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use hyper_util::client::legacy::connect::dns::Name as HyperName;
use tower_service::Service;

use std::collections::HashMap;
use std::future::Future;
use std::net::SocketAddr;
use std::pin::Pin;
use std::str::FromStr;
use std::sync::Arc;
use std::task::{Context, Poll};

use crate::error::BoxError;

/// Alias for an `Iterator` trait object over `SocketAddr`.
pub type Addrs = Box<dyn Iterator<Item = SocketAddr> + Send>;

/// Alias for the `Future` type returned by a DNS resolver.
pub type Resolving = Pin<Box<dyn Future<Output = Result<Addrs, BoxError>> + Send>>;

/// Trait for customizing DNS resolution in reqwest.
pub trait Resolve: Send + Sync {
    /// Performs DNS resolution on a `Name`.
    /// The return type is a future containing an iterator of `SocketAddr`.
    ///
    /// It differs from `tower_service::Service<Name>` in several ways:
    ///  * It is assumed that `resolve` will always be ready to poll.
    ///  * It does not need a mutable reference to `self`.
    ///  * Since trait objects cannot make use of associated types, it requires
    ///    wrapping the returned `Future` and its contained `Iterator` with `Box`.
    fn resolve(&self, name: Name) -> Resolving;
}

/// A name that must be resolved to addresses.
#[derive(Debug)]
pub struct Name(pub(super) HyperName);

impl Name {
    /// View the name as a string.
    pub fn as_str(&self) -> &str {
        self.0.as_str()
    }
}

impl FromStr for Name {
    type Err = sealed::InvalidNameError;

    fn from_str(host: &str) -> Result<Self, Self::Err> {
        HyperName::from_str(host.into())
            .map(Name)
            .map_err(|_| sealed::InvalidNameError { _ext: () })
    }
}

#[derive(Clone)]
pub(crate) struct DynResolver {
    resolver: Arc<dyn Resolve>,
}

impl DynResolver {
    pub(crate) fn new(resolver: Arc<dyn Resolve>) -> Self {
        Self { resolver }
    }
}

impl Service<HyperName> for DynResolver {
    type Response = Addrs;
    type Error = BoxError;
    type Future = Resolving;

    fn poll_ready(&mut self, _: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        Poll::Ready(Ok(()))
    }

    fn call(&mut self, name: HyperName) -> Self::Future {
        self.resolver.resolve(Name(name))
    }
}

pub(crate) struct DnsResolverWithOverrides {
    dns_resolver: Arc<dyn Resolve>,
    overrides: Arc<HashMap<String, Vec<SocketAddr>>>,
}

impl DnsResolverWithOverrides {
    pub(crate) fn new(
        dns_resolver: Arc<dyn Resolve>,
        overrides: HashMap<String, Vec<SocketAddr>>,
    ) -> Self {
        DnsResolverWithOverrides {
            dns_resolver,
            overrides: Arc::new(overrides),
        }
    }
}

impl Resolve for DnsResolverWithOverrides {
    fn resolve(&self, name: Name) -> Resolving {
        match self.overrides.get(name.as_str()) {
            Some(dest) => {
                let addrs: Addrs = Box::new(dest.clone().into_iter());
                Box::pin(futures_util::future::ready(Ok(addrs)))
            }
            None => self.dns_resolver.resolve(name),
        }
    }
}

mod sealed {
    use std::fmt;

    #[derive(Debug)]
    pub struct InvalidNameError {
        pub(super) _ext: (),
    }

    impl fmt::Display for InvalidNameError {
        fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
            f.write_str("invalid DNS name")
        }
    }

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