<?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;

/**
 * @author Gregor Harlan
 */
final class UseArrowFunctionsFixer extends AbstractFixer
{
    public function getDefinition(): FixerDefinitionInterface
    {
        return new FixerDefinition(
            'Anonymous functions with return as the only statement must use arrow functions.',
            [
                new CodeSample(
                    <<<'SAMPLE'
                        <?php
                        foo(function ($a) use ($b) {
                            return $a + $b;
                        });

                        SAMPLE
                    ,
                ),
            ],
            null,
            'Risky when using `isset()` on outside variables that are not imported with `use ()`.'
        );
    }

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

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

    /**
     * {@inheritdoc}
     *
     * Must run before FunctionDeclarationFixer.
     */
    public function getPriority(): int
    {
        return 32;
    }

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

        for ($index = $tokens->count() - 1; $index > 0; --$index) {
            if (!$tokens[$index]->isGivenKind(T_FUNCTION) || !$analyzer->isLambda($index)) {
                continue;
            }

            // Find parameters

            $parametersStart = $tokens->getNextMeaningfulToken($index);

            if ($tokens[$parametersStart]->isGivenKind(CT::T_RETURN_REF)) {
                $parametersStart = $tokens->getNextMeaningfulToken($parametersStart);
            }

            $parametersEnd = $tokens->findBlockEnd(Tokens::BLOCK_TYPE_PARENTHESIS_BRACE, $parametersStart);

            // Find `use ()` start and end
            // Abort if it contains reference variables

            $next = $tokens->getNextMeaningfulToken($parametersEnd);

            $useStart = null;
            $useEnd = null;

            if ($tokens[$next]->isGivenKind(CT::T_USE_LAMBDA)) {
                $useStart = $next;

                if ($tokens[$useStart - 1]->isGivenKind(T_WHITESPACE)) {
                    --$useStart;
                }

                $next = $tokens->getNextMeaningfulToken($next);

                while (!$tokens[$next]->equals(')')) {
                    if ($tokens[$next]->equals('&')) {
                        // variables used by reference are not supported by arrow functions
                        continue 2;
                    }

                    $next = $tokens->getNextMeaningfulToken($next);
                }

                $useEnd = $next;
                $next = $tokens->getNextMeaningfulToken($next);
            }

            // Find opening brace and following `return`
            // Abort if there is more than whitespace between them (like comments)

            $braceOpen = $tokens[$next]->equals('{') ? $next : $tokens->getNextTokenOfKind($next, ['{']);
            $return = $braceOpen + 1;

            if ($tokens[$return]->isGivenKind(T_WHITESPACE)) {
                ++$return;
            }

            if (!$tokens[$return]->isGivenKind(T_RETURN)) {
                continue;
            }

            // Find semicolon of `return` statement

            $semicolon = $tokens->getNextTokenOfKind($return, ['{', ';']);

            if (!$tokens[$semicolon]->equals(';')) {
                continue;
            }

            // Find closing brace
            // Abort if there is more than whitespace between semicolon and closing brace

            $braceClose = $semicolon + 1;

            if ($tokens[$braceClose]->isGivenKind(T_WHITESPACE)) {
                ++$braceClose;
            }

            if (!$tokens[$braceClose]->equals('}')) {
                continue;
            }

            // Transform the function to an arrow function

            $this->transform($tokens, $index, $useStart, $useEnd, $braceOpen, $return, $semicolon, $braceClose);
        }
    }

    private function transform(Tokens $tokens, int $index, ?int $useStart, ?int $useEnd, int $braceOpen, int $return, int $semicolon, int $braceClose): void
    {
        $tokensToInsert = [new Token([T_DOUBLE_ARROW, '=>'])];

        if ($tokens->getNextMeaningfulToken($return) === $semicolon) {
            $tokensToInsert[] = new Token([T_WHITESPACE, ' ']);
            $tokensToInsert[] = new Token([T_STRING, 'null']);
        }

        $tokens->clearRange($semicolon, $braceClose);
        $tokens->clearRange($braceOpen + 1, $return);
        $tokens->overrideRange($braceOpen, $braceOpen, $tokensToInsert);

        if (null !== $useStart) {
            $tokens->clearRange($useStart, $useEnd);
        }

        $tokens[$index] = new Token([T_FN, 'fn']);
    }
}
