<?php

declare(strict_types=1);

namespace Box\Mod\Mailgateway;

use FOSSBilling\InformationException;

class InboundPolicy
{
    private const FIELDS = [
        'auto-submitted', 'precedence', 'return-path', 'content-type',
        'x-auto-response-suppress', 'x-autoreply', 'x-autorespond', 'list-id',
    ];

    /** Normalize parsed MIME headers and supported flat header fields. */
    public function headers(array $data): array
    {
        $raw = $data['headers'] ?? [];
        if (!is_array($raw)) {
            throw new InformationException('headers must be an array of header values');
        }
        foreach (self::FIELDS as $field) {
            $flat = str_replace('-', '_', $field);
            if (array_key_exists($flat, $data)) {
                $raw[$field] = array_merge((array) ($raw[$field] ?? []), (array) $data[$flat]);
            }
        }
        $headers = [];
        foreach ($raw as $name => $values) {
            if (!is_string($name)) {
                throw new InformationException('Header names must be strings');
            }
            $name = strtolower(str_replace('_', '-', $name));
            if (!in_array($name, self::FIELDS, true)) {
                continue;
            }
            $values = is_array($values) ? $values : [$values];
            if (count($values) > 20) {
                throw new InformationException('Too many repeated header values');
            }
            foreach ($values as $value) {
                if (!is_string($value) || strlen($value) > 16384) {
                    throw new InformationException('Header values must be strings of at most 16384 bytes');
                }
                $value = preg_replace('/\r?\n[ \t]+/', ' ', $value);
                if (preg_match('/[\x00-\x08\x0A-\x1F\x7F]/', $value)) {
                    throw new InformationException('Invalid control character in header value');
                }
                $headers[$name][] = strtolower(trim($value));
            }
        }
        ksort($headers);

        return $headers;
    }

    public function ignoreReason(array $headers): ?string
    {
        foreach ($headers['auto-submitted'] ?? [] as $value) {
            if (trim(explode(';', $value, 2)[0]) !== 'no') {
                return 'auto_submitted';
            }
        }
        foreach ($headers['return-path'] ?? [] as $value) {
            if (preg_match('/^<\s*>$/D', $value)) {
                return 'null_return_path';
            }
        }
        foreach ($headers['content-type'] ?? [] as $value) {
            if (preg_match('/^multipart\/report\s*(?:;|$)/', $value)
                || preg_match('/^message\/(?:delivery-status|disposition-notification|global-delivery-status)\s*(?:;|$)/', $value)) {
                return 'delivery_report';
            }
        }
        foreach ($headers['precedence'] ?? [] as $value) {
            if (in_array(trim(explode(';', $value, 2)[0]), ['bulk', 'list', 'junk'], true)) {
                return 'bulk_mail';
            }
        }
        foreach ($headers['list-id'] ?? [] as $value) {
            if ($value !== '') {
                return 'mailing_list';
            }
        }
        foreach ($headers['x-auto-response-suppress'] ?? [] as $value) {
            if (preg_match('/(?:^|[\s,;])(?:all|autoreply|oof|dr|ndr|rn|nrn)(?:$|[\s,;])/', $value)) {
                return 'response_suppressed';
            }
        }
        foreach (['x-autoreply', 'x-autorespond'] as $field) {
            foreach ($headers[$field] ?? [] as $value) {
                if (!in_array($value, ['', 'no', 'false', '0'], true)) {
                    return 'legacy_autoresponder';
                }
            }
        }

        return null;
    }
}