//! OpenHarmony doesn't have `/etc/localtime`, we have to use it's "Time Service" to get the timezone information:

//!

//! - [API Reference](https://gitee.com/openharmony/docs/blob/43726785b4033887cd1a838aaaca5e255897a71e/en/application-dev/reference/apis-basic-services-kit/_time_service.md#oh_timeservice_gettimezone)

use crate::ffi_utils::buffer::{tzname_buf, MAX_LEN};

use crate::GetTimezoneError;

use std::ffi::{c_char, CStr};

#[derive(Debug, Copy, Clone, Eq, PartialEq)]

#[repr(C)]

#[allow(non_camel_case_types)]

#[allow(dead_code)]

enum TimeService_ErrCode {

    TIMESERVICE_ERR_OK = 0,

    TIMESERVICE_ERR_INTERNAL_ERROR = 13000001,

    TIMESERVICE_ERR_INVALID_PARAMETER = 13000002,

}

#[link(name = "time_service_ndk", kind = "dylib")]

extern "C" {

    fn OH_TimeService_GetTimeZone(timeZone: *mut c_char, len: u32) -> TimeService_ErrCode;

}

/// TODO: Change this `CStr::from_bytes_until_nul` once MSRV was bumped above 1.69.0

fn from_bytes_until_nul(bytes: &[u8]) -> Option<&CStr> {

    let nul_pos = bytes.iter().position(|&b| b == 0)?;

    // SAFETY:

    // 1. nul_pos + 1 <= bytes.len()

    // 2. We know there is a nul byte at nul_pos, so this slice (ending at the nul byte) is a well-formed C string.

    Some(unsafe { CStr::from_bytes_with_nul_unchecked(&bytes[..=nul_pos]) })

}

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

    let mut time_zone = tzname_buf();

    // SAFETY:

    // `time_zone` is a valid buffer with a length of 40 bytes.

    let ret = unsafe {

        OH_TimeService_GetTimeZone(time_zone.as_mut_ptr().cast::<c_char>(), MAX_LEN as u32 - 1)

    };

    if ret != TimeService_ErrCode::TIMESERVICE_ERR_OK {

        return Err(GetTimezoneError::OsError);

    }

    from_bytes_until_nul(&time_zone)

        .and_then(|x| x.to_str().ok())

        .map(|x| x.to_owned())

        .ok_or(GetTimezoneError::OsError)

}