//! Implementation of `std::os` functionality for teeos

use core::marker::PhantomData;

use super::unsupported;
use crate::error::Error as StdError;
use crate::ffi::{OsStr, OsString};
use crate::path::PathBuf;
use crate::{fmt, io, path};

pub fn errno() -> i32 {
    unsafe { (*libc::__errno_location()) as i32 }
}

// Hardcoded to return 4096, since `sysconf` is only implemented as a stub.
pub fn page_size() -> usize {
    // unsafe { libc::sysconf(libc::_SC_PAGESIZE) as usize };
    4096
}

// Everything below are stubs and copied from unsupported.rs

pub fn error_string(_errno: i32) -> String {
    "error string unimplemented".to_string()
}

pub fn getcwd() -> io::Result<PathBuf> {
    unsupported()
}

pub fn chdir(_: &path::Path) -> io::Result<()> {
    unsupported()
}

pub struct SplitPaths<'a>(!, PhantomData<&'a ()>);

pub fn split_paths(_unparsed: &OsStr) -> SplitPaths<'_> {
    panic!("unsupported")
}

impl<'a> Iterator for SplitPaths<'a> {
    type Item = PathBuf;
    fn next(&mut self) -> Option<PathBuf> {
        self.0
    }
}

#[derive(Debug)]
pub struct JoinPathsError;

pub fn join_paths<I, T>(_paths: I) -> Result<OsString, JoinPathsError>
where
    I: Iterator<Item = T>,
    T: AsRef<OsStr>,
{
    Err(JoinPathsError)
}

impl fmt::Display for JoinPathsError {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        "not supported on this platform yet".fmt(f)
    }
}

impl StdError for JoinPathsError {
    #[allow(deprecated)]
    fn description(&self) -> &str {
        "not supported on this platform yet"
    }
}

pub fn current_exe() -> io::Result<PathBuf> {
    unsupported()
}

pub struct Env(!);

impl Env {
    // FIXME(https://github.com/rust-lang/rust/issues/114583): Remove this when <OsStr as Debug>::fmt matches <str as Debug>::fmt.
    pub fn str_debug(&self) -> impl fmt::Debug + '_ {
        let Self(inner) = self;
        match *inner {}
    }
}

impl fmt::Debug for Env {
    fn fmt(&self, _: &mut fmt::Formatter<'_>) -> fmt::Result {
        let Self(inner) = self;
        match *inner {}
    }
}

impl Iterator for Env {
    type Item = (OsString, OsString);
    fn next(&mut self) -> Option<(OsString, OsString)> {
        let Self(inner) = self;
        match *inner {}
    }
}

pub fn env() -> Env {
    panic!("not supported on this platform")
}

pub fn getenv(_: &OsStr) -> Option<OsString> {
    None
}

pub unsafe fn setenv(_: &OsStr, _: &OsStr) -> io::Result<()> {
    Err(io::Error::new(io::ErrorKind::Unsupported, "cannot set env vars on this platform"))
}

pub unsafe fn unsetenv(_: &OsStr) -> io::Result<()> {
    Err(io::Error::new(io::ErrorKind::Unsupported, "cannot unset env vars on this platform"))
}

pub fn temp_dir() -> PathBuf {
    panic!("no filesystem on this platform")
}

pub fn home_dir() -> Option<PathBuf> {
    None
}

pub fn exit(_code: i32) -> ! {
    panic!("TA should not call `exit`")
}

pub fn getpid() -> u32 {
    panic!("no pids on this platform")
}
