graceful_degradation_example.cpp

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// BSD 3-Clause License
// Copyright (c) 2021-2025, 🍀☀🌕🌥 🌊
// See the LICENSE file in the project root for full license information.
 
#include <atomic>
#include <chrono>
#include <iostream>
#include <random>
#include <thread>
 
#include "kcenon/monitoring/core/error_codes.h"
#include "kcenon/monitoring/core/result_types.h"
#include "kcenon/monitoring/reliability/circuit_breaker.h"
#include "kcenon/monitoring/reliability/fault_tolerance_manager.h"
#include "kcenon/monitoring/reliability/retry_policy.h"
 
using namespace kcenon::monitoring;
using namespace std::chrono_literals;
 
// Simulated unreliable service
class unreliable_service {
private:
    std::mt19937 rng_;
    std::uniform_real_distribution<> dist_;
    double failure_rate_;
    std::atomic<int> call_count_{0};
 
public:
    explicit unreliable_service(double failure_rate)
        : rng_(std::random_device{}())
        , dist_(0.0, 1.0)
        , failure_rate_(failure_rate) {}
 
    kcenon::common::Result<std::string> call() {
        call_count_++;
        std::this_thread::sleep_for(50ms);
 
        if (dist_(rng_) < failure_rate_) {
            return kcenon::common::Result<std::string>::err(
                error_info{monitoring_error_code::service_unavailable,
                          "Service temporarily unavailable"}.to_common_error()
            );
        }
 
        return kcenon::common::ok(std::string("Service response: SUCCESS"));
    }
 
    void set_failure_rate(double rate) {
        failure_rate_ = rate;
    }
};
 
// Demonstrate circuit breaker pattern
void demonstrate_circuit_breaker() {
    std::cout << "=== Circuit Breaker Pattern ===" << std::endl;
    std::cout << std::endl;
 
    unreliable_service service(0.7);  // 70% failure rate
 
    circuit_breaker_config config;
    config.failure_threshold = 3;
    config.timeout = 5000ms;
 
    circuit_breaker breaker(config);
 
    std::cout << "Circuit Breaker Configuration:" << std::endl;
    std::cout << "- Failure threshold: " << config.failure_threshold << std::endl;
    std::cout << "- Reset timeout: 5000ms" << std::endl;
    std::cout << std::endl;
 
    std::cout << "Making calls to unreliable service (70% failure rate):" << std::endl;
    std::cout << std::endl;
 
    for (int i = 0; i < 10; ++i) {
        std::cout << "Call " << (i + 1) << ": ";
 
        auto result = execute_with_circuit_breaker<std::string>(breaker, "external_service", [&service]() {
            return service.call();
        });
 
        if (result.is_ok()) {
            std::cout << "SUCCESS" << std::endl;
        } else {
            std::cout << "FAILED" << std::endl;
        }
 
        std::this_thread::sleep_for(200ms);
    }
 
    std::cout << std::endl;
 
    auto stats = breaker.get_stats();
    std::cout << "Circuit Breaker Stats:" << std::endl;
    for (const auto& [key, val] : stats) {
        std::visit([&key](const auto& v) {
            std::cout << "- " << key << ": " << v << std::endl;
        }, val);
    }
    std::cout << std::endl;
}
 
// Demonstrate retry policy
void demonstrate_retry_policy() {
    std::cout << "=== Retry Policy with Exponential Backoff ===" << std::endl;
    std::cout << std::endl;
 
    unreliable_service service(0.4);  // 40% failure rate
 
    retry_config retry_cfg;
    retry_cfg.max_attempts = 5;
    retry_cfg.strategy = retry_strategy::exponential_backoff;
    retry_cfg.initial_delay = 100ms;
    retry_cfg.backoff_multiplier = 2.0;
 
    retry_executor<std::string> policy("service_retry", retry_cfg);
 
    std::cout << "Retry Policy Configuration:" << std::endl;
    std::cout << "- Strategy: Exponential backoff" << std::endl;
    std::cout << "- Max attempts: 5" << std::endl;
    std::cout << "- Initial delay: 100ms" << std::endl;
    std::cout << std::endl;
 
    std::cout << "Making calls with retry policy:" << std::endl;
    std::cout << std::endl;
 
    for (int i = 0; i < 5; ++i) {
        std::cout << "Request " << (i + 1) << ": ";
 
        auto result = policy.execute([&service]() {
            return service.call();
        });
 
        if (result.is_ok()) {
            std::cout << "SUCCESS" << std::endl;
        } else {
            std::cout << "FAILED after retries" << std::endl;
        }
    }
 
    std::cout << std::endl;
 
    auto metrics = policy.get_metrics();
    std::cout << "Retry Policy Metrics:" << std::endl;
    std::cout << "- Total executions: " << metrics.total_executions << std::endl;
    std::cout << "- Successful: " << metrics.successful_executions << std::endl;
    std::cout << "- Failed: " << metrics.failed_executions << std::endl;
    std::cout << "- Total retries: " << metrics.total_retries << std::endl;
    std::cout << std::endl;
}
 
// Demonstrate combined patterns
void demonstrate_combined_patterns() {
    std::cout << "=== Combined Reliability Patterns ===" << std::endl;
    std::cout << std::endl;
 
    unreliable_service primary_service(0.5);
 
    circuit_breaker_config cb_config;
    cb_config.failure_threshold = 3;
    circuit_breaker breaker(cb_config);
 
    retry_config retry_cfg2;
    retry_cfg2.max_attempts = 3;
    retry_cfg2.strategy = retry_strategy::exponential_backoff;
    retry_cfg2.initial_delay = 100ms;
 
    retry_executor<std::string> policy2("combined_retry", retry_cfg2);
 
    std::cout << "Combining Circuit Breaker + Retry Policy" << std::endl;
    std::cout << std::endl;
 
    for (int i = 0; i < 10; ++i) {
        std::cout << "Request " << (i + 1) << ": ";
 
        auto result = execute_with_circuit_breaker<std::string>(breaker, "primary", [&]() {
            return policy2.execute([&]() {
                return primary_service.call();
            });
        });
 
        if (result.is_ok()) {
            std::cout << "SUCCESS" << std::endl;
        } else {
            std::cout << "FAILED" << std::endl;
        }
 
        std::this_thread::sleep_for(300ms);
    }
 
    std::cout << std::endl;
 
    auto cb_stats = breaker.get_stats();
    std::cout << "Circuit Breaker Stats:" << std::endl;
    for (const auto& [key, val] : cb_stats) {
        std::visit([&key](const auto& v) {
            std::cout << "- " << key << ": " << v << std::endl;
        }, val);
    }
    std::cout << std::endl;
 
    auto retry_metrics = policy2.get_metrics();
    std::cout << "Retry Policy:" << std::endl;
    std::cout << "- Total executions: " << retry_metrics.total_executions << std::endl;
    std::cout << "- Total retries: " << retry_metrics.total_retries << std::endl;
    std::cout << std::endl;
}
 
int main() {
    std::cout << "=== Graceful Degradation and Reliability Patterns ===" << std::endl;
    std::cout << std::endl;
 
    try {
        demonstrate_circuit_breaker();
        std::cout << std::string(70, '=') << std::endl;
        std::cout << std::endl;
 
        demonstrate_retry_policy();
        std::cout << std::string(70, '=') << std::endl;
        std::cout << std::endl;
 
        demonstrate_combined_patterns();
        std::cout << std::string(70, '=') << std::endl;
        std::cout << std::endl;
 
        std::cout << "=== All Reliability Patterns Demonstrated Successfully ===" << std::endl;
 
    } catch (const std::exception& e) {
        std::cerr << "Exception: " << e.what() << std::endl;
        return 1;
    }
 
    return 0;
}