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use std::boxed::Box;
use std::error::Error;

/// Struct representing uname
///
/// Based on the [utsname](https://www.gnu.org/software/libc/manual/html_node/Platform-Type.html#Platform-Type) struct in GNU libc
#[derive(Debug)]
pub struct UtsName {
    /// The name of the operating system in use.
    pub sysname: String,

    /// The current release level of the operating system implementation.
    pub release: String,

    /// The current version level within the release of the operating system.
    pub version: String,

    /// The description of the type of hardware that is in use.
    pub machine: String,

    /// The host name of this particular computer.
    ///
    /// Returns the same value as the `hostname` command on the command line.
    pub nodename: String,

    /// The NIS or YP domain name.
    pub domainname: String,
}

/// Represents an error when creating an instance of UtsName
#[derive(Debug)]
pub struct UnameError;

impl std::fmt::Display for UnameError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "invalid uname.")
    }
}

impl Error for UnameError {
    fn description(&self) -> &str {
        "Error initializing UtsName (EFAULT)."
    }
}

impl UtsName {
    /// Initializes UtsName with the fields populated.
    ///
    /// Returns an instance of UtsName if successful and an Error object if failed.
    ///
    /// # Examples
    /// ```
    /// assert!(rpsutil::system::UtsName::new().is_ok())
    /// ```
    pub fn new() -> Result<UtsName, Box<Error>> {
        let b_utsname: Box<libc::utsname>;
        let code: libc::c_int;

        unsafe {
            let r_utsname = Box::into_raw(Box::new(Self::c_utsname()));
            code = libc::uname(r_utsname);

            if code != 0 {
                return Err(Box::new(UnameError));
            }

            b_utsname = Box::from_raw(r_utsname);
        }

        Ok(UtsName {
            sysname: Self::char_ary_to_string(&b_utsname.sysname)?,
            release: Self::char_ary_to_string(&b_utsname.release)?,
            version: Self::char_ary_to_string(&b_utsname.version)?,
            machine: Self::char_ary_to_string(&b_utsname.machine)?,
            nodename: Self::char_ary_to_string(&b_utsname.nodename)?,
            domainname: Self::char_ary_to_string(&b_utsname.domainname)?,
        })
    }

    // Creates an instance of the libc utsname struct with all fields populated with dummy values
    fn c_utsname() -> libc::utsname {
        libc::utsname {
            sysname: [' ' as libc::c_char; 65],
            release: [' ' as libc::c_char; 65],
            version: [' ' as libc::c_char; 65],
            machine: [' ' as libc::c_char; 65],
            nodename: [' ' as libc::c_char; 65],
            domainname: [' ' as libc::c_char; 65],
        }
    }

    fn char_ary_to_string(c_ary: &[libc::c_char]) -> Result<String, Box<Error>> {
        let (index, _val) = c_ary
            .iter()
            .enumerate()
            .find(|&(_i, ele)| ele == &(0 as libc::c_char)) // check if the element is a null char
            .expect("byte array representation of string should have a null terminator.");

        let c_slice: &[u8] =
            unsafe { std::slice::from_raw_parts(c_ary.as_ptr() as *const u8, index) };

        Ok(String::from_utf8(c_slice.to_vec())?)
    }
}

/// Get the name of the host
///
/// [reference](https://www.gnu.org/software/libc/manual/html_node/Host-Identification.html#Host-Identification)
///
/// # Examples
///
/// ```
/// match rpsutil::system::hostname() {
///     Ok(name) => println!("hostname: {}", name),
///     Err(err) => println!("err: {}", err),
/// }
/// ```
pub fn hostname() -> Result<String, String> {
    let len = (libc::_SC_HOST_NAME_MAX + 1) as usize;
    let rstr = std::boxed::Box::new(String::new());
    let cstr: std::ffi::CString;

    unsafe {
        let name = std::boxed::Box::into_raw(rstr) as *mut i8;
        let code = libc::gethostname(name, len);

        if code != 0 {
            return Err(format!("name is too long > {}", len));
        }

        cstr = std::ffi::CString::from_raw(name as *mut libc::c_char);
    }

    match cstr.to_str() {
        Err(err) => Err(format!("{}", err)),
        Ok(val) => Ok(String::from(val)),
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_hostname() {
        assert!(hostname().is_ok());
    }

    #[test]
    fn test_uname_error() {
        let err = UnameError {};
        assert_eq!(err.description(), "Error initializing UtsName (EFAULT).");
    }
}