/*
 * Copyright 2024, gRPC Authors All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import GRPCCore

extension ResolvableTargets {
  /// A resolvable target for IPv4 addresses.
  ///
  /// IPv4 addresses can be resolved by the ``NameResolvers/IPv4`` resolver which creates a
  /// separate ``Endpoint`` for each address.
  public struct IPv4: ResolvableTarget {
    /// The IPv4 addresses.
    public var addresses: [SocketAddress.IPv4]

    /// Create a new IPv4 target.
    /// - Parameter addresses: The IPv4 addresses.
    public init(addresses: [SocketAddress.IPv4]) {
      self.addresses = addresses
    }
  }
}

extension ResolvableTarget where Self == ResolvableTargets.IPv4 {
  /// Creates a new resolvable IPv4 target for a single address.
  /// - Parameters:
  ///   - host: The host address.
  ///   - port: The port on the host.
  /// - Returns: A ``ResolvableTarget``.
  public static func ipv4(host: String, port: Int = 443) -> Self {
    let address = SocketAddress.IPv4(host: host, port: port)
    return Self(addresses: [address])
  }

  /// Creates a new resolvable IPv4 target from the provided host-port pairs.
  ///
  /// - Parameter pairs: An array of host-port pairs.
  /// - Returns: A ``ResolvableTarget``.
  public static func ipv4(pairs: [(host: String, port: Int)]) -> Self {
    let address = pairs.map { SocketAddress.IPv4(host: $0.host, port: $0.port) }
    return Self(addresses: address)
  }
}

@available(macOS 13.0, iOS 16.0, watchOS 9.0, tvOS 16.0, *)
extension NameResolvers {
  /// A ``NameResolverFactory`` for ``ResolvableTargets/IPv4`` targets.
  ///
  /// The name resolver for a given target always produces the same values, with one endpoint per
  /// address in the target. This resolver doesn't support fetching service configuration.
  public struct IPv4: NameResolverFactory {
    public typealias Target = ResolvableTargets.IPv4

    /// Create a new IPv4 resolver factory.
    public init() {}

    public func resolver(for target: Target) -> NameResolver {
      let endpoints = target.addresses.map { Endpoint(addresses: [.ipv4($0)]) }
      let resolutionResult = NameResolutionResult(endpoints: endpoints, serviceConfiguration: nil)
      return NameResolver(names: .constant(resolutionResult), updateMode: .pull)
    }
  }
}