<?php

declare(strict_types=1);

namespace App;

/**
 * Sehr einfache Migrationen: jede Migration ist eine PHP-Datei in
 * /migrations, die ein Array ['sqlite' => [...SQL], 'mysql' => [...SQL]]
 * zurueckgibt. Bereits ausgefuehrte Migrationen werden in der Tabelle
 * "migrations" vermerkt. Laeuft automatisch beim ersten Request.
 */
final class Migrator
{
    public function __construct(
        private readonly Database $db,
        private readonly string $migrationsDir,
    ) {
    }

    /**
     * @return list<string> Namen der ausgefuehrten Migrationen
     */
    public function migrate(): array
    {
        $this->ensureMigrationsTable();

        $applied = [];
        $already = $this->appliedMigrations();

        foreach ($this->availableMigrations() as $name => $file) {
            if (in_array($name, $already, true)) {
                continue;
            }

            /** @var array<string,list<string>> $definition */
            $definition = require $file;
            $statements = $definition[$this->db->driver()] ?? $definition['sqlite'] ?? [];

            foreach ($statements as $sql) {
                $sql = trim($sql);
                if ($sql !== '') {
                    $this->db->pdo()->exec($sql);
                }
            }

            $this->db->execute(
                'INSERT INTO migrations (name, applied_at) VALUES (?, ?)',
                [$name, gmdate('Y-m-d H:i:s')],
            );
            $applied[] = $name;
        }

        return $applied;
    }

    private function ensureMigrationsTable(): void
    {
        $sql = $this->db->driver() === 'mysql'
            ? 'CREATE TABLE IF NOT EXISTS migrations (
                   id INT AUTO_INCREMENT PRIMARY KEY,
                   name VARCHAR(190) NOT NULL UNIQUE,
                   applied_at DATETIME NOT NULL
               ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4'
            : 'CREATE TABLE IF NOT EXISTS migrations (
                   id INTEGER PRIMARY KEY AUTOINCREMENT,
                   name TEXT NOT NULL UNIQUE,
                   applied_at TEXT NOT NULL
               )';

        $this->db->pdo()->exec($sql);
    }

    /**
     * @return list<string>
     */
    private function appliedMigrations(): array
    {
        $rows = $this->db->fetchAll('SELECT name FROM migrations');

        return array_map(static fn (array $row): string => (string) $row['name'], $rows);
    }

    /**
     * @return array<string,string> name => absoluter Pfad
     */
    private function availableMigrations(): array
    {
        $files = glob($this->migrationsDir . '/*.php') ?: [];
        sort($files, SORT_STRING);

        $result = [];
        foreach ($files as $file) {
            $result[basename($file, '.php')] = $file;
        }

        return $result;
    }
}