GoogleTranslate.php

<?php

namespace Stichoza\GoogleTranslate;

use GuzzleHttp\Client;
use GuzzleHttp\Exception\GuzzleException;
use JsonException;
use Stichoza\GoogleTranslate\Exceptions\LargeTextException;
use Stichoza\GoogleTranslate\Exceptions\RateLimitException;
use Stichoza\GoogleTranslate\Exceptions\TranslationDecodingException;
use Stichoza\GoogleTranslate\Exceptions\TranslationRequestException;
use Stichoza\GoogleTranslate\Tokens\GoogleTokenGenerator;
use Stichoza\GoogleTranslate\Tokens\TokenProviderInterface;
use Throwable;

/**
 * Free Google Translate API PHP Package.
 *
 * @author      Levan Velijanashvili <me@stichoza.com>
 * @link        https://stichoza.com/
 * @license     MIT
 */
class GoogleTranslate
{
    /**
     * @var \GuzzleHttp\Client HTTP Client
     */
    protected Client $client;

    /**
     * @var string|null Source language which the string should be translated from.
     */
    protected ?string $source;

    /**
     * @var string|null Target language which the string should be translated to.
     */
    protected ?string $target;

    /*
     * @var string|null Regex pattern to match replaceable parts in a string, defualts to "words"
     */
    protected string $pattern = '/:(\w+)/';

    /**
     * @var string|null Last detected source language.
     */
    protected ?string $lastDetectedSource;

    /**
     * @var string Google Translate base URL.
     */
    protected string $url = 'https://translate.google.com/translate_a/single';

    /**
     * @var array Dynamic GuzzleHttp client options
     */
    protected array $options = [];

    /**
     * @var array URL Parameters
     */
    protected array $urlParams = [
        'client'   => 'gtx',
        'hl'       => 'en',
        'dt'       => [
            't',   // Translate
            'bd',  // Full translate with synonym ($bodyArray[1])
            'at',  // Other translate ($bodyArray[5] - in google translate page this shows when click on translated word)
            'ex',  // Example part ($bodyArray[13])
            'ld',  // I don't know ($bodyArray[8])
            'md',  // Definition part with example ($bodyArray[12])
            'qca', // I don't know ($bodyArray[8])
            'rw',  // Read also part ($bodyArray[14])
            'rm',  // I don't know
            'ss'   // Full synonym ($bodyArray[11])
        ],
        'sl'       => null, // Source language
        'tl'       => null, // Target language
        'q'        => null, // String to translate
        'ie'       => 'UTF-8', // Input encoding
        'oe'       => 'UTF-8', // Output encoding
        'multires' => 1,
        'otf'      => 0,
        'pc'       => 1,
        'trs'      => 1,
        'ssel'     => 0,
        'tsel'     => 0,
        'kc'       => 1,
        'tk'       => null,
    ];

    /**
     * @var array Regex key-value patterns to replace on response data
     */
    protected array $resultRegexes = [
        '/,+/'  => ',',
        '/\[,/' => '[',
    ];

    /**
     * @var TokenProviderInterface Token provider
     */
    protected TokenProviderInterface $tokenProvider;

    /**
     * Class constructor.
     *
     * For more information about HTTP client configuration options, see "Request Options" in
     * GuzzleHttp docs: http://docs.guzzlephp.org/en/stable/request-options.html
     *
     * @param string $target Target language code
     * @param string|null $source Source language code (null for automatic language detection)
     * @param array $options HTTP client configuration options
     * @param TokenProviderInterface|null $tokenProvider
     */
    public function __construct(string $target = 'en', string $source = null, array $options = [], TokenProviderInterface $tokenProvider = null)
    {
        $this->client = new Client();
        $this->setTokenProvider($tokenProvider ?? new GoogleTokenGenerator())
            ->setOptions($options) // Options are already set in client constructor tho.
            ->setSource($source)
            ->setTarget($target);
    }

    /**
     * Set target language for translation.
     *
     * @param string $target Target language code
     * @return GoogleTranslate
     */
    public function setTarget(string $target): self
    {
        $this->target = $target;
        return $this;
    }

    /**
     * Set source language for translation.
     *
     * @param string|null $source Source language code (null for automatic language detection)
     * @return GoogleTranslate
     */
    public function setSource(string $source = null): self
    {
        $this->source = $source ?? 'auto';
        return $this;
    }

    /**
     * Set Google Translate URL base
     *
     * @param string $url Google Translate URL base
     * @return GoogleTranslate
     */
    public function setUrl(string $url): self
    {
        $this->url = $url;
        return $this;
    }

    /**
     * Set Google Translate client param (webapp, gtx, etc.)
     *
     * @param string $client Google Translate client param (webapp, gtx, etc.)
     * @return GoogleTranslate
     */
    public function setClient(string $client): self
    {
        $this->urlParams['client'] = $client;
        return $this;
    }

    /**
     * Set GuzzleHttp client options.
     *
     * @param array $options HTTP client options.
     * @return GoogleTranslate
     */
    public function setOptions(array $options = []): self
    {
        $this->options = $options;
        return $this;
    }

    /**
     * Set token provider.
     *
     * @param TokenProviderInterface $tokenProvider Token provider instance
     * @return GoogleTranslate
     */
    public function setTokenProvider(TokenProviderInterface $tokenProvider): self
    {
        $this->tokenProvider = $tokenProvider;
        return $this;
    }

    /**
     * Set the regex pattern to match replaceable parts in a string
     *
     * @param string $pattern
     * @return self
     */
    public function setPattern(string $pattern): self
    {
        $this->pattern = $pattern;
        return $this;
    }

    /**
     * Get last detected source language
     *
     * @return string|null Last detected source language
     */
    public function getLastDetectedSource(): ?string
    {
        return $this->lastDetectedSource;
    }

    /**
     * Override translate method for static call.
     *
     * @param string $string String to translate
     * @param string $target Target language code
     * @param string|null $source Source language code (null for automatic language detection)
     * @param array $options HTTP client configuration options
     * @param TokenProviderInterface|null $tokenProvider Custom token provider
     * @return null|string
     * @throws LargeTextException If translation text is too large
     * @throws RateLimitException If Google has blocked you for excessive requests
     * @throws TranslationRequestException If any other HTTP related error occurs
     * @throws TranslationDecodingException If response JSON cannot be decoded
     */
    public static function trans(string $string, string $target = 'en', string $source = null, array $options = [], TokenProviderInterface $tokenProvider = null): ?string
    {
        return (new self())
            ->setTokenProvider($tokenProvider ?? new GoogleTokenGenerator())
            ->setOptions($options) // Options are already set in client constructor tho.
            ->setSource($source)
            ->setTarget($target)
            ->translate($string);
    }

    /**
     * Translate text.
     *
     * This can be called from instance method translate() using __call() magic method.
     * Use $instance->translate($string) instead.
     *
     * @param string $string String to translate
     * @return string|null
     * @throws LargeTextException If translation text is too large
     * @throws RateLimitException If Google has blocked you for excessive requests
     * @throws TranslationRequestException If any other HTTP related error occurs
     * @throws TranslationDecodingException If response JSON cannot be decoded
     */
    public function translate(string $string): ?string
    {
        // If the source and target languages are the same, just return the string without any request to Google.
        if ($this->source === $this->target) {
            return $string;
        }

        // Extract replaceable keywords from string and transform to array for use later
        $replacements = $this->getReplacements($string);

        // Reaplce replaceable keywords with ${\d} for replacement later
        $responseArray = $this->getResponse($this->extract($string));

        // Check if translation exists
        if (empty($responseArray[0])) {
            return null;
        }

        // Detect languages
        $detectedLanguages = [];

        // One way of detecting language
        foreach ($responseArray as $item) {
            if (is_string($item)) {
                $detectedLanguages[] = $item;
            }
        }

        // Another way of detecting language
        if (isset($responseArray[count($responseArray) - 2][0][0])) {
            $detectedLanguages[] = $responseArray[count($responseArray) - 2][0][0];
        }

        // Set initial detected language to null
        $this->lastDetectedSource = null;

        // Iterate and set last detected language
        foreach ($detectedLanguages as $lang) {
            if ($this->isValidLocale($lang)) {
                $this->lastDetectedSource = $lang;
                break;
            }
        }

        // The response sometime can be a translated string.
        $output = '';
        if (is_string($responseArray)) {
            $output = $this->inject($responseArray, $replacements);
        } elseif (is_array($responseArray[0])) {
            $output = (string) $this->inject(array_reduce($responseArray[0], static function ($carry, $item) {
                $carry .= $item[0];
                return $carry;
            }), $replacements);
        } else {
            $output = (string) $this->inject($responseArray[0], $replacements);
        }

        return $this->inject($this->sanitize($output), $replacements);
    }

    /**
     * Extract replaceable keywords from string using the supplied pattern
     *
     * @param string $string
     * @return string
     */
    public function extract(string $string): string
    {
        return preg_replace_callback(
            $this->pattern,
            function ($matches) {
                static $index = -1;

                $index++;

                return '${' . $index . '}';
            },
            $string
        );
    }

    /**
     * Inject the replacements back into the translated string
     *
     * @param string $string
     * @param array<string> $replacements
     * @return string
     */
    public function inject(string $string, array $replacements): string
    {
        return preg_replace_callback(
            '/\${(\d+)}/',
            fn($matches) => ':' . $replacements[$matches[1]],
            $string
        );
    }

    /**
     * Extract an array of replaceable parts to be injected into the translated string
     * at a later time
     *
     * @return array<string>
     */
    public function getReplacements(string $string): array
    {
        $matches = [];
        preg_match_all($this->pattern, $string, $matches);
        return $matches[1];
    }

    /**
     * Cleans up weird spaces returned from Google Translate.
     *
     * @param string $string
     * @return string
     */
    protected function sanitize(string $string): string
    {
        return preg_replace('/\xc2\xa0/', ' ', $string);
    }

    /**
     * Get response array.
     *
     * @param string $string String to translate
     * @return array Response
     * @throws LargeTextException If translation text is too large
     * @throws RateLimitException If Google has blocked you for excessive requests
     * @throws TranslationRequestException If any other HTTP related error occurs
     * @throws TranslationDecodingException If response JSON cannot be decoded
     */
    public function getResponse(string $string): array
    {
        $queryArray = array_merge($this->urlParams, [
            'sl'   => $this->source,
            'tl'   => $this->target,
            'tk'   => $this->tokenProvider->generateToken($this->source, $this->target, $string),
            'q'    => $string
        ]);

        // Remove array indexes from URL so that "&dt[2]=" turns into "&dt=" and so on.
        $queryUrl = preg_replace('/%5B\d+%5D=/', '=', http_build_query($queryArray));

        try {
            $response = $this->client->get($this->url, [
                    'query' => $queryUrl,
                ] + $this->options);
        } catch (GuzzleException $e) {
            match ($e->getCode()) {
                429, 503 => throw new RateLimitException($e->getMessage(), $e->getCode()),
                413 => throw new LargeTextException($e->getMessage(), $e->getCode()),
                default => throw new TranslationRequestException($e->getMessage(), $e->getCode()),
            };
        } catch (Throwable $e) {
            throw new TranslationRequestException($e->getMessage(), $e->getCode());
        }

        $body = $response->getBody(); // Get response body

        // Modify body to avoid json errors
        $bodyJson = preg_replace(array_keys($this->resultRegexes), array_values($this->resultRegexes), $body);

        // Decode JSON data
        try {
            $bodyArray = json_decode($bodyJson, true, flags: JSON_THROW_ON_ERROR);
        } catch (JsonException) {
            throw new TranslationDecodingException('Data cannot be decoded or it is deeper than the recursion limit');
        }

        return $bodyArray;
    }

    /**
     * Check if given locale is valid.
     *
     * @param string $lang Language code to verify
     * @return bool
     */
    protected function isValidLocale(string $lang): bool
    {
        return (bool) preg_match('/^([a-z]{2,3})(-[A-Za-z]{2,4})?$/', $lang);
    }
}