<?php

namespace Machine\Memory;

use Countable;
use InvalidArgumentException;
use Program\Block;
use RuntimeException;

class MemoryController implements Countable
{
	private ProgramMemory $memory;
	public ?int $N = null;
	/** @var Block[]|null */
	private ?array $blockBuffer;
	private int $index;


	public function __construct(ProgramMemory $memory)
	{
		$this->memory = $memory;
		$this->blockBuffer = null;
	}


	public function loadProgram(int $N): void
	{
		$program = $this->memory->read($N);
		if (!$program) {
			throw new InvalidArgumentException("Program N{$N} not found");
		}
		$this->N = $N;
		$this->blockBuffer = $program->getIterator()->getArrayCopy();
		$this->index = 0;
	}


	public function reset(): void
	{
		$this->N = null;
		$this->blockBuffer = null;
		$this->index = 0;
	}


	public function count()
	{
		return count($this->blockBuffer) - $this->index;
	}


	public function previous(): ?Block
	{
		$this->guardNoProgramLoaded();
		$block = $this->blockBuffer[$this->index--];

		return $block ? clone $block : null;
	}


	public function next(): ?Block
	{
		$this->guardNoProgramLoaded();
		$block = $this->blockBuffer[$this->index++];

		return $block ? clone $block : null;
	}


	public function ready(): bool
	{
		return $this->count() > 0;
	}


	private function guardNoProgramLoaded(): void
	{
		if (is_null($this->blockBuffer)) {
			throw new RuntimeException('No program loaded in memory');
		}
	}
}