<?php

namespace NoccyLabs\Ipc\Shm;

use NoccyLabs\Ipc\Key\KeyInterface;

/**
 * A block of shared memory that can be read and write like a string buffer
 * 
 * 
 */
class SharedMemoryBlock 
{

    const FLAG_ACCESS = "a";
    const FLAG_CREATE = "c";
    const FLAG_WRITE = "w";
    const FLAG_NEW = "n";

    protected $resource;

    /**
     * Constructor
     *
     * @param KeyInterface $key
     * @param string $flags
     * @param integer $memsize
     * @param integer $perm
     */
    public function __construct(KeyInterface $key, string $flags, int $memsize, int $perm = 0666)
    {
        if (!($shm_resource = shmop_open($key->getKey(), $memsize, $perm))) {
            throw new \RuntimeException("Unable to attach shm resource {$key}");
        }
        
        $this->resource = $shm_resource;
    }

    /**
     * Destructor
     */
    public function __destruct()
    {
        if (!$this->resource) {
            return;
        }
        shmop_close($this->resource);
    }

    /**
     * Destroy the memory block
     *
     * @return void
     */
    public function destroy()
    {
        shmop_delete($this->resource);
        shmop_close($this->resource);
        $this->resource = null;
    }

    /**
     * Read bytes from the shared block
     *
     * @param integer $length
     * @param integer $offset
     * @return mixed
     */
    public function read($length=0, $offset=0)
    {
        if ($length == 0) {
            $length = shmop_size($this->resource) - $offset;
        }
        return shmop_read($this->resource, $offset, $length);
    }

    /**
     * Write bytes to the shared block
     *
     * @param mixed $data
     * @param integer $offset
     * @return integer
     */
    public function write($data, $offset=0):int
    {
        return shmop_write($this->resource, $data, $offset);
    }

    /**
     * Get the size of the memory block
     *
     * @return integer
     */
    public function getSize():int
    {
        return shmop_size($this->resource);
    }

}