//! Run the PostgreSQL server off a temporary data directory.
//!
//! See the [supported command-line arguments](Args).

use std::{
    collections::HashMap,
    ffi::{OsStr, OsString},
    os::unix::fs::PermissionsExt,
    path::PathBuf,
    process::{ExitCode, ExitStatus, Stdio},
    time::Duration,
};

use anyhow::{Context, bail};
use clap::{Parser, ValueHint, builder::NonEmptyStringValueParser};
use tokio::{process::Command, signal::unix::SignalKind, time::Instant};
use tokio_util::sync::CancellationToken;
use tracing::{debug, info, trace, warn};
use url::Url;

// For clap.
macro_rules! version {
    () => {
        crate::version()
    };
}

const EXTRA_HELP: &str = color_print::cstr!(
    r#"<strong><underline>Exit status:</underline></strong>

Exits 0 on success, and >0 if an error occurs. Specifically, exits 2 on usage error, and 130 when interrupted. Propagates the exit status of the given command, if any.
"#
);

/// Command-line arguments.
#[derive(Debug, Clone, Parser)]
#[command(name = "temp-postgres", version, long_version = version!(), about, author, after_long_help = EXTRA_HELP, next_display_order = None)]
#[deny(clippy::missing_docs_in_private_items)]
struct Args {
    /// Database name.
    ///
    /// Defaults to the PostgreSQL user name.
    #[arg(short = 'd', long, env = "PGDATABASE", value_parser = NonEmptyStringValueParser::new())]
    dbname: Option<String>,

    /// PostgreSQL user name.
    ///
    /// If not set, PostgreSQL uses the current operating system user.
    #[arg(short = 'u', long, env = "PGUSER", value_parser = NonEmptyStringValueParser::new())]
    username: Option<String>,

    /// Create a symbolic link to the temporary directory.
    ///
    /// The given path must not exist.
    ///
    /// The symbolic link will be created when the PostgreSQL server is ready.
    /// It will be removed when the program ends if it (still) points to the temporary directory.
    ///
    /// Example: Static client configuration.
    ///
    /// ```sh
    /// temp-postgres --symlink db
    /// psql --host "$(realpath db)"
    /// ```
    // Clap ensures that arguments passed on the command-line are non-empty.
    // Add a value parser when binding to an environment variable.
    #[arg(long, value_name = "PATH", value_hint = ValueHint::FilePath)]
    symlink: Option<OsString>,

    /// Log level.
    #[arg(long, value_enum, default_value_t = LogLevel::Info)]
    log_level: LogLevel,

    /// Postgres startup timeout.
    #[arg(long, value_name = "DURATION", value_parser = humantime::parse_duration, default_value = "5s")]
    startup_timeout: Duration,

    /// Graceful shutdown timeout.
    ///
    /// `temp-postgres` performs a graceful shutdown upon SIGINT.
    /// The signal is propagated to child processes, namely the `postgres` command, and the wrapped command, if any.
    /// Child processes are killed (with SIGKILL) if they don't shut down in time.
    #[arg(long, value_name = "DURATION", value_parser = humantime::parse_duration, default_value = "5s")]
    shutdown_timeout: Duration,

    /// Command to execute once the PostgreSQL server is ready.
    ///
    /// The following environment variables will be passed to the command:
    ///
    /// - PGHOST, the absolute path to the directory in which the UNIX domain socket file is stored
    /// - PGDATABASE, the database name
    /// - PGUSER, the PostgreSQL user name
    /// - DATABASE_URL, a connection URI
    ///
    /// See also the PostgreSQL documentation on environment variables and connection URIs:
    ///
    /// - <https://www.postgresql.org/docs/current/libpq-envars.html>
    /// - <https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-CONNSTRING-URIS>
    ///
    /// Example: Wrap the `psql` command to connect to the temporary database once the server is ready.
    ///
    /// ```sh
    /// temp-postgres -- psql
    /// ```
    #[arg(last = true, value_hint = ValueHint::CommandWithArguments)]
    command: Vec<OsString>,
}

/// Log level.
#[derive(Debug, Copy, Clone, PartialEq, Eq, PartialOrd, Ord, clap::ValueEnum)]
enum LogLevel {
    Off,
    Error,
    Warn,
    Info,
    Debug,
    Trace,
}

impl From<LogLevel> for tracing_subscriber::filter::LevelFilter {
    fn from(value: LogLevel) -> Self {
        match value {
            LogLevel::Off => tracing_subscriber::filter::LevelFilter::OFF,
            LogLevel::Error => tracing_subscriber::filter::LevelFilter::ERROR,
            LogLevel::Warn => tracing_subscriber::filter::LevelFilter::WARN,
            LogLevel::Info => tracing_subscriber::filter::LevelFilter::INFO,
            LogLevel::Debug => tracing_subscriber::filter::LevelFilter::DEBUG,
            LogLevel::Trace => tracing_subscriber::filter::LevelFilter::TRACE,
        }
    }
}

#[tokio::main]
async fn main() -> ExitCode {
    let args = Args::parse(); // May exit 0 or 2. Respects `NO_COLOR`.
    let result = async {
        let mut subscriber = tracing_subscriber::fmt()
            .with_max_level(args.log_level.to_owned())
            .with_writer(std::io::stderr); // Enable user to capture standard output of wrapped command.
        if std::env::var_os("NO_COLOR").is_some() {
            subscriber = subscriber.with_ansi(false);
        }
        subscriber.init();
        debug!(version = version(), "starting");
        debug!(arguments = ?args, "parsed command-line arguments");

        run(args).await
    };
    match result.await {
        Ok(_) => ExitCode::SUCCESS,
        Err(err) => {
            // Relying on tracing to print error.
            //eprintln!("Error: {err:?}");
            if err.is::<InterruptError>() {
                ExitCode::from(130)
            } else if let Some(err) = err.downcast_ref::<WrappedCommandError>() {
                match err.0.code().and_then(|code| u8::try_from(code).ok()) {
                    Some(code) => ExitCode::from(code),
                    None => ExitCode::FAILURE,
                }
            } else {
                ExitCode::FAILURE
            }
        }
    }
}

#[tracing::instrument(level = "info", skip_all, err(Debug))]
async fn run(args: Args) -> Result<(), anyhow::Error> {
    let mut sigint = tokio::signal::unix::signal(SignalKind::interrupt())
        .context("Failed to register SIGINT handler")?;
    debug!("registered SIGINT handler");

    let tmp = tempfile::Builder::new()
        .prefix("temp-postgres-")
        .permissions(std::fs::Permissions::from_mode(0o700))
        .tempdir()
        .context("Failed to create temporary directory")?;
    debug!(directory = %&tmp.path().display(), "created temporary directory");

    let token = CancellationToken::new();
    let mut server = tokio::spawn(serve(args.clone(), tmp.path().to_path_buf(), token.clone()));
    debug!("spawned server task");

    let result = tokio::select! {
        _ = sigint.recv() => {
            info!("received SIGINT, shutting down ...");
            token.cancel();
            tokio::select! {
                _ = tokio::time::sleep(args.shutdown_timeout) => {
                    warn!("graceful shutdown timed out, aborting ...");
                    server.abort();
                    server.await?
                }
                r = &mut server => {
                    debug!("server task finished");
                    r?
                }
            }
        }
        r = &mut server => {
            debug!("server task finished");
            r?
        },
    };

    if let Some(symlink) = &args.symlink {
        if let Ok(target) = tokio::fs::canonicalize(&symlink).await
            && let Ok(tmp) = tokio::fs::canonicalize(&tmp.path()).await
            && target == tmp
        {
            match tokio::fs::remove_file(symlink).await {
                Ok(()) => debug!(?symlink, "removed symlink"),
                Err(err) => warn!(?symlink, error = ?err, "failed to remove symlink"),
            }
        } else {
            warn!(?symlink, directory = %&tmp.path().display(), "keeping symlink because it doesn't point to temporary directory");
        }
    }

    let tmp_dir = tmp.path().to_path_buf();
    match tmp.close() {
        Ok(()) => debug!(directory = %tmp_dir.display(), "removed temporary directory"),
        Err(err) => {
            warn!(directory = %tmp_dir.display(), error = ?err, "failed to remove temporary directory")
        }
    }
    result
}

#[tracing::instrument(level = "info", skip_all, err)]
async fn serve(
    args: Args,
    tmp_dir: PathBuf,
    token: CancellationToken,
) -> Result<(), anyhow::Error> {
    // WORKAROUND: PostgreSQL expects a non-empty dbname when username is set.
    let args = Args {
        dbname: args.dbname.clone().or(args.username.clone()),
        ..args
    };

    // TODO: Check token.is_cancelled() before every command?
    let mut optional_initdb_args = Vec::<&OsStr>::new();
    if let Some(ref username) = args.username {
        optional_initdb_args.push("--username".as_ref());
        optional_initdb_args.push(username.as_ref());
    }
    let status = Command::new("initdb")
        .arg("--pgdata")
        .arg(&tmp_dir)
        .args(optional_initdb_args)
        .stdin(Stdio::null())
        .stdout(Stdio::null())
        .stderr(Stdio::null())
        .kill_on_drop(true) // In case this task gets aborted
        .status()
        .await
        .context("Failed to spawn or wait for initdb command")?;
    if !status.success() {
        bail!("initdb command exited error: {status}");
    }
    debug!("initialized database");

    let mut postgres = Command::new("postgres")
        .arg("-h")
        .arg("") // Don't bind to a TCP/IP address
        .arg("-k")
        .arg(&tmp_dir)
        .arg("-D")
        .arg(&tmp_dir)
        .stdin(Stdio::null())
        .stdout(Stdio::null())
        .stderr(Stdio::null())
        .kill_on_drop(true)
        .spawn()
        .context("Failed to spawn postgres command")?;
    debug!("spawned postgres command");

    let now = Instant::now();
    tokio::time::sleep(Duration::from_millis(50)).await;
    for i in 1.. {
        match is_ready(tmp_dir.as_ref(), args.username.as_deref()).await {
            Ok(status) => {
                if status.success() {
                    debug!("PostgreSQL server is ready");
                    break;
                } else if status.code() == Some(1) || status.code() == Some(2) {
                    if now.elapsed() < args.startup_timeout {
                        trace!("retrying pg_isready command ...");
                    } else {
                        bail!("pg_isready timed out after {i} attempts");
                    }
                } else {
                    bail!("pg_isready command exited error: {status}");
                }
            }
            Err(err) => return Err(err),
        }
        tokio::time::sleep(Duration::from_millis(200)).await;
    }

    let mut optional_createdb_args = Vec::<&OsStr>::new();
    if let Some(ref username) = args.username {
        optional_createdb_args.push("--username".as_ref());
        optional_createdb_args.push(username.as_ref());
    }
    if let Some(ref dbname) = args.dbname {
        // Positional argument
        optional_createdb_args.push(dbname.as_ref());
    }
    let status = Command::new("createdb")
        .arg("--host")
        .arg(&tmp_dir)
        .arg("--no-password")
        .args(optional_createdb_args)
        .stdin(Stdio::null())
        .stdout(Stdio::null())
        .stderr(Stdio::null())
        .kill_on_drop(true)
        .status()
        .await
        .context("Failed to spawn or wait for createdb command")?;
    if !status.success() {
        bail!("createdb command exited error: {status}");
    }
    debug!("Created PostgreSQL database");

    let mut url = Url::parse("postgresql://")?;
    if let Some(ref dbname) = args.dbname {
        url.set_path(dbname);
    }
    url.query_pairs_mut()
        .append_pair("host", &tmp_dir.display().to_string());
    if let Some(ref username) = args.username {
        url.query_pairs_mut().append_pair("user", username);
    }

    info!(
        PGHOST = %&tmp_dir.display(),
        PGDATABASE = &args.dbname,
        PGUSER = &args.username,
        DATABASE_URL = %&url,
        "You can connect using the following parameters"
    );

    if let Some(symlink) = &args.symlink {
        tokio::fs::symlink(&tmp_dir, symlink)
            .await
            .context("Failed to create symlink")?;
        debug!(?symlink, "created symlink");
    }

    let mut wrapped_command = match args.command.split_first() {
        None => None,
        Some((head, tail)) => {
            let mut optional_env = HashMap::new();
            if let Some(ref username) = args.username {
                optional_env.insert("PGUSER", username);
            }
            if let Some(ref dbname) = args.dbname {
                optional_env.insert("PGDATABASE", dbname);
            }
            let command = Command::new(head)
                .args(tail)
                .env("PGHOST", &tmp_dir)
                .env("DATABASE_URL", url.as_str()) // for SQLx with SQLX_OFFLINE=true
                .envs(optional_env)
                .kill_on_drop(true)
                .spawn()
                .context("Failed to spawn wrapped command")?;
            debug!("spawned wrapped command");
            Some(command)
        }
    };

    tokio::select! {
        _ = token.cancelled() => {
            debug!("token cancelled");
            debug!("shutting down child processes ...");
            // Propagating SIGINT to child processes in case it was send to temp-postgres only.
            // Halving shutdown timeout to avoid being aborted by parent task.
            let shutdown_timeout = args.shutdown_timeout.checked_div(2).unwrap();
            let (wrapped_command_result, postgres_result) = tokio::join!(
                async {
                    if let Some(ref mut c) = wrapped_command {
                        interrupt_or_kill(c, shutdown_timeout).await
                    } else {
                        Ok(None)
                    }
                },
                interrupt_or_kill(&mut postgres, shutdown_timeout),
            );
            if wrapped_command.is_some() {
                match wrapped_command_result {
                    // Exit code is probably 130
                    Ok(status) => debug!(?status, "successfully shut down wrapped command"),
                    Err(err) => warn!(error = ?err, "failed to shut down wrapped command"),
                }
            }
            match postgres_result {
                // Exit code is probably 130
                Ok(status) => debug!(?status, "successfully shut down postgres command"),
                Err(err) => warn!(error = ?err, "failed to shut down postgres command"),
            }
            Err(InterruptError{})?
        },
        r = postgres.wait() => {
            debug!("postgres command finished");
            debug!("shutting down wrapped command ...");
            if let Some(ref mut c) = wrapped_command {
                match interrupt_or_kill(c, args.shutdown_timeout).await {
                    // Exit code is probably 130
                    Ok(status) => debug!(?status, "successfully shut down wrapped command"),
                    Err(err) => warn!(error = ?err, "failed to shut down wrapped command"),
                }
            }
            let status = r.context("failed to wait for postgres command")?;
            if !status.success() {
                bail!("postgres command exited error: {status}");
            }
            Ok(())
        },
        r = conditional_wait(&mut wrapped_command) => {
            debug!("wrapped command finished");
            debug!("shutting down postgres command ...");
            match interrupt_or_kill(&mut postgres, args.shutdown_timeout).await {
                // Exit code is probably 130
                Ok(status) => debug!(?status, "successfully shut down postgres command"),
                Err(err) => warn!(error = ?err, "failed to shut down postgres command"),
            }
            let status = r.context("failed to wait for wrapped command")?;
            if !status.success() {
                return Err(WrappedCommandError(status))?;
            }
            Ok(())
        },
    }
}

fn interrupt(child: &tokio::process::Child) -> Result<(), anyhow::Error> {
    // std::os::unix::process::ChildExt::send_signal is nightly-only experimental
    if let Some(id) = child.id() {
        nix::sys::signal::kill(
            nix::unistd::Pid::from_raw(id as i32),
            nix::sys::signal::Signal::SIGINT,
        )
        .context("Failed to send SIGINT to process {id}")?;
    }
    Ok(())
}

async fn interrupt_or_kill(
    child: &mut tokio::process::Child,
    timeout: Duration,
) -> Result<Option<ExitStatus>, anyhow::Error> {
    interrupt(child)?;
    tokio::select! {
        r = child.wait() => {
            r.map(Some).context("Failed to wait for child process")
        },
        _ = tokio::time::sleep(timeout) => {
            child.kill().await.context("Failed to kill child process")?;
            Ok(None)
        }
    }
}

async fn is_ready(tmp_dir: &OsStr, username: Option<&str>) -> Result<ExitStatus, anyhow::Error> {
    let mut optional_isready_args = Vec::<&OsStr>::new();
    if let Some(ref username) = username {
        optional_isready_args.push("--username".as_ref());
        optional_isready_args.push(username.as_ref());
    }
    Command::new("pg_isready")
        .arg("--host")
        .arg(tmp_dir)
        .arg("--dbname")
        .arg("dummy") // No database created yet
        .arg("--timeout")
        .arg("3") // Default
        .args(optional_isready_args)
        .stdin(Stdio::null())
        .stdout(Stdio::null())
        .stderr(Stdio::null())
        .kill_on_drop(true)
        .status()
        .await
        .context("Failed to spawn or wait for pg_isready command")
}

async fn conditional_wait(
    child: &mut Option<tokio::process::Child>,
) -> Result<std::process::ExitStatus, std::io::Error> {
    match child {
        None => std::future::pending().await,
        Some(child) => child.wait().await,
    }
}

#[derive(Debug)]
struct WrappedCommandError(ExitStatus);

impl std::fmt::Display for WrappedCommandError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "Wrapped command exited error: {}", self.0)
    }
}

impl std::error::Error for WrappedCommandError {}

#[derive(Debug)]
struct InterruptError {}

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

impl std::error::Error for InterruptError {}

fn version() -> String {
    // https://doc.rust-lang.org/cargo/reference/environment-variables.html#environment-variables-cargo-sets-for-crates
    let package_version = option_env!("CARGO_PKG_VERSION").unwrap_or("unknown");
    let revision = option_env!("VERGEN_GIT_SHA").unwrap_or("unknown");
    let dirty = option_env!("VERGEN_GIT_DIRTY").and_then(|s| s.trim().parse::<bool>().ok());

    let mut version = format!("{package_version}-{revision}");
    if let Some(true) = dirty {
        version.push_str("-dirty");
    }
    version
}

#[test]
fn cli() {
    use clap::CommandFactory;
    Args::command().debug_assert();
}