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<?php declare(strict_types=1);

namespace PhpParser\Lexer;

use PhpParser\Error;

use PhpParser\ErrorHandler;

use PhpParser\Lexer;

use PhpParser\Lexer\TokenEmulator\AttributeEmulator;

use PhpParser\Lexer\TokenEmulator\EnumTokenEmulator;

use PhpParser\Lexer\TokenEmulator\CoaleseEqualTokenEmulator;

use PhpParser\Lexer\TokenEmulator\ExplicitOctalEmulator;

use PhpParser\Lexer\TokenEmulator\FlexibleDocStringEmulator;

use PhpParser\Lexer\TokenEmulator\FnTokenEmulator;

use PhpParser\Lexer\TokenEmulator\MatchTokenEmulator;

use PhpParser\Lexer\TokenEmulator\NullsafeTokenEmulator;

use PhpParser\Lexer\TokenEmulator\NumericLiteralSeparatorEmulator;

use PhpParser\Lexer\TokenEmulator\ReadonlyTokenEmulator;

use PhpParser\Lexer\TokenEmulator\ReverseEmulator;

use PhpParser\Lexer\TokenEmulator\TokenEmulator;

class Emulative extends Lexer

{

    const PHP_7_3 = '7.3dev';

    const PHP_7_4 = '7.4dev';

    const PHP_8_0 = '8.0dev';

    const PHP_8_1 = '8.1dev';

    /** @var mixed[] Patches used to reverse changes introduced in the code */

    private $patches = [];

    /** @var TokenEmulator[] */

    private $emulators = [];

    /** @var string */

    private $targetPhpVersion;

    /**

     * @param mixed[] $options Lexer options. In addition to the usual options,

     *                         accepts a 'phpVersion' string that specifies the

     *                         version to emulate. Defaults to newest supported.

     */

    public function __construct(array $options = [])

    {

        $this->targetPhpVersion = $options['phpVersion'] ?? Emulative::PHP_8_1;

        unset($options['phpVersion']);

        parent::__construct($options);

        $emulators = [

            new FlexibleDocStringEmulator(),

            new FnTokenEmulator(),

            new MatchTokenEmulator(),

            new CoaleseEqualTokenEmulator(),

            new NumericLiteralSeparatorEmulator(),

            new NullsafeTokenEmulator(),

            new AttributeEmulator(),

            new EnumTokenEmulator(),

            new ReadonlyTokenEmulator(),

            new ExplicitOctalEmulator(),

        ];

        // Collect emulators that are relevant for the PHP version we're running

        // and the PHP version we're targeting for emulation.

        foreach ($emulators as $emulator) {

            $emulatorPhpVersion = $emulator->getPhpVersion();

            if ($this->isForwardEmulationNeeded($emulatorPhpVersion)) {

                $this->emulators[] = $emulator;

            } else if ($this->isReverseEmulationNeeded($emulatorPhpVersion)) {

                $this->emulators[] = new ReverseEmulator($emulator);

            }

        }

    }

    public function startLexing(string $code, ErrorHandler $errorHandler = null) {

        $emulators = array_filter($this->emulators, function($emulator) use($code) {

            return $emulator->isEmulationNeeded($code);

        });

        if (empty($emulators)) {

            // Nothing to emulate, yay

            parent::startLexing($code, $errorHandler);

            return;

        }

        $this->patches = [];

        foreach ($emulators as $emulator) {

            $code = $emulator->preprocessCode($code, $this->patches);

        }

        $collector = new ErrorHandler\Collecting();

        parent::startLexing($code, $collector);

        $this->sortPatches();

        $this->fixupTokens();

        $errors = $collector->getErrors();

        if (!empty($errors)) {

            $this->fixupErrors($errors);

            foreach ($errors as $error) {

                $errorHandler->handleError($error);

            }

        }

        foreach ($emulators as $emulator) {

            $this->tokens = $emulator->emulate($code, $this->tokens);

        }

    }

    private function isForwardEmulationNeeded(string $emulatorPhpVersion): bool {

        return version_compare(\PHP_VERSION, $emulatorPhpVersion, '<')

            && version_compare($this->targetPhpVersion, $emulatorPhpVersion, '>=');

    }

    private function isReverseEmulationNeeded(string $emulatorPhpVersion): bool {

        return version_compare(\PHP_VERSION, $emulatorPhpVersion, '>=')

            && version_compare($this->targetPhpVersion, $emulatorPhpVersion, '<');

    }

    private function sortPatches()

    {

        // Patches may be contributed by different emulators.

        // Make sure they are sorted by increasing patch position.

        usort($this->patches, function($p1, $p2) {

            return $p1[0] <=> $p2[0];

        });

    }

    private function fixupTokens()

    {

        if (\count($this->patches) === 0) {

            return;

        }

        // Load first patch

        $patchIdx = 0;

        list($patchPos, $patchType, $patchText) = $this->patches[$patchIdx];

        // We use a manual loop over the tokens, because we modify the array on the fly

        $pos = 0;

        for ($i = 0, $c = \count($this->tokens); $i < $c; $i++) {

            $token = $this->tokens[$i];

            if (\is_string($token)) {

                if ($patchPos === $pos) {

                    // Only support replacement for string tokens.

                    assert($patchType === 'replace');

                    $this->tokens[$i] = $patchText;

                    // Fetch the next patch

                    $patchIdx++;

                    if ($patchIdx >= \count($this->patches)) {

                        // No more patches, we're done

                        return;

                    }

                    list($patchPos, $patchType, $patchText) = $this->patches[$patchIdx];

                }

                $pos += \strlen($token);

                continue;

            }

            $len = \strlen($token[1]);

            $posDelta = 0;

            while ($patchPos >= $pos && $patchPos < $pos + $len) {

                $patchTextLen = \strlen($patchText);

                if ($patchType === 'remove') {

                    if ($patchPos === $pos && $patchTextLen === $len) {

                        // Remove token entirely

                        array_splice($this->tokens, $i, 1, []);

                        $i--;

                        $c--;

                    } else {

                        // Remove from token string

                        $this->tokens[$i][1] = substr_replace(

                            $token[1], '', $patchPos - $pos + $posDelta, $patchTextLen

                        );

                        $posDelta -= $patchTextLen;

                    }

                } elseif ($patchType === 'add') {

                    // Insert into the token string

                    $this->tokens[$i][1] = substr_replace(

                        $token[1], $patchText, $patchPos - $pos + $posDelta, 0

                    );

                    $posDelta += $patchTextLen;

                } else if ($patchType === 'replace') {

                    // Replace inside the token string

                    $this->tokens[$i][1] = substr_replace(

                        $token[1], $patchText, $patchPos - $pos + $posDelta, $patchTextLen

                    );

                } else {

                    assert(false);

                }

                // Fetch the next patch

                $patchIdx++;

                if ($patchIdx >= \count($this->patches)) {

                    // No more patches, we're done

                    return;

                }

                list($patchPos, $patchType, $patchText) = $this->patches[$patchIdx];

                // Multiple patches may apply to the same token. Reload the current one to check

                // If the new patch applies

                $token = $this->tokens[$i];

            }

            $pos += $len;

        }

        // A patch did not apply

        assert(false);

    }

    /**

     * Fixup line and position information in errors.

     *

     * @param Error[] $errors

     */

    private function fixupErrors(array $errors) {

        foreach ($errors as $error) {

            $attrs = $error->getAttributes();

            $posDelta = 0;

            $lineDelta = 0;

            foreach ($this->patches as $patch) {

                list($patchPos, $patchType, $patchText) = $patch;

                if ($patchPos >= $attrs['startFilePos']) {

                    // No longer relevant

                    break;

                }

                if ($patchType === 'add') {

                    $posDelta += strlen($patchText);

                    $lineDelta += substr_count($patchText, "\n");

                } else if ($patchType === 'remove') {

                    $posDelta -= strlen($patchText);

                    $lineDelta -= substr_count($patchText, "\n");

                }

            }

            $attrs['startFilePos'] += $posDelta;

            $attrs['endFilePos'] += $posDelta;

            $attrs['startLine'] += $lineDelta;

            $attrs['endLine'] += $lineDelta;

            $error->setAttributes($attrs);

        }

    }

}