// Copyright 2011, 2018 Yuya Nishihara <yuya@tcha.org>

//

// This software may be used and distributed according to the terms of the

// GNU General Public License version 2 or any later version.

//! Utility for locating command-server process.

use log::debug;

use std::env;

use std::ffi::{OsStr, OsString};

use std::fs::{self, DirBuilder};

use std::io;

use std::os::unix::ffi::{OsStrExt, OsStringExt};

use std::os::unix::fs::{DirBuilderExt, MetadataExt};

use std::path::{Path, PathBuf};

use std::process::{self, Child, Command};

use std::time::{Duration, Instant};

use tokio::time;

use crate::clientext::ChgClient;

use crate::message::{Instruction, ServerSpec};

use crate::procutil;

const REQUIRED_SERVER_CAPABILITIES: &[&str] = &[

    "attachio",

    "chdir",

    "runcommand",

    "setenv",

    "setumask2",

    "validate",

];

/// Helper to connect to and spawn a server process.

#[derive(Clone, Debug)]

pub struct Locator {

    hg_command: OsString,

    hg_early_args: Vec<OsString>,

    current_dir: PathBuf,

    env_vars: Vec<(OsString, OsString)>,

    process_id: u32,

    base_sock_path: PathBuf,

    redirect_sock_path: Option<PathBuf>,

    timeout: Duration,

}

impl Locator {

    /// Creates locator capturing the current process environment.

    ///

    /// If no `$CHGSOCKNAME` is specified, the socket directory will be

    /// created as necessary.

    pub fn prepare_from_env() -> io::Result<Locator> {

        Ok(Locator {

            hg_command: default_hg_command(),

            hg_early_args: Vec::new(),

            current_dir: env::current_dir()?,

            env_vars: env::vars_os().collect(),

            process_id: process::id(),

            base_sock_path: prepare_server_socket_path()?,

            redirect_sock_path: None,

            timeout: default_timeout(),

        })

    }

    /// Temporary socket path for this client process.

    fn temp_sock_path(&self) -> PathBuf {

        let src = self.base_sock_path.as_os_str().as_bytes();

        let mut buf = Vec::with_capacity(src.len() + 6); // "{src}.{pid}".len()

        buf.extend_from_slice(src);

        buf.extend_from_slice(format!(".{}", self.process_id).as_bytes());

        OsString::from_vec(buf).into()

    }

    /// Specifies the arguments to be passed to the server at start.

    }

    /// Connects to the server.

    ///

    /// The server process will be spawned if not running.

    pub async fn connect(&mut self) -> io::Result<ChgClient> {

        for _cnt in 0..10 {

            let mut client = self.try_connect().await?;

            let instructions = client.validate(&self.hg_early_args).await?;

            let reconnect = self.run_instructions(&instructions)?;

            if !reconnect {

                return Ok(client);

            }

        }

        let msg = format!(

            concat!(

                "too many redirections.\n",

                "Please make sure {:?} is not a wrapper which ",

                "changes sensitive environment variables ",

                "before executing hg. If you have to use a ",

                "wrapper, wrap chg instead of hg.",

            ),

            self.hg_command

        );

        Err(io::Error::new(io::ErrorKind::Other, msg))

    }

    /// Runs instructions received from the server.

    ///

    /// Returns true if the client should try connecting to the other server.

        let mut reconnect = false;

        for inst in instructions {

            debug!("instruction: {:?}", inst);

            match inst {

                Instruction::Exit(_) => {

                    // Just returns the current connection to run the

                    // unparsable command and report the error

                    return Ok(false);

                }

                Instruction::Reconnect => {

                    reconnect = true;

                }

                Instruction::Redirect(path) => {

                    if path.parent() != self.base_sock_path.parent() {

                        let msg = format!(

                            "insecure redirect instruction from server: {}",

                            path.display()

                        );

                    }

                    self.redirect_sock_path = Some(path.to_owned());

                    reconnect = true;

                }

                Instruction::Unlink(path) => {

                    if path.parent() != self.base_sock_path.parent() {

                        let msg = format!(

                            "insecure unlink instruction from server: {}",

                            path.display()

                        );

                    }

                    fs::remove_file(path).unwrap_or(()); // may race

                }

            }

        }

        Ok(reconnect)

    }

    /// Tries to connect to the existing server, or spawns new if not running.

    async fn try_connect(&mut self) -> io::Result<ChgClient> {

        let sock_path = self

            .redirect_sock_path

            .as_ref()

            .unwrap_or(&self.base_sock_path)

            .clone();

        debug!("try connect to {}", sock_path.display());

        let mut client = match ChgClient::connect(sock_path).await {

            Ok(client) => client,

            Err(_) => {

                // Prevent us from being re-connected to the outdated

                // master server: We were told by the server to redirect

                // to redirect_sock_path, which didn't work. We do not

                // want to connect to the same master server again

                // because it would probably tell us the same thing.

                if self.redirect_sock_path.is_some() {

                    fs::remove_file(&self.base_sock_path).unwrap_or(());

                    // may race

                }

                self.spawn_connect().await?

            }

        };

        check_server_capabilities(client.server_spec())?;

        // It's purely optional, and the server might not support this command.

        if client.server_spec().capabilities.contains("setprocname") {

            client

                .set_process_name(format!("chg[worker/{}]", self.process_id))

                .await?;

        }

        client.set_current_dir(&self.current_dir).await?;

        client

            .set_env_vars_os(self.env_vars.iter().cloned())

            .await?;

        Ok(client)

    }

    /// Spawns new server process and connects to it.

    ///

    /// The server will be spawned at the current working directory, then

    /// chdir to "/", so that the server will load configs from the target

    /// repository.

    async fn spawn_connect(&mut self) -> io::Result<ChgClient> {

        let sock_path = self.temp_sock_path();

        debug!("start cmdserver at {}", sock_path.display());

        let server = Command::new(&self.hg_command)

            .arg("serve")

            .arg("--cmdserver")

            .arg("chgunix")

            .arg("--address")

            .arg(&sock_path)

            .arg("--daemon-postexec")

            .arg("chdir:/")

            .args(&self.hg_early_args)

            .current_dir(&self.current_dir)

            .env_clear()

            .envs(self.env_vars.iter().cloned())

            .env("CHGINTERNALMARK", "")

            .spawn()?;

        let client = self.connect_spawned(server, &sock_path).await?;

        debug!(

            "rename {} to {}",

            sock_path.display(),

            self.base_sock_path.display()

        );

        fs::rename(&sock_path, &self.base_sock_path)?;

        Ok(client)

    }

    /// Tries to connect to the just spawned server repeatedly until timeout

    /// exceeded.

    async fn connect_spawned(

        &mut self,

        mut server: Child,

        sock_path: &Path,

    ) -> io::Result<ChgClient> {

        debug!("try connect to {} repeatedly", sock_path.display());

        // waits for either connection established or server failed to start

        let start_time = Instant::now();

        while start_time.elapsed() < self.timeout {

            if let Ok(client) = ChgClient::connect(&sock_path).await {

                // server handle is dropped here, but the detached process

                // will continue running in background

                return Ok(client);

            }

            if let Some(st) = server.try_wait()? {

                return Err(io::Error::new(

                    io::ErrorKind::Other,

                    format!("server exited too early: {}", st),

                ));

            }

            // try again with slight delay

            time::delay_for(Duration::from_millis(10)).await;

        }

        Err(io::Error::new(

            io::ErrorKind::TimedOut,

            "timed out while connecting to server",

        ))

    }

}

/// Determines the server socket to connect to.

///

/// If no `$CHGSOCKNAME` is specified, the socket directory will be created

/// as necessary.

fn prepare_server_socket_path() -> io::Result<PathBuf> {

    if let Some(s) = env::var_os("CHGSOCKNAME") {

        Ok(PathBuf::from(s))

    } else {

        let mut path = default_server_socket_dir();

        create_secure_dir(&path)?;

        path.push("server");

        Ok(path)

    }

}

/// Determines the default server socket path as follows.

///

/// 1. `$XDG_RUNTIME_DIR/chg`

/// 2. `$TMPDIR/chg$UID`

/// 3. `/tmp/chg$UID`

pub fn default_server_socket_dir() -> PathBuf {

    // XDG_RUNTIME_DIR should be ignored if it has an insufficient permission.

    // https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html

    if let Some(Ok(s)) = env::var_os("XDG_RUNTIME_DIR").map(check_secure_dir) {

        let mut path = PathBuf::from(s);

        path.push("chg");

        path

    } else {

        let mut path = env::temp_dir();

        path.push(format!("chg{}", procutil::get_effective_uid()));

        path

    }

}

/// Determines the default hg command.

pub fn default_hg_command() -> OsString {

    // TODO: maybe allow embedding the path at compile time (or load from hgrc)

    env::var_os("CHGHG")

        .or(env::var_os("HG"))

        .unwrap_or(OsStr::new("hg").to_owned())

}

fn default_timeout() -> Duration {

    let secs = env::var("CHGTIMEOUT")

        .ok()

        .and_then(|s| s.parse().ok())

        .unwrap_or(60);

    Duration::from_secs(secs)

}

/// Creates a directory which the other users cannot access to.

///

/// If the directory already exists, tests its permission.

fn create_secure_dir(path: impl AsRef<Path>) -> io::Result<()> {

    DirBuilder::new()

        .mode(0o700)

        .create(path.as_ref())

        .or_else(|err| {

            if err.kind() == io::ErrorKind::AlreadyExists {

                check_secure_dir(path).map(|_| ())

            } else {

                Err(err)

            }

        })

}

fn check_secure_dir<P>(path: P) -> io::Result<P>

where

    P: AsRef<Path>,

{

    let a = fs::symlink_metadata(path.as_ref())?;

        Ok(path)

    } else {

        Err(io::Error::new(io::ErrorKind::Other, "insecure directory"))

    }

}

fn check_server_capabilities(spec: &ServerSpec) -> io::Result<()> {

    let unsupported: Vec<_> = REQUIRED_SERVER_CAPABILITIES

        .iter()

        .cloned()

        .filter(|&s| !spec.capabilities.contains(s))