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use std::collections::HashMap;
use std::net::{IpAddr, Ipv6Addr, SocketAddr};

use futures::{Future, future};

use Error;
use service::locator::Locator;

/// Cloud name resolution for services.
///
/// Used before service connection establishing to determine where to connect, i.e where a service
/// with the given name is located.
/// For common usage the most reasonable choice is a [`Resolver`][resolver] implementation that
/// uses [`Locator`][locator] for name resolution.
///
/// [locator]: service/locator/struct.Locator.html
/// [resolver]: struct.Resolver.html
pub trait Resolve {
    /// Future type that is returned during resolving.
    type Future: Future<Item = ResolveInfo<SocketAddr>, Error = Error>;

    /// Resolves a service name into the network endpoints.
    fn resolve(&self, name: &str) -> Self::Future;
}

/// Describes a protocol graph node.
#[derive(Clone, Debug, Deserialize)]
pub struct GraphNode {
    /// Event name.
    pub event: String,
    /// Optional downstream protocol description.
    pub rx: Option<HashMap<u64, GraphNode>>,
}

/// Describes a protocol graph for an event.
#[derive(Clone, Debug, Deserialize)]
pub struct EventGraph {
    /// Event name.
    pub name: String,
    /// Optional upstream protocol description.
    pub tx: HashMap<u64, GraphNode>,
    /// Optional downstream protocol description.
    pub rx: HashMap<u64, GraphNode>,
}

/// Response that is returned from either a resolver or [`Locator::resolve`][resolve] method.
///
/// [resolve]: service/locator/struct.Locator.html#method.resolve
#[derive(Clone, Debug, Deserialize)]
pub struct ResolveInfo<T> {
    pub(crate) addrs: Vec<T>,
    pub(crate) version: u64,
    pub(crate) methods: HashMap<u64, EventGraph>,
}

impl ResolveInfo<SocketAddr> {
    /// Returns a view of socket addresses for this resolve info.
    pub fn addrs(&self) -> &[SocketAddr] {
        &self.addrs
    }
}

/// A no-op resolver, that always returns preliminarily specified endpoints.
///
/// Used primarily while resolving a `Locator` itself, but can be also used, when you're sure about
/// service's location.
///
/// The default value returns the default `Locator` endpoints, i.e `["::", 10053]` assuming that
/// IPv6 is enabled.
#[derive(Clone, Debug)]
pub struct FixedResolver {
    addrs: Vec<SocketAddr>,
}

impl FixedResolver {
    /// Constructs a fixed resolver, which will always resolve any service name into the specified
    /// endpoints.
    pub fn new(addrs: Vec<SocketAddr>) -> Self {
        Self { addrs }
    }

    /// Returns endpoints given at construction time.
    pub fn addrs(&self) -> &[SocketAddr] {
        &self.addrs
    }
}

/// An implementation of trait for giving a `FixedResolver` a useful default value.
///
/// The default endpoint for a fixed resolver is: `[::1]:10053`.
impl Default for FixedResolver {
    fn default() -> Self {
        Self {
            addrs: vec![
                SocketAddr::new(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1)), 10053),
            ],
        }
    }
}

impl Resolve for FixedResolver {
    type Future = future::FutureResult<ResolveInfo<SocketAddr>, Error>;

    fn resolve(&self, _name: &str) -> Self::Future {
        let result = ResolveInfo {
            addrs: self.addrs.clone(),
            version: 1,
            methods: HashMap::new(),
        };

        future::ok(result)
    }
}

/// A `Resolver` that uses the `Locator` for name resolution.
///
/// It is cloneable, thread-safe and implements both `Send` and `Sync` traits, allowing to share
/// across multiple threads.
///
/// # Examples
///
/// ```no_run
/// use cocaine::{Core, Resolve, Resolver, Service};
/// use cocaine::service::Locator;
///
/// let mut core = Core::new().unwrap();
///
/// let resolver = Resolver::new(Locator::new(Service::new("locator", &core.handle())));
///
/// core.run(resolver.resolve("storage")).unwrap();
/// ```
#[derive(Clone, Debug)]
pub struct Resolver {
    locator: Locator,
}

impl Resolver {
    /// Constructs a new `Resolver` using the specified `Locator` for name resolution.
    pub fn new(locator: Locator) -> Self {
        Self { locator }
    }
}

impl Resolve for Resolver {
    type Future = Box<Future<Item = ResolveInfo<SocketAddr>, Error = Error>>;

    fn resolve(&self, name: &str) -> Self::Future {
        Box::new(self.locator.resolve(name))
    }
}

fn _assert_kinds() {
    fn _assert_send<T: Send>() {}
    fn _assert_sync<T: Sync>() {}
    fn _assert_clone<T: Clone>() {}

    _assert_send::<Resolver>();
    _assert_sync::<Resolver>();
    _assert_clone::<Resolver>();
}

#[cfg(test)]
mod test {
    use std::net::{IpAddr, Ipv4Addr, Ipv6Addr, SocketAddr};

    use super::FixedResolver;

    #[test]
    fn fixed_resolver_saves_addrs() {
        let addrs = vec![
            SocketAddr::new(IpAddr::V4(Ipv4Addr::new(127, 0, 0, 1)), 10053),
        ];
        let resolver = FixedResolver::new(addrs.clone());

        assert_eq!(addrs, resolver.addrs());
    }

    #[test]
    fn fixed_resolver_default_addrs() {
        let resolver = FixedResolver::default();

        assert_eq!(
            vec![
                SocketAddr::new(IpAddr::V6(Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1)), 10053),
            ],
            resolver.addrs()
        );
    }
}