<?php
declare(strict_types=1);
/** Strumieniowy eksport SQL na podstawie działającego eksportu POLANA (bez auth/UI). */
function pbk_sql_identifier(string $name): string
{
    return '`' . str_replace('`', '``', $name) . '`';
}

function pbk_sql_write($stream, string $value): void
{
    $length = strlen($value);
    // Zamiast fatalnego "Allowed memory size exhausted" zwracamy bezpieczny błąd,
    // zanim niekompletny SQL trafi do przeglądarki. php://memory zajmuje RAM.
    static $memLimit = null;
    if ($memLimit === null) {
        $ini = trim((string)ini_get('memory_limit'));
        if ($ini === '-1' || $ini === '') {
            $memLimit = PHP_INT_MAX;
        } else {
            $amount = (int)$ini;
            $suffix = strtolower(substr($ini, -1));
            $scale = ['k' => 1024, 'm' => 1048576, 'g' => 1073741824];
            $memLimit = $amount * ($scale[$suffix] ?? 1);
        }
    }
    if ($memLimit !== PHP_INT_MAX && memory_get_usage(true) + ($length * 2) + 12 * 1048576 > $memLimit) {
        throw new RuntimeException('Kopia SQL wymaga więcej RAM niż pozwala limit memory_limit PHP.');
    }
    $offset = 0;
    while ($offset < $length) {
        $written = fwrite($stream, substr($value, $offset));
        if (!is_int($written) || $written < 1) {
            throw new RuntimeException('Błąd zapisu do pamięci backupu.');
        }
        $offset += $written;
    }
}

function pbk_sql_sql_value(PDO $pdo, mixed $value, bool $binary): string
{
    if ($value === null) return 'NULL';
    if ($binary) return '0x' . bin2hex((string)$value);
    $result = $pdo->quote((string)$value);
    if (!is_string($result)) {
        throw new RuntimeException('Nie udało się zakodować wartości SQL.');
    }
    return $result;
}

/** @param resource $stream */
function pbk_sql_build(PDO $pdo, $stream, bool $onlyReservations): array
{
    $dbName = (string)$pdo->query('SELECT DATABASE()')->fetchColumn();
    $objects = $pdo->query('SHOW FULL TABLES')->fetchAll(PDO::FETCH_NUM);
    $tables = [];
    $views = [];
    $selected = $onlyReservations ? ['reservations', 'reservation_events'] : null;
    foreach ($objects as $item) {
        $name = (string)($item[0] ?? '');
        $kind = strtoupper((string)($item[1] ?? ''));
        if ($name === '' || ($selected !== null && !in_array($name, $selected, true))) continue;
        if ($kind === 'BASE TABLE') $tables[] = $name;
        elseif ($kind === 'VIEW') $views[] = $name;
        else throw new RuntimeException('Nieznany typ obiektu bazy: ' . $kind);
    }
    sort($tables, SORT_STRING);
    sort($views, SORT_STRING);
    if ($onlyReservations && !in_array('reservations', $tables, true)) {
        throw new RuntimeException('Brak tabeli reservations w bazie.');
    }
    if (!$tables) throw new RuntimeException('Brak tabel do eksportu.');
    pbk_sql_write($stream, '-- TKLM / MOJA POLANA SMAKÓW – KOPIA SQL' . "\n"
        . '-- Utworzono: ' . date(DATE_ATOM) . "\n"
        . '-- Typ: ' . ($onlyReservations ? 'Rezerwacje + historia' : 'Pełna baza (tabele + widoki + triggery)') . "\n"
        . '-- Uwaga: zawiera dane osobowe; przechowuj bezpiecznie i NIE udostępniaj publicznie!' . "\n"
        . '-- Eksportowana baza: ' . str_replace(["\r", "\n"], '', $dbName) . "\n"
        . '-- Odtwarzanie może NADPISAĆ dane. Importuj tylko do właściwej bazy.' . "\n\n"
        . 'SET NAMES utf8mb4;' . "\n"
        . 'SET FOREIGN_KEY_CHECKS=0;' . "\n\n");

    // Metadane przed rozpoczęciem niebuforowanych odczytów.
    $defs = [];
    $columns = [];
    foreach ($tables as $table) {
        $id = pbk_sql_identifier($table);
        $row = $pdo->query('SHOW CREATE TABLE ' . $id)->fetch(PDO::FETCH_ASSOC);
        $defs[$table] = (string)($row['Create Table'] ?? '');
        if ($defs[$table] === '') throw new RuntimeException('Brak definicji tabeli: ' . $table);
        $cols = $pdo->query('SHOW FULL COLUMNS FROM ' . $id)->fetchAll(PDO::FETCH_ASSOC);
        if (!$cols) throw new RuntimeException('Brak kolumn tabeli: ' . $table);
        $columns[$table] = $cols;
    }
    $viewDefs = [];
    foreach ($views as $view) {
        $row = $pdo->query('SHOW CREATE VIEW ' . pbk_sql_identifier($view))->fetch(PDO::FETCH_ASSOC);
        $definition = (string)($row['Create View'] ?? '');
        if ($definition === '') throw new RuntimeException('Brak definicji widoku: ' . $view);
        // Nie wymuszamy nieistniejącego użytkownika DEFINER przy odtwarzaniu.
        $viewDefs[$view] = preg_replace('/\s+DEFINER\s*=\s*`[^`]+`@`[^`]+`/i', '', $definition) ?? $definition;
    }

    // Nie ukrywamy problemów z uprawnieniami: błąd = brak pobierania niepełnego backupu.
    $triggers = $pdo->query('SHOW TRIGGERS')->fetchAll(PDO::FETCH_ASSOC);
    if ($selected !== null) {
        $triggers = array_values(array_filter($triggers, static fn(array $x): bool => in_array((string)($x['Table'] ?? ''), $selected, true)));
    }
    foreach ($tables as $table) {
        $id = pbk_sql_identifier($table);
        pbk_sql_write($stream, "-- Struktura: $table\nDROP TABLE IF EXISTS $id;\n" . $defs[$table] . ";\n\n");
    }

    // START TRANSACTION WITH CONSISTENT SNAPSHOT dla InnoDB. Pozostałe silniki mogą
    // nie zapewniać spójności transakcyjnej – warto zrobić backup przy małym ruchu.
    $pdo->exec('SET TRANSACTION ISOLATION LEVEL REPEATABLE READ');
    $pdo->exec('START TRANSACTION WITH CONSISTENT SNAPSHOT');
    $rowCounts = [];
    try {
        foreach ($tables as $table) {
            $id = pbk_sql_identifier($table);
            $cols = $columns[$table];
            $names = array_map(static fn(array $c): string => (string)$c['Field'], $cols);
            $quotedNames = implode(',', array_map('pbk_sql_identifier', $names));
            $binCols = [];
            foreach ($cols as $col) {
                $binCols[(string)$col['Field']] = (bool)preg_match('/\b(blob|binary|varbinary|bit)\b/i', (string)($col['Type'] ?? ''));
            }
            $count = 0;
            $unbuffered = defined('PDO::MYSQL_ATTR_USE_BUFFERED_QUERY');
            if ($unbuffered) $pdo->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, false);
            try {
                $statement = $pdo->query('SELECT * FROM ' . $id);
                while (($record = $statement->fetch(PDO::FETCH_ASSOC)) !== false) {
                    $values = [];
                    foreach ($names as $column) {
                        $values[] = pbk_sql_sql_value($pdo, $record[$column] ?? null, $binCols[$column]);
                    }
                    pbk_sql_write($stream, 'INSERT INTO ' . $id . ' (' . $quotedNames . ') VALUES (' . implode(',', $values) . ");\n");
                    $count++;
                }
                $statement->closeCursor();
            } finally {
                if ($unbuffered) $pdo->setAttribute(PDO::MYSQL_ATTR_USE_BUFFERED_QUERY, true);
            }
            pbk_sql_write($stream, "\n");
            $rowCounts[$table] = $count;
        }
        $pdo->exec('COMMIT');
    } catch (Throwable $e) {
        try { $pdo->exec('ROLLBACK'); } catch (Throwable $ignored) {}
        throw $e;
    }

    foreach ($viewDefs as $name => $definition) {
        $id = pbk_sql_identifier($name);
        pbk_sql_write($stream, "-- Widok: $name\nDROP VIEW IF EXISTS $id;\n" . $definition . ";\n\n");
    }
    if ($triggers) {
        pbk_sql_write($stream, "DELIMITER $$\n");
        foreach ($triggers as $trigger) {
            $name = pbk_sql_identifier((string)$trigger['Trigger']);
            $table = pbk_sql_identifier((string)$trigger['Table']);
            $timing = strtoupper((string)$trigger['Timing']);
            $event = strtoupper((string)$trigger['Event']);
            if (!in_array($timing, ['BEFORE', 'AFTER'], true)
                || !in_array($event, ['INSERT', 'UPDATE', 'DELETE'], true)) {
                throw new RuntimeException('Nieobsługiwany trigger.');
            }
            pbk_sql_write($stream,
                "DROP TRIGGER IF EXISTS $name$$\n"
                . "CREATE TRIGGER $name $timing $event ON $table FOR EACH ROW "
                . (string)$trigger['Statement'] . "$$\n\n");
        }
        pbk_sql_write($stream, "DELIMITER ;\n\n");
    }
    pbk_sql_write($stream, "SET FOREIGN_KEY_CHECKS=1;\n-- KONIEC POPRAWNEGO BACKUPU SQL\n");
    return ['rows' => $rowCounts, 'tables' => count($tables), 'views' => count($views), 'triggers' => count($triggers)];
}