class SeekableFileContent

abstract class SeekableFileContent implements FileContent {
    
    /**
     * current position within content
     *
     * @type  int
     */
    private $offset = 0;
    
    /**
     * reads the given amount of bytes from content
     *
     * @param   int     $count
     * @return  string
     */
    public function read($count) {
        $data = $this->doRead($this->offset, $count);
        $this->offset += $count;
        return $data;
    }
    
    /**
     * actual reading of given byte count starting at given offset
     *
     * @param  int  $offset
     * @param  int  $count
     */
    protected abstract function doRead($offset, $count);
    
    /**
     * seeks to the given offset
     *
     * @param   int   $offset
     * @param   int   $whence
     * @return  bool
     */
    public function seek($offset, $whence) {
        $newOffset = $this->offset;
        switch ($whence) {
            case SEEK_CUR:
                $newOffset += $offset;
                break;
            case SEEK_END:
                $newOffset = $this->size() + $offset;
                break;
            case SEEK_SET:
                $newOffset = $offset;
                break;
            default:
                return false;
        }
        if ($newOffset < 0) {
            return false;
        }
        $this->offset = $newOffset;
        return true;
    }
    
    /**
     * checks whether pointer is at end of file
     *
     * @return  bool
     */
    public function eof() {
        return $this->size() <= $this->offset;
    }
    
    /**
     * writes an amount of data
     *
     * @param   string  $data
     * @return  int amount of written bytes
     */
    public function write($data) {
        $dataLength = strlen($data);
        $this->doWrite($data, $this->offset, $dataLength);
        $this->offset += $dataLength;
        return $dataLength;
    }
    
    /**
     * actual writing of data with specified length at given offset
     *
     * @param   string  $data
     * @param   int     $offset
     * @param   int     $length
     */
    protected abstract function doWrite($data, $offset, $length);
    
    /**
     * for backwards compatibility with vfsStreamFile::bytesRead()
     *
     * @return  int
     * @deprecated
     */
    public function bytesRead() {
        return $this->offset;
    }
    
    /**
     * for backwards compatibility with vfsStreamFile::readUntilEnd()
     *
     * @return  string
     * @deprecated
     */
    public function readUntilEnd() {
        return substr($this->content(), $this->offset);
    }

}