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       1                 :             : /*
       2                 :             :  * Copyright 2025 Jinwoo Sung
       3                 :             :  *
       4                 :             :  * Licensed under the Apache License, Version 2.0 (the "License");
       5                 :             :  * you may not use this file except in compliance with the License.
       6                 :             :  * You may obtain a copy of the License at
       7                 :             :  *
       8                 :             :  *     http://www.apache.org/licenses/LICENSE-2.0
       9                 :             :  *
      10                 :             :  * Unless required by applicable law or agreed to in writing, software
      11                 :             :  * distributed under the License is distributed on an "AS IS" BASIS,
      12                 :             :  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
      13                 :             :  * See the License for the specific language governing permissions and
      14                 :             :  * limitations under the License.
      15                 :             :  */
      16                 :             : 
      17                 :             : #pragma once
      18                 :             : 
      19                 :             : #include <cassert>
      20                 :             : #include <cstdint>
      21                 :             : 
      22                 :             : namespace wirestead::wrapper {
      23                 :             : 
      24                 :             : // Immediate send rejection only. Loss after acceptance belongs in statistics.
      25                 :             : // The enum may grow; consumers should provide a default case when switching.
      26                 :             : enum class SendRejection : std::uint8_t {
      27                 :             :   NotStarted,
      28                 :             :   Stopping,
      29                 :             :   NotReady,
      30                 :             :   WouldBlock,
      31                 :             :   QueueFull,
      32                 :             :   TooLarge,
      33                 :             :   InvalidArgument,
      34                 :             :   CancelledWhileWaiting
      35                 :             : };
      36                 :             : 
      37                 :             : // An admission outcome, never a delivery receipt. Construct an explicit outcome
      38                 :             : // through accept()/reject(); there is no default or implicit bool constructor.
      39                 :             : class [[nodiscard]] SendResult {
      40                 :             :  public:
      41                 :      857228 :   static constexpr SendResult accept() noexcept { return SendResult(true, SendRejection::NotStarted); }
      42                 :       17948 :   static constexpr SendResult reject(SendRejection reason) noexcept { return SendResult(false, reason); }
      43                 :             : 
      44                 :      888355 :   constexpr bool accepted() const noexcept { return accepted_; }
      45                 :        7594 :   constexpr explicit operator bool() const noexcept { return accepted(); }
      46                 :             : 
      47                 :             :   // Precondition: !accepted(). The stored reason has no meaning on success.
      48                 :        5267 :   constexpr SendRejection reason() const noexcept {
      49         [ -  + ]:        5267 :     assert(!accepted_ && "SendResult::reason() requires a rejected result");
      50                 :        5267 :     return reason_;
      51                 :             :   }
      52                 :             : 
      53                 :             :  private:
      54                 :      875176 :   constexpr SendResult(bool accepted, SendRejection reason) noexcept : accepted_(accepted), reason_(reason) {}
      55                 :             :   bool accepted_;
      56                 :             :   SendRejection reason_;
      57                 :             : };
      58                 :             : 
      59                 :             : }  // namespace wirestead::wrapper