<?php

namespace App\Support;

/**
 * Lightweight UA → OS / browser fields for page-visit grouping.
 */
final class UserAgentParser
{
    /**
     * @return array{os: string, os_version: string, browser: string, browser_version: string}
     */
    public static function parse(?string $ua): array
    {
        $ua = trim((string) $ua);
        if ($ua === '') {
            return [
                'os' => 'Unknown',
                'os_version' => '',
                'browser' => 'Unknown',
                'browser_version' => '',
            ];
        }

        [$os, $osVersion] = self::parseOs($ua);
        [$browser, $browserVersion] = self::parseBrowser($ua);

        // iOS 26+ Safari still reports "iPhone OS 18_7" for compatibility.
        // When Version/ is 26+ and the OS token is 18.7, use Version/ for both fields.
        $compatVersion = self::ios26CompatVersion($ua);
        if ($compatVersion !== null && self::isIos187CompatToken($os, $osVersion)) {
            $osVersion = $compatVersion;
            $browserVersion = $compatVersion;
        }

        return [
            'os' => $os,
            'os_version' => $osVersion,
            'browser' => $browser,
            'browser_version' => $browserVersion,
        ];
    }

    private static function isIos187CompatToken(string $os, string $osVersion): bool
    {
        if (! in_array($os, ['iOS', 'iPadOS'], true)) {
            return false;
        }

        return $osVersion === '18.7' || str_starts_with($osVersion, '18.7.');
    }

    private static function ios26CompatVersion(string $ua): ?string
    {
        if (! preg_match('/Version\/(\d+(?:\.\d+){0,2})/i', $ua, $m)) {
            return null;
        }

        $major = (int) explode('.', $m[1])[0];
        if ($major < 26) {
            return null;
        }

        return $m[1];
    }

    /**
     * @return array{0: string, 1: string}
     */
    private static function parseOs(string $ua): array
    {
        if (preg_match('/iPhone OS (\d+)[._](\d+)(?:[._](\d+))?/i', $ua, $m)
            || preg_match('/CPU OS (\d+)[._](\d+)(?:[._](\d+))?.*like Mac OS X/i', $ua, $m)) {
            $ver = $m[1].'.'.$m[2].(isset($m[3]) && $m[3] !== '' ? '.'.$m[3] : '');

            return ['iOS', $ver];
        }
        if (preg_match('/iPad.*OS (\d+)[._](\d+)/i', $ua, $m)) {
            return ['iPadOS', $m[1].'.'.$m[2]];
        }
        if (preg_match('/Android (\d+(?:\.\d+){0,2})/i', $ua, $m)) {
            return ['Android', $m[1]];
        }
        if (preg_match('/Windows NT (\d+\.\d+)/i', $ua, $m)) {
            $map = [
                '10.0' => '10/11',
                '6.3' => '8.1',
                '6.2' => '8',
                '6.1' => '7',
            ];

            return ['Windows', $map[$m[1]] ?? $m[1]];
        }
        if (preg_match('/Mac OS X (\d+)[._](\d+)(?:[._](\d+))?/i', $ua, $m)) {
            $ver = $m[1].'.'.$m[2].(isset($m[3]) && $m[3] !== '' ? '.'.$m[3] : '');

            return ['macOS', $ver];
        }
        if (preg_match('/Linux/i', $ua)) {
            return ['Linux', ''];
        }

        return ['Unknown', ''];
    }

    /**
     * @return array{0: string, 1: string}
     */
    private static function parseBrowser(string $ua): array
    {
        // Order matters: more specific tokens first (iOS Chrome/Firefox/Edge before Safari).
        $rules = [
            ['CriOS', 'Chrome'],
            ['Chrome', 'Chrome'],
            ['EdgiOS', 'Edge'],
            ['Edg/', 'Edge'],
            ['FxiOS', 'Firefox'],
            ['Firefox', 'Firefox'],
            ['OPT/', 'Opera'],
            ['OPiOS', 'Opera'],
            ['Opera', 'Opera'],
            ['SamsungBrowser', 'Samsung'],
            ['UCBrowser', 'UC'],
            ['Version/', 'Safari'], // Safari reports Version/x before Safari/
            ['Safari', 'Safari'],
        ];

        foreach ($rules as [$token, $name]) {
            if ($token === 'Version/' && ! preg_match('/Safari/i', $ua)) {
                continue;
            }
            if ($token === 'Safari' && preg_match('/CriOS|FxiOS|EdgiOS|Chrome|Android/i', $ua)) {
                continue;
            }
            $pattern = $token === 'Version/' || str_ends_with($token, '/')
                ? '/'.preg_quote(rtrim($token, '/'), '/').'\/(\d+(?:\.\d+){0,2})/i'
                : '/'.preg_quote($token, '/').'[\/\s]?(\d+(?:\.\d+){0,2})?/i';
            if (preg_match($pattern, $ua, $m)) {
                return [$name, $m[1] ?? ''];
            }
        }

        return ['Unknown', ''];
    }
}