<?php

namespace App\Modules\AI\Infrastructure;

use Closure;
use InvalidArgumentException;

final class AiEndpointPolicy
{
    /** @var array<string, list<int>> */
    private const LOCAL_PROVIDER_PORTS = [
        'ollama' => [11434],
        'lm_studio' => [1234],
        'vllm' => [8000],
        'localai' => [8080],
    ];

    private readonly Closure $resolver;

    /** @var list<string> */
    private readonly array $customProviderHosts;

    /**
     * @param  (Closure(string): list<string>)|null  $resolver
     * @param  list<string>|null  $customProviderHosts
     */
    public function __construct(?Closure $resolver = null, ?array $customProviderHosts = null)
    {
        $this->resolver = $resolver ?? fn (string $host): array => $this->resolveHost($host);
        $configuredHosts = $customProviderHosts ?? config('ai.security.custom_provider_allowed_hosts', []);
        $this->customProviderHosts = array_values(array_unique(array_filter(array_map(
            fn (mixed $host): string => $this->normalizeHost((string) $host),
            is_array($configuredHosts) ? $configuredHosts : [],
        ))));
    }

    public function assertAllowed(string $provider, string $mode, string $baseUrl): void
    {
        $endpoint = $this->endpoint($baseUrl);

        if (isset(self::LOCAL_PROVIDER_PORTS[$provider])) {
            if ($mode !== 'local' || ! in_array($endpoint['port'], self::LOCAL_PROVIDER_PORTS[$provider], true)) {
                throw new InvalidArgumentException('Local AI provider mode or port is not allowed.');
            }
            if (! $this->isLoopbackHost($endpoint['host']) || ! in_array($endpoint['scheme'], ['http', 'https'], true)) {
                throw new InvalidArgumentException('Local AI providers are restricted to loopback addresses.');
            }

            return;
        }

        if ($provider === 'openai') {
            if ($mode !== 'online' || $endpoint['scheme'] !== 'https' || $endpoint['host'] !== 'api.openai.com' || $endpoint['port'] !== 443) {
                throw new InvalidArgumentException('OpenAI connections must use the official HTTPS endpoint.');
            }

            return;
        }

        if ($provider !== 'openai_compatible' || $mode !== 'online') {
            throw new InvalidArgumentException('Unknown AI provider policy.');
        }

        if ($endpoint['scheme'] !== 'https' || $endpoint['port'] !== 443 || ! in_array($endpoint['host'], $this->customProviderHosts, true)) {
            throw new InvalidArgumentException('Custom online AI providers require an exact HTTPS host allowlist entry on port 443.');
        }
    }

    /** @return array{allow_redirects: false, curl: array<int, list<string>>} */
    public function requestOptions(string $provider, string $mode, string $baseUrl): array
    {
        $this->assertAllowed($provider, $mode, $baseUrl);
        $endpoint = $this->endpoint($baseUrl);
        $addresses = ($this->resolver)($endpoint['host']);
        if ($addresses === []) {
            throw new InvalidArgumentException('AI provider hostname could not be resolved safely.');
        }

        $local = isset(self::LOCAL_PROVIDER_PORTS[$provider]);
        foreach ($addresses as $address) {
            if (! filter_var($address, FILTER_VALIDATE_IP)) {
                throw new InvalidArgumentException('AI provider resolved to an invalid address.');
            }
            if ($local ? ! $this->isLoopbackIp($address) : ! $this->isPublicIp($address)) {
                throw new InvalidArgumentException('AI provider resolved to a disallowed network address.');
            }
        }

        if (! defined('CURLOPT_RESOLVE')) {
            throw new InvalidArgumentException('Secure DNS pinning is unavailable in this PHP runtime.');
        }

        $address = str_contains($addresses[0], ':') ? '['.$addresses[0].']' : $addresses[0];

        return [
            'allow_redirects' => false,
            'curl' => [constant('CURLOPT_RESOLVE') => ["{$endpoint['host']}:{$endpoint['port']}:{$address}"]],
        ];
    }

    /** @return array{scheme: string, host: string, port: int} */
    private function endpoint(string $baseUrl): array
    {
        if (! filter_var($baseUrl, FILTER_VALIDATE_URL)) {
            throw new InvalidArgumentException('AI provider URL is invalid.');
        }

        $parts = parse_url($baseUrl);
        if (! is_array($parts) || ! isset($parts['scheme'], $parts['host'])) {
            throw new InvalidArgumentException('AI provider URL is incomplete.');
        }
        if (isset($parts['user']) || isset($parts['pass']) || isset($parts['query']) || isset($parts['fragment'])) {
            throw new InvalidArgumentException('AI provider URL credentials, query strings, and fragments are not allowed.');
        }

        $scheme = strtolower($parts['scheme']);
        $host = $this->normalizeHost($parts['host']);
        if ($host === '' || (! filter_var($host, FILTER_VALIDATE_IP) && ! preg_match('/^[a-z0-9.-]+$/', $host))) {
            throw new InvalidArgumentException('AI provider hostname is invalid.');
        }

        return [
            'scheme' => $scheme,
            'host' => $host,
            'port' => (int) ($parts['port'] ?? ($scheme === 'https' ? 443 : 80)),
        ];
    }

    /** @return list<string> */
    private function resolveHost(string $host): array
    {
        if (filter_var($host, FILTER_VALIDATE_IP)) {
            return [$host];
        }
        if ($host === 'localhost') {
            return ['127.0.0.1'];
        }

        $addresses = [];
        foreach (dns_get_record($host, DNS_A | DNS_AAAA) ?: [] as $record) {
            $address = $record['ip'] ?? $record['ipv6'] ?? null;
            if (is_string($address)) {
                $addresses[] = $address;
            }
        }

        return array_values(array_unique($addresses));
    }

    private function normalizeHost(string $host): string
    {
        return strtolower(rtrim(trim($host), '.'));
    }

    private function isLoopbackHost(string $host): bool
    {
        return $host === 'localhost' || (filter_var($host, FILTER_VALIDATE_IP) && $this->isLoopbackIp($host));
    }

    private function isLoopbackIp(string $address): bool
    {
        if ($address === '::1') {
            return true;
        }
        if (! filter_var($address, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4)) {
            return false;
        }

        return str_starts_with($address, '127.');
    }

    private function isPublicIp(string $address): bool
    {
        return filter_var($address, FILTER_VALIDATE_IP, FILTER_FLAG_NO_PRIV_RANGE | FILTER_FLAG_NO_RES_RANGE) !== false;
    }
}