rstango 0.3.0

//! The Tango database of a test, which answers the commands of the database device the
//! way `Databaseds` does, see [`super::TestContext`]. It is held in memory and made to tell
//! what it was asked and to fail on demand, which is what a test needs, and not what a
//! database meant to be used for real does.
//!
//! Its content is only ever altered through those very commands, that is through the
//! methods of a [`crate::database::DatabaseProxy`], so that what a test sets up is what a
//! real database would have been told.

use std::collections::HashMap;
use std::sync::{Arc, Mutex};
use std::time::SystemTime;
use std::fmt;

use futures::future::{ready, BoxFuture};
use futures::stream::BoxStream;

use crate::dev::{AttrConfig, AttrInfo, AttrRead, AttrValueEvent, CommandInfo, DevInfo, DevSource, DevState, Named, NamedResult};
use crate::error::{Error, ErrorKind, Result, reason};
use crate::value::{Scalar, Spectrum, Value};
use crate::backend::BackendDev;


/// The name the database device answers with, the one of a real database.
pub const NAME: &str = "sys/database/2";

/// The class of the admin device of every server.
const ADMIN_CLASS: &str = "DServer";

// =========================== //
//          Database           //
// =========================== //

/// The database of a test, held in memory, every name being looked up regardless of its
/// case, as `Databaseds` does.
///
/// Besides answering the commands of the database device, it records them, see
/// [`Self::log`], and can be made to fail some of them, see [`Self::add_fail`], which
/// is what testing how a server or a client copes with its database takes.
#[derive(Default)]
pub struct TestDatabase {
    state: Mutex<State>,
    /// Every command answered, in order, with its argument.
    log: Mutex<Vec<(String, Value)>>,
    /// The error each failing command fails with, by name.
    failing: Mutex<HashMap<String, FailWith>>,
}

/// What makes the error a failing command fails with, once for every time it is sent.
type FailWith = Box<dyn Fn() -> Error + Send + Sync>;

impl fmt::Debug for TestDatabase {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("TestDatabase")
            .field("state", &self.state)
            .field("log", &self.log)
            .field("failing", &self.failing.lock().unwrap().keys())
            .finish()
    }
}

impl TestDatabase {

    /// Every command answered so far, in order, with its argument, those that failed
    /// included.
    pub fn log(&self) -> Vec<(String, Value)> {
        self.log.lock().unwrap().clone()
    }

    /// Forget every command answered so far, see [`Self::log`].
    pub fn clear_log(&self) {
        self.log.lock().unwrap().clear();
    }

    /// Fail every command of that name from now on, with the error that makes, as a broken
    /// database does, until [`Self::remove_fail`].
    pub fn add_fail(&self, name: &str, err: impl Fn() -> Error + Send + Sync + 'static) {
        self.failing.lock().unwrap().insert(name.to_string(), Box::new(err));
    }

    /// Answer the commands of that name again, see [`Self::add_fail`].
    pub fn remove_fail(&self, name: &str) {
        self.failing.lock().unwrap().remove(name);
    }

    /// Answer a command of the database device.
    pub fn command(&self, name: &str, input: Value) -> Result<Value> {

        self.log.lock().unwrap().push((name.to_string(), input.clone()));

        if let Some(err) = self.failing.lock().unwrap().get(name) {
            return Err(err());
        }

        let mut state = self.state.lock().unwrap();

        let res = match name {

            // Servers and devices.
            "DbAddServer" => state.add_server_cmd(input),
            "DbDeleteServer" => state.delete_server_cmd(input),
            "DbAddDevice" => state.add_dev_cmd(input),
            "DbDeleteDevice" => state.delete_dev_cmd(input),
            "DbGetDeviceClassList" => state.list_server_dev(input),

            // Exporting and importing.
            "DbExportDevice" | "DbExportServer" => state.export(input),
            "DbUnExportDevice" => state.unexport_dev(input),
            "DbUnExportServer" => state.unexport_server(input),
            "DbImportDevice" => state.import_dev(input),

            // Properties of devices and classes.
            "DbGetDeviceProperty" | "DbGetClassProperty" => state.get_prop(Kind::of(name), input),
            "DbGetDevicePropertyList" | "DbGetClassPropertyList" => state.list_prop(Kind::of(name), input),
            "DbPutDeviceProperty" | "DbPutClassProperty" => state.put_prop(Kind::of(name), input),
            "DbDeleteDeviceProperty" | "DbDeleteClassProperty" => state.delete_prop(Kind::of(name), input),

            // Properties of the attributes of devices and classes.
            "DbGetDeviceAttributeProperty2" | "DbGetClassAttributeProperty2" => state.get_attr_prop(Kind::of(name), input),
            "DbGetDeviceAttributeList" | "DbGetClassAttributeList" => state.list_attr(Kind::of(name), input),
            "DbPutDeviceAttributeProperty2" | "DbPutClassAttributeProperty2" => state.put_attr_prop(Kind::of(name), input),
            "DbDeleteDeviceAttributeProperty" | "DbDeleteClassAttributeProperty" => state.delete_attr_prop(Kind::of(name), input),

            _ => Err(Error::not_implemented()),

        };

        res.map_err(|err| err.with_append_description(format_args!("The command {name} of the database of a test")))

    }

}

/// What the database holds.
#[derive(Debug, Default)]
struct State {
    /// The lowercase names of the devices of each server, by lowercase `exe/inst` name, in
    /// the order they were added.
    servers: HashMap<String, Vec<String>>,
    /// The devices, by lowercase name.
    devs: HashMap<String, Dev>,
    /// The properties of each object.
    props: HashMap<Object, Props>,
    /// The properties of the attributes of each object.
    attr_props: HashMap<Object, Entries<Props>>,
}

/// One device, as it was defined and as it was last exported.
#[derive(Debug)]
struct Dev {
    name: String,
    class: String,
    server: String,
    /// What the device was last exported with, which a real database keeps once it is
    /// unexported, only the flag telling it is not running anymore.
    export: Option<Export>,
    exported: bool,
}

#[derive(Debug)]
struct Export {
    itr: String,
    host: String,
    version: String,
    pid: i32,
}

/// An object properties are of, a device or a class, by its lowercase name.
type Object = (Kind, String);

/// The kind of object a property is of.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
enum Kind {
    Device,
    Class,
}

impl Kind {

    /// What a property command is about.
    fn of(command: &str) -> Self {
        if command.contains("Class") { Self::Class } else { Self::Device }
    }

    fn object(self, name: &str) -> Object {
        (self, name.to_lowercase())
    }

}

/// The properties of an object or an attribute, each with its values.
type Props = Entries<Vec<String>>;

/// Named entries, kept in the order they were first written and looked up regardless of
/// the case of their name, which keeps the case it was first written with.
#[derive(Debug)]
struct Entries<T>(Vec<(String, T)>);

impl<T> Default for Entries<T> {
    fn default() -> Self {
        Self(Vec::new())
    }
}

impl<T> Entries<T> {

    fn get(&self, name: &str) -> Option<&T> {
        self.0.iter().find(|(other, _)| other.eq_ignore_ascii_case(name)).map(|(_, value)| value)
    }

    /// The entry of that name, added empty if there is none.
    fn entry(&mut self, name: &str) -> &mut T where T: Default {
        let index = match self.0.iter().position(|(other, _)| other.eq_ignore_ascii_case(name)) {
            Some(index) => index,
            None => {
                self.0.push((name.to_string(), T::default()));
                self.0.len() - 1
            }
        };
        &mut self.0[index].1
    }

    /// Remove the entries of those names.
    fn remove(&mut self, names: &[String]) {
        self.0.retain(|(name, _)| !names.iter().any(|removed| removed.eq_ignore_ascii_case(name)));
    }

    /// The names matching a filter, see [`wildcard`].
    fn names(&self, filter: &str) -> Vec<&str> {
        self.0.iter().map(|(name, _)| name.as_str()).filter(|name| wildcard(filter, name)).collect()
    }

}

// -- Servers and devices --

impl State {

    /// The server, then a device and its class, as many times as it has some.
    fn add_server_cmd(&mut self, input: Value) -> Result<Value> {
        let args = strings(input)?;
        let [server, pairs @ ..] = &args[..] else { return Err(malformed_err()) };
        if pairs.len() % 2 != 0 {
            return Err(malformed_err());
        }
        self.add_server(server);
        for pair in pairs.chunks_exact(2) {
            self.add_dev(server, &pair[0], &pair[1]);
        }
        Ok(Value::Void)
    }

    fn delete_server_cmd(&mut self, input: Value) -> Result<Value> {
        let server = String::try_from(input)?;
        for dev in self.servers.remove(&server.to_lowercase()).unwrap_or_default() {
            self.devs.remove(&dev);
        }
        Ok(Value::Void)
    }

    /// The server, the device and its class.
    fn add_dev_cmd(&mut self, input: Value) -> Result<Value> {
        let args = strings(input)?;
        let [server, dev, class] = &args[..] else { return Err(malformed_err()) };
        self.add_server(server);
        self.add_dev(server, dev, class);
        Ok(Value::Void)
    }

    fn delete_dev_cmd(&mut self, input: Value) -> Result<Value> {
        let dev = String::try_from(input)?.to_lowercase();
        if let Some(removed) = self.devs.remove(&dev) {
            self.server_devs(&removed.server).retain(|other| *other != dev);
        }
        Ok(Value::Void)
    }

    /// Every device of the server, then its class, one after the other.
    fn list_server_dev(&mut self, input: Value) -> Result<Value> {
        let server = String::try_from(input)?;
        let listing = self.servers.get(&server.to_lowercase())
            .into_iter()
            .flatten()
            .filter_map(|dev| self.devs.get(dev))
            .flat_map(|dev| [dev.name.as_str(), dev.class.as_str()])
            .collect::<Vec<_>>();
        Ok(Value::from(Spectrum::<str>::from(&listing[..])))
    }

    /// Define a server if it is not already, along with its admin device, as the tools
    /// registering a server do, since a server always exports it.
    fn add_server(&mut self, server: &str) {
        if !self.servers.contains_key(&server.to_lowercase()) {
            self.add_dev(server, &format!("dserver/{server}"), ADMIN_CLASS);
        }
    }

    /// Define a device in a server, moving it there if it was already defined in another
    /// one, as `Databaseds` does, what it was last exported with being kept.
    fn add_dev(&mut self, server: &str, name: &str, class: &str) {

        let key = name.to_lowercase();
        let previous = self.devs.remove(&key);

        if let Some(previous) = &previous {
            self.server_devs(&previous.server).retain(|other| *other != key);
        }
        self.server_devs(server).push(key.clone());

        let (export, exported) = previous.map_or((None, false), |dev| (dev.export, dev.exported));
        self.devs.insert(key, Dev {
            name: name.to_string(),
            class: class.to_string(),
            server: server.to_string(),
            export,
            exported,
        });

    }

    /// The devices of a server, which is defined with none if it was not.
    fn server_devs(&mut self, server: &str) -> &mut Vec<String> {
        self.servers.entry(server.to_lowercase()).or_default()
    }

}

// -- Exporting and importing --

impl State {

    /// Five strings per device: its name, its reference, its host, the process running it
    /// and its version.
    fn export(&mut self, input: Value) -> Result<Value> {
        let args = strings(input)?;
        if args.len() % 5 != 0 {
            return Err(malformed_err());
        }
        for info in args.chunks_exact(5) {
            let [name, itr, host, pid, version] = info else { unreachable!() };
            let dev = self.devs.get_mut(&name.to_lowercase())
                .ok_or_else(|| not_defined_err(name))?;
            dev.export = Some(Export {
                itr: itr.clone(),
                host: host.clone(),
                pid: pid.parse().map_err(|_| malformed_err())?,
                version: version.clone(),
            });
            dev.exported = true;
        }
        Ok(Value::Void)
    }

    fn unexport_dev(&mut self, input: Value) -> Result<Value> {
        let dev = String::try_from(input)?;
        if let Some(dev) = self.devs.get_mut(&dev.to_lowercase()) {
            dev.exported = false;
        }
        Ok(Value::Void)
    }

    fn unexport_server(&mut self, input: Value) -> Result<Value> {
        let server = String::try_from(input)?;
        for dev in self.servers.get(&server.to_lowercase()).into_iter().flatten() {
            if let Some(dev) = self.devs.get_mut(dev) {
                dev.exported = false;
            }
        }
        Ok(Value::Void)
    }

    /// The exported flag and the process, then the name, the reference, the version, the
    /// server, the host and the class.
    fn import_dev(&mut self, input: Value) -> Result<Value> {
        let name = String::try_from(input)?;
        let dev = self.devs.get(&name.to_lowercase())
            .ok_or_else(|| not_defined_err(&name))?;
        let (itr, version, host, pid) = match &dev.export {
            Some(export) => (&*export.itr, &*export.version, &*export.host, export.pid),
            None => ("nada", "0", "nada", 0),
        };
        let strings = [&*dev.name, itr, version, &*dev.server, host, &*dev.class];
        Ok(Value::LongString(
            Spectrum::from(vec![i32::from(dev.exported), pid]),
            Spectrum::<str>::from(&strings[..]),
        ))
    }

}

// -- Properties --

impl State {

    /// The object, then the properties, answered with the object and how many properties,
    /// then each property with how many values it has and its values, a property that has
    /// none being said to have none.
    fn get_prop(&mut self, kind: Kind, input: Value) -> Result<Value> {
        let args = strings(input)?;
        let [obj_name, prop_names @ ..] = &args[..] else { return Err(malformed_err()) };
        let props = self.props.get(&kind.object(obj_name));
        let mut listing = vec![obj_name.clone(), prop_names.len().to_string()];
        for prop_name in prop_names {
            let values = props.and_then(|props| props.get(prop_name)).map_or(&[][..], Vec::as_slice);
            listing.push(prop_name.clone());
            listing.push(values.len().to_string());
            listing.extend(values.iter().cloned());
        }
        Ok(Value::from(Spectrum::<str>::from(&listing[..])))
    }

    /// The object and a filter.
    fn list_prop(&mut self, kind: Kind, input: Value) -> Result<Value> {
        let args = strings(input)?;
        let [obj_name, filter] = &args[..] else { return Err(malformed_err()) };
        let names = self.props.get(&kind.object(obj_name)).map_or_else(Vec::new, |props| props.names(filter));
        Ok(Value::from(Spectrum::<str>::from(&names[..])))
    }

    /// The object and how many properties, then each property with how many values it has
    /// and its values.
    fn put_prop(&mut self, kind: Kind, input: Value) -> Result<Value> {
        let args = strings(input)?;
        let mut cursor = Cursor::new(&args);
        let props = self.props.entry(kind.object(cursor.next()?)).or_default();
        for _ in 0..cursor.count()? {
            let prop_name = cursor.next()?;
            *props.entry(prop_name) = cursor.values()?.to_vec();
        }
        cursor.end()?;
        Ok(Value::Void)
    }

    /// The object, then the properties.
    fn delete_prop(&mut self, kind: Kind, input: Value) -> Result<Value> {
        let args = strings(input)?;
        let [obj_name, prop_names @ ..] = &args[..] else { return Err(malformed_err()) };
        if let Some(props) = self.props.get_mut(&kind.object(obj_name)) {
            props.remove(prop_names);
        }
        Ok(Value::Void)
    }

}

// -- Properties of attributes --

impl State {

    /// The object, then the attributes, answered with the object and how many attributes,
    /// then each attribute with how many properties it has, then each property with how
    /// many values it has and its values.
    fn get_attr_prop(&mut self, kind: Kind, input: Value) -> Result<Value> {
        let args = strings(input)?;
        let [obj_name, attr_names @ ..] = &args[..] else { return Err(malformed_err()) };
        let attrs = self.attr_props.get(&kind.object(obj_name));
        let mut listing = vec![obj_name.clone(), attr_names.len().to_string()];
        for attr_name in attr_names {
            let props = attrs.and_then(|attrs| attrs.get(attr_name)).map_or(&[][..], |props| &props.0[..]);
            listing.push(attr_name.clone());
            listing.push(props.len().to_string());
            for (prop_name, values) in props {
                listing.push(prop_name.clone());
                listing.push(values.len().to_string());
                // A property holding no value is followed by a placeholder, which is what
                // the database server sends for one.
                if values.is_empty() {
                    listing.push(" ".to_string());
                }
                listing.extend(values.iter().cloned());
            }
        }
        Ok(Value::from(Spectrum::<str>::from(&listing[..])))
    }

    /// The object and a filter.
    fn list_attr(&mut self, kind: Kind, input: Value) -> Result<Value> {
        let args = strings(input)?;
        let [obj_name, filter] = &args[..] else { return Err(malformed_err()) };
        let names = self.attr_props.get(&kind.object(obj_name)).map_or_else(Vec::new, |attrs| attrs.names(filter));
        Ok(Value::from(Spectrum::<str>::from(&names[..])))
    }

    /// The object and how many attributes, then each attribute with how many properties it
    /// has, then each property with how many values it has and its values.
    fn put_attr_prop(&mut self, kind: Kind, input: Value) -> Result<Value> {
        let args = strings(input)?;
        let mut cursor = Cursor::new(&args);
        let attrs = self.attr_props.entry(kind.object(cursor.next()?)).or_default();
        for _ in 0..cursor.count()? {
            let props = attrs.entry(cursor.next()?);
            for _ in 0..cursor.count()? {
                let prop_name = cursor.next()?;
                *props.entry(prop_name) = cursor.values()?.to_vec();
            }
        }
        cursor.end()?;
        Ok(Value::Void)
    }

    /// The object and the attribute, then the properties.
    fn delete_attr_prop(&mut self, kind: Kind, input: Value) -> Result<Value> {
        let args = strings(input)?;
        let [obj_name, attr_name, prop_names @ ..] = &args[..] else { return Err(malformed_err()) };
        if let Some(attrs) = self.attr_props.get_mut(&kind.object(obj_name)) {
            attrs.entry(attr_name).remove(prop_names);
            // An attribute left with no property is no longer listed.
            attrs.0.retain(|(_, props)| !props.0.is_empty());
        }
        Ok(Value::Void)
    }

}

// -- Arguments --

/// Reading a command argument made of counted runs of strings.
struct Cursor<'a> {
    args: &'a [String],
    pos: usize,
}

impl<'a> Cursor<'a> {

    fn new(args: &'a [String]) -> Self {
        Self { args, pos: 0 }
    }

    fn next(&mut self) -> Result<&'a str> {
        let arg = self.args.get(self.pos).ok_or_else(malformed_err)?;
        self.pos += 1;
        Ok(arg)
    }

    fn count(&mut self) -> Result<usize> {
        self.next()?.parse().map_err(|_| malformed_err())
    }

    /// A count, then that many values.
    fn values(&mut self) -> Result<&'a [String]> {
        let len = self.count()?;
        let values = self.args.get(self.pos..self.pos + len).ok_or_else(malformed_err)?;
        self.pos += len;
        Ok(values)
    }

    /// Fail if anything was left unread, which is a count that does not match.
    fn end(&self) -> Result<()> {
        match self.pos == self.args.len() {
            true => Ok(()),
            false => Err(malformed_err()),
        }
    }

}

/// The strings of a command argument.
fn strings(input: Value) -> Result<Vec<String>> {
    Vec::<String>::try_from(input)
}

/// Whether a name matches a filter of the database, in which `*` stands for anything,
/// regardless of case.
fn wildcard(filter: &str, name: &str) -> bool {

    let (filter, name) = (filter.to_lowercase(), name.to_lowercase());
    let mut parts = filter.split('*');

    // Without any star the filter is the name itself.
    let first = parts.next().unwrap_or_default();
    let Some(mut rest) = name.strip_prefix(first) else { return false };

    let parts = parts.collect::<Vec<_>>();
    let Some((last, middle)) = parts.split_last() else { return rest.is_empty() };

    for part in middle {
        match rest.find(part) {
            Some(index) => rest = &rest[index + part.len()..],
            None => return false,
        }
    }

    rest.ends_with(last)

}

fn malformed_err() -> Error {
    Error::new(ErrorKind::InvalidData)
        .with_description("The argument is malformed")
}

fn not_defined_err(dev: &str) -> Error {
    Error::new(ErrorKind::Reason(reason::DB_DeviceNotDefined))
        .with_description(format!("The device {dev} is not defined in the database"))
}

// =========================== //
//      Device and backend     //
// =========================== //

/// The database device, as a client reaches it.
#[derive(Debug)]
pub struct TestDatabaseDev(pub Arc<TestDatabase>);

fn not_implemented<'a, T: Send + 'a>(what: &'static str) -> BoxFuture<'a, Result<T>> {
    Box::pin(ready(Err(Error::not_implemented()
        .with_append_description(format_args!("{what} of the database of a test")))))
}

impl BackendDev for TestDatabaseDev {

    fn name(&self) -> BoxFuture<'_, Result<Arc<str>>> {
        Box::pin(ready(Ok(Arc::from(NAME))))
    }

    fn admin_dev_name(&self) -> BoxFuture<'_, Result<Arc<str>>> {
        not_implemented("The admin device")
    }

    fn description(&self) -> BoxFuture<'_, Result<Arc<str>>> {
        Box::pin(ready(Ok(Arc::from("The Tango database of a test"))))
    }

    fn info(&self) -> BoxFuture<'_, Result<DevInfo>> {
        not_implemented("The info")
    }

    fn ping(&self) -> BoxFuture<'_, Result<()>> {
        Box::pin(ready(Ok(())))
    }

    fn state(&self) -> BoxFuture<'_, Result<DevState>> {
        Box::pin(ready(Ok(DevState::On)))
    }

    fn status(&self) -> BoxFuture<'_, Result<String>> {
        Box::pin(ready(Ok("The database of a test".to_string())))
    }

    fn black_box(&self, _max: Option<usize>) -> BoxFuture<'_, Result<Vec<String>>> {
        not_implemented("The black box")
    }

    fn command(&self, name: Scalar<str>, input: Value, _source: DevSource) -> BoxFuture<'_, Result<Value>> {
        Box::pin(ready(self.0.command(name.value(), input)))
    }

    fn read_attr(&self, _names: Option<Spectrum<str>>, _source: DevSource) -> BoxFuture<'_, Result<Vec<NamedResult<AttrRead<Value>>>>> {
        not_implemented("Reading the attributes")
    }

    fn write_attr(&self, _values: Vec<Named<Value>>) -> BoxFuture<'_, Result<Vec<Result<()>>>> {
        not_implemented("Writing the attributes")
    }

    fn write_read_attr(&self, _values: Vec<Named<Value>>) -> BoxFuture<'_, Result<Vec<NamedResult<AttrRead<Value>>>>> {
        not_implemented("Writing the attributes")
    }

    fn command_info(&self, _names: Option<Spectrum<str>>) -> BoxFuture<'_, Result<Vec<NamedResult<CommandInfo>>>> {
        not_implemented("The commands")
    }

    fn attr_info(&self, _names: Option<Spectrum<str>>) -> BoxFuture<'_, Result<Vec<NamedResult<AttrInfo>>>> {
        not_implemented("The attributes")
    }

    fn set_attr_config(&self, _configs: Vec<Named<AttrConfig>>) -> BoxFuture<'_, Result<Vec<Result<()>>>> {
        Box::pin(ready(Err(Error::not_implemented()
            .with_append_description("Writing the configuration of an attribute"))))
    }

    fn command_history<'a>(&'a self, _name: &'a str, _max: usize) -> BoxFuture<'a, Result<Vec<(SystemTime, Result<Value>)>>> {
        Box::pin(ready(Err(Error::not_implemented()
            .with_append_description("The recorded history of a command"))))
    }

    fn attr_history<'a>(&'a self, _name: &'a str, _max: usize) -> BoxFuture<'a, Result<Vec<Result<AttrRead<Value>>>>> {
        Box::pin(ready(Err(Error::not_implemented()
            .with_append_description("The recorded history of an attribute"))))
    }

    fn subscribe_attr_value<'a>(&'a self, _admin: Arc<dyn BackendDev>, _name: &'a str, _event: AttrValueEvent) -> BoxFuture<'a, Result<BoxStream<'static, Result<AttrRead<Value>>>>> {
        Box::pin(ready(Err(Error::not_implemented()
            .with_append_description("Subscribing to the readings of an attribute"))))
    }

    fn subscribe_attr_ready<'a>(&'a self, _admin: Arc<dyn BackendDev>, _name: &'a str) -> BoxFuture<'a, Result<BoxStream<'static, Result<()>>>> {
        Box::pin(ready(Err(Error::not_implemented()
            .with_append_description("Subscribing to an attribute being ready"))))
    }

    fn subscribe_attr_conf<'a>(&'a self, _admin: Arc<dyn BackendDev>, _name: &'a str) -> BoxFuture<'a, Result<BoxStream<'static, Result<AttrInfo>>>> {
        Box::pin(ready(Err(Error::not_implemented()
            .with_append_description("Subscribing to the configuration of an attribute"))))
    }

}

#[cfg(test)]
mod tests {

    use super::*;

    use crate::database::ExportDevInfo;
    use crate::testing::TestContext;

    fn context() -> TestContext {
        TestContext::new().unwrap()
    }

    #[test]
    fn wildcards() {
        assert!(wildcard("*", "anything"));
        assert!(wildcard("Pos*", "position"));
        assert!(wildcard("*tion", "Position"));
        assert!(wildcard("p*s*n", "position"));
        assert!(wildcard("position", "POSITION"));
        assert!(!wildcard("pos", "position"));
        assert!(!wildcard("p*x*n", "position"));
    }

    #[test]
    fn servers_and_devices() {

        let ctx = context();
        let db = ctx.database();
        db.add_server("Motor/test", &[("test/motor/1", "Motor"), ("test/motor/2", "Motor")]).unwrap();
        db.add_dev("test/axis/1", "Axis", "Motor/test").unwrap();

        let listed = db.list_server_dev("motor/TEST").unwrap();
        let listed = listed.iter().map(|dev| (dev.name.value(), dev.value.value())).collect::<Vec<_>>();
        assert_eq!(listed, [
            ("dserver/Motor/test", "DServer"),
            ("test/motor/1", "Motor"),
            ("test/motor/2", "Motor"),
            ("test/axis/1", "Axis"),
        ]);

        db.delete_dev("TEST/MOTOR/2").unwrap();
        assert_eq!(db.list_server_dev("Motor/test").unwrap().len(), 3);

        db.delete_server("Motor/test").unwrap();
        assert!(db.list_server_dev("Motor/test").unwrap().is_empty());
        assert_eq!(db.import_dev("test/motor/1").unwrap_err().kind(), ErrorKind::DevNotFound);

    }

    #[test]
    fn export_and_import() {

        let ctx = context();
        let db = ctx.database();
        db.add_dev("test/motor/1", "Motor", "Motor/test").unwrap();

        let info = db.import_dev("test/motor/1").unwrap();
        assert!(!info.exported);
        assert_eq!(info.class.as_ref().map(|class| class.value()), Some("Motor"));

        db.export_server(&[ExportDevInfo {
            name: "test/motor/1".into(),
            itr: "IOR:0123".into(),
            host: "localhost".into(),
            version: "6".into(),
            pid: 42,
        }]).unwrap();

        let info = db.import_dev("test/motor/1").unwrap();
        assert!(info.exported);
        assert_eq!((info.itr.value(), info.host.value(), info.version.value(), info.server.value(), info.pid),
            ("IOR:0123", "localhost", "6", "Motor/test", 42));

        // Unexported, the reference stays, only the flag goes down.
        db.unexport_server("motor/test").unwrap();
        let info = db.import_dev("test/motor/1").unwrap();
        assert!(!info.exported);
        assert_eq!(info.itr.value(), "IOR:0123");

    }

    #[test]
    fn properties() {

        let ctx = context();
        let db = ctx.database();

        db.set_dev_prop("test/motor/1", [("Limit", "90"), ("Unit", "deg")]).unwrap();
        db.set_dev_prop("TEST/motor/1", ("limit", "45")).unwrap();
        assert_eq!(db.get_dev_prop::<f64, _>("test/motor/1", "Limit").unwrap(), 45.0);
        assert_eq!(db.list_dev_prop("test/motor/1", "*").unwrap().len(), 2);

        db.del_dev_prop("test/motor/1", "unit").unwrap();
        assert_eq!(db.list_dev_prop("test/motor/1", "*").unwrap().len(), 1);

        // Classes and devices do not share their properties.
        db.set_class_prop("Motor", ("Limit", "10")).unwrap();
        assert_eq!(db.get_class_prop::<f64, _>("Motor", "Limit").unwrap(), 10.0);
        assert_eq!(db.get_dev_prop::<f64, _>("test/motor/1", "Limit").unwrap(), 45.0);

        db.set_dev_attr_prop("test/motor/1", ("Position", [("unit", "mm"), ("min_value", "-5")])).unwrap();
        assert_eq!(db.get_dev_attr_prop::<String, _, _>("test/motor/1", "position", "Unit").unwrap(), "mm");

        db.del_dev_attr_prop("test/motor/1", "Position", ["unit", "min_value"]).unwrap();
        // A property that has no value anymore reads as one holding nothing.
        assert_eq!(db.get_dev_attr_prop::<String, _, _>("test/motor/1", "Position", "unit").unwrap(), "");

    }

    /// Every clone of the proxy reaches the same database, and two databases are two.
    #[test]
    fn clones_share() {
        let ctx = context();
        let db = ctx.database();
        let clone = db.clone();
        clone.add_dev("test/motor/1", "Motor", "Motor/test").unwrap();
        assert_eq!(db.list_server_dev("Motor/test").unwrap().len(), 2);
        let other = context();
        assert!(other.database().list_server_dev("Motor/test").unwrap().is_empty());
        assert_ne!(db, other.database());
    }

}