<?php
/**
 * router.php — multi-hop journey planner (RAPTOR-style, up to 3 transfers).
 * (run-day aware build)
 */

const RT_MIN_TRANSFER = 20;
const RT_MAX_LAYOVER  = 360;     // 6h
const RT_HORIZON      = 1800;    // ~30h window for first boarding
const RT_MAX_ROUNDS   = 4;       // up to 3 transfers
const RT_INF          = PHP_INT_MAX;
const RT_STALE_DAYS   = 90;      // harvested run-days older than this are flagged stale
const RT_VERIFIED_ONLY = true;   // true = only trains with a verified run_days mask are routed

function rt_load_timetable(PDO $db): array {
    if (function_exists('apcu_fetch')) {
        $c = apcu_fetch('tt_v3', $ok);
        if ($ok && is_array($c)) return $c;
    }
    $cacheFile = sys_get_temp_dir() . '/trainchain_tt_v3.ser';
    if (is_file($cacheFile)) {
        $c = @unserialize((string)file_get_contents($cacheFile));
        if (is_array($c)) { if (function_exists('apcu_store')) apcu_store('tt_v3', $c, 86400); return $c; }
    }
    $tt = rt_build_timetable($db);
    if (function_exists('apcu_store')) apcu_store('tt_v3', $tt, 86400);
    @file_put_contents($cacheFile, serialize($tt));
    return $tt;
}

function rt_build_timetable(PDO $db): array {
    $stId = []; $stRev = []; $trainNo = []; $trips = []; $dep = [];
    // stops: 5 ints per stop now -> [sid, arrMin, depMin, depTod, dayOff]
    $cur = null; $tid = -1; $flat = [];
    // When verified-only is on, the graph contains ONLY trains with a run_days mask;
    // unverified trains (untried or no_schedule) are excluded from routing entirely.
    $verifiedOnly = defined('RT_VERIFIED_ONLY') ? RT_VERIFIED_ONLY : true;
    try {
        if ($verifiedOnly) {
            $stmt = $db->query(
                'SELECT ts.train_no, ts.station_code, ts.arr_min, ts.dep_min, ts.departure, ts.day_offset
                 FROM train_stops ts JOIN trains t ON t.train_no = ts.train_no
                 WHERE t.run_days IS NOT NULL ORDER BY ts.train_no, ts.seq'
            );
        } else {
            $stmt = $db->query(
                'SELECT train_no, station_code, arr_min, dep_min, departure, day_offset
                 FROM train_stops ORDER BY train_no, seq'
            );
        }
    } catch (Throwable $e) {  // older schema without run_days -> fall back to all trains
        $stmt = $db->query(
            'SELECT train_no, station_code, arr_min, dep_min, departure, day_offset
             FROM train_stops ORDER BY train_no, seq'
        );
    }
    $flush = function() use (&$trips, &$tid, &$flat) { if ($tid >= 0) $trips[$tid] = $flat; };
    foreach ($stmt as $row) {
        if ($row['train_no'] !== $cur) {
            $flush();
            $cur = $row['train_no']; $tid = count($trainNo); $trainNo[] = $cur; $flat = [];
        }
        $code = $row['station_code'];
        if (!isset($stId[$code])) { $stId[$code] = count($stRev); $stRev[] = $code; }
        $sid = $stId[$code];
        $arrMin = $row['arr_min'] === null ? -1 : (int)$row['arr_min'];
        $depMin = $row['dep_min'] === null ? -1 : (int)$row['dep_min'];
        $depTod = $row['departure'] === null ? -1 : rt_tod($row['departure']);
        $dayOff = (int)$row['day_offset'];
        $idx = intdiv(count($flat), 5);
        $flat[] = $sid; $flat[] = $arrMin; $flat[] = $depMin; $flat[] = $depTod; $flat[] = $dayOff;
        if ($depTod >= 0) { $dep[$sid][] = $tid; $dep[$sid][] = $idx; }
    }
    $flush();

    // Per-train run-day mask + freshness, keyed to tid via train number.
    $noToTid = array_flip($trainNo);          // train_no => tid
    $runmask = array_fill(0, count($trainNo), null);   // '1111111' (Mon..Sun) or null = unharvested
    $fresh   = array_fill(0, count($trainNo), 0);      // unix ts of refreshed_at, 0 = never
    // run_days / refreshed_at live on trains; tolerate older schemas without them.
    try {
        $q = $db->query('SELECT train_no, run_days, refreshed_at FROM trains');
        foreach ($q as $r) {
            $tn = $r['train_no'];
            if (!isset($noToTid[$tn])) continue;
            $i = $noToTid[$tn];
            $m = $r['run_days'] ?? null;
            if (is_string($m) && preg_match('/^[01]{7}$/', $m)) $runmask[$i] = $m;
            $fresh[$i] = !empty($r['refreshed_at']) ? (int)strtotime($r['refreshed_at']) : 0;
        }
    } catch (Throwable $e) { /* columns not present yet -> everything stays daily */ }

    return ['stId'=>$stId, 'stRev'=>$stRev, 'trainNo'=>$trainNo,
            'trips'=>$trips, 'dep'=>$dep, 'runmask'=>$runmask, 'fresh'=>$fresh];
}

function rt_tod(?string $time): int {
    if ($time === null || $time === '') return -1;
    $p = explode(':', $time);
    return count($p) >= 2 ? ((int)$p[0]) * 60 + (int)$p[1] : -1;
}

/* next absolute minute >= E whose time-of-day == tod (daily instances) */
function rt_next(int $tod, int $E): int {
    $d = (($tod - $E) % 1440 + 1440) % 1440;
    return $E + $d;
}

/* Does this train run for a boarding at $depAbs?  mask null => assume daily (true).
 * baseDow = ISO weekday (1=Mon..7=Sun) of the SEARCH date (midnight = abs minute 0).
 * dayOff  = boarding stop's day_offset (calendar days after the train's origin dep).
 * Origin departure weekday = searchDOW + floor(depAbs/1440) - dayOff (mod 7). */
function rt_runs(?string $mask, int $baseDow, int $depAbs, int $dayOff): bool {
    if ($mask === null) return true;
    $boardDayIdx = intdiv($depAbs, 1440);
    $idx = (($baseDow - 1) + $boardDayIdx - $dayOff) % 7;
    $idx = ($idx + 7) % 7;             // Mon=0 .. Sun=6
    return $mask[$idx] === '1';
}

/* First daily instance >= earliest, within window, on a day the train ACTUALLY runs. -1 if none. */
function rt_first_run(?string $mask, int $baseDow, int $dayOff, int $depTod, int $earliest, int $window): int {
    $start = rt_next($depTod, $earliest);
    for ($cand = $start; $cand <= $earliest + $window; $cand += 1440) {
        if (rt_runs($mask, $baseDow, $cand, $dayOff)) return $cand;
    }
    return -1;
}

function rt_plan(array $tt, string $fromCode, string $toCode, int $queryDep, array $opt = []): array {
    $minT = $opt['min_transfer'] ?? RT_MIN_TRANSFER;
    $maxL = $opt['max_layover']  ?? RT_MAX_LAYOVER;
    $hor  = $opt['horizon']      ?? RT_HORIZON;
    $ymd  = $opt['date']         ?? date('Y-m-d');
    $baseDow = (int)date('N', strtotime($ymd));   // 1=Mon..7=Sun

    if (!isset($tt['stId'][$fromCode], $tt['stId'][$toCode])) return ['direct'=>[], 'hops'=>[]];
    $from = $tt['stId'][$fromCode]; $to = $tt['stId'][$toCode];
    $trips = $tt['trips']; $dep = $tt['dep'];
    $runmask = $tt['runmask'] ?? []; 

    $direct = rt_direct($tt, $from, $to, $queryDep, $hor, $baseDow);
    if (!isset($dep[$from])) return ['direct'=>rt_label_journey($tt, $direct), 'hops'=>[]];

    $arr  = [0 => [$from => $queryDep]];
    $pred = [0 => []];
    $marked = [$from => $queryDep];

    for ($r = 1; $r <= RT_MAX_ROUNDS; $r++) {
        $arr[$r]  = $arr[$r-1];
        $pred[$r] = $pred[$r-1];
        $ridden = [];
        $newMarked = [];

        foreach ($marked as $s => $a) {
            if (!isset($dep[$s])) continue;
            $earliest = ($r === 1) ? $a : $a + $minT;
            $window   = ($r === 1) ? $hor : $maxL;
            $arrivedOn = ($r > 1 && isset($pred[$r-1][$s])) ? $pred[$r-1][$s]['train'] : -1;
            $d = $dep[$s]; $dn = count($d);

            for ($e = 0; $e < $dn; $e += 2) {
                $tid = $d[$e]; $idx = $d[$e+1];
                if ($tid === $arrivedOn) continue;
                $trip = $trips[$tid]; $off = $idx * 5;
                $depTod = $trip[$off+3]; $depMin = $trip[$off+2]; $dayOff = $trip[$off+4];
                $mask = $runmask[$tid] ?? null;
                $depAbs = rt_first_run($mask, $baseDow, $dayOff, $depTod, $earliest, $window);
                if ($depAbs < 0) continue;                      // doesn't run within the window
                if (isset($ridden[$tid]) && $depAbs >= $ridden[$tid]) continue;
                $ridden[$tid] = $depAbs;

                $bestDest = $arr[$r][$to] ?? RT_INF;
                $m = count($trip);
                for ($j = $off + 5; $j < $m; $j += 5) {
                    $arrMin = $trip[$j+1];
                    if ($arrMin < 0) continue;
                    $arrAbs = $depAbs + ($arrMin - $depMin);
                    if ($arrAbs >= $bestDest) continue;
                    $code2 = $trip[$j];
                    if ($arrAbs < ($arr[$r][$code2] ?? RT_INF)) {
                        $arr[$r][$code2] = $arrAbs;
                        $pred[$r][$code2] = ['from'=>$s, 'train'=>$tid, 'board'=>$depAbs, 'arr'=>$arrAbs];
                        $newMarked[$code2] = $arrAbs;
                    }
                }
            }
        }
        $marked = $newMarked;
        if (!$marked) break;
    }

    $hops = [];
    for ($r = 1; $r <= RT_MAX_ROUNDS; $r++) {
        if (!isset($arr[$r][$to])) continue;
        if ($r > 1 && isset($arr[$r-1][$to]) && $arr[$r][$to] >= $arr[$r-1][$to]) continue;
        $journey = rt_reconstruct($pred, $r, $from, $to);
        $changes = count($journey) - 1;
        if ($changes >= 1) $hops[$changes] = rt_label_journey($tt, $journey);
    }
    return ['direct'=>rt_label_journey($tt, $direct), 'hops'=>$hops];
}

function rt_reconstruct(array $pred, int $R, int $from, int $to): array {
    $legs = []; $code = $to; $r = $R; $guard = 0;
    while ($code !== $from && $r >= 1 && $guard++ < 12) {
        if (!isset($pred[$r][$code])) break;
        $leg = $pred[$r][$code];
        $legs[] = ['from'=>$leg['from'], 'to'=>$code, 'train'=>$leg['train'], 'board'=>$leg['board'], 'arr'=>$leg['arr']];
        $code = $leg['from']; $r--;
    }
    return array_reverse($legs);
}

function rt_direct(array $tt, int $from, int $to, int $queryDep, int $hor, int $baseDow): array {
    $out = [];
    if (!isset($tt['dep'][$from])) return $out;
    $runmask = $tt['runmask'] ?? [];
    $d = $tt['dep'][$from]; $dn = count($d);
    for ($e = 0; $e < $dn; $e += 2) {
        $tid = $d[$e]; $idx = $d[$e+1];
        $trip = $tt['trips'][$tid]; $off = $idx*5; $m = count($trip);
        $depTod = $trip[$off+3]; $depMin = $trip[$off+2]; $dayOff = $trip[$off+4];
        $mask = $runmask[$tid] ?? null;
        for ($j = $off+5; $j < $m; $j += 5) {
            if ($trip[$j] !== $to || $trip[$j+1] < 0) continue;
            $depAbs = rt_first_run($mask, $baseDow, $dayOff, $depTod, $queryDep, $hor);
            if ($depAbs < 0) break;                       // doesn't run in window
            $arrAbs = $depAbs + ($trip[$j+1] - $depMin);
            $out[] = ['from'=>$from, 'to'=>$to, 'train'=>$tid, 'board'=>$depAbs, 'arr'=>$arrAbs];
            break;
        }
    }
    usort($out, fn($a,$b) => $a['arr'] <=> $b['arr']);
    return $out;
}

/* map ids back to codes / train numbers, and attach run-day label + freshness */
function rt_label_journey(array $tt, array $legs): array {
    $now = time();
    foreach ($legs as &$l) {
        $tid = $l['train'];
        $mask = $tt['runmask'][$tid] ?? null;
        $ts   = $tt['fresh'][$tid] ?? 0;
        $l['from']  = $tt['stRev'][$l['from']];
        $l['to']    = $tt['stRev'][$l['to']];
        $l['train'] = $tt['trainNo'][$tid];
        $l['days']  = $mask === null ? null
                      : (function_exists('rd_label') ? rd_label($mask) : $mask);
        $l['harvested'] = $mask !== null;
        $l['stale'] = $mask !== null && ($ts === 0 || $ts < $now - RT_STALE_DAYS*86400);
    }
    return $legs;
}