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use std::fmt;
use std::io;

/// Errors that occur when interacting with a remote process.
#[derive(Debug)]
pub enum Error {
    /// The master connection failed.
    Master(io::Error),
    /// Failed to establish initial connection to the remote host.
    Connect(io::Error),
    /// Failed to run the `ssh` command locally.
    Ssh(io::Error),
    /// The remote process failed.
    Remote(io::Error),
    /// The connection to the remote host was severed.
    ///
    /// Note that this is a best-effort error, and it _may_ instead signify that the remote process
    /// exited with an error code of 255. You should call [`Session::check`](crate::Session::check)
    /// to verify if you get this error back.
    Disconnected,
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match *self {
            Error::Master(_) => write!(f, "the master connection failed"),
            Error::Connect(_) => write!(f, "failed to connect to the remote host"),
            Error::Ssh(_) => write!(f, "the local ssh command could not be executed"),
            Error::Remote(_) => write!(f, "the remote command could not be executed"),
            Error::Disconnected => write!(f, "the connection was terminated"),
        }
    }
}

impl std::error::Error for Error {
    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
        match *self {
            Error::Master(ref e)
            | Error::Connect(ref e)
            | Error::Ssh(ref e)
            | Error::Remote(ref e) => Some(e),
            Error::Disconnected => None,
        }
    }
}

impl Error {
    pub(crate) fn interpret_ssh_error(stderr: &str) -> Self {
        // we want to turn the string-only ssh error into something a little more "handleable".
        // we do this by trying to interpret the output from `ssh`. this is error-prone, but
        // the best we can do. if you find ways to impove this, even just through heuristics,
        // please file an issue or PR :)
        //
        // format is:
        //
        //     ssh: ssh error: io error
        let mut stderr = stderr.trim();
        if stderr.starts_with("ssh: ") {
            stderr = &stderr["ssh: ".len()..];
        }
        if stderr.starts_with("Warning: Permanently added ") {
            // added to hosts file -- let's ignore that message
            stderr = stderr.splitn(2, "\r\n").nth(1).unwrap_or("");
        }
        let mut kind = io::ErrorKind::ConnectionAborted;
        let mut err = stderr.splitn(2, ": ");
        if let Some(ssh_error) = err.next() {
            if ssh_error.starts_with("Could not resolve") {
                // match what `std` gives: https://github.com/rust-lang/rust/blob/a5de254862477924bcd8b9e1bff7eadd6ffb5e2a/src/libstd/sys/unix/net.rs#L40
                // we _could_ match on "Name or service not known" from io_error,
                // but my guess is that the ssh error is more stable.
                kind = io::ErrorKind::Other;
            }

            if let Some(io_error) = err.next() {
                match io_error {
                    "Network is unreachable" => {
                        kind = io::ErrorKind::Other;
                    }
                    "Connection refused" => {
                        kind = io::ErrorKind::ConnectionRefused;
                    }
                    e if ssh_error.starts_with("connect to host")
                        && e == "Connection timed out" =>
                    {
                        kind = io::ErrorKind::TimedOut;
                    }
                    e if ssh_error.starts_with("connect to host") && e == "Operation timed out" => {
                        // this is the macOS version of "connection timed out"
                        kind = io::ErrorKind::TimedOut;
                    }
                    e if ssh_error.starts_with("connect to host") && e == "Permission denied" => {
                        // this is the macOS version of "network is unreachable".
                        kind = io::ErrorKind::Other;
                    }
                    e if e.contains("Permission denied (") => {
                        kind = io::ErrorKind::PermissionDenied;
                    }
                    _ => {}
                }
            }
        }

        // NOTE: we may want to provide more structured connection errors than just io::Error?
        // NOTE: can we re-use this method for non-connect cases?
        Error::Connect(io::Error::new(kind, stderr))
    }
}

#[test]
fn parse_error() {
    let err = "ssh: Warning: Permanently added \'login.csail.mit.edu,128.52.131.0\' (ECDSA) to the list of known hosts.\r\nopenssh-tester@login.csail.mit.edu: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password,keyboard-interactive).";
    let err = Error::interpret_ssh_error(err);
    let target = io::Error::new(io::ErrorKind::PermissionDenied, "openssh-tester@login.csail.mit.edu: Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password,keyboard-interactive).");
    if let Error::Connect(e) = err {
        assert_eq!(e.kind(), target.kind());
        assert_eq!(format!("{}", e), format!("{}", target));
    } else {
        unreachable!("{:?}", err);
    }
}

#[test]
fn error_sanity() {
    use std::error::Error as _;

    let ioe = || io::Error::new(io::ErrorKind::Other, "test");
    let expect = ioe();

    let e = Error::Master(ioe());
    assert!(!format!("{}", e).is_empty());
    let e = e
        .source()
        .expect("source failed")
        .downcast_ref::<io::Error>()
        .expect("source not io");
    assert_eq!(e.kind(), expect.kind());
    assert_eq!(format!("{}", e), format!("{}", expect));

    let e = Error::Connect(ioe());
    assert!(!format!("{}", e).is_empty());
    let e = e
        .source()
        .expect("source failed")
        .downcast_ref::<io::Error>()
        .expect("source not io");
    assert_eq!(e.kind(), expect.kind());
    assert_eq!(format!("{}", e), format!("{}", expect));

    let e = Error::Ssh(ioe());
    assert!(!format!("{}", e).is_empty());
    let e = e
        .source()
        .expect("source failed")
        .downcast_ref::<io::Error>()
        .expect("source not io");
    assert_eq!(e.kind(), expect.kind());
    assert_eq!(format!("{}", e), format!("{}", expect));

    let e = Error::Remote(ioe());
    assert!(!format!("{}", e).is_empty());
    let e = e
        .source()
        .expect("source failed")
        .downcast_ref::<io::Error>()
        .expect("source not io");
    assert_eq!(e.kind(), expect.kind());
    assert_eq!(format!("{}", e), format!("{}", expect));

    let e = Error::Disconnected;
    assert!(!format!("{}", e).is_empty());
    assert!(e.source().is_none());
}