//! Cross platform FFI helpers.

use std::ffi::CStr;

// The system property named 'persist.sys.timezone' contains the name of the

// current timezone.

//

// From https://android.googlesource.com/platform/bionic/+/gingerbread-release/libc/docs/OVERVIEW.TXT#79:

//

// > The name of the current timezone is taken from the TZ environment variable,

// > if defined. Otherwise, the system property named 'persist.sys.timezone' is

// > checked instead.

const ANDROID_TIMEZONE_PROPERTY_NAME: &[u8] = b"persist.sys.timezone\0";

/// Return a [`CStr`] to access the timezone from an Android system properties

/// environment.

pub(crate) fn android_timezone_property_name() -> &'static CStr {

    // In tests or debug mode, opt into extra runtime checks.

    if cfg!(any(test, debug_assertions)) {

        return CStr::from_bytes_with_nul(ANDROID_TIMEZONE_PROPERTY_NAME).unwrap();

    }

    // SAFETY: the key is NUL-terminated and there are no other NULs, this

    // invariant is checked in tests.

    unsafe { CStr::from_bytes_with_nul_unchecked(ANDROID_TIMEZONE_PROPERTY_NAME) }

}

#[cfg(test)]

mod tests {

    use std::ffi::CStr;

    use super::{android_timezone_property_name, ANDROID_TIMEZONE_PROPERTY_NAME};

    #[test]

    fn test_android_timezone_property_name_is_valid_cstr() {

        CStr::from_bytes_with_nul(ANDROID_TIMEZONE_PROPERTY_NAME).unwrap();

        let mut invalid_property_name = ANDROID_TIMEZONE_PROPERTY_NAME.to_owned();

        invalid_property_name.push(b'\0');

        CStr::from_bytes_with_nul(&invalid_property_name).unwrap_err();

    }

    #[test]

    fn test_android_timezone_property_name_getter() {

        let key = android_timezone_property_name().to_bytes_with_nul();

        assert_eq!(key, ANDROID_TIMEZONE_PROPERTY_NAME);

        std::str::from_utf8(key).unwrap();

    }

}