<?php

namespace App\Services;

use RuntimeException;

final class MailerService
{
    private readonly string $rootPath;

    public function __construct(private readonly array $config = [])
    {
        $this->rootPath = dirname(__DIR__, 2);
    }

    public function send(string $to, string $subject, string $textBody, array $headers = []): bool
    {
        $to = trim($to);
        $subject = trim($subject);
        $textBody = trim($textBody);

        if ($to === '' || !filter_var($to, FILTER_VALIDATE_EMAIL)) {
            throw new RuntimeException('Die Zieladresse für den Mailversand ist ungültig.');
        }

        if ($subject === '' || $textBody === '') {
            throw new RuntimeException('Betreff und Inhalt für den Mailversand sind erforderlich.');
        }

        $subjectLine = $this->encodeSubject($this->sanitizeHeaderValue($this->subjectPrefix() . $subject));
        $headerLines = $this->buildHeaders($headers);
        $body = $this->normalizeBody($textBody);

        $sent = false;

        if (function_exists('mail')) {
            $sent = @mail($to, $subjectLine, $body, implode("\r\n", $headerLines));
        }

        if ($sent) {
            return true;
        }

        if (!$this->usesLogFallback()) {
            throw new RuntimeException('Die E-Mail konnte nicht versendet werden.');
        }

        $this->writeFallbackLog([
            'to' => $to,
            'subject' => $this->subjectPrefix() . $subject,
            'headers' => $headerLines,
            'body' => $textBody,
        ]);

        return false;
    }

    private function buildHeaders(array $headers): array
    {
        $headerLines = [
            'MIME-Version: 1.0',
            'Content-Type: text/plain; charset=UTF-8',
            'Content-Transfer-Encoding: 8bit',
            'X-Mailer: Kaffeeliste',
        ];

        $from = trim((string) ($this->config['from'] ?? ''));

        if ($from !== '') {
            $headerLines[] = 'From: ' . $this->sanitizeHeaderValue($from);
        }

        $replyTo = trim((string) ($this->config['reply_to'] ?? ''));

        if ($replyTo !== '') {
            $headerLines[] = 'Reply-To: ' . $this->sanitizeHeaderValue($replyTo);
        }

        foreach ($headers as $name => $value) {
            if (is_int($name)) {
                $line = trim((string) $value);

                if ($line !== '' && str_contains($line, ':')) {
                    [$rawName, $rawValue] = array_pad(explode(':', $line, 2), 2, '');
                    $this->appendHeader($headerLines, $rawName, $rawValue);
                }

                continue;
            }

            $this->appendHeader($headerLines, (string) $name, (string) $value);
        }

        return $headerLines;
    }

    private function appendHeader(array &$headerLines, string $name, string $value): void
    {
        $name = trim($name);

        if ($name === '' || preg_match('/[^A-Za-z0-9-]/', $name)) {
            return;
        }

        $headerLines[] = $name . ': ' . $this->sanitizeHeaderValue($value);
    }

    private function writeFallbackLog(array $payload): void
    {
        $path = $this->resolveLogPath();
        $directory = dirname($path);

        if (!is_dir($directory) && !mkdir($directory, 0775, true) && !is_dir($directory)) {
            throw new RuntimeException('Das Mail-Log-Verzeichnis konnte nicht erstellt werden.');
        }

        $encodedPayload = json_encode($payload, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);

        if (!is_string($encodedPayload)) {
            $encodedPayload = '{"error":"mail payload could not be encoded"}';
        }

        $entry = '[' . gmdate(DATE_ATOM) . "] mail_fallback\n" . $encodedPayload . "\n\n";

        if (file_put_contents($path, $entry, FILE_APPEND | LOCK_EX) === false) {
            throw new RuntimeException('Das Mail-Fallback-Log konnte nicht geschrieben werden.');
        }
    }

    private function resolveLogPath(): string
    {
        $configuredPath = trim((string) ($this->config['log_file'] ?? ''));

        if ($configuredPath === '') {
            return $this->rootPath . '/storage/logs/mail.log';
        }

        if (str_starts_with($configuredPath, '/')) {
            return $configuredPath;
        }

        return $this->rootPath . '/' . ltrim($configuredPath, '/');
    }

    private function usesLogFallback(): bool
    {
        return (bool) ($this->config['log_fallback'] ?? true);
    }

    private function subjectPrefix(): string
    {
        return (string) ($this->config['subject_prefix'] ?? '');
    }

    private function sanitizeHeaderValue(string $value): string
    {
        return trim(str_replace(["\r", "\n"], ' ', $value));
    }

    private function encodeSubject(string $subject): string
    {
        if ($subject === '') {
            return $subject;
        }

        if (function_exists('mb_encode_mimeheader')) {
            return mb_encode_mimeheader($subject, 'UTF-8', 'B', "\r\n");
        }

        return $subject;
    }

    private function normalizeBody(string $textBody): string
    {
        return str_replace("\n", "\r\n", str_replace(["\r\n", "\r"], "\n", $textBody));
    }
}