<?php
// ============================================
//  includes/db.php
//  PDO připojení + pomocné funkce
// ============================================

require_once __DIR__ . '/config.php';

function db(): PDO {
    static $pdo = null;
    if ($pdo === null) {
        $dsn = sprintf('mysql:host=%s;dbname=%s;charset=%s', DB_HOST, DB_NAME, DB_CHARSET);
        $pdo = new PDO($dsn, DB_USER, DB_PASS, [
            PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
            PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
            PDO::ATTR_EMULATE_PREPARES   => true,
        ]);
    }
    return $pdo;
}

// -----------------------------------------------
//  Nastavení salónu z DB (cache na request)
// -----------------------------------------------

function nastaveni(string $klic, mixed $vychozi = null): mixed {
    static $cache = null;
    if ($cache === null) {
        $cache = [];
        try {
            $rows = db()->query("SELECT klic, hodnota FROM nastaveni")->fetchAll();
            foreach ($rows as $r) {
                $cache[$r['klic']] = $r['hodnota'];
            }
        } catch (Exception $e) {
            // Tabulka ještě neexistuje při první instalaci – vrátí výchozí hodnoty
        }
    }
    return $cache[$klic] ?? $vychozi;
}

function slot_minut(): int     { return (int) nastaveni('slot_minut', 30); }
function salon_nazev(): string { return (string) nastaveni('salon_nazev', 'Kadeřnictví Stella'); }

// Načte pracovní dobu pro konkrétní den (1=Po…7=Ne), nebo null pokud zavřeno
function pracovni_doba_dne(int $dow): ?array {
    static $cache = [];
    if (!isset($cache[$dow])) {
        try {
            $stmt = db()->prepare("SELECT od_min, do_min FROM pracovni_doba WHERE den = ? AND aktivni = 1");
            $stmt->execute([$dow]);
            $row = $stmt->fetch();
            $cache[$dow] = $row ?: null;
        } catch (Exception $e) {
            // Tabulka ještě neexistuje — fallback na nastaveni
            $od = (int) nastaveni('pracovni_od', 480);
            $do = (int) nastaveni('pracovni_do', 1020);
            $dny = array_map('intval', explode(',', nastaveni('pracovni_dny', '1,2,3,4,5,6')));
            $cache[$dow] = in_array($dow, $dny) ? ['od_min' => $od, 'do_min' => $do] : null;
        }
    }
    return $cache[$dow];
}

// Vrátí všechny aktivní pracovní dny s jejich dobou
function vsechna_pracovni_doba(): array {
    static $cache = null;
    if ($cache === null) {
        try {
            $stmt = db()->query("SELECT den, od_min, do_min FROM pracovni_doba WHERE aktivni = 1 ORDER BY den");
            $cache = $stmt->fetchAll(PDO::FETCH_KEY_PAIR | PDO::FETCH_UNIQUE) ?: [];
            // Přegeneruj jako den => [od_min, do_min]
            $stmt2 = db()->query("SELECT den, od_min, do_min FROM pracovni_doba WHERE aktivni = 1 ORDER BY den");
            $cache = [];
            foreach ($stmt2->fetchAll() as $r) {
                $cache[$r['den']] = ['od_min' => (int)$r['od_min'], 'do_min' => (int)$r['do_min']];
            }
        } catch (Exception $e) {
            $cache = [];
        }
    }
    return $cache;
}

// -----------------------------------------------
//  Pomocné funkce
// -----------------------------------------------

function json_response(array $data, int $status = 200): void {
    http_response_code($status);
    header('Content-Type: application/json; charset=utf-8');
    header('X-Content-Type-Options: nosniff');
    echo json_encode($data, JSON_UNESCAPED_UNICODE);
    exit;
}

function json_error(string $message, int $status = 400): void {
    json_response(['ok' => false, 'error' => $message], $status);
}

function generate_token(): string {
    return bin2hex(random_bytes(32));
}

function sanitize(string $value): string {
    return trim($value);
}

function valid_email(string $email): bool {
    return filter_var($email, FILTER_VALIDATE_EMAIL) !== false;
}

function valid_date(string $date): bool {
    $d = DateTime::createFromFormat('Y-m-d', $date);
    return $d && $d->format('Y-m-d') === $date;
}

// -----------------------------------------------
//  Logika volných termínů
// -----------------------------------------------

function obsazene_sloty(string $datum): array {
    $stmt = db()->prepare("
        SELECT cas_od, cas_do FROM rezervace
        WHERE datum = ? AND stav != 'zrusena'
    ");
    $stmt->execute([$datum]);

    $obsazene = [];
    foreach ($stmt->fetchAll() as $r) {
        $od = strtotime($r['cas_od']);
        $do = strtotime($r['cas_do']);
        for ($t = $od; $t < $do; $t += slot_minut() * 60) {
            $obsazene[] = date('H:i', $t);
        }
    }
    return array_unique($obsazene);
}

function volne_casy(string $datum, int $trvani_min): array {
    if (je_blokovany_den($datum)) return [];

    $dow  = (int) date('N', strtotime($datum)); // 1=Po, 7=Ne
    $doba = pracovni_doba_dne($dow);
    if (!$doba) return []; // Tento den je zavřeno

    $y = (int) substr($datum, 0, 4);
    $m = (int) substr($datum, 5, 2);
    $d = (int) substr($datum, 8, 2);

    $denni_od = mktime(intdiv($doba['od_min'], 60), $doba['od_min'] % 60, 0, $m, $d, $y);
    $denni_do = mktime(intdiv($doba['do_min'], 60), $doba['do_min'] % 60, 0, $m, $d, $y);

    $obsazene = obsazene_sloty($datum);
    $slot     = slot_minut() * 60;
    $volne    = [];

    for ($t = $denni_od; $t + $trvani_min * 60 <= $denni_do; $t += $slot) {
        $ok = true;
        for ($s = $t; $s < $t + $trvani_min * 60; $s += $slot) {
            if (in_array(date('H:i', $s), $obsazene)) { $ok = false; break; }
        }
        if ($ok) $volne[] = date('H:i', $t);
    }
    return $volne;
}

function je_blokovany_den(string $datum): bool {
    $stmt = db()->prepare("
        SELECT id FROM blokovane_terminy
        WHERE datum_od <= ? AND datum_do >= ? LIMIT 1
    ");
    $stmt->execute([$datum, $datum]);
    return (bool) $stmt->fetch();
}