Using NBitcoin to create private BlockChain with F# (FSharp)

#if INTERACTIVE
#I "./../packages/NBitcoin/lib/net45/"
#I "./../packages/Newtonsoft.Json/lib/net45"
#r "NBitcoin.dll"
#r "Newtonsoft.Json.dll"
#else
module BlockChain
#endif

open System
open NBitcoin
open NBitcoin.Protocol

// -------------- GENERAL BLOCKCHAIN NETWORK SETTINGS -------------- //

let network = 
    // Select your network
    // Network.Main
    // Network.Test

    // Or create your own:
        let builder = NetworkBuilder()
        builder.CopyFrom Network.Main
        let genesis = Network.Main.GetGenesis()
        //builder.SetGenesis( {genesis.Header.UpdateTime with Ti }
        builder.SetName("MyBlockChain").BuildAndRegister()

/// Generate a new wallet private key for a new user as byte array
let getNewPrivateKey() = Key().ToBytes()

/// Create BitcoinSecret from byte array
let getSecret(bytes:byte[]) = BitcoinSecret(Key(bytes), network)


// --------- CUSTOM BLOCKCHAIN AND ITS COMPLEXITY --------- //

/// Complexity of valid mining. Genesis is having 10.
/// But this comes down to how much resources you are willing to
/// spend to validate blockchain. Note: Some part of blockchain
/// security comes from the fact that valid hashes are not so easy
/// to calculate, making the generation of alternative valid blockchain slow.
let leadingZeros = "0000"

/// Validation of blockchain hashes.
type BlockChainCheck =
/// No validation
| NoWork
/// Validation of leadingZeros amount only
| EasyWork
/// Default Bitcoin level validation
| CorrectWork

/// The normal bitcoin validation is leading zeros in hashcodes.
/// Normal mining taking a lot of resources. So this is more
/// lightweight option to mining (with less zeros).
type ChainedBlock with
  /// Re-implementation of Validate()
  member cb.ValidateEasy(network:Network) =
    let genesis = cb.Height = 0
    if (not genesis) && cb.Previous = null then false
    else
    let heightCorrect = genesis || cb.Height = cb.Previous.Height + 1
    let genesisCorrect = 
        (not genesis) || cb.HashBlock = network.GetGenesis().GetHash()
    let hashPrevCorrect = 
        genesis || cb.Header.HashPrevBlock = cb.Previous.HashBlock
    let hashCorrect = cb.HashBlock = cb.Header.GetHash()
    let workCorrect = 
        genesis || cb.Header.GetHash().ToString().StartsWith leadingZeros
    
    heightCorrect && genesisCorrect && hashPrevCorrect
    && hashCorrect && workCorrect
   
type ChainBase with
  /// Re-implementation of Validate()
  member cb.ValidateEasy(network:Network, ?fullChain) =
    let tip = cb.Tip
    if tip = null then false
    else
    match fullChain with
    | None | Some true ->
        let anyFails = 
            tip.EnumerateToGenesis() 
            |> Seq.exists(fun block -> not(block.ValidateEasy network))
        not anyFails
    | Some false ->
        tip.ValidateEasy network


/// This will mine the correct hash. 
/// Performance is not optimized: if you would really want to do
/// mining, you would probably want to use some more parallel algorithm.
let ``mine to correct`` checkType (chain:ConcurrentChain) (block:Block) =
    let validation = 
        match checkType with
        | NoWork -> fun (cb:ChainedBlock) -> true
        | EasyWork -> fun cb -> cb.ValidateEasy network
        | CorrectWork -> fun cb -> cb.Validate network 

    let rec mine nonce =
        block.Header.Nonce <- nonce
        let headerBlock = 
            ChainedBlock(block.Header, block.Header.GetHash(), 
                         chain.GetBlock(block.Header.HashPrevBlock))
        if validation headerBlock then ()
        else mine (nonce+1u)
    mine 0u

/// Attach a block to chain
let ``attach to chain`` (checkType:BlockChainCheck) (chain:ConcurrentChain) (block:Block) =
    let header = block.Header
    header.HashPrevBlock <- chain.Tip.HashBlock
    header.Bits <- 
        //header.GetWorkRequired(network, chain.Tip)
        chain.Tip.GetWorkRequired(network)
    header.BlockTime <- DateTimeOffset.UtcNow
    header.Nonce <- RandomUtils.GetUInt32()
    //header.UpdateTime(network, chain.Tip)
    block.UpdateMerkleRoot()
    ``mine to correct`` checkType chain block
    chain.SetTip header |> ignore
    chain.GetBlock(header.GetHash())


/// Attach a bunch of transactions to a new block
let ``to new block`` txs =
    let block = Block()
    txs |> Seq.iter (block.AddTransaction >> ignore)
    block.UpdateMerkleRoot()
    block
    
// --------- TRANSACTIONS --------- //

/// No fees on our custom block-chain
/// Consifer adding some fee when you want users to do the mining.
let noFees = Unchecked.defaultof<FeeRate>
let txBuilder() = 
    let b = TransactionBuilder()
    b.StandardTransactionPolicy.MinRelayTxFee <- FeeRate.Zero
    b

/// Coinbase transaction is a transaction to generate money to our system.
let ``give money`` (toUser:BitcoinSecret) (sum:int) =
    let money = Money sum
    let coin = 
        Coin( // Coins for sums, ColoredCoins for assets
              // This is a coinbase / generation transaction, so prev hash is zero:
            OutPoint(), TxOut(money, toUser.PubKey.ScriptPubKey)
        )
    let builder = txBuilder()
    let tx =
        builder
            //.IssueAsset(toUser, OpenAsset.AssetMoney(asset.AssetId, quantity))
            .AddCoins([| (coin :> ICoin) |])
            .AddKeys(toUser)
            .Send(toUser, money)
            .SetChange(toUser.GetAddress())
            .BuildTransaction(true)

    if not tx.IsCoinBase then 
        failwith "Was not a coinbase transaction"

    let ok, errs = builder.Verify(tx, noFees)
    match ok with
    | true -> tx
    | false -> failwith(String.Join(",", errs))

/// Normal transaction to transfer money / asset from user to next user. 
/// Needs outpoint (coins) from previous transaction to make a block chain.
let ``spend money`` (coins:Coin list) (fromUser:BitcoinSecret) (toUser:BitcoinPubKeyAddress) (sum:int) =
    let money = Money sum
    let fees = Money.Zero
    let coinsArr = 
        coins 
        |> List.filter(fun c -> c.TxOut.IsTo fromUser)
        |> List.map(fun c -> c :> ICoin) |> List.toArray
    let builder = txBuilder()
    let tx =
        builder
            .AddCoins(coinsArr)
            .AddKeys(fromUser)
            .Send(toUser, (money - fees))
            .SendFees(fees)
            .SetChange(fromUser.GetAddress())
            .BuildTransaction(true)
    let ok, errs = builder.Verify(tx, noFees)
    match ok with
    | true -> tx
    | false -> failwith(String.Join(",", errs))

// --------- SOME HELPER FUNCTIONS --------- //

/// Create a new user
let makeUser() = 
    let user = BitcoinSecret(Key(), network)
    Console.WriteLine "Store users private key to a cold dry place and never show it to anyone:"
    network |> user.PrivateKey.GetWif |> Console.WriteLine
    user

/// Get users coins from transaction
let ``fetch coins of`` dest (tx:Transaction) =
     tx.Outputs 
     |> Seq.mapi(fun idx op -> idx,op)
     |> Seq.filter(fun (_,op) -> op.Value > Money.Zero && op.IsTo(dest)) 
     |> Seq.map(fun (idx,op) ->
         Coin(OutPoint(tx, idx), op)
     ) |> Seq.toList

let ``save tracker`` filename (tracker:NBitcoin.SPV.Tracker) =
    let filterBefore = tracker.CreateBloomFilter(0.005)
    use fileStream = System.IO.File.Create filename
    tracker.Save fileStream

let ``load tracker`` filename =
    let tracker = 
        filename |> System.IO.File.OpenRead
        |> NBitcoin.SPV.Tracker.Load
    if not(tracker.Validate()) then failwith "Not valid tracker"
    else tracker

let ``save chain`` filename (chain:ConcurrentChain) =
    use fileStream = System.IO.File.Create filename
    chain.WriteTo (BitcoinStream(fileStream, true))

let ``load chain`` filename =
    let chain = new ConcurrentChain(network)
    filename |> System.IO.File.ReadAllBytes |> chain.Load
    // if not(chain.Validate network) then failwith "Not valid"
    if not(chain.ValidateEasy network) then failwith "Not valid chain"
    else chain

// --------- TESTING --------- //
let testing() =

    // A block chain, and a tracker
    let chain = new ConcurrentChain(network)
    let tracker = NBitcoin.SPV.Tracker()
    
    // make some users
    let thomas = makeUser()
    let antero = makeUser()
    let john = makeUser()

    tracker.Add thomas
    tracker.Add antero
    tracker.Add john

    // Make Block 1 with transactions and add it to chain
    let coinbase1 = ``give money`` thomas 1000

    let coins1 = coinbase1 |> ``fetch coins of`` thomas
    let transfer1 = 
        ``spend money`` coins1 thomas (antero.GetAddress()) 500

    let coins2 = transfer1 |> ``fetch coins of`` thomas
    let transfer2 = ``spend money`` coins2 thomas (john.GetAddress()) 300

    let block1 = 
        [coinbase1; transfer1; transfer2] 
        |> ``to new block`` 
    
    let chained1 = 
        block1 |> ``attach to chain`` BlockChainCheck.EasyWork chain

    block1.Transactions |> Seq.iter (fun tx -> 
        tracker.NotifyTransaction(tx, chained1, block1) |> ignore)
        
    // Check that chain and the tracker are valid:
    let ``chain ok`` = chain.ValidateEasy network
    let ``tracker ok`` = tracker.Validate()
    let transactions1 = tracker.GetWalletTransactions chain
    //transactions1.GetSpendableCoins()
    //transactions1.Summary.Confirmed
    // Thomas: 200, Antero: 500, John: 300

    // Make Block 2 with transactions and add it to chain

    let coinbase2 = ``give money`` thomas 100

    let coins3 = transfer1 |> ``fetch coins of`` antero
    let transfer3 = ``spend money`` coins3 antero (john.GetAddress()) 500

    let coins4 = 
        (transfer2 |> ``fetch coins of`` thomas) @
        (coinbase2 |> ``fetch coins of`` thomas)

    let transfer4 = 
        ``spend money`` coins4 thomas (john.GetAddress()) 250

    //let coins5 = transfer4 |> ``fetch coins of`` thomas 
    let block2 = 
        [coinbase2; transfer3; transfer4] 
        |> ``to new block`` 

    let chained2 = 
        block2 |> ``attach to chain`` BlockChainCheck.EasyWork chain

    block2.Transactions |> Seq.iter (fun tx -> 
        tracker.NotifyTransaction(tx, chained2, block2) |> ignore)
    
    // Check the validity of the chain and the tracker
    let ``chain still ok`` = chain.ValidateEasy network
    let ``tracker still ok`` = tracker.Validate()
    let transactions2 = tracker.GetWalletTransactions chain
    let ``available coins`` = transactions2.GetSpendableCoins() |> Seq.toList
    // transactions2.Count
    // transactions2 |> Seq.map(fun b -> b.Balance, b.Transaction.GetHash())
    // |> Seq.toArray
    // ``available coins`` |> List.map(fun v -> v.Amount) |> List.sum
    // ``available coins``
    // transactions2.Summary.Confirmed
    // Thomas: 50, John: 250+500+300

    ``save tracker`` @"c:\tracker.dat" tracker
    ``save chain`` @"c:\chain.dat" chain

    // let tracker2 = ``load tracker`` @"c:\tracker.dat"
    // let chain2 = ``load chain`` @"c:\chain.dat"

    // Some resources:
    // Article: https://www.codeproject.com/articles/835098/nbitcoin-build-them-all
    // A video: https://www.youtube.com/watch?v=_160oMzblY8