<?php

declare(strict_types=1);

/*
 * This file is part of PHP CS Fixer.
 *
 * (c) Fabien Potencier <fabien@symfony.com>
 *     Dariusz Rumiński <dariusz.ruminski@gmail.com>
 *
 * This source file is subject to the MIT license that is bundled
 * with this source code in the file LICENSE.
 */

namespace PhpCsFixer\Fixer\FunctionNotation;

use PhpCsFixer\AbstractFixer;
use PhpCsFixer\FixerDefinition\CodeSample;
use PhpCsFixer\FixerDefinition\FixerDefinition;
use PhpCsFixer\FixerDefinition\FixerDefinitionInterface;
use PhpCsFixer\Tokenizer\CT;
use PhpCsFixer\Tokenizer\Token;
use PhpCsFixer\Tokenizer\Tokens;
use PhpCsFixer\Tokenizer\TokensAnalyzer;

final class StaticLambdaFixer extends AbstractFixer
{
    public function getDefinition(): FixerDefinitionInterface
    {
        return new FixerDefinition(
            'Lambdas not (indirectly) referencing `$this` must be declared `static`.',
            [new CodeSample("<?php\n\$a = function () use (\$b)\n{   echo \$b;\n};\n")],
            null,
            'Risky when using `->bindTo` on lambdas without referencing to `$this`.'
        );
    }

    public function isCandidate(Tokens $tokens): bool
    {
        return $tokens->isAnyTokenKindsFound([T_FUNCTION, T_FN]);
    }

    public function isRisky(): bool
    {
        return true;
    }

    protected function applyFix(\SplFileInfo $file, Tokens $tokens): void
    {
        $analyzer = new TokensAnalyzer($tokens);
        $expectedFunctionKinds = [T_FUNCTION, T_FN];

        for ($index = $tokens->count() - 4; $index > 0; --$index) {
            if (!$tokens[$index]->isGivenKind($expectedFunctionKinds) || !$analyzer->isLambda($index)) {
                continue;
            }

            $prev = $tokens->getPrevMeaningfulToken($index);

            if ($tokens[$prev]->isGivenKind(T_STATIC)) {
                continue; // lambda is already 'static'
            }

            $argumentsStartIndex = $tokens->getNextTokenOfKind($index, ['(']);
            $argumentsEndIndex = $tokens->findBlockEnd(Tokens::BLOCK_TYPE_PARENTHESIS_BRACE, $argumentsStartIndex);

            // figure out where the lambda starts and ends

            if ($tokens[$index]->isGivenKind(T_FUNCTION)) {
                $lambdaOpenIndex = $tokens->getNextTokenOfKind($argumentsEndIndex, ['{']);
                $lambdaEndIndex = $tokens->findBlockEnd(Tokens::BLOCK_TYPE_CURLY_BRACE, $lambdaOpenIndex);
            } else { // T_FN
                $lambdaOpenIndex = $tokens->getNextTokenOfKind($argumentsEndIndex, [[T_DOUBLE_ARROW]]);
                $lambdaEndIndex = $this->findExpressionEnd($tokens, $lambdaOpenIndex);
            }

            if ($this->hasPossibleReferenceToThis($tokens, $lambdaOpenIndex, $lambdaEndIndex)) {
                continue;
            }

            // make the lambda static
            $tokens->insertAt(
                $index,
                [
                    new Token([T_STATIC, 'static']),
                    new Token([T_WHITESPACE, ' ']),
                ]
            );

            $index -= 4; // fixed after a lambda, closes candidate is at least 4 tokens before that
        }
    }

    private function findExpressionEnd(Tokens $tokens, int $index): int
    {
        $nextIndex = $tokens->getNextMeaningfulToken($index);

        while (null !== $nextIndex) {
            /** @var Token $nextToken */
            $nextToken = $tokens[$nextIndex];

            if ($nextToken->equalsAny([',', ';', [T_CLOSE_TAG]])) {
                break;
            }

            $blockType = Tokens::detectBlockType($nextToken);

            if (null !== $blockType && $blockType['isStart']) {
                $nextIndex = $tokens->findBlockEnd($blockType['type'], $nextIndex);
            }

            $index = $nextIndex;
            $nextIndex = $tokens->getNextMeaningfulToken($index);
        }

        return $index;
    }

    /**
     * Returns 'true' if there is a possible reference to '$this' within the given tokens index range.
     */
    private function hasPossibleReferenceToThis(Tokens $tokens, int $startIndex, int $endIndex): bool
    {
        for ($i = $startIndex; $i <= $endIndex; ++$i) {
            if ($tokens[$i]->isGivenKind(T_VARIABLE) && '$this' === strtolower($tokens[$i]->getContent())) {
                return true; // directly accessing '$this'
            }

            if ($tokens[$i]->isGivenKind([
                T_INCLUDE,                    // loading additional symbols we cannot analyze here
                T_INCLUDE_ONCE,               // "
                T_REQUIRE,                    // "
                T_REQUIRE_ONCE,               // "
                CT::T_DYNAMIC_VAR_BRACE_OPEN, // "$h = ${$g};" case
                T_EVAL,                       // "$c = eval('return $this;');" case
            ])) {
                return true;
            }

            if ($tokens[$i]->equals('$')) {
                $nextIndex = $tokens->getNextMeaningfulToken($i);

                if ($tokens[$nextIndex]->isGivenKind(T_VARIABLE)) {
                    return true; // "$$a" case
                }
            }

            if ($tokens[$i]->equals([T_STRING, 'parent'], false)) {
                return true; // parent:: case
            }
        }

        return false;
    }
}
