// Example 05 — Error Handling & Diagnostics
//
// Demonstrates observable failure modes and the diagnostics system:
//
// 1. ChannelOverflowError — a fast producer saturates a slow consumer.
//    When the channel is full, push() throws ChannelOverflowError.
//    The node's run_loop catches it and prints to stderr.
//    Channel statistics (overflows, peak fill) accumulate for the report.
//
// 2. Custom diagnostics handler — instead of the default periodic table,
//    install a handler that surfaces only the metrics you care about.
//
// 3. net.print_diagnostics() — print a full report at any time.
//
// Pipeline:  [producer] --int--> [slow_consumer]

#include <kpn/kpn.hpp>
#include <chrono>
#include <iostream>
#include <thread>

// ── Node functions ────────────────────────────────────────────────────────────

// Produces at ~100/s — faster than the consumer can keep up (50 ms each)
static int producer() {
    std::this_thread::sleep_for(std::chrono::milliseconds(10));
    static int n = 0;
    return ++n;
}

// Slow consumer: 50 ms per item — will cause channel to fill and overflow
static void slow_consumer(int x) {
    std::this_thread::sleep_for(std::chrono::milliseconds(50));
    std::cout << "[consumed] " << x << '\n';
}

// ── main ──────────────────────────────────────────────────────────────────────

int main() {
    using namespace kpn;

    // Capacity=4: fills up quickly when producer outpaces consumer 5:1
    auto prod = make_node<producer>      (out<"v">{}, /*capacity=*/4);
    auto cons = make_node<slow_consumer> (in<"v">{},  /*capacity=*/4);

    Network net;

    // --8<-- [start:diagnostics_handler]
    // Custom diagnostics handler — fires on the watchdog interval.
    // Print a concise one-liner rather than the full table.
    net.set_diagnostics_handler([](const std::vector<NodeSnapshot>& nodes,
                                   const std::vector<ChannelSnapshot>& channels) {
        std::cout << "[diag] ";
        for (auto& n : nodes)
            std::cout << n.name << "=" << n.throughput_fps << "fps  ";
        for (auto& c : channels)
            std::cout << "channel fill=" << static_cast<int>(c.fill_pct()) << "% "
                      << "overflows=" << c.overflows;
        std::cout << '\n';
    });
    // --8<-- [end:diagnostics_handler]

    net.set_watchdog_interval(std::chrono::milliseconds(200));

    net.add("prod", prod)
       .add("cons", cons)
       .connect("prod", prod.template output<"v">(), "cons", cons.template input<"v">())
       .build();

    std::cout << "producer: 10ms/item, consumer: 50ms/item, capacity=4\n"
              << "Overflow messages appear on stderr; diagnostics on stdout.\n\n";

    net.start();
    std::this_thread::sleep_for(std::chrono::milliseconds(800));
    net.stop();

    // Full report after shutdown — overflow and drop counts are preserved
    std::cout << '\n';
    net.print_diagnostics();
}