<?php
// list.php – receives selected activity IDs, creates/reuses a hash, redirects to packing.php
require_once __DIR__ . '/db.php';

$pdo = get_pdo();

// Sanitize input
$raw = isset($_GET['aID']) && is_array($_GET['aID']) ? $_GET['aID'] : [];
$ids = [];
foreach ($raw as $v) {
    $v = (int)$v;
    if ($v > 0) $ids[] = $v;
}
$ids = array_unique($ids);
sort($ids);

if (empty($ids)) {
    header('Location: index.php?error=no_selection');
    exit;
}

// Validate IDs exist in DB
$placeholders = implode(',', array_fill(0, count($ids), '?'));
$stmt = $pdo->prepare("SELECT activityID FROM activities WHERE activityID IN ($placeholders)");
$stmt->execute($ids);
$validIds = $stmt->fetchAll(PDO::FETCH_COLUMN);

if (empty($validIds)) {
    header('Location: index.php?error=invalid_selection');
    exit;
}
sort($validIds);
$idsStr = implode(',', $validIds);

// Generate deterministic 5-character hash from the sorted activity IDs
$hash = substr(hash('sha256', $idsStr), 0, 5);

// Check if this exact selection already has a hash stored
$stmt = $pdo->prepare("SELECT hash FROM selection_hashes WHERE activity_ids = ?");
$stmt->execute([$idsStr]);
$existing = $stmt->fetchColumn();

if ($existing) {
    if ($existing !== $hash) {
        // Overwrite old (long) hash with the new short hash
        $stmt = $pdo->prepare("UPDATE selection_hashes SET hash = ? WHERE activity_ids = ?");
        $stmt->execute([$hash, $idsStr]);
    }
} else {
    // Store new hash
    $stmt = $pdo->prepare("INSERT INTO selection_hashes (hash, activity_ids) VALUES (?, ?)");
    $stmt->execute([$hash, $idsStr]);
}

// Redirect to the shareable packing list URL
header("Location: packing.php?h=" . urlencode($hash));
exit;