/*
 * Copyright 2016, 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.
 */
#if SWIFT_PACKAGE
  import CgRPC
#endif
import Foundation // for String.Encoding

/// A gRPC request handler
public class Handler {
  /// Pointer to underlying C representation
  fileprivate let underlyingHandler: UnsafeMutableRawPointer

  /// Completion queue for handler response operations
  let completionQueue: CompletionQueue

  /// Metadata received with the request
  public let requestMetadata: Metadata

  /// A Call object that can be used to respond to the request
  private(set) lazy var call: Call = {
    Call(underlyingCall: cgrpc_handler_get_call(self.underlyingHandler),
         owned: false,
         completionQueue: self.completionQueue)
  }()

  /// The host name sent with the request
  public lazy var host: String? = {
    // We actually know that this method will never return nil,
    // so we can forcibly unwrap the result. (Also below.)
    let string = cgrpc_handler_copy_host(self.underlyingHandler)!
    defer { cgrpc_free_copied_string(string) }
    return String(cString: string, encoding: .utf8)
  }()

  /// The method name sent with the request
  public lazy var method: String? = {
    let string = cgrpc_handler_copy_method(self.underlyingHandler)!
    defer { cgrpc_free_copied_string(string) }
    return String(cString: string, encoding: .utf8)
  }()

  /// The caller address associated with the request
  public lazy var caller: String? = {
    let string = cgrpc_handler_call_peer(self.underlyingHandler)!
    defer { cgrpc_free_copied_string(string) }
    return String(cString: string, encoding: .utf8)
  }()

  /// Initializes a Handler
  ///
  /// - Parameter underlyingServer: the underlying C representation of the associated server
  init(underlyingServer: UnsafeMutableRawPointer) {
    underlyingHandler = cgrpc_handler_create_with_server(underlyingServer)
    requestMetadata = Metadata()
    completionQueue = CompletionQueue(
      underlyingCompletionQueue: cgrpc_handler_get_completion_queue(underlyingHandler), name: "Handler")
  }

  deinit {
    cgrpc_handler_destroy(self.underlyingHandler)
  }

  /// Requests a call for the handler
  ///
  /// Fills the handler properties with information about the received request
  ///
  func requestCall(tag: Int) throws {
    let error = cgrpc_handler_request_call(underlyingHandler, requestMetadata.underlyingArray, tag)
    if error != GRPC_CALL_OK {
      throw CallError.callError(grpcCallError: error)
    }
  }

  /// Receive the message sent with a call
  ///
  public func receiveMessage(initialMetadata: Metadata,
                             completion: @escaping (Data?) throws -> Void) throws {
    let operations = OperationGroup(call: call,
                                    operations: [
                                      .sendInitialMetadata(initialMetadata),
                                      .receiveMessage
    ]) { operationGroup in
      if operationGroup.success {
        try completion(operationGroup.receivedMessage()?.data())
      } else {
        try completion(nil)
      }
    }
    try call.perform(operations)
  }

  /// Sends the response to a request
  ///
  /// - Parameter message: the message to send
  /// - Parameter statusCode: status code to send
  /// - Parameter statusMessage: status message to send
  /// - Parameter trailingMetadata: trailing metadata to send
  public func sendResponse(message: Data,
                           statusCode: StatusCode,
                           statusMessage: String,
                           trailingMetadata: Metadata) throws {
    let messageBuffer = ByteBuffer(data: message)
    let operations = OperationGroup(call: call,
                                    operations: [
                                      .receiveCloseOnServer,
                                      .sendStatusFromServer(statusCode, statusMessage, trailingMetadata),
                                      .sendMessage(messageBuffer)
    ]) { operationGroup in
      self.shutdown()
    }
    try call.perform(operations)
  }

  /// Sends the response to a request
  ///
  /// - Parameter statusCode: status code to send
  /// - Parameter statusMessage: status message to send
  /// - Parameter trailingMetadata: trailing metadata to send
  public func sendResponse(statusCode: StatusCode,
                           statusMessage: String,
                           trailingMetadata: Metadata) throws {
    let operations = OperationGroup(call: call,
                                    operations: [
                                      .receiveCloseOnServer,
                                      .sendStatusFromServer(statusCode, statusMessage, trailingMetadata)
    ]) { operationGroup in
      self.shutdown()
    }
    try call.perform(operations)
  }

  /// Shuts down the handler's completion queue
  public func shutdown() {
    completionQueue.shutdown()
  }

  /// Send initial metadata in response to a connection
  ///
  /// - Parameter initialMetadata: initial metadata to send
  /// - Parameter completion: a completion handler to call after the metadata has been sent
  public func sendMetadata(initialMetadata: Metadata,
                           completion: ((Bool) throws -> Void)? = nil) throws {
    let operations = OperationGroup(call: call,
                                    operations: [.sendInitialMetadata(initialMetadata)],
                                    completion: completion != nil
                                      ? { operationGroup in try completion?(operationGroup.success) }
                                      : nil)
    try call.perform(operations)
  }
  
  /// Receive the message sent with a call
  ///
  /// - Parameter completion: a completion handler to call after the message has been received
  /// - Returns: a tuple containing status codes and a message (if available)
  public func receiveMessage(completion: @escaping (Data?) throws -> Void) throws {
    try call.receiveMessage(completion: completion)
  }
  
  /// Sends the response to a request
  ///
  /// - Parameter message: the message to send
  /// - Parameter completion: a completion handler to call after the response has been sent
  public func sendResponse(message: Data,
                           completion: ((Error?) -> Void)? = nil) throws {
    try call.sendMessage(data: message, completion: completion)
  }
  
  /// Recognize when the client has closed a request
  ///
  /// - Parameter completion: a completion handler to call after request has been closed
  public func receiveClose(completion: @escaping (Bool) throws -> Void) throws {
    let operations = OperationGroup(call: call,
                                    operations: [.receiveCloseOnServer]) { operationGroup in
                                      try completion(operationGroup.success)
    }
    try call.perform(operations)
  }

  /// Send final status to the client
  ///
  /// - Parameter statusCode: status code to send
  /// - Parameter statusMessage: status message to send
  /// - Parameter trailingMetadata: trailing metadata to send
  /// - Parameter completion: a completion handler to call after the status has been sent
  public func sendStatus(statusCode: StatusCode,
                         statusMessage: String,
                         trailingMetadata: Metadata,
                         completion: ((Bool) -> Void)? = nil) throws {
    let operations = OperationGroup(call: call,
                                    operations: [
                                      .sendStatusFromServer(statusCode,
                                                            statusMessage,
                                                            trailingMetadata)
    ]) { operationGroup in
      completion?(operationGroup.success)
      self.shutdown()
    }
    try call.perform(operations)
  }
}

extension Handler: Hashable {
  public var hashValue: Int { return underlyingHandler.hashValue }
  
  public static func ==(A: Handler, B: Handler) -> Bool {
    return A === B
  }
}