//! Various utilities.
//!
//! All the little things that are useful through the spirit's or user's code, and don't really fit
//! anywhere else.

use std::env;
use std::error::Error;
use std::ffi::OsStr;
use std::fmt::{Debug, Display, Formatter, Result as FmtResult};
use std::ops::{Deref, DerefMut};
use std::path::PathBuf;
use std::str::FromStr;
use std::sync::atomic::AtomicBool;
use std::sync::Arc;
use std::time::Duration;

use err_context::prelude::*;
use libc::c_int;
use log::{debug, error, warn};
use serde::de::{Deserializer, Error as DeError, Unexpected};
use serde::ser::Serializer;
use serde::{Deserialize, Serialize};

use crate::AnyError;

/// Tries to read an absolute path from the given OS string.
///
/// This converts the path to PathBuf. Then it tries to make it absolute and canonical, so changing
/// current directory later on doesn't make it invalid.
///
/// The function never fails. However, the substeps (finding current directory to make it absolute
/// and canonization) might fail. In such case, the failing step is skipped.
///
/// The motivation is parsing command line arguments using the
/// [`structopt`](https://lib.rs/crates/structopt) crate. Users are used
/// to passing relative paths to command line (as opposed to configuration files). However, if the
/// daemon changes the current directory (for example during daemonization), the relative paths now
/// point somewhere else.
///
/// # Examples
///
/// ```rust
/// use std::path::PathBuf;
///
/// use structopt::StructOpt;
///
/// # #[allow(dead_code)]
/// #[derive(Debug, StructOpt)]
/// struct MyOpts {
///     #[structopt(short = "p", parse(from_os_str = spirit::utils::absolute_from_os_str))]
///     path: PathBuf,
/// }
///
/// # fn main() { }
/// ```
pub fn absolute_from_os_str(path: &OsStr) -> PathBuf {
    let mut current = env::current_dir().unwrap_or_else(|e| {
        warn!(
            "Some paths may not be turned to absolute. Couldn't read current dir: {}",
            e,
        );
        PathBuf::new()
    });
    current.push(path);
    if let Ok(canonicized) = current.canonicalize() {
        canonicized
    } else {
        current
    }
}

/// An error returned when the user passes a key-value option without the equal sign.
///
/// Some internal options take a key-value pairs on the command line. If such option is expected,
/// but it doesn't contain the equal sign, this is the used error.
#[derive(Copy, Clone, Debug)]
pub struct MissingEquals;

impl Display for MissingEquals {
    fn fmt(&self, fmt: &mut Formatter) -> FmtResult {
        write!(fmt, "Missing = in map option")
    }
}

impl Error for MissingEquals {}

/// A helper for deserializing map-like command line arguments.
///
/// # Examples
///
/// ```rust
/// # use structopt::StructOpt;
/// # #[allow(dead_code)]
/// #[derive(Debug, StructOpt)]
/// struct MyOpts {
///     #[structopt(
///         short = "D",
///         long = "define",
///         parse(try_from_str = spirit::utils::key_val),
///         number_of_values(1),
///     )]
///     defines: Vec<(String, String)>,
/// }
///
/// # fn main() {}
/// ```
pub fn key_val<K, V>(opt: &str) -> Result<(K, V), AnyError>
where
    K: FromStr,
    K::Err: Error + Send + Sync + 'static,
    V: FromStr,
    V::Err: Error + Send + Sync + 'static,
{
    let pos = opt.find('=').ok_or(MissingEquals)?;
    Ok((opt[..pos].parse()?, opt[pos + 1..].parse()?))
}

/// A wrapper to hide a configuration field from logs.
///
/// This acts in as much transparent way as possible towards the field inside. It only replaces the
/// [`Debug`] and [`Serialize`] implementations with returning `"******"`.
///
/// The idea is if the configuration contains passwords, they shouldn't leak into the logs.
/// Therefore, wrap them in this, eg:
///
/// ```rust
/// use std::io::Write;
/// use std::str;
///
/// use spirit::utils::Hidden;
///
/// # #[allow(dead_code)]
/// #[derive(Debug)]
/// struct Cfg {
///     username: String,
///     password: Hidden<String>,
/// }
///
/// # fn main() -> Result<(), Box<dyn std::error::Error>> {
/// let cfg = Cfg {
///     username: "me".to_owned(),
///     password: "secret".to_owned().into(),
/// };
///
/// let mut buffer: Vec<u8> = Vec::new();
/// write!(&mut buffer, "{:?}", cfg)?;
/// assert_eq!(r#"Cfg { username: "me", password: "******" }"#, str::from_utf8(&buffer)?);
/// # Ok(())
/// # }
/// ```
#[derive(Clone, Default, Deserialize, Eq, PartialEq, Ord, PartialOrd, Hash)]
#[cfg_attr(feature = "cfg-help", derive(structdoc::StructDoc))]
#[repr(transparent)]
#[serde(transparent)]
pub struct Hidden<T>(pub T);

impl<T> From<T> for Hidden<T> {
    fn from(val: T) -> Self {
        Hidden(val)
    }
}

impl<T> Deref for Hidden<T> {
    type Target = T;
    fn deref(&self) -> &T {
        &self.0
    }
}

impl<T> DerefMut for Hidden<T> {
    fn deref_mut(&mut self) -> &mut T {
        &mut self.0
    }
}

impl<T> Debug for Hidden<T> {
    fn fmt(&self, fmt: &mut Formatter) -> FmtResult {
        write!(fmt, "\"******\"")
    }
}

impl<T> Serialize for Hidden<T> {
    fn serialize<S: Serializer>(&self, s: S) -> Result<S::Ok, S::Error> {
        s.serialize_str("******")
    }
}

/// Serialize a duration.
///
/// This can be used in configuration structures containing durations. See [`deserialize_duration`]
/// for the counterpart.
///
/// The default serialization produces human unreadable values, this is more suitable for dumping
/// configuration users will read.
///
/// # Examples
///
/// ```rust
/// use std::time::Duration;
///
/// use serde::{Deserialize, Serialize};
///
/// #[derive(Clone, Debug, Eq, PartialEq, Deserialize, Serialize)]
/// struct Cfg {
///     #[serde(
///         serialize_with = "spirit::utils::serialize_duration",
///         deserialize_with = "spirit::utils::deserialize_duration",
///     )]
///     how_long: Duration,
/// }
/// ```
pub fn serialize_duration<S: Serializer>(dur: &Duration, s: S) -> Result<S::Ok, S::Error> {
    s.serialize_str(&humantime::format_duration(*dur).to_string())
}

/// Deserialize a human-readable duration.
///
/// # Examples
///
/// ```rust
/// use std::time::Duration;
///
/// use serde::{Deserialize, Serialize};
///
/// #[derive(Clone, Debug, Eq, PartialEq, Deserialize, Serialize)]
/// struct Cfg {
///     #[serde(
///         serialize_with = "spirit::utils::serialize_duration",
///         deserialize_with = "spirit::utils::deserialize_duration",
///     )]
///     how_long: Duration,
/// }
/// ```
pub fn deserialize_duration<'de, D: Deserializer<'de>>(d: D) -> Result<Duration, D::Error> {
    let s = String::deserialize(d)?;

    humantime::parse_duration(&s)
        .map_err(|_| DeError::invalid_value(Unexpected::Str(&s), &"Human readable duration"))
}

/// Deserialize an `Option<Duration>` using the [`humantime`](https://lib.rs/crates/humantime) crate.
///
/// This allows reading human-friendly representations of time, like `30s` or `5days`. It should be
/// paired with [`serialize_opt_duration`]. Also, to act like [`Option`] does when deserializing by
/// default, the `#[serde(default)]` is recommended.
///
/// # Examples
///
/// ```rust
/// use std::time::Duration;
///
/// use serde::{Deserialize, Serialize};
///
/// #[derive(Clone, Debug, Eq, PartialEq, Deserialize, Serialize)]
/// struct Cfg {
///     #[serde(
///         serialize_with = "spirit::utils::serialize_opt_duration",
///         deserialize_with = "spirit::utils::deserialize_opt_duration",
///         default,
///     )]
///     how_long: Option<Duration>,
/// }
/// ```
pub fn deserialize_opt_duration<'de, D: Deserializer<'de>>(
    d: D,
) -> Result<Option<Duration>, D::Error> {
    if let Some(dur) = Option::<String>::deserialize(d)? {
        humantime::parse_duration(&dur)
            .map_err(|_| DeError::invalid_value(Unexpected::Str(&dur), &"Human readable duration"))
            .map(Some)
    } else {
        Ok(None)
    }
}

/// Serialize an `Option<Duration>` in a human friendly form.
///
/// See the [`deserialize_opt_duration`] for more details and an example.
pub fn serialize_opt_duration<S: Serializer>(
    dur: &Option<Duration>,
    s: S,
) -> Result<S::Ok, S::Error> {
    match dur {
        Some(d) => serialize_duration(d, s),
        None => s.serialize_none(),
    }
}

#[deprecated(note = "Abstraction at the wrong place. Use support_emergency_shutdown instead.")]
#[doc(hidden)]
pub fn cleanup_signals() {
    debug!("Resetting termination signal handlers to defaults");
    // Originally, this was done by removing all signals and resetting to defaults. We now install
    // default-handler emulation instead. That's a little bit problematic, if it's the signal
    // handlers that get stuck, but folks are recommended to use the support_emergency_shutdown
    // instead anyway.
    for sig in signal_hook::consts::TERM_SIGNALS {
        let registered =
            signal_hook::flag::register_conditional_default(*sig, Arc::new(AtomicBool::new(true)));
        if let Err(e) = registered {
            let name = signal_hook::low_level::signal_name(*sig).unwrap_or_default();
            error!(
                "Failed to register forced shutdown signal {}/{}: {}",
                name, sig, e
            );
        }
    }
}

/// Installs a stage-shutdown handling.
///
/// If CTRL+C (or some other similar signal) is received for the first time, a graceful shutdown is
/// initiated and a flag is set to true. If it is received for a second time, the application is
/// terminated abruptly.
///
/// The flag handle is returned to the caller, so the graceful shutdown and second stage kill can
/// be aborted.
///
/// Note that this API doesn't allow for removing the staged shutdown (due to the needed API
/// clutter). If that is needed, you can use [`signal_hook`] directly.
///
/// # Usage
///
/// This is supposed to be called early in the program (usually as the first thing in `main`). This
/// is for two reasons:
///
/// * One usually wants this kind of emergency handling even during startup ‒ if something gets
///   stuck during the initialization.
/// * Installing signal handlers once there are multiple threads is inherently racy, therefore it
///   is better to be done before any additional threads are started.
///
/// # Examples
///
/// ```rust
/// use spirit::prelude::*;
/// use spirit::{utils, Empty, Spirit};
///
/// fn main() {
///     // Do this first, so double CTRL+C works from the very beginning.
///     utils::support_emergency_shutdown().expect("This doesn't fail on healthy systems");
///     // Proceed to doing something useful.
///     Spirit::<Empty, Empty>::new()
///         .run(|_spirit| {
///             println!("Hello world");
///             Ok(())
///         });
/// }
/// ```
///
/// # Errors
///
/// This manipulates low-level signal handlers internally, so in theory this can fail. But this is
/// not expected to fail in practice (not on a system that isn't severely broken anyway). As such,
/// it is probably reasonable to unwrap here.
pub fn support_emergency_shutdown() -> Result<Arc<AtomicBool>, AnyError> {
    let flag = Arc::new(AtomicBool::new(false));

    let install = |sig: c_int| -> Result<(), AnyError> {
        signal_hook::flag::register_conditional_shutdown(sig, 2, Arc::clone(&flag))?;
        signal_hook::flag::register(sig, Arc::clone(&flag))?;
        Ok(())
    };

    for sig in signal_hook::consts::TERM_SIGNALS {
        let name = signal_hook::low_level::signal_name(*sig).unwrap_or_default();
        debug!("Installing emergency shutdown support for {}/{}", name, sig);
        install(*sig).with_context(|_| {
            format!(
                "Failed to install staged shutdown handler for {}/{}",
                name, sig
            )
        })?
    }

    Ok(flag)
}

/// Checks if value is default.
///
/// Useful in `#[serde(skip_serializing_if = "is_default")]`
pub fn is_default<T: Default + PartialEq>(v: &T) -> bool {
    v == &T::default()
}

/// Checks if value is set to true.
///
/// Useful in `#[serde(skip_serializing_if = "is_true")]`
pub fn is_true(v: &bool) -> bool {
    *v
}

pub(crate) struct FlushGuard;

impl Drop for FlushGuard {
    fn drop(&mut self) {
        log::logger().flush();
    }
}

#[cfg(test)]
mod tests {
    use std::ffi::OsString;
    use std::net::{AddrParseError, IpAddr};
    use std::num::ParseIntError;

    use super::*;

    #[test]
    fn abs() {
        let current = env::current_dir().unwrap();
        let parent = absolute_from_os_str(&OsString::from(".."));
        assert!(parent.is_absolute());
        assert!(current.starts_with(parent));

        let child = absolute_from_os_str(&OsString::from("this-likely-doesn't-exist"));
        assert!(child.is_absolute());
        assert!(child.starts_with(current));
    }

    /// Valid inputs for the key-value parser
    #[test]
    fn key_val_success() {
        assert_eq!(
            ("hello".to_owned(), "world".to_owned()),
            key_val("hello=world").unwrap()
        );
        let ip: IpAddr = "192.0.2.1".parse().unwrap();
        assert_eq!(("ip".to_owned(), ip), key_val("ip=192.0.2.1").unwrap());
        assert_eq!(("count".to_owned(), 4), key_val("count=4").unwrap());
    }

    /// The extra equals sign go into the value part.
    #[test]
    fn key_val_extra_equals() {
        assert_eq!(
            ("greeting".to_owned(), "hello=world".to_owned()),
            key_val("greeting=hello=world").unwrap(),
        );
    }

    /// Test when the key or value doesn't get parsed.
    #[test]
    fn key_val_parse_fail() {
        key_val::<String, IpAddr>("hello=192.0.2.1.0")
            .unwrap_err()
            .downcast_ref::<AddrParseError>()
            .expect("Different error returned");
        key_val::<usize, String>("hello=world")
            .unwrap_err()
            .downcast_ref::<ParseIntError>()
            .expect("Different error returned");
    }

    #[test]
    fn key_val_missing_eq() {
        key_val::<String, String>("no equal sign")
            .unwrap_err()
            .downcast_ref::<MissingEquals>()
            .expect("Different error returned");
    }
}