<?php

namespace App\Services\Proxmox;

use App\Models\Host;
use Illuminate\Support\Facades\Cache;
use Throwable;

/**
 * The last hour of a host's CPU and memory load, as two percentage series.
 *
 * Read from Proxmox's OWN recorded history (`/nodes/{node}/rrddata`) rather
 * than sampled into a table of ours. PVE keeps hour/day/week/month/year for
 * every node whether we ask or not, so a sampler would mean a new table, a
 * minutely job, a pruning job and ~1440 rows per host per day — to reproduce,
 * less accurately, something already on disk. It also means the curve is full
 * from the first second, including the hour before anyone opened the page, and
 * that it cannot disagree with what Proxmox's own interface shows.
 *
 * The price is stated rather than hidden: a host that is not reachable has no
 * curve. See `available` below.
 */
final class HostLoadSeries
{
    /** Just under the minute at which PVE writes a fresh sample. */
    private const TTL_SECONDS = 55;

    public function __construct(private ProxmoxClient $pve) {}

    /** Bytes per second → MiB/s. The tiles carry the unit, so nobody has to guess. */
    private const MIB = 1048576;

    /**
     * @return array{labels: array<int, int>, cpu: array<int, ?float>, ram: array<int, ?float>, netin: array<int, ?float>, netout: array<int, ?float>, available: bool}
     */
    public function forHost(Host $host): array
    {
        // The `v2` is not decoration. A cache entry outlives a deploy, and an
        // entry written by the version before the network series has no
        // `netin`/`netout` — read as one of today's it kills the host page with
        // an undefined key for the length of the TTL, which is exactly the
        // minute somebody is looking to see whether the update went through.
        // The key moves with the shape; the old entry is simply never read
        // again and expires on its own.
        return Cache::remember(
            'host-load:v2:'.$host->id,
            self::TTL_SECONDS,
            fn () => $this->read($host),
        );
    }

    /**
     * @return array{labels: array<int, int>, cpu: array<int, ?float>, ram: array<int, ?float>, netin: array<int, ?float>, netout: array<int, ?float>, available: bool}
     */
    private function read(Host $host): array
    {
        $empty = ['labels' => [], 'cpu' => [], 'ram' => [], 'netin' => [], 'netout' => [], 'available' => false];

        try {
            $rows = $this->pve->forHost($host)->nodeRrdData($host->node ?? 'pve', 'hour');
        } catch (Throwable) {
            // Deliberately not a series of zeros. A flat line at zero is a
            // claim about the host — that it was idle — and this is the one
            // case where we know nothing at all. The panel says so instead.
            return $empty;
        }

        if ($rows === []) {
            return $empty;
        }

        $labels = [];
        $cpu = [];
        $ram = [];
        $netin = [];
        $netout = [];

        foreach ($rows as $row) {
            $labels[] = (int) ($row['time'] ?? 0);
            $cpu[] = $this->percent($row['cpu'] ?? null, 1);
            $ram[] = $this->percent($row['memused'] ?? null, $row['memtotal'] ?? null);
            $netin[] = $this->rate($row['netin'] ?? null);
            $netout[] = $this->rate($row['netout'] ?? null);
        }

        return [
            'labels' => $labels,
            'cpu' => $cpu,
            'ram' => $ram,
            'netin' => $netin,
            'netout' => $netout,
            'available' => true,
        ];
    }

    /** Bytes per second as MiB/s — or null, for the same reason percent() returns null. */
    private function rate(mixed $bytesPerSecond): ?float
    {
        if (! is_numeric($bytesPerSecond)) {
            return null;
        }

        return round((float) $bytesPerSecond / self::MIB, 2);
    }

    /**
     * A share of a whole, in percent — or null when either half is missing.
     *
     * Null rather than 0.0, and that is the whole care taken here: Proxmox
     * simply omits the fields for a sample it has no data for, and charting
     * that omission as zero draws a quiet hour the host never had. The same
     * distinction `instance_metrics` makes for its nullable columns, for the
     * same reason.
     */
    private function percent(mixed $part, mixed $whole): ?float
    {
        if (! is_numeric($part) || ! is_numeric($whole) || (float) $whole <= 0.0) {
            return null;
        }

        return round((float) $part / (float) $whole * 100, 2);
    }
}