use std::ffi::{CStr, CString};
use std::os::raw::{c_char, c_int, c_void};

#[link(name = "guile-3.0")]
#[allow(dead_code)]
extern "C" {
    fn scm_init_guile();
    fn scm_c_define_gsubr(
        name: *const c_char,
        req: c_int,
        opt: c_int,
        rst: c_int,
        func: extern "C" fn() -> *mut c_void,
    );
    fn scm_c_eval_string(expr: *const c_char) -> *mut c_void;
    fn scm_to_locale_string(scm_obj: *mut c_void) -> *const c_char;
    fn scm_c_write(scm_obj: *mut c_void, port: *mut c_void);
    fn scm_open_output_string() -> *mut c_void;
    fn scm_get_output_string(port: *mut c_void) -> *mut c_void;
    fn scm_is_string(scm_obj: *mut c_void) -> c_int;
    fn scm_is_number(scm_obj: *mut c_void) -> c_int;
    fn scm_object_to_string(scm_obj: *mut c_void, printer: *mut c_void) -> *mut c_void;
}

#[link(name = "guiledefs")]
extern "C" {
    pub static scm_undefined: *mut c_void;
}

extern "C" fn my_rust_function() -> *mut c_void {
    println!("Hello from Rust!");
    unsafe { scm_undefined }
}

/// Convert a scm object into a string using Guile-builtins
fn string_from_scm(scm_obj: *mut c_void) -> Result<String, ()> {
    unsafe {
        if scm_obj.is_null() {
            return Err(());
        }
        if scm_is_string(scm_obj) != 0 {
            let res_str = CStr::from_ptr(scm_to_locale_string(scm_obj))
                .to_string_lossy()
                .into_owned();
            return Ok(res_str);
        } else {
            let port = scm_open_output_string();
            if port.is_null() {
                return Err(());
            }
            let res = scm_object_to_string(scm_obj, scm_undefined);
            if res.is_null() {
                return Err(());
            }
            let res_str = CStr::from_ptr(scm_to_locale_string(res))
                .to_string_lossy()
                .into_owned();
            return Ok(res_str);
        }
    }
}

pub fn smp_guile_init() {}

pub fn testguile() {
    unsafe {
        scm_init_guile();

        let func_name = CString::new("my-rust-function").unwrap();
        scm_c_define_gsubr(
            func_name.as_ptr(),
            0, // required arguments
            0, // optional arguments
            0, // rest arguments
            my_rust_function,
        );

        let expr = CString::new("(+ 2 3)").unwrap();
        let result = scm_c_eval_string(expr.as_ptr());
        println!("{:?}", string_from_scm(result));

        let expr = CString::new("(my-rust-function)").unwrap();
        let result = scm_c_eval_string(expr.as_ptr());
        println!("{:?}", string_from_scm(result));
    }
}