use mlua::prelude::*;
use std::{env, path::PathBuf};

pub fn make() -> LuaResult<Lua> {
    let (dylib_path, dylib_ext, separator);
    if cfg!(target_os = "macos") {
        dylib_path = env::var("DYLD_FALLBACK_LIBRARY_PATH").unwrap();
        dylib_ext = "dylib";
        separator = ":";
    } else if cfg!(target_os = "linux") {
        dylib_path = env::var("LD_LIBRARY_PATH").unwrap();
        dylib_ext = "so";
        separator = ":";
    } else if cfg!(target_os = "windows") {
        dylib_path = env::var("PATH").unwrap();
        dylib_ext = "dll";
        separator = ";";
    } else {
        panic!("unknown target os");
    };

    let mut cpath = dylib_path
        .split(separator)
        .take(3)
        .map(|p| {
            let mut path = PathBuf::from(p);
            path.push(format!("lib?.{}", dylib_ext));
            path.to_str().unwrap().to_owned()
        })
        .collect::<Vec<_>>()
        .join(";");

    if cfg!(target_os = "windows") {
        cpath = cpath.replace("\\", "\\\\");
        cpath = cpath.replace("lib?.", "?.");
    }

    let lua = unsafe { Lua::unsafe_new() }; // To be able to load C modules
    lua.load(&format!("package.cpath = \"{}\"", cpath)).exec()?;
    Ok(lua)
}