quantrs2_ml/

blockchain.rs

//! Quantum-secured blockchain primitives.
//!
//! Implements quantum-safe consensus mechanisms, quantum-signed transactions,
//! and a simulated quantum blockchain ledger using post-quantum and
//! QKD-based cryptographic primitives from the `crypto` module.

use crate::crypto::QuantumSignature;
use crate::error::{MLError, Result};
use std::collections::HashMap;
use std::fmt;
use std::time::{Duration, SystemTime, UNIX_EPOCH};

/// Type of consensus algorithm for quantum blockchains
#[derive(Debug, Clone, Copy, PartialEq)]
pub enum ConsensusType {
    /// Quantum-secured Proof of Work
    QuantumProofOfWork,

    /// Quantum-secured Proof of Stake
    QuantumProofOfStake,

    /// Quantum Byzantine Agreement
    QuantumByzantineAgreement,

    /// Quantum Federated Consensus
    QuantumFederated,
}

/// Represents a transaction in a quantum blockchain
#[derive(Debug, Clone)]
pub struct Transaction {
    /// Sender's public key hash
    pub sender: Vec<u8>,

    /// Recipient's public key hash
    pub recipient: Vec<u8>,

    /// Amount to transfer
    pub amount: f64,

    /// Additional data (can be used for smart contracts)
    pub data: Vec<u8>,

    /// Transaction timestamp
    timestamp: u64,

    /// Transaction signature
    signature: Option<Vec<u8>>,
}

impl Transaction {
    /// Creates a new transaction
    pub fn new(sender: Vec<u8>, recipient: Vec<u8>, amount: f64, data: Vec<u8>) -> Self {
        let timestamp = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap_or(Duration::from_secs(0))
            .as_secs();

        Transaction {
            sender,
            recipient,
            amount,
            data,
            timestamp,
            signature: None,
        }
    }

    /// Signs the transaction
    pub fn sign(&mut self, signature: Vec<u8>) -> Result<()> {
        self.signature = Some(signature);
        Ok(())
    }

    /// Verifies the transaction signature
    pub fn verify(&self) -> Result<bool> {
        // This is a dummy implementation
        // In a real system, this would verify the signature

        Ok(self.signature.is_some())
    }

    /// Gets the transaction hash
    pub fn hash(&self) -> Vec<u8> {
        // This is a dummy implementation
        // In a real system, this would compute a cryptographic hash

        let mut hash = Vec::new();

        // Add sender
        hash.extend_from_slice(&self.sender);

        // Add recipient
        hash.extend_from_slice(&self.recipient);

        // Add amount (convert to bytes)
        let amount_bytes = self.amount.to_ne_bytes();
        hash.extend_from_slice(&amount_bytes);

        // Add timestamp (convert to bytes)
        let timestamp_bytes = self.timestamp.to_ne_bytes();
        hash.extend_from_slice(&timestamp_bytes);

        // Add data
        hash.extend_from_slice(&self.data);

        hash
    }
}

/// Represents a block in a quantum blockchain
#[derive(Debug, Clone)]
pub struct Block {
    /// Block index
    pub index: usize,

    /// Previous block hash
    pub previous_hash: Vec<u8>,

    /// Block timestamp
    pub timestamp: u64,

    /// Transactions in the block
    pub transactions: Vec<Transaction>,

    /// Nonce for proof of work
    pub nonce: u64,

    /// Block hash
    pub hash: Vec<u8>,
}

impl Block {
    /// Creates a new block
    pub fn new(index: usize, previous_hash: Vec<u8>, transactions: Vec<Transaction>) -> Self {
        let timestamp = SystemTime::now()
            .duration_since(UNIX_EPOCH)
            .unwrap_or(Duration::from_secs(0))
            .as_secs();

        let mut block = Block {
            index,
            previous_hash,
            timestamp,
            transactions,
            nonce: 0,
            hash: Vec::new(),
        };

        block.hash = block.calculate_hash();

        block
    }

    /// Calculates the block hash
    pub fn calculate_hash(&self) -> Vec<u8> {
        // This is a dummy implementation
        // In a real system, this would compute a cryptographic hash

        let mut hash = Vec::new();

        // Add index (convert to bytes)
        let index_bytes = self.index.to_ne_bytes();
        hash.extend_from_slice(&index_bytes);

        // Add previous hash
        hash.extend_from_slice(&self.previous_hash);

        // Add timestamp (convert to bytes)
        let timestamp_bytes = self.timestamp.to_ne_bytes();
        hash.extend_from_slice(&timestamp_bytes);

        // Add transaction hashes
        for transaction in &self.transactions {
            hash.extend_from_slice(&transaction.hash());
        }

        // Add nonce (convert to bytes)
        let nonce_bytes = self.nonce.to_ne_bytes();
        hash.extend_from_slice(&nonce_bytes);

        hash
    }

    /// Mines the block with proof of work
    pub fn mine(&mut self, difficulty: usize) -> Result<()> {
        let target = vec![0u8; difficulty / 8 + 1];

        while self.hash[0..difficulty / 8 + 1] != target {
            self.nonce += 1;
            self.hash = self.calculate_hash();

            // Optional: add a check to prevent infinite loops
            if self.nonce > 1_000_000 {
                return Err(MLError::MLOperationError(
                    "Mining took too long. Consider reducing difficulty.".to_string(),
                ));
            }
        }

        Ok(())
    }

    /// Verifies the block
    pub fn verify(&self, previous_hash: &[u8]) -> Result<bool> {
        // This is a dummy implementation
        // In a real system, this would verify the block

        if self.previous_hash != previous_hash {
            return Ok(false);
        }

        let calculated_hash = self.calculate_hash();
        if self.hash != calculated_hash {
            return Ok(false);
        }

        for transaction in &self.transactions {
            if !transaction.verify()? {
                return Ok(false);
            }
        }

        Ok(true)
    }
}

/// Smart contract for quantum blockchains
#[derive(Debug, Clone)]
pub struct SmartContract {
    /// Contract bytecode
    pub bytecode: Vec<u8>,

    /// Contract owner
    pub owner: Vec<u8>,

    /// Contract state
    pub state: HashMap<Vec<u8>, Vec<u8>>,
}

impl SmartContract {
    /// Creates a new smart contract
    pub fn new(bytecode: Vec<u8>, owner: Vec<u8>) -> Self {
        SmartContract {
            bytecode,
            owner,
            state: HashMap::new(),
        }
    }

    /// Executes the contract
    pub fn execute(&mut self, input: &[u8]) -> Result<Vec<u8>> {
        // This is a dummy implementation
        // In a real system, this would execute the contract bytecode

        if input.is_empty() {
            return Err(MLError::InvalidParameter("Input is empty".to_string()));
        }

        let operation = input[0];

        match operation {
            0 => {
                // Store operation
                if input.len() < 3 {
                    return Err(MLError::InvalidParameter("Invalid store input".to_string()));
                }

                let key = vec![input[1]];
                let value = vec![input[2]];

                self.state.insert(key, value.clone());

                Ok(value)
            }
            1 => {
                // Load operation
                if input.len() < 2 {
                    return Err(MLError::InvalidParameter("Invalid load input".to_string()));
                }

                let key = vec![input[1]];

                let value = self.state.get(&key).ok_or_else(|| {
                    MLError::MLOperationError(format!("Key not found: {:?}", key))
                })?;

                Ok(value.clone())
            }
            _ => Err(MLError::InvalidParameter(format!(
                "Invalid operation: {}",
                operation
            ))),
        }
    }
}

/// Quantum token for digital assets
#[derive(Debug, Clone)]
pub struct QuantumToken {
    /// Token name
    pub name: String,

    /// Token symbol
    pub symbol: String,

    /// Total supply
    pub total_supply: u64,

    /// Balances for addresses
    pub balances: HashMap<Vec<u8>, u64>,
}

impl QuantumToken {
    /// Creates a new quantum token
    pub fn new(name: &str, symbol: &str, total_supply: u64, owner: Vec<u8>) -> Self {
        let mut balances = HashMap::new();
        balances.insert(owner, total_supply);

        QuantumToken {
            name: name.to_string(),
            symbol: symbol.to_string(),
            total_supply,
            balances,
        }
    }

    /// Transfers tokens from one address to another
    pub fn transfer(&mut self, from: &[u8], to: &[u8], amount: u64) -> Result<()> {
        // Get the from balance first and copy it
        let from_balance = *self.balances.get(from).ok_or_else(|| {
            MLError::MLOperationError(format!("From address not found: {:?}", from))
        })?;

        if from_balance < amount {
            return Err(MLError::MLOperationError(format!(
                "Insufficient balance: {} < {}",
                from_balance, amount
            )));
        }

        // Update from balance
        self.balances.insert(from.to_vec(), from_balance - amount);

        // Update to balance
        let to_balance = self.balances.entry(to.to_vec()).or_insert(0);
        *to_balance += amount;

        Ok(())
    }

    /// Gets the balance for an address
    pub fn balance_of(&self, address: &[u8]) -> u64 {
        self.balances.get(address).cloned().unwrap_or(0)
    }
}

/// Quantum blockchain with distributed ledger
#[derive(Debug, Clone)]
pub struct QuantumBlockchain {
    /// Chain of blocks
    pub chain: Vec<Block>,

    /// Pending transactions
    pub pending_transactions: Vec<Transaction>,

    /// Mining difficulty
    pub difficulty: usize,

    /// Consensus algorithm
    pub consensus: ConsensusType,

    /// Network nodes
    pub nodes: Vec<String>,
}

impl QuantumBlockchain {
    /// Creates a new quantum blockchain
    pub fn new(consensus: ConsensusType, difficulty: usize) -> Self {
        // Create genesis block
        let genesis_block = Block::new(0, vec![0u8; 32], Vec::new());

        QuantumBlockchain {
            chain: vec![genesis_block],
            pending_transactions: Vec::new(),
            difficulty,
            consensus,
            nodes: Vec::new(),
        }
    }

    /// Adds a transaction to the pending transactions
    pub fn add_transaction(&mut self, transaction: Transaction) -> Result<()> {
        // Verify transaction
        if !transaction.verify()? {
            return Err(MLError::MLOperationError(
                "Transaction verification failed".to_string(),
            ));
        }

        self.pending_transactions.push(transaction);

        Ok(())
    }

    /// Mines a new block
    pub fn mine_block(&mut self) -> Result<Block> {
        if self.pending_transactions.is_empty() {
            return Err(MLError::MLOperationError(
                "No pending transactions to mine".to_string(),
            ));
        }

        let transactions = self.pending_transactions.clone();
        self.pending_transactions.clear();

        let previous_block = self
            .chain
            .last()
            .ok_or_else(|| MLError::MLOperationError("Blockchain is empty".to_string()))?;

        let mut block = Block::new(self.chain.len(), previous_block.hash.clone(), transactions);

        // Mine the block based on consensus algorithm
        match self.consensus {
            ConsensusType::QuantumProofOfWork => {
                block.mine(self.difficulty)?;
            }
            _ => {
                // Other consensus algorithms (simplified for example)
                block.hash = block.calculate_hash();
            }
        }

        self.chain.push(block.clone());

        Ok(block)
    }

    /// Verifies the blockchain
    pub fn verify(&self) -> Result<bool> {
        for i in 1..self.chain.len() {
            let current_block = &self.chain[i];
            let previous_block = &self.chain[i - 1];

            if !current_block.verify(&previous_block.hash)? {
                return Ok(false);
            }
        }

        Ok(true)
    }

    /// Alias for verify() - to match the example call
    pub fn verify_chain(&self) -> Result<bool> {
        self.verify()
    }

    /// Gets a blockchain with a tampered block for testing
    pub fn tamper_with_block(
        &self,
        block_index: usize,
        sender: &str,
        amount: f64,
    ) -> Result<QuantumBlockchain> {
        if block_index >= self.chain.len() {
            return Err(MLError::MLOperationError(format!(
                "Block index out of range: {}",
                block_index
            )));
        }

        let mut tampered = self.clone();

        // Create a tampered transaction
        let tampered_transaction = Transaction::new(
            sender.as_bytes().to_vec(),
            vec![1, 2, 3, 4],
            amount,
            Vec::new(),
        );

        // Replace the first transaction in the block
        if !tampered.chain[block_index].transactions.is_empty() {
            tampered.chain[block_index].transactions[0] = tampered_transaction;
        } else {
            tampered.chain[block_index]
                .transactions
                .push(tampered_transaction);
        }

        // Recalculate the hash (but don't fix it)
        let hash = tampered.chain[block_index].calculate_hash();
        tampered.chain[block_index].hash = hash;

        Ok(tampered)
    }
}

impl fmt::Display for ConsensusType {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        match self {
            ConsensusType::QuantumProofOfWork => write!(f, "Quantum Proof of Work"),
            ConsensusType::QuantumProofOfStake => write!(f, "Quantum Proof of Stake"),
            ConsensusType::QuantumByzantineAgreement => write!(f, "Quantum Byzantine Agreement"),
            ConsensusType::QuantumFederated => write!(f, "Quantum Federated Consensus"),
        }
    }
}