use crate::GetTimezoneError;

use std::ffi::CStr;

use std::os::raw::c_char;

use std::ptr::NonNull;

extern "C" {

    fn emscripten_run_script_string(script: *const c_char) -> *mut c_char;

}

pub(crate) fn get_timezone_inner() -> Result<String, GetTimezoneError> {

    const SCRIPT: &CStr = {

        match CStr::from_bytes_with_nul(

            "Intl.DateTimeFormat().resolvedOptions().timeZone\0".as_bytes(),

        ) {

            Ok(s) => s,

            Err(_) => panic!("Invalid UTF-8 data"),

        }

    };

    unsafe {

        NonNull::new(emscripten_run_script_string(SCRIPT.as_ptr()))

            .ok_or_else(|| GetTimezoneError::OsError)

            .and_then(|ptr| {

                CStr::from_ptr(ptr.as_ptr())

                    .to_owned()

                    .into_string()

                    .map_err(|_| GetTimezoneError::FailedParsingString)

            })

    }

}