<?php
// ═══════════════════════════════════════════════════════════════════════════════════════════════
// PURPOSE
//   Sample per-peer Tailscale byte counters, once a minute, so the Partnership page can report
//   how much has actually moved between the servers in this mesh over a window.
//
// OPERATIONAL MODEL
//   Appends one line per mesh peer to data/db/mesh_traffic.db:
//
//       epoch|peer-hostname|txbytes|rxbytes
//
//   Called from Tools/api_cache_writer.sh, which already runs every minute. A window total is
//   then the difference between the newest sample and the oldest one still inside that window.
//
// DESIGN PRINCIPLES
//   Measure the link, not the tool.
//       The previous card totalled rsync's own logs, so it could only ever describe rsync — and
//       said "no data moved" while SSH, the arr APIs, conf pushes and the Unraid API were all
//       using the same link. Tailscale counts the bytes on the wire, whatever sent them.
//
//   Mesh peers only.
//       The tailnet holds phones and workstations. Filtered against the HOST* hostnames in
//       master.conf so this measures the partnership, not the tailnet.
//
//   Absolute counters are stored, never deltas.
//       A delta computed at write time bakes in whatever the sampling interval happened to be
//       and cannot be re-derived if a run is missed. Storing the raw counter means a gap costs
//       resolution, not correctness.
//
// OPERATIONAL SAFEGUARDS
//   Counter resets are the reader's problem, not this file's — tailscaled restarting returns
//   the counters to zero, and a sampler that tried to compensate would have to guess when.
//   Storing raw values leaves the evidence intact: a sample lower than the one before it is a
//   restart, and it is unambiguous.
//
//   Trimmed to VV_MESH_KEEP_DAYS on every run, so the file cannot grow without bound. At one
//   sample per peer per minute that is ~1,440 lines/peer/day.
//
//   Silent no-op when tailscale is absent or returns nothing parseable. This runs every minute
//   from a cache writer; a mesh sampler is not worth a log line per minute when it has nothing
//   to add.
//
// RUNTIME MODES
//   php mesh_traffic_sample.php            append one sample per mesh peer
//   php mesh_traffic_sample.php --show     print what it would record, write nothing
//
// DEPENDS ON
//   tailscale status --json     the counters
//   include/config.php          DATA_DIR, vv_conf_vars() for the HOST* list
// ═══════════════════════════════════════════════════════════════════════════════════════════════
require_once dirname(__DIR__) . '/include/config.php';

define('VV_MESH_DB',        DATA_DIR . '/db/mesh_traffic.db');
define('VV_MESH_KEEP_DAYS', 40);          // a 30-day window needs a sample older than 30 days

$show = in_array('--show', $argv ?? [], true);

$raw = shell_exec('tailscale status --json 2>/dev/null');
$js  = json_decode((string)$raw, true);
if (!is_array($js) || empty($js['Peer'])) exit(0);

// The hostnames this mesh is made of. Anything else on the tailnet is somebody's laptop.
$vars = vv_conf_vars();
$mesh = [];
foreach ($vars as $k => $v) {
    if (preg_match('/^HOST\d+$/', $k) && trim((string)$v) !== '') $mesh[strtolower(trim($v))] = true;
}
if (!$mesh) exit(0);

$now   = time();
$lines = [];
foreach ($js['Peer'] as $peer) {
    $host = strtolower(trim((string)($peer['HostName'] ?? '')));
    if ($host === '') continue;

    // Same unambiguous-prefix rule the rest of the partnership layer uses: the tailnet name and
    // the conf hostname are different strings and nothing keeps them in step.
    $match = null;
    if (isset($mesh[$host])) {
        $match = $host;
    } else {
        $cand = [];
        foreach (array_keys($mesh) as $m) {
            if (str_starts_with($host, $m) || str_starts_with($m, $host)) $cand[] = $m;
        }
        if (count($cand) === 1) $match = $cand[0];
    }
    if ($match === null) continue;

    $tx = (int)($peer['TxBytes'] ?? 0);
    $rx = (int)($peer['RxBytes'] ?? 0);
    if ($tx === 0 && $rx === 0) continue;
    $lines[] = $now . '|' . $match . '|' . $tx . '|' . $rx;
}
if (!$lines) exit(0);

if ($show) { echo implode("\n", $lines) . "\n"; exit(0); }

@mkdir(dirname(VV_MESH_DB), 0755, true);
@file_put_contents(VV_MESH_DB, implode("\n", $lines) . "\n", FILE_APPEND | LOCK_EX);

// Trim in place. Read-filter-rewrite rather than append-only truncation, because the cut is by
// age and the file is not ordered by peer.
$cutoff = $now - (VV_MESH_KEEP_DAYS * 86400);
$all    = @file(VV_MESH_DB, FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES) ?: [];
if (count($all) > 200) {
    $keep = [];
    foreach ($all as $l) {
        $ts = (int)strtok($l, '|');
        if ($ts >= $cutoff) $keep[] = $l;
    }
    if (count($keep) !== count($all)) {
        $tmp = VV_MESH_DB . '.tmp';
        if (@file_put_contents($tmp, implode("\n", $keep) . "\n") !== false) @rename($tmp, VV_MESH_DB);
    }
}