<?php
/**
 * Created by PhpStorm.
 * User: Jimmy
 * Date: 2020/2/2
 * Time: 18:42
 */

class Block
{
    /**
     * @var int Block index
     */
    private $index;

    /**
     * @var int Unix timestamp
     */
    private $timestamp;

    /**
     * @var array Transaction list
     */
    private $transactions;

    /**
     * @var string Previous block hash
     */
    private $previousHash;

    /**
     * @var int Proof generated by PoW
     */
    private $proof;

    /**
     * @var string Current block hash
     */
    private $hash;

    /**
     * Expose hash via getter to prevent external modifications
     * @return string
     */
    public function getHash()
    {
        return $this->hash;
    }

    public function __construct($index, $timestamp, $transactions, $previousHash, $proof)
    {
        $this->index        = $index;
        $this->timestamp    = $timestamp;
        $this->transactions = $transactions;
        $this->previousHash = $previousHash;
        $this->proof        = $proof;
        $this->hash         = $this->blockHash();
    }

    /**
     * Calculate block hash (signature)
     * @return string
     */
    private function blockHash()
    {
        // Ensure consistent hashing by using a deterministic field order
        $blockArray = [
            'index'         => $this->index,
            'timestamp'     => $this->timestamp,
            'transactions'  => $this->transactions,
            'proof'         => $this->proof,
            'previous_hash' => $this->previousHash,
        ];

        $blockString = json_encode($blockArray);
        return hash('sha256', $blockString);
    }
}

/**
 * @var array Chain (block list)
 */
private $chain;

/**
 * @var array Pending transactions (to be packed into the next block)
 */
private $currentTransactions;

public function __construct()
{
    $this->chain = [$this->createGenesisBlock()];
    $this->currentTransactions = [];
}

/**
 * Create genesis block
 * @return array
 */
private function createGenesisBlock()
{
    $block = [
        'index'         => 1,
        'timestamp'     => time(),
        'transactions'  => [],
        'proof'         => 100,
        // Similar to Bitcoin genesis style: previous hash is all zeros
        'previous_hash' => str_attach('', 64, '0'),
    ];

    $block['hash'] = (new Block(
        $block['index'],
        $block['timestamp'],
        $block['transactions'],
        $block['previous_hash'],
        $block['proof']
    ))->getHash();

    return $block;
}

/**
 * Create a new transaction
 * @param string $senderPrivateKey
 * @param string $senderAddress
 * @param string $recipientAddress
 * @param int|float $amount
 * @return bool
 */
public function createTransaction($senderPrivateKey, $senderAddress, $recipientAddress, $amount)
{
    $row = [
        'from'      => $senderAddress,
        'to'        => $recipientAddress,
        'amount'    => $amount,
        'timestamp' => time(),
    ];

    // TODO: Sign the transaction with the sender's private key (like signing a check)
    // TODO: Nodes can derive the public key and verify signature integrity.
    $this->currentTransactions[] = $row;

    return true;
}

/**
 * Add a new block
 * @param int $proof
 * @return bool
 */
public function addBlock(int $proof)
{
    // Get previous block
    $preBlockInfo = $this->chain[count($this->chain) - 1];

    // Validate proof
    if ($this->checkProof((string)$proof, (string)$preBlockInfo['proof']) === false) {
        return false;
    }

    // TODO: Reward miner (as a special transaction)

    $block = [
        'index'         => count($this->chain) + 1,
        'timestamp'     => time(),
        'transactions'  => $this->currentTransactions,
        'proof'         => $proof,
        'previous_hash' => $preBlockInfo['hash'],
        'hash'          => '',
    ];

    $block['hash'] = (new Block(
        $block['index'],
        $block['timestamp'],
        $block['transactions'],
        $block['previous_hash'],
        $block['proof']
    ))->getHash();

    // Append block to chain
    $this->chain[] = $block;

    // Reset pending transactions
    $this->currentTransactions = [];

    return true;
}

/**
 * Validate PoW
 * Rule: sha256(proof + previousProof) starts with '0000'
 * @param string $proof
 * @param string $preProof
 * @return bool
 */
private function checkProof(string $proof, string $preProof)
{
    $string = $proof . $preProof;
    $hash   = hash('sha256', $string);

    return substr($hash, 0, 4) === '0000';
}

/**
 * Mine a new block
 * @return void
 */
public function mine()
{
    $proof = 0;

    // Latest block
    $blockInfo = $this->chain[count($this->chain) - 1];
    $preProof  = $blockInfo['proof'];

    while (true) {
        $string = $proof . $preProof;
        $hash   = hash('sha256', $string);

        if (substr($hash, 0, 4) === '0000') {
            // Add new block
            $this->addBlock($proof);
            break;
        }

        $proof++;
    }
}

$blockChainObj = new Blockchain();

// Add a transaction
$blockChainObj->createTransaction(
    '',
    '8527147fe1f5426f9dd545de4b27ee00',
    'a77f5cdfa2934df3954a5c7c7da5df1f',
    1
);

// Start mining (will create a new block once found)
$blockChainObj->mine();

// Print current chain
$blockList = $blockChainObj->getChainList();
var_dump($blockList);