use super::*;
use std::{
    num::{
	NonZeroUsize,
	ParseIntError,
    },
};
use lazy_static::lazy_static;

#[inline] pub fn program_name() -> &'static str
{
    lazy_static!{
	static ref PROG: &'static str = Box::leak(std::env::args().next().unwrap().into_boxed_str());
    }
    &PROG[..]
}

pub fn usage() -> !
{
    #[cfg(feature="splash")] 
    splash::print();
    
    println!(r"Usage: {prog} [--max-children <number>] [-] <files...>
Usage: {prog} --help

OPTIONS:
  --max-children <number>	Max subprocesses allowed to live at once. Infinite by default.

ENVIRONMENT VARS:
  LEANIFY=<process name>	Path to leanify executable, defaults to looking in `PATH' if set.", prog = program_name());
    
    std::process::exit(1)
}

#[derive(Debug)]
pub enum Error {
    #[cfg(nightly)] BadNumber(std::num::IntErrorKind),
    #[cfg(not(nightly))] BadNumber(()),
    NoFiles,
}
impl std::error::Error for Error{}
impl std::fmt::Display for Error
{
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result
    {
	//write!(f, "arg parsing failed: ")?;
	match self {
	    Self::BadNumber(_v) => {
		write!(f, "expected non-zero integer")?;

		#[cfg(nightly)] use std::num::IntErrorKind;
		#[cfg(nightly)] return match _v {
		    IntErrorKind::Empty => write!(f, ": argument empty"),
		    IntErrorKind::InvalidDigit => write!(f, ": invalid digit"),
		    IntErrorKind::Overflow => write!(f, ": conversion would result in overflow"),
		    IntErrorKind::Underflow => write!(f, ": conversion would result in underflow"),
		    IntErrorKind::Zero => write!(f, ": found zero"),
		    _=> Ok(()),
		};
		#[cfg(not(nightly))] Ok(())
	    },
	    Self::NoFiles => write!(f, "need at least one argument")
	}
    }
}

impl From<ParseIntError> for Error
{
    fn from(_er: ParseIntError) -> Self
    {
	#[cfg(nightly)] return Self::BadNumber(_er.kind().clone());
	#[cfg(not(nightly))] Self::BadNumber
    }
}


#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Config
{
    pub max_children: Option<NonZeroUsize>,
    pub files: Vec<String>,
}

impl Default for Config
{
    #[inline]
    fn default() -> Self
    {
	Self {
	    max_children: None,
	    files: Vec::new(),
	}
    }
}

/// Parse the `env::args()`
#[inline] pub fn parse_args() -> Result<Config, Error>
{
    let args = std::env::args();
    if args.len() <= 1 {
	println!("Warning: No arguments specified, try passing `--help`.");
    }
    parse(args.skip(1))
}

fn parse<I,T>(args: I) -> Result<Config, Error>
where I: IntoIterator<Item=T>,
      T: Into<String>
{
    let mut args = args.into_iter().map(|x| x.into());
    let mut cfg = Config::default();
    let mut reading=true;
    let mut first=true;
    while let Some(arg) = args.next() {
	if reading {
	    let lw_arg = arg.trim().to_lowercase();
	    if first {
		match lw_arg.as_str() {
		    "--help" => {
			usage()
		    },
		    _ => (),
		}
	    }
	    first=false;
	    
	    match lw_arg.as_str() {
		"--max-children" => {
		    if let Some(nzi) = args.next() {
			cfg.max_children = Some(nzi.parse()?);
			continue;
		    }
		}
		"-" => {
		    reading= false;
		    continue;
		},
		_ => (),
	    }
	}
	reading = false;
	cfg.files.push(arg);
    }
    if cfg.files.len() == 0 {
	return Err(Error::NoFiles);
    }
    Ok(cfg)
}