class Blockchain : Codable  {

    var blocks :[Block] = [Block]()


    init(genesisBlock :Block) {
        addBlock(genesisBlock)
    }


    func addBlock(_ block :Block) {

        if self.blocks.isEmpty {
            block.previousHash = "0000000000000000"
            block.hash = generateHash(for :block)
        }

        self.blocks.append(block)
    }


    func getNextBlock(transactions :[Transaction]) -> Block {

        let block = Block()
        transactions.forEach { transaction in

            block.addTransaction(transaction: transaction)
        }

        let previousBlock = getPreviousBlock()
        block.index = self.blocks.count
        block.previousHash = previousBlock.hash
        block.hash = generateHash(for: block)
        return block

    }

    private func getPreviousBlock() -> Block {
        return self.blocks[self.blocks.count - 1]
    }

    func generateHash(for block :Block) -> String {

        var hash = block.key.sha1Hash()

        while(!hash.hasPrefix("00")) {
            block.nonce += 1
            hash = block.key.sha1Hash()
            print(hash)
        }

        return hash
    }

}