for arg in args.skip(1) {
    if arg == OsString::from("[") {
        depth = depth + 1;
    } else if arg == OsString::from("]") {
        depth = depth - 1;
        cmd.push(prepend_block_depth(depth, &OsString::from("")));
    } else {
        cmd.push(prepend_block_depth(depth, &arg));
    }
  }

  Err(match cmd.len() {
      0 => {
          dbg(format!("e: Exiting, no commands given"));
          std::process::exit(0)
      },
      1 => {
          dbg(format!("e: Executing {:?}", cmd));
          Command::new(&cmd[0]).exec()
      },
      _ => {
          dbg(format!("e: Executing {:?}", cmd));
          Command::new(&cmd[0])
             .args(&cmd[1..])
             .exec()
      }
  })
}

fn prepend_block_depth(depth: usize, arg: &OsStr) -> OsString {
    let mut s = OsString::from(" ".repeat(depth));
    s.push(arg);
    s
}