// Copyright 2014 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef COMPONENTS_POLICY_CORE_COMMON_PROXY_POLICY_PROVIDER_H_
#define COMPONENTS_POLICY_CORE_COMMON_PROXY_POLICY_PROVIDER_H_

#include <memory>
#include <variant>

#include "base/memory/raw_ptr.h"
#include "components/policy/core/common/configuration_policy_provider.h"
#include "components/policy/policy_export.h"

namespace policy {

// A policy provider implementation that acts as a proxy for another policy
// provider, swappable at any point.
//
// Note that ProxyPolicyProvider correctly forwards RefreshPolicies() calls to
// the delegate if present. If there is no delegate, the refresh results in an
// immediate (empty) policy update.
//
// Furthermore, IsInitializationComplete() is implemented trivially - it always
// returns true. Given that the delegate may be swapped at any point, there's no
// point in trying to carry over initialization status from the delegate.
//
// This policy provider implementation is used to inject browser-global policy
// originating from the user policy configured on the primary Chrome OS user
// (i.e. the user logging in from the login screen). This way, policy settings
// on the primary user propagate into g_browser_process->local_state_().
//
// The bizarre situation of user-scoped policy settings which are implemented
// browser-global wouldn't exist in an ideal world. However, for historic
// and technical reasons there are policy settings that are scoped to the user
// but are implemented to take effect for the entire browser instance. A good
// example for this are policies that affect the Chrome network stack in areas
// where there's no profile-specific context. The meta data in
// policy_templates.json allows to identify the policies in this bucket; they'll
// have per_profile set to False, supported_on including chrome_os, and
// dynamic_refresh set to True.
class POLICY_EXPORT ProxyPolicyProvider
    : public ConfigurationPolicyProvider,
      public ConfigurationPolicyProvider::Observer {
 public:
  // Unspecified vs. nullptr:
  // - Unspecified: The delegate has never been set since construction.
  // - nullptr: The delegate has been set to nullptr explicitly via
  //   SetOwnedDelegate/SetUnownedDelegate. This makes IsFirstPolicyLoadComplete
  //   return true.
  // Can transition from Unspecified to Owned/Unowned, but cannot transition
  // back to Unspecified afterwards.
  //
  // State transition diagram:
  //
  //  ctor --> Unspecified
  //               |
  //               +--SetOwnedDelegate----> OwnedDelegate
  //               |                              ^
  //               |                              | SetOwned/UnownedDelegate
  //               |                              v
  //               +--SetUnownedDelegate-> UnownedDelegate
  using Unspecified = std::monostate;
  using OwnedDelegate = std::unique_ptr<ConfigurationPolicyProvider>;
  using UnownedDelegate = raw_ptr<ConfigurationPolicyProvider>;

  ProxyPolicyProvider();
  ProxyPolicyProvider(const ProxyPolicyProvider&) = delete;
  ProxyPolicyProvider& operator=(const ProxyPolicyProvider&) = delete;
  ~ProxyPolicyProvider() override;

  // Updates the provider this proxy delegates to.
  void SetOwnedDelegate(OwnedDelegate delegate);
  void SetUnownedDelegate(UnownedDelegate delegate);

  // ConfigurationPolicyProvider:
  void Shutdown() override;
  void RefreshPolicies(PolicyFetchReason reason) override;
  bool IsFirstPolicyLoadComplete(PolicyDomain domain) const override;

  // ConfigurationPolicyProvider::Observer:
  void OnUpdatePolicy(ConfigurationPolicyProvider* provider) override;

  // When set to true, this ProxyPolicyProvider will ignore subsequent policy
  // updates.
  void SetBlockPolicyUpdatesForTesting(bool block_policy_updates_for_testing) {
    block_policy_updates_for_testing_ = block_policy_updates_for_testing;
  }

 private:
  ConfigurationPolicyProvider* delegate();
  const ConfigurationPolicyProvider* delegate() const;

  void ResetDelegate();
  void OnDelegateChanged();

  std::variant<Unspecified, UnownedDelegate, OwnedDelegate> delegate_ =
      Unspecified();
  bool block_policy_updates_for_testing_ = false;
};

}  // namespace policy

#endif  // COMPONENTS_POLICY_CORE_COMMON_PROXY_POLICY_PROVIDER_H_