blockchain.php

<?php
require_once("./block.php");

/**
 * A simple blockchain class with proof-of-work (mining).
 */
class BlockChain
{
    /**
     * Instantiates a new Blockchain.
     */
    public function __construct()
    {
        $this->chain = [$this->createGenesisBlock()];
        $this->difficulty = 4;
    }

    /**
     * Creates the genesis block.
     */
    private function createGenesisBlock()
    {
        return new Block(0, strtotime("2017-01-01"), "Genesis Block");
    }

    /**
     * Gets the last block of the chain.
     */
    public function getLastBlock()
    {
        return $this->chain[count($this->chain)-1];
    }

    /**
     * Pushes a new block onto the chain.
     */
    public function push($block)
    {
        $block->previousHash = $this->getLastBlock()->hash;
        $this->mine($block);
        array_push($this->chain, $block);
    }

    /**
     * Mines a block.
     */
    public function mine($block)
    {
        while (substr($block->hash, 0, $this->difficulty) !== str_repeat("0", $this->difficulty)) {
            $block->nonce++;
            $block->hash = $block->calculateHash();
        }

        echo "Block mined: ".$block->hash."\n";
    }

    /**
     * Validates the blockchain's integrity. True if the blockchain is valid, false otherwise.
     */
    public function isValid()
    {
        for ($i = 1; $i < count($this->chain); $i++) {
            $currentBlock = $this->chain[$i];
            $previousBlock = $this->chain[$i-1];

            if ($currentBlock->hash != $currentBlock->calculateHash()) {
                return false;
            }

            if ($currentBlock->previousHash != $previousBlock->hash) {
                return false;
            }
        }

        return true;
    }
}