clio/src/data/BackendCounters.hpp

#pragma once

#include "util/prometheus/Counter.hpp"
#include "util/prometheus/Gauge.hpp"
#include "util/prometheus/Histogram.hpp"

#include <boost/json/object.hpp>

#include <chrono>
#include <cstdint>
#include <functional>
#include <memory>
#include <string>

namespace data {

/**
 * @brief A concept for a class that can be used to count backend operations.
 */
template <typename T>
concept SomeBackendCounters = requires(T a) {
    typename T::PtrType;
    { a.registerTooBusy() } -> std::same_as<void>;
    { a.registerWriteSync(std::chrono::steady_clock::time_point{}) } -> std::same_as<void>;
    { a.registerWriteSyncRetry() } -> std::same_as<void>;
    { a.registerWriteStarted() } -> std::same_as<void>;
    { a.registerWriteFinished(std::chrono::steady_clock::time_point{}) } -> std::same_as<void>;
    { a.registerWriteRetry() } -> std::same_as<void>;
    { a.registerReadStarted(std::uint64_t{}) } -> std::same_as<void>;
    {
        a.registerReadFinished(std::chrono::steady_clock::time_point{}, std::uint64_t{})
    } -> std::same_as<void>;
    { a.registerReadRetry(std::uint64_t{}) } -> std::same_as<void>;
    { a.registerReadError(std::uint64_t{}) } -> std::same_as<void>;
    { a.report() } -> std::same_as<boost::json::object>;
};

/**
 * @brief Holds statistics about the backend.
 *
 * @note This class is thread-safe.
 */
class BackendCounters {
public:
    using PtrType = std::shared_ptr<BackendCounters>;

    /**
     * @brief Create a new BackendCounters object
     *
     * @return A shared pointer to the new BackendCounters object
     */
    static PtrType
    make();

    /**
     * @brief Register that the backend was too busy to process a request
     */
    void
    registerTooBusy();

    /**
     * @brief Register that a write operation was started
     *
     * @param startTime The time the operation was started
     */
    void
    registerWriteSync(std::chrono::steady_clock::time_point startTime);

    /**
     * @brief Register that a write operation was retried
     */
    void
    registerWriteSyncRetry();

    /**
     * @brief Register that a write operation was started
     */
    void
    registerWriteStarted();

    /**
     * @brief Register that a write operation was finished
     *
     * @param startTime The time the operation was started
     */
    void
    registerWriteFinished(std::chrono::steady_clock::time_point startTime);

    /**
     * @brief Register that a write operation was retried
     */
    void
    registerWriteRetry();

    /**
     * @brief Register that one or more read operations were started
     *
     * @param count The number of operations started
     */
    void
    registerReadStarted(std::uint64_t count = 1u);

    /**
     * @brief Register that one or more read operations were finished
     *
     * @param startTime The time the operations were started
     * @param count The number of operations finished
     */
    void
    registerReadFinished(std::chrono::steady_clock::time_point startTime, std::uint64_t count = 1u);

    /**
     * @brief Register that one or more read operations were retried
     *
     * @param count The number of operations retried
     */
    void
    registerReadRetry(std::uint64_t count = 1u);

    /**
     * @brief Register that one or more read operations had an error
     *
     * @param count The number of operations with an error
     */
    void
    registerReadError(std::uint64_t count = 1u);

    /**
     * @brief Get a report of the backend counters
     *
     * @return The report
     */
    [[nodiscard]] boost::json::object
    report() const;

private:
    BackendCounters();

    class AsyncOperationCounters {
    public:
        AsyncOperationCounters(std::string name);

        void
        registerStarted(std::uint64_t count);

        void
        registerFinished(std::uint64_t count);

        void
        registerRetry(std::uint64_t count);

        void
        registerError(std::uint64_t count);

        [[nodiscard]] boost::json::object
        report() const;

    private:
        std::string name_;
        std::reference_wrapper<util::prometheus::GaugeInt> pendingCounter_;
        std::reference_wrapper<util::prometheus::CounterInt> completedCounter_;
        std::reference_wrapper<util::prometheus::CounterInt> retryCounter_;
        std::reference_wrapper<util::prometheus::CounterInt> errorCounter_;
    };

    std::reference_wrapper<util::prometheus::CounterInt> tooBusyCounter_;

    std::reference_wrapper<util::prometheus::CounterInt> writeSyncCounter_;
    std::reference_wrapper<util::prometheus::CounterInt> writeSyncRetryCounter_;

    AsyncOperationCounters asyncWriteCounters_{"write_async"};
    AsyncOperationCounters asyncReadCounters_{"read_async"};

    std::reference_wrapper<util::prometheus::HistogramInt> readDurationHistogram_;
    std::reference_wrapper<util::prometheus::HistogramInt> writeDurationHistogram_;
};

}  // namespace data