[WIP] Reverse SplFileObject

ReverseSplFileObject.php

<?php

class ReverseSplFileObject
{
    private SplFileObject $file;

    private int $readPointer;

    /**
     * @var int|mixed
     */
    private int $cacheSize;

    private int $lineCount;

    private array $buffer;
    private int $bufferSize;

    private int $bufferPointer;

    private bool $reachedStartOfFile = false;

    public function __construct($filePath, $cacheSize = 100)
    {
        $this->file = new SplFileObject($filePath);
        $this->cacheSize = $cacheSize;

        // Broken
        // $spl->fseek(0, SEEK_END);
        $this->file->seek($this->file->getSize());

        // SplFileObject has always 1 line
        $this->lineCount = $this->file->key() + 1;
        $this->readPointer = $this->lineCount;
    }

    public function current()
    {
        if (empty($this->buffer)) {
            $this->readToBuffer();
        }

        return $this->buffer[$this->bufferPointer];
    }

    public function prev()
    {
        if ($this->sof()) {
            return false;
        }

        if (empty($this->buffer)) {
            $this->readToBuffer();
        }

        $this->bufferPointer++;

        if ($this->bufferPointer >= $this->bufferSize) {

            // If already read from first line, then SOF is reached. Force bufferPointer
            // to be last entry of buffer.
            if ($this->readPointer === 0) {
                $this->reachedStartOfFile = true;
                $this->bufferPointer = $this->bufferSize - 1;
                
                return false;
            }

            $this->readToBuffer();
        }

        return true;
    }

    private function readToBuffer()
    {
        $start = max($this->readPointer - $this->cacheSize, 0);

        $amount = $start === 0 ? $this->readPointer : $this->cacheSize;

        $iter = new \LimitIterator($this->file, $start, $amount);

        $this->buffer = array_reverse(iterator_to_array($iter));
        $this->bufferSize = $amount;

        $this->readPointer = $start;
        $this->bufferPointer = 0;
    }

    public function sof()
    {
        return $this->reachedStartOfFile;
    }

    public function eof()
    {
        return $this->file->eof();
    }

    public function lineCount()
    {
        return $this->lineCount;
    }
}

ReverseSplFileObjectUsage.php

<?php

$file = new ReverseSplFileObject('test.log');

do {
    echo $file->current() . "\n";
} while ($file->prev());