#pragma once

#include "envoy/common/optref.h"

#include "envoy/common/pure.h"

#include "envoy/config/endpoint/v3/endpoint.pb.h"

#include "absl/strings/string_view.h"

namespace Envoy {

namespace Config {

// An interface for cached resource removed callback.

class EdsResourceRemovalCallback {

public:

  // Invoked when a cached resource is removed from the cache.

  virtual void onCachedResourceRemoved(absl::string_view resource_name) PURE;

};

// Represents an xDS resources cache for EDS resources, and currently supports

// a single config-source (ADS). The motivation is that clusters that are

// updated (not added) during a CDS response will be able to use the current EDS

// configuration, thus avoiding the need of the xDS server to send an additional

// EDS response that is identical to what was already sent.

// However, using the cached EDS config is not always desired, for example when

// the cluster changes from non-TLS to TLS (see discussion in

// https://github.com/envoyproxy/envoy/issues/5168). Thus, this cache allows

// the EDS subscription to decide whether to use the cache or not.

//

// This cache will be instantiated once and owned by the ADS Mux, and passed to

// the EDS subscriptions.

//

// Resources lifetime in the cache is determined by the gRPC mux that adds/updates a

// resource when it receives its contents, and removes a resource when there is

// no longer interest in that resource.

// An EDS subscription may fetch a resource from the cache, and optionally

// install a callback to be triggered if the resource is removed from the cache.

// In addition, a resource in the cache may have an expiration timer if

// "endpoint_stale_after" (TTL) is set for that resource. Once the timer

// expires, the callbacks will be triggered to remove the resource.

class EdsResourcesCache {

public:

  /**

   * Adds or updates a given resource name with its resource.

   * Any callback that was previously assigned to the resource will be removed

   * without any notification.

   * @param resource_name the name of the resource to add/update.

   * @param resource the contents of the resource.

   */

  virtual void setResource(absl::string_view resource_name,

                           const envoy::config::endpoint::v3::ClusterLoadAssignment& resource) PURE;

  /**

   * Removes a resource from the resource cache given the resource name.

   * The callbacks for the resource will be invoked, notifying that the resource

   * is removed.

   * @param resource_name the name of the resource that will be removed from

   *        the cache.

   */

  virtual void removeResource(absl::string_view resource_name) PURE;

  /**

   * Retrieves a resource from the cache, and adds the given callback (if any)

   * to the resource's removal list. if the resource is removed, all callbacks

   * for that resource will be invoked.

   * @param resource_name the name of the resource to fetch.

   * @param removal_cb an optional callback that will be invoked if the resource is removed

   *        in the future. Note that updating the resource (`setResource()`) will also

   *        remove the callback. The caller of this function can also call

   *        `removeCallback()` to explicitly remove the callback. The callback

   *        is owned by the caller as it is part of the EDS subscription.

   * @return A reference to the cluster load assignment resource, or nullopt if the

   *         resource doesn't exist.

   */

  virtual OptRef<const envoy::config::endpoint::v3::ClusterLoadAssignment>

  getResource(absl::string_view resource_name, EdsResourceRemovalCallback* removal_cb) PURE;

  /**

   * Removes a callback for a given resource name (if it was previously added).

   * @param resource_name the name of the resource for which the callback should be removed.

   * @param removal_cb a pointer to the callback that needs to be removed.

   */

  virtual void removeCallback(absl::string_view resource_name,

                              EdsResourceRemovalCallback* removal_cb) PURE;

  /**

   * Sets an expiry timer for the given resource_name after the given ms milliseconds.

   * Once the timer expires, the callbacks for that resource (if any) will be

   * @param resource_name the name of the resource for which the timer should be added.

   * @param ms the number of milliseconds until expiration.

   */

  virtual void setExpiryTimer(absl::string_view resource_name, std::chrono::milliseconds ms) PURE;

  /**

   * Disables the expiration timer for the given resource_name.

   * @param resource_name the name of the resource for which the timer should be disabled.

   */

  virtual void disableExpiryTimer(absl::string_view resource_name) PURE;

  /**

   * Returns the number of items in the cache. Only used in tests.

   * @return the number of items in the cache.

   */

  virtual uint32_t cacheSizeForTest() const PURE;

};

using EdsResourcesCachePtr = std::unique_ptr<EdsResourcesCache>;

using EdsResourcesCacheOptRef = OptRef<EdsResourcesCache>;

} // namespace Config

} // namespace Envoy