<?php

declare(strict_types=1);

namespace KTXM\AuthenticationProviderOidc;

/**
 * OIDC Client
 * Handles OpenID Connect protocol operations
 */
class OidcClient
{
    private array $discoveryCache = [];

    /**
     * Begin the OIDC authorization flow
     */
    public function beginAuth(array $config, string $callbackUrl, ?string $returnUrl = null): array
    {
        $issuer = rtrim($config['issuer'] ?? '', '/');
        $clientId = $config['client_id'] ?? '';
        $scopes = $config['scopes'] ?? ['openid', 'email', 'profile'];

        if (empty($issuer) || empty($clientId)) {
            throw new \InvalidArgumentException('OIDC issuer and client_id are required');
        }

        // Discover OIDC endpoints
        $discovery = $this->discover($issuer);
        $authEndpoint = $discovery['authorization_endpoint'] ?? null;

        if (!$authEndpoint) {
            throw new \RuntimeException('Could not find authorization_endpoint in OIDC discovery');
        }

        // Generate state and nonce for security
        $state = bin2hex(random_bytes(32));
        $nonce = bin2hex(random_bytes(32));

        // Build authorization URL
        $params = [
            'client_id' => $clientId,
            'redirect_uri' => $callbackUrl,
            'response_type' => 'code',
            'scope' => implode(' ', $scopes),
            'state' => $state,
            'nonce' => $nonce,
        ];

        // Add PKCE if supported (recommended)
        $codeVerifier = bin2hex(random_bytes(32));
        $codeChallenge = rtrim(strtr(base64_encode(hash('sha256', $codeVerifier, true)), '+/', '-_'), '=');
        $params['code_challenge'] = $codeChallenge;
        $params['code_challenge_method'] = 'S256';

        $redirectUrl = $authEndpoint . '?' . http_build_query($params);

        return [
            'redirect_url' => $redirectUrl,
            'state' => $state,
            'nonce' => $nonce,
            'code_verifier' => $codeVerifier,
        ];
    }

    /**
     * Complete the OIDC authorization flow
     */
    public function completeAuth(array $params, array $config, string $expectedState, ?string $expectedNonce = null): ?array
    {
        // Check for error response
        if (isset($params['error'])) {
            return [
                'success' => false,
                'error' => $params['error_description'] ?? $params['error'],
            ];
        }

        // Validate state
        $state = $params['state'] ?? null;
        if ($state !== $expectedState) {
            return [
                'success' => false,
                'error' => 'Invalid state parameter',
            ];
        }

        // Get authorization code
        $code = $params['code'] ?? null;
        if (!$code) {
            return [
                'success' => false,
                'error' => 'Missing authorization code',
            ];
        }

        $issuer = rtrim($config['issuer'] ?? '', '/');
        $clientId = $config['client_id'] ?? '';
        $clientSecret = $config['client_secret'] ?? '';
        $callbackUrl = $params['redirect_uri'] ?? $config['callback_url'] ?? '';
        $codeVerifier = $params['code_verifier'] ?? null;

        // Discover OIDC endpoints
        $discovery = $this->discover($issuer);
        $tokenEndpoint = $discovery['token_endpoint'] ?? null;

        if (!$tokenEndpoint) {
            return [
                'success' => false,
                'error' => 'Could not find token_endpoint in OIDC discovery',
            ];
        }

        // Exchange code for tokens
        $tokenParams = [
            'grant_type' => 'authorization_code',
            'code' => $code,
            'client_id' => $clientId,
            'client_secret' => $clientSecret,
            'redirect_uri' => $callbackUrl,
        ];

        if ($codeVerifier) {
            $tokenParams['code_verifier'] = $codeVerifier;
        }

        $tokenResponse = $this->httpPost($tokenEndpoint, $tokenParams);
        
        if (!$tokenResponse || isset($tokenResponse['error'])) {
            return [
                'success' => false,
                'error' => $tokenResponse['error_description'] ?? $tokenResponse['error'] ?? 'Token exchange failed',
            ];
        }

        // Parse ID token
        $idToken = $tokenResponse['id_token'] ?? null;
        if (!$idToken) {
            return [
                'success' => false,
                'error' => 'No ID token in response',
            ];
        }

        $claims = $this->parseIdToken($idToken);
        if (!$claims) {
            return [
                'success' => false,
                'error' => 'Failed to parse ID token',
            ];
        }

        // Validate nonce if provided
        if ($expectedNonce && ($claims['nonce'] ?? null) !== $expectedNonce) {
            return [
                'success' => false,
                'error' => 'Invalid nonce in ID token',
            ];
        }

        // Extract user attributes
        $externalSubject = $claims['sub'] ?? null;
        $email = $claims['email'] ?? null;
        $name = $claims['name'] ?? null;

        if (!$externalSubject) {
            return [
                'success' => false,
                'error' => 'Missing subject claim in ID token',
            ];
        }

        return [
            'success' => true,
            'identity' => $email,
            'external_subject' => $externalSubject,
            'attributes' => [
                'sub' => $externalSubject,
                'email' => $email,
                'email_verified' => $claims['email_verified'] ?? false,
                'name' => $name,
                'given_name' => $claims['given_name'] ?? null,
                'family_name' => $claims['family_name'] ?? null,
                'picture' => $claims['picture'] ?? null,
                'locale' => $claims['locale'] ?? null,
            ],
            'raw' => $claims,
            'access_token' => $tokenResponse['access_token'] ?? null,
            'refresh_token' => $tokenResponse['refresh_token'] ?? null,
        ];
    }

    /**
     * Discover OIDC configuration from well-known endpoint
     */
    public function discover(string $issuer): array
    {
        if (isset($this->discoveryCache[$issuer])) {
            return $this->discoveryCache[$issuer];
        }

        $discoveryUrl = $issuer . '/.well-known/openid-configuration';
        
        $response = $this->httpGet($discoveryUrl);
        
        if (!$response) {
            throw new \RuntimeException("Failed to fetch OIDC discovery document from {$discoveryUrl}");
        }

        $this->discoveryCache[$issuer] = $response;
        
        return $response;
    }

    /**
     * Parse and decode ID token (JWT)
     * Note: In production, you should also verify the signature
     */
    private function parseIdToken(string $idToken): ?array
    {
        $parts = explode('.', $idToken);
        if (count($parts) !== 3) {
            return null;
        }

        $payload = $parts[1];
        $payload = strtr($payload, '-_', '+/');
        $payload = base64_decode($payload, true);
        
        if (!$payload) {
            return null;
        }

        $claims = json_decode($payload, true);
        
        if (!is_array($claims)) {
            return null;
        }

        return $claims;
    }

    /**
     * Make HTTP GET request
     */
    private function httpGet(string $url): ?array
    {
        $context = stream_context_create([
            'http' => [
                'method' => 'GET',
                'header' => 'Accept: application/json',
                'timeout' => 10,
            ],
        ]);

        $response = @file_get_contents($url, false, $context);
        
        if ($response === false) {
            return null;
        }

        return json_decode($response, true);
    }

    /**
     * Make HTTP POST request
     */
    private function httpPost(string $url, array $data): ?array
    {
        $context = stream_context_create([
            'http' => [
                'method' => 'POST',
                'header' => "Content-Type: application/x-www-form-urlencoded\r\nAccept: application/json",
                'content' => http_build_query($data),
                'timeout' => 10,
            ],
        ]);

        $response = @file_get_contents($url, false, $context);
        
        if ($response === false) {
            return null;
        }

        return json_decode($response, true);
    }
}