use crate::escape::escape;

use super::child::Child;
use super::stdio::TryFromChildIo;
use super::Stdio;
use super::{Error, Session};

use std::borrow::Cow;
use std::ffi::OsStr;
use std::ops::Deref;
use std::process;

#[derive(Debug)]
pub(crate) enum CommandImp {
    #[cfg(feature = "process-mux")]
    ProcessImpl(super::process_impl::Command),

    #[cfg(feature = "native-mux")]
    NativeMuxImpl(super::native_mux_impl::Command),
}
#[cfg(feature = "process-mux")]
impl From<super::process_impl::Command> for CommandImp {
    fn from(imp: super::process_impl::Command) -> Self {
        CommandImp::ProcessImpl(imp)
    }
}

#[cfg(feature = "native-mux")]
impl From<super::native_mux_impl::Command> for CommandImp {
    fn from(imp: super::native_mux_impl::Command) -> Self {
        CommandImp::NativeMuxImpl(imp)
    }
}

#[cfg(any(feature = "process-mux", feature = "native-mux"))]
macro_rules! delegate {
    ($impl:expr, $var:ident, $then:block) => {{
        match $impl {
            #[cfg(feature = "process-mux")]
            CommandImp::ProcessImpl($var) => $then,

            #[cfg(feature = "native-mux")]
            CommandImp::NativeMuxImpl($var) => $then,
        }
    }};
}

#[cfg(not(any(feature = "process-mux", feature = "native-mux")))]
macro_rules! delegate {
    ($impl:expr, $var:ident, $then:block) => {{
        unreachable!("Neither feature process-mux nor native-mux is enabled")
    }};
}

/// If a command is `OverSsh` then it can be executed over an SSH session.
///
/// Primarily a way to allow `std::process::Command` to be turned directly into an `openssh::Command`.
pub trait OverSsh {
    /// Given an ssh session, return a command that can be executed over that ssh session.
    ///
    /// ### Notes
    ///
    /// The command to be executed on the remote machine should not explicitly
    /// set environment variables or the current working directory. It errors if the source command
    /// has environment variables or a current working directory set, since `openssh` doesn't (yet) have
    /// a method to set environment variables and `ssh` doesn't support setting a current working directory
    /// outside of `bash/dash/zsh` (which is not always available).
    ///
    /// ###  Examples
    ///
    /// 1. Consider the implementation of `OverSsh` for `std::process::Command`. Let's build a
    /// `ls -l -a -h` command and execute it over an SSH session.
    ///
    /// ```no_run
    /// # #[tokio::main(flavor = "current_thread")]
    /// async fn main() -> Result<(), Box<dyn std::error::Error>> {
    ///     use std::process::Command;
    ///     use openssh::{Session, KnownHosts, OverSsh};
    ///
    ///     let session = Session::connect_mux("me@ssh.example.com", KnownHosts::Strict).await?;
    ///     let ls =
    ///         Command::new("ls")
    ///         .arg("-l")
    ///         .arg("-a")
    ///         .arg("-h")
    ///         .over_ssh(&session)?
    ///         .output()
    ///         .await?;
    ///
    ///     assert!(String::from_utf8(ls.stdout).unwrap().contains("total"));
    /// #   Ok(())
    /// }
    ///
    /// ```
    /// 2. Building a command with environment variables or a current working directory set will
    /// results in an error.
    ///
    /// ```no_run
    /// # #[tokio::main(flavor = "current_thread")]
    /// async fn main() -> Result<(), Box<dyn std::error::Error>> {
    ///     use std::process::Command;
    ///     use openssh::{Session, KnownHosts, OverSsh};
    ///
    ///     let session = Session::connect_mux("me@ssh.example.com", KnownHosts::Strict).await?;
    ///     let echo =
    ///         Command::new("echo")
    ///         .env("MY_ENV_VAR", "foo")
    ///         .arg("$MY_ENV_VAR")
    ///         .over_ssh(&session);
    ///     assert!(matches!(echo, Err(openssh::Error::CommandHasEnv)));
    ///
    /// #   Ok(())
    /// }
    ///
    /// ```
    fn over_ssh<S: Deref<Target = Session> + Clone>(
        &self,
        session: S,
    ) -> Result<OwningCommand<S>, crate::Error>;
}

impl OverSsh for std::process::Command {
    fn over_ssh<S: Deref<Target = Session> + Clone>(
        &self,
        session: S,
    ) -> Result<OwningCommand<S>, crate::Error> {
        // I'd really like `!self.get_envs().is_empty()` here, but that's
        // behind a `exact_size_is_empty` feature flag.
        if self.get_envs().len() > 0 {
            return Err(crate::Error::CommandHasEnv);
        }

        if self.get_current_dir().is_some() {
            return Err(crate::Error::CommandHasCwd);
        }

        let program_escaped: Cow<'_, OsStr> = escape(self.get_program());
        let mut command = Session::to_raw_command(session, program_escaped);

        let args = self.get_args().map(escape);
        command.raw_args(args);
        Ok(command)
    }
}

impl OverSsh for tokio::process::Command {
    fn over_ssh<S: Deref<Target = Session> + Clone>(
        &self,
        session: S,
    ) -> Result<OwningCommand<S>, crate::Error> {
        self.as_std().over_ssh(session)
    }
}

impl<S> OverSsh for &S
where
    S: OverSsh,
{
    fn over_ssh<U: Deref<Target = Session> + Clone>(
        &self,
        session: U,
    ) -> Result<OwningCommand<U>, crate::Error> {
        <S as OverSsh>::over_ssh(self, session)
    }
}

impl<S> OverSsh for &mut S
where
    S: OverSsh,
{
    fn over_ssh<U: Deref<Target = Session> + Clone>(
        &self,
        session: U,
    ) -> Result<OwningCommand<U>, crate::Error> {
        <S as OverSsh>::over_ssh(self, session)
    }
}

/// A remote process builder, providing fine-grained control over how a new remote process should
/// be spawned.
///
/// A default configuration can be generated using [`Session::command(program)`](Session::command)
/// or [`Session::arc_command(program)`](Session::arc_command), where `program` gives a path to
/// the program to be executed. Additional builder methods allow the configuration to be changed
/// (for example, by adding arguments) prior to spawning. The interface is almost identical to
/// that of [`std::process::Command`].
///
/// `OwningCommand` can be reused to spawn multiple remote processes. The builder methods change
/// the command without needing to immediately spawn the process. Similarly, you can call builder
/// methods after spawning a process and then spawn a new process with the modified settings.
///
/// # Environment variables and current working directory.
///
/// You'll notice that unlike its `std` counterpart, `OwningCommand` does not have any methods for
/// setting environment variables or the current working directory for the remote command. This is
/// because the SSH protocol does not support this (at least not in its standard configuration).
/// For more details on this, see the `ENVIRONMENT` section of [`ssh(1)`]. To work around this,
/// give [`env(1)`] a try. If the remote shell supports it, you can also prefix your command with
/// `["cd", "dir", "&&"]` to run the rest of the command in some directory `dir`.
///
/// # Exit status
///
/// The `ssh` command generally forwards the exit status of the remote process. The exception is if
/// a protocol-level error occured, in which case it will return with exit status 255. Since the
/// remote process _could_ also return with exit status 255, we have no reliable way to distinguish
/// between remote errors and errors from `ssh`, but this library _assumes_ that 255 means the
/// error came from `ssh`, and acts accordingly.
///
///   [`ssh(1)`]: https://linux.die.net/man/1/ssh
///   [`env(1)`]: https://linux.die.net/man/1/env
#[derive(Debug)]
pub struct OwningCommand<S> {
    session: S,
    imp: CommandImp,

    stdin_set: bool,
    stdout_set: bool,
    stderr_set: bool,
}

impl<S> OwningCommand<S> {
    pub(crate) fn new(session: S, imp: CommandImp) -> Self {
        Self {
            session,
            imp,

            stdin_set: false,
            stdout_set: false,
            stderr_set: false,
        }
    }

    /// Adds an argument to pass to the remote program.
    ///
    /// Before it is passed to the remote host, `arg` is escaped so that special characters aren't
    /// evaluated by the remote shell. If you do not want this behavior, use
    /// [`raw_arg`](Self::raw_arg).
    ///
    /// Only one argument can be passed per use. So instead of:
    ///
    /// ```no_run
    /// # fn foo(c: &mut openssh::Command<'_>) { c
    /// .arg("-C /path/to/repo")
    /// # ; }
    /// ```
    ///
    /// usage would be:
    ///
    /// ```no_run
    /// # fn foo(c: &mut openssh::Command<'_>) { c
    /// .arg("-C")
    /// .arg("/path/to/repo")
    /// # ; }
    /// ```
    ///
    /// To pass multiple arguments see [`args`](Self::args).
    pub fn arg<A: AsRef<str>>(&mut self, arg: A) -> &mut Self {
        self.raw_arg(&*shell_escape::unix::escape(Cow::Borrowed(arg.as_ref())))
    }

    /// Adds an argument to pass to the remote program.
    ///
    /// Unlike [`arg`](Self::arg), this method does not shell-escape `arg`. The argument is passed as written
    /// to `ssh`, which will pass it again as an argument to the remote shell. Since the remote
    /// shell may do argument parsing, characters such as spaces and `*` may be interpreted by the
    /// remote shell.
    ///
    /// To pass multiple unescaped arguments see [`raw_args`](Self::raw_args).
    pub fn raw_arg<A: AsRef<OsStr>>(&mut self, arg: A) -> &mut Self {
        delegate!(&mut self.imp, imp, {
            imp.raw_arg(arg.as_ref());
        });
        self
    }

    /// Adds multiple arguments to pass to the remote program.
    ///
    /// Before they are passed to the remote host, each argument in `args` is escaped so that
    /// special characters aren't evaluated by the remote shell. If you do not want this behavior,
    /// use [`raw_args`](Self::raw_args).
    ///
    /// To pass a single argument see [`arg`](Self::arg).
    pub fn args<I, A>(&mut self, args: I) -> &mut Self
    where
        I: IntoIterator<Item = A>,
        A: AsRef<str>,
    {
        for arg in args {
            self.arg(arg);
        }
        self
    }

    /// Adds multiple arguments to pass to the remote program.
    ///
    /// Unlike [`args`](Self::args), this method does not shell-escape `args`. The arguments are passed as
    /// written to `ssh`, which will pass them again as arguments to the remote shell. However,
    /// since the remote shell may do argument parsing, characters such as spaces and `*` may be
    /// interpreted by the remote shell.
    ///
    /// To pass a single argument see [`raw_arg`](Self::raw_arg).
    pub fn raw_args<I, A>(&mut self, args: I) -> &mut Self
    where
        I: IntoIterator<Item = A>,
        A: AsRef<OsStr>,
    {
        for arg in args {
            self.raw_arg(arg);
        }
        self
    }

    /// Configuration for the remote process's standard input (stdin) handle.
    ///
    /// Defaults to [`inherit`] when used with `spawn` or `status`, and
    /// defaults to [`null`] when used with `output`.
    ///
    /// [`inherit`]: struct.Stdio.html#method.inherit
    /// [`null`]: struct.Stdio.html#method.null
    pub fn stdin<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Self {
        delegate!(&mut self.imp, imp, {
            imp.stdin(cfg.into());
        });
        self.stdin_set = true;
        self
    }

    /// Configuration for the remote process's standard output (stdout) handle.
    ///
    /// Defaults to [`inherit`] when used with `spawn` or `status`, and
    /// defaults to [`piped`] when used with `output`.
    ///
    /// [`inherit`]: struct.Stdio.html#method.inherit
    /// [`piped`]: struct.Stdio.html#method.piped
    pub fn stdout<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Self {
        delegate!(&mut self.imp, imp, {
            imp.stdout(cfg.into());
        });
        self.stdout_set = true;
        self
    }

    /// Configuration for the remote process's standard error (stderr) handle.
    ///
    /// Defaults to [`inherit`] when used with `spawn` or `status`, and
    /// defaults to [`piped`] when used with `output`.
    ///
    /// [`inherit`]: struct.Stdio.html#method.inherit
    /// [`piped`]: struct.Stdio.html#method.piped
    pub fn stderr<T: Into<Stdio>>(&mut self, cfg: T) -> &mut Self {
        delegate!(&mut self.imp, imp, {
            imp.stderr(cfg.into());
        });
        self.stderr_set = true;
        self
    }
}

impl<S: Clone> OwningCommand<S> {
    async fn spawn_impl(&mut self) -> Result<Child<S>, Error> {
        Ok(Child::new(
            self.session.clone(),
            delegate!(&mut self.imp, imp, {
                let (imp, stdin, stdout, stderr) = imp.spawn().await?;
                (
                    imp.into(),
                    stdin.map(TryFromChildIo::try_from).transpose()?,
                    stdout.map(TryFromChildIo::try_from).transpose()?,
                    stderr.map(TryFromChildIo::try_from).transpose()?,
                )
            }),
        ))
    }

    /// Executes the remote command without waiting for it, returning a handle to it
    /// instead.
    ///
    /// By default, stdin, stdout and stderr are inherited.
    pub async fn spawn(&mut self) -> Result<Child<S>, Error> {
        if !self.stdin_set {
            self.stdin(Stdio::inherit());
        }
        if !self.stdout_set {
            self.stdout(Stdio::inherit());
        }
        if !self.stderr_set {
            self.stderr(Stdio::inherit());
        }

        self.spawn_impl().await
    }

    /// Executes the remote command, waiting for it to finish and collecting all of its output.
    ///
    /// By default, stdout and stderr are captured (and used to provide the resulting
    /// output) and stdin is set to `Stdio::null()`.
    pub async fn output(&mut self) -> Result<process::Output, Error> {
        if !self.stdin_set {
            self.stdin(Stdio::null());
        }
        if !self.stdout_set {
            self.stdout(Stdio::piped());
        }
        if !self.stderr_set {
            self.stderr(Stdio::piped());
        }

        self.spawn_impl().await?.wait_with_output().await
    }

    /// Executes the remote command, waiting for it to finish and collecting its exit status.
    ///
    /// By default, stdin, stdout and stderr are inherited.
    pub async fn status(&mut self) -> Result<process::ExitStatus, Error> {
        self.spawn().await?.wait().await
    }
}