use hyper::client::HttpConnector;
use hyper::Client;
 
// HttpConnector is the default connector for hyper clients
// It handles:
// 1. DNS resolution (hostname to IP address)
// 2. TCP connection establishment
// 3. TLS handshake (with optional TLS configuration)
 
fn basic_http_connector() {
    // Create a client with the default HttpConnector
    let client = Client::new();
    
    // This uses HttpConnector with:
    // - System DNS resolver (blocking, in thread pool)
    // - Default TCP configuration
    // - No TLS (HTTP only)
    
    // For HTTPS, use HttpsConnector which wraps HttpConnector
}

use hyper::client::HttpConnector;
use hyper::Client;
 
fn default_dns_behavior() {
    // HttpConnector uses the system's DNS resolver
    // - getaddrinfo on Unix systems
    // - Windows DNS API on Windows
    
    let connector = HttpConnector::new();
    
    // DNS resolution is synchronous/blocking
    // hyper runs it in a thread pool to avoid blocking the async runtime
    
    // The default behavior:
    // 1. Parse the URL to extract hostname and port
    // 2. Call system resolver to get IP addresses
    // 3. Try connecting to resolved addresses
    // 4. Return first successful connection
}

use hyper::service::Service;
use hyper::Uri;
use tower::Service as TowerService;
use std::task::{Context, Poll};
use std::future::Future;
 
// A custom connector implements Service<Uri>
// It returns a connected stream (impl AsyncRead + AsyncWrite)
 
pub trait Connector: Service<Uri> {
    // The connector trait is essentially Service<Uri>
    // with Output = impl AsyncRead + AsyncWrite + Send + 'static
}
 
// Custom connector structure
pub struct CustomConnector {
    // Custom state: DNS cache, resolver config, etc.
    dns_cache: DnsCache,
}
 
impl Service<Uri> for CustomConnector {
    type Response = impl tokio::io::AsyncRead + tokio::io::AsyncWrite + Send;
    type Error = std::io::Error;
    type Future = impl Future<Output = Result<Self::Response, Self::Error>>;
    
    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        // Check if connector is ready to handle new requests
        Poll::Ready(Ok(()))
    }
    
    fn call(&mut self, uri: Uri) -> Self::Future {
        // Custom DNS resolution logic
        async move {
            // 1. Extract hostname from URI
            // 2. Resolve using custom logic
            // 3. Establish connection
            todo!()
        }
    }
}

use hyper::client::HttpConnector;
use std::net::IpAddr;
 
fn dns_resolution_comparison() {
    // ┌─────────────────────────────────────────────────────────────────────────┐
    // │ Aspect               │ HttpConnector              │ Custom Connector   │
    // ├─────────────────────────────────────────────────────────────────────────┤
    // │ Resolution method    │ System resolver (blocking) │ Any method         │
    // │ Async support        │ Thread pool emulation      │ True async         │
    // │ Caching              │ None (OS-level only)       │ Custom caching     │
    // │ DNS server           │ System configured          │ Any server         │
    // │ Timeout control      │ Limited                    │ Full control       │
    // │ Service discovery    │ None                       │ Fully custom       │
    // │ DNS-over-HTTPS       │ No                         │ Implementable      │
    // │ Load balancing       │ Client-side (first IP)     │ Custom strategies  │
    // └─────────────────────────────────────────────────────────────────────────┘
}

use hyper::client::HttpConnector;
use std::time::Duration;
 
fn http_connector_config() {
    // HttpConnector has limited configuration options
    
    let mut connector = HttpConnector::new();
    
    // Set connection timeout
    connector.set_connect_timeout(Some(Duration::from_secs(30)));
    
    // Enable connection reuse (keep-alive)
    connector.set_keepalive(true);
    
    // Set keep-alive timeout
    connector.set_keepalive_timeout(Some(Duration::from_secs(60)));
    
    // Configure nodelay (disable Nagle's algorithm)
    connector.set_nodelay(true);
    
    // Set local address for binding
    // connector.set_local_address(Some(local_addr));
    
    // But you CANNOT:
    // - Change DNS resolution method
    // - Add DNS caching
    // - Use custom DNS servers
    // - Implement service discovery
    // - Add DNS-over-HTTPS/TLS
}

use hyper::Uri;
use hyper::client::connect::dns::GaiResolver;
use tower::Service;
use std::task::{Context, Poll};
use std::net::SocketAddr;
use std::future::Future;
 
// A custom connector with async DNS resolution
 
pub struct AsyncDnsConnector<R = GaiResolver> {
    // The DNS resolver
    resolver: R,
    // Connection timeout
    connect_timeout: Option<std::time::Duration>,
}
 
impl<R> Service<Uri> for AsyncDnsConnector<R>
where
    R: DnsResolver + Clone + Send + Sync + 'static,
{
    type Response = tokio::net::TcpStream;
    type Error = std::io::Error;
    type Future = impl Future<Output = Result<Self::Response, Self::Error>>;
    
    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
        Poll::Ready(Ok(()))
    }
    
    fn call(&mut self, uri: Uri) -> Self::Future {
        let resolver = self.resolver.clone();
        let timeout = self.connect_timeout;
        
        async move {
            // Extract host and port
            let host = uri.host().ok_or_else(|| {
                std::io::Error::new(std::io::ErrorKind::InvalidInput, "missing host")
            })?;
            let port = uri.port_u16().unwrap_or(80);
            
            // Resolve DNS asynchronously
            let addrs = resolver.resolve(host).await?;
            
            // Try each address until connection succeeds
            for addr in addrs {
                let socket_addr = SocketAddr::new(addr, port);
                
                match connect_with_timeout(socket_addr, timeout).await {
                    Ok(stream) => return Ok(stream),
                    Err(_) => continue,
                }
            }
            
            Err(std::io::Error::new(
                std::io::ErrorKind::AddrNotAvailable,
                "all addresses failed"
            ))
        }
    }
}
 
async fn connect_with_timeout(
    addr: SocketAddr,
    timeout: Option<std::time::Duration>,
) -> Result<tokio::net::TcpStream, std::io::Error> {
    match timeout {
        Some(d) => tokio::time::timeout(d, tokio::net::TcpStream::connect(&addr))
            .await
            .map_err(|_| std::io::Error::new(std::io::ErrorKind::TimedOut, "connection timeout"))?,
        None => tokio::net::TcpStream::connect(&addr).await,
    }
}
 
pub trait DnsResolver {
    fn resolve(&self, host: &str) -> impl Future<Output = Result<Vec<IpAddr>, std::io::Error>> + Send;
}

use std::collections::HashMap;
use std::net::IpAddr;
use std::time::Instant;
use std::sync::Arc;
use tokio::sync::RwLock;
 
// DNS cache entry
struct CachedDns {
    addrs: Vec<IpAddr>,
    expires_at: Instant,
}
 
// Cached DNS resolver
pub struct CachedDnsResolver {
    cache: Arc<RwLock<HashMap<String, CachedDns>>>,
    // Underlying resolver (e.g., system resolver or DNS-over-HTTPS)
    underlying: GaiResolver,
    ttl: std::time::Duration,
}
 
impl CachedDnsResolver {
    pub fn new(ttl: std::time::Duration) -> Self {
        Self {
            cache: Arc::new(RwLock::new(HashMap::new())),
            underlying: GaiResolver::new(),
            ttl,
        }
    }
}
 
impl DnsResolver for CachedDnsResolver {
    async fn resolve(&self, host: &str) -> Result<Vec<IpAddr>, std::io::Error> {
        // Check cache first
        {
            let cache = self.cache.read().await;
            if let Some(cached) = cache.get(host) {
                if Instant::now() < cached.expires_at {
                    return Ok(cached.addrs.clone());
                }
            }
        }
        
        // Resolve using underlying resolver
        let addrs = self.underlying.resolve(host).await?;
        
        // Cache the result
        {
            let mut cache = self.cache.write().await;
            cache.insert(
                host.to_string(),
                CachedDns {
                    addrs: addrs.clone(),
                    expires_at: Instant::now() + self.ttl,
                },
            );
        }
        
        Ok(addrs)
    }
}

use std::net::SocketAddr;
use trust_dns_resolver::TokioAsyncResolver;
use trust_dns_resolver::config::*;
 
// Custom connector using specific DNS servers
 
pub struct CustomDnsConnector {
    resolver: TokioAsyncResolver,
}
 
impl CustomDnsConnector {
    pub fn new(dns_servers: Vec<SocketAddr>) -> Self {
        let mut resolver_config = ResolverConfig::new();
        
        for server in dns_servers {
            resolver_config.add_name_server(NameServerConfig {
                socket_addr: server,
                protocol: Protocol::Udp,
                tls_config: None,
            });
        }
        
        let resolver_opts = ResolverOpts::default();
        
        let resolver = TokioAsyncResolver::tokio(resolver_config, resolver_opts);
        
        Self { resolver }
    }
    
    pub async fn resolve(&self, host: &str) -> Result<Vec<IpAddr>, std::io::Error> {
        self.resolver
            .lookup_ip(host)
            .await
            .map(|lookup| lookup.iter().collect())
            .map_err(|e| std::io::Error::new(std::io::ErrorKind::Other, e))
    }
}
 
// Usage: Use Google DNS servers
fn use_custom_dns_servers() {
    let connector = CustomDnsConnector::new(vec![
        "8.8.8.8:53".parse().unwrap(),
        "8.8.4.4:53".parse().unwrap(),
    ]);
}

// Custom connector with DNS-over-HTTPS for privacy
 
pub struct DohConnector {
    doh_endpoint: String,
    http_client: reqwest::Client,
}
 
impl DohConnector {
    pub fn new(doh_endpoint: &str) -> Self {
        Self {
            doh_endpoint: doh_endpoint.to_string(),
            http_client: reqwest::Client::new(),
        }
    }
    
    pub async fn resolve(&self, host: &str) -> Result<Vec<IpAddr>, std::io::Error> {
        // Use DNS-over-HTTPS (RFC 8484)
        let url = format!("{}?name={}&type=A", self.doh_endpoint, host);
        
        let response = self.http_client
            .get(&url)
            .header("Accept", "application/dns-message")
            .send()
            .await
            .map_err(|e| std::io::Error::new(std::io::ErrorKind::Other, e))?;
        
        // Parse DNS response (simplified)
        // Real implementation would parse DNS wire format
        
        todo!("Parse DNS-over-HTTPS response")
    }
}
 
// Usage: Use Cloudflare DNS-over-HTTPS
fn use_doh() {
    let connector = DohConnector::new("https://cloudflare-dns.com/dns-query");
}

use std::collections::HashMap;
 
// Custom connector with service discovery (e.g., Consul, Kubernetes)
 
pub struct ServiceDiscoveryConnector {
    discovery_client: ServiceDiscoveryClient,
    dns_fallback: GaiResolver,
}
 
pub struct ServiceDiscoveryClient {
    // Client for Consul, Kubernetes API, etc.
    services: HashMap<String, Vec<SocketAddr>>,
}
 
impl ServiceDiscoveryConnector {
    pub async fn resolve(&self, host: &str) -> Result<Vec<SocketAddr>, std::io::Error> {
        // Check service discovery first
        if let Some(addrs) = self.discovery_client.resolve_service(host).await? {
            return Ok(addrs);
        }
        
        // Fall back to DNS for external hosts
        let ip_addrs = self.dns_fallback.resolve(host).await?;
        let port = 80; // Would need to determine from context
        Ok(ip_addrs.into_iter().map(|ip| SocketAddr::new(ip, port)).collect())
    }
}
 
// Usage: Connect to services by name without DNS
fn service_discovery_example() {
    // "my-service.internal" resolves directly from service registry
    // No DNS lookup needed
}

use hyper::client::HttpConnector;
 
fn performance_comparison() {
    // ┌─────────────────────────────────────────────────────────────────────────┐
    // │ Aspect               │ HttpConnector          │ Custom Connector        │
    // ├─────────────────────────────────────────────────────────────────────────┤
    // │ First request       │ DNS lookup + connect   │ Depends on impl         │
    // │ Cached DNS          │ OS cache only          │ Custom cache control    │
    // │ Thread usage        │ Thread pool for DNS    │ Async, no threads       │
    // │ Memory overhead     │ Minimal                │ Depends on cache        │
    // │ Latency             │ Variable (DNS)         │ Can optimize             │
    // │ Throughput          │ Good                   │ Can be better            │
    // └─────────────────────────────────────────────────────────────────────────┘
    
    // HttpConnector thread pool:
    // - Uses blocking getaddrinfo
    // - Runs in separate thread pool
    // - Default pool size varies by system
    // - Each DNS call blocks a thread
    
    // Custom async connector:
    // - Uses async DNS (e.g., trust-dns)
    // - No thread pool needed
    // - Better for high concurrency
    // - Can implement caching
}

use hyper::client::HttpConnector;
use std::io;
 
fn error_handling() {
    // HttpConnector error handling:
    // - Returns io::Error with basic context
    // - Limited visibility into DNS failures
    // - Cannot distinguish DNS timeout vs connection timeout
    
    // Custom connector error handling:
    // - Can return rich error types
    // - Distinguish DNS errors from connection errors
    // - Include resolution details in errors
    
    pub enum ConnectorError {
        DnsResolutionFailed {
            host: String,
            source: Box<dyn std::error::Error + Send + Sync>,
        },
        DnsTimeout {
            host: String,
            duration: std::time::Duration,
        },
        ConnectionFailed {
            addresses: Vec<SocketAddr>,
            errors: Vec<io::Error>,
        },
        ConnectionTimeout {
            address: SocketAddr,
            duration: std::time::Duration,
        },
    }
}

use std::net::SocketAddr;
use std::collections::HashMap;
use std::sync::atomic::{AtomicUsize, Ordering};
 
// Custom connector with load balancing across resolved addresses
 
pub struct LoadBalancedConnector {
    dns_resolver: CachedDnsResolver,
    // Round-robin counter per host
    counters: HashMap<String, AtomicUsize>,
}
 
impl LoadBalancedConnector {
    async fn resolve_and_balance(&self, host: &str, port: u16) -> Result<tokio::net::TcpStream, io::Error> {
        let addrs = self.dns_resolver.resolve(host).await?;
        
        if addrs.is_empty() {
            return Err(io::Error::new(io::ErrorKind::AddrNotAvailable, "no addresses"));
        }
        
        // Round-robin through addresses
        let counter = self.counters.entry(host.to_string()).or_insert(AtomicUsize::new(0));
        let index = counter.fetch_add(1, Ordering::Relaxed) % addrs.len();
        
        let addr = SocketAddr::new(addrs[index], port);
        tokio::net::TcpStream::connect(addr).await
    }
}
 
// HttpConnector connects to first successful address
// LoadBalancedConnector distributes across addresses

use hyper::client::HttpConnector;
 
fn complete_summary() {
    // ┌─────────────────────────────────────────────────────────────────────────┐
    // │ Feature                  │ HttpConnector        │ Custom Connector    │
    // ├─────────────────────────────────────────────────────────────────────────┤
    // │ DNS resolution           │ System (blocking)    │ Fully customizable  │
    // │ Async                    │ Thread pool          │ Native async       │
    // │ Caching                  │ OS-level             │ Custom TTL/cache    │
    // │ DNS servers              │ System config        │ Any server          │
    // │ DNS-over-HTTPS/TLS       │ No                   │ Implementable       │
    // │ Service discovery        │ No                   │ Fully supported     │
    // │ Load balancing           │ First address        │ Custom strategies   │
    // │ Error detail             │ Basic                │ Rich/custom         │
    // │ Configuration            │ Limited              │ Full control        │
    // │ Complexity               │ Simple               │ More code           │
    // └─────────────────────────────────────────────────────────────────────────┘
    
    // Use HttpConnector when:
    // - System DNS is acceptable
    // - Simple use case
    // - No custom DNS requirements
    // - Default behavior is fine
    
    // Use custom connector when:
    // - Need async DNS resolution
    // - Require DNS caching
    // - Must use specific DNS servers
    // - Need DNS-over-HTTPS/TLS
    // - Integrating service discovery
    // - Implementing load balancing
    // - Want detailed error information
}
 
// Key insight:
// hyper::client::HttpConnector uses synchronous system DNS resolution
// (getaddrinfo on Unix, Windows DNS API) executed in a thread pool.
// This is simple but limited:
//
// - No DNS caching beyond OS-level
// - No control over DNS servers
// - No DNS-over-HTTPS/TLS support
// - Blocks threads during resolution
// - Limited error information
//
// Custom connectors implement Service<Uri> and can:
//
// 1. Use async DNS resolvers (trust-dns, custom implementations)
//    - No thread pool needed
//    - Better for high concurrency
//
// 2. Cache DNS results
//    - Reduce DNS lookups
//    - Lower latency
//    - Custom TTL per domain
//
// 3. Use specific DNS servers
//    - Google DNS, Cloudflare, internal servers
//    - Avoid ISP DNS issues
//
// 4. Implement DNS-over-HTTPS/TLS
//    - Privacy from network observers
//    - Bypass DNS filtering
//
// 5. Integrate service discovery
//    - Consul, Kubernetes, Zookeeper
//    - Direct service-to-service communication
//
// 6. Provide rich errors
//    - Distinguish DNS vs connection errors
//    - Include resolution details
//    - Better debugging
//
// 7. Load balance across addresses
//    - Round-robin, weighted, health-based
//    - Client-side load distribution
//
// The trade-off is complexity: HttpConnector works for most cases,
// while custom connectors require more code but enable advanced features.