text: /*
   * Copyright (c) Facebook, Inc. and its affiliates.
   *
   * 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.
   */
  
  #pragma once
  
  #include <map>
  #include <string>
  #include <unordered_map>
  #include <vector>
  
  #include <folly/CPortability.h>
  #include <folly/Memory.h>
  
  namespace folly {
  namespace experimental {
  
  // Class to model the process environment in idiomatic C++
  //
  // Changes to the modeled environment do not change the process environment
  // unless `setAsCurrentEnvironment()` is called.
  struct EnvironmentState {
    using EnvType = std::unordered_map<std::string, std::string>;
  
    // Returns an EnvironmentState containing a copy of the current process
    // environment. Subsequent changes to the process environment do not
    // alter the stored model. If the process environment is altered during the
    // execution of this method the results are not defined.
    //
    // Throws MalformedEnvironment if the process environment cannot be modeled.
    static EnvironmentState fromCurrentEnvironment();
  
    // Returns an empty EnvironmentState
    static EnvironmentState empty() { return {}; }
  
    explicit EnvironmentState(EnvType const& env) : env_(env) {}
    explicit EnvironmentState(EnvType&& env) : env_(std::move(env)) {}
  
    // Get the model environment for querying.
    EnvType const& operator*() const { return env_; }
    EnvType const* operator->() const { return &env_; }
  
    // Get the model environment for mutation or querying.
    EnvType& operator*() { return env_; }
    EnvType* operator->() { return &env_; }
  
    // Update the process environment with the one in the stored model.
    // Subsequent changes to the model do not alter the process environment. The
    // state of the process environment during execution of this method is not
    // defined. If the process environment is altered by another thread during the
    // execution of this method the results are not defined.
    void setAsCurrentEnvironment();
  
    // Get a copy of the model environment in the form used by `folly::Subprocess`
    std::vector<std::string> toVector() const;
  
    // Get a copy of the model environment in the form commonly used by C routines
    // such as execve, execle, etc. Example usage:
    //
    // EnvironmentState forChild{};
    // ... manipulate `forChild` as needed ...
    // execve("/bin/program",pArgs,forChild.toPointerArray().get());
    std::unique_ptr<char*, void (*)(char**)> toPointerArray() const;
  
   private:
    EnvironmentState() {}
    EnvType env_;
  };
  
  struct FOLLY_EXPORT MalformedEnvironment : std::runtime_error {
    using std::runtime_error::runtime_error;
  };
  } // namespace experimental
  
  namespace test {
  // RAII class allowing scoped changes to the process environment. The
  // environment state at the time of its construction is restored at the time
  // of its destruction.
  struct EnvVarSaver {
    EnvVarSaver()
        : state_(std::make_unique<experimental::EnvironmentState>(
              experimental::EnvironmentState::fromCurrentEnvironment())) {}
  
    EnvVarSaver(EnvVarSaver&& other) noexcept : state_(std::move(other.state_)) {}
  
    EnvVarSaver& operator=(EnvVarSaver&& other) noexcept {
      state_ = std::move(other.state_);
      return *this;
    }
  
    ~EnvVarSaver() {
      if (state_) {
        state_->setAsCurrentEnvironment();
      }
    }
  
   private:
    std::unique_ptr<experimental::EnvironmentState> state_;
  };
  } // namespace test
  } // namespace folly
  