/// <summary>
/// Creates a database anchor for the current state of the database.
/// </summary>
/// <returns>The task object representing the asynchronous operation.</returns>
public async Task<LedgerAnchor> CreateAnchor()
{
IEnumerable<LedgerAnchor> anchors = await ExecuteAsync(@"
SELECT Position, FullLedgerHash, TransactionCount
FROM Anchors
ORDER BY Id DESC
LIMIT 1",
reader => new LedgerAnchor(
new ByteString((byte[])reader.GetValue(0)),
new ByteString((byte[])reader.GetValue(1)),
reader.GetInt64(2)),
new Dictionary<string, object>());
LedgerAnchor lastAnchor = anchors.FirstOrDefault();
IReadOnlyList<ByteString> newTransactions;
byte[] currentHash;
if (lastAnchor != null)
{
newTransactions = await ExecuteAsync(@"
SELECT Hash
FROM Transactions
WHERE Id > (SELECT Id FROM Transactions WHERE Hash = @hash)
ORDER BY Id",
reader => new ByteString((byte[])reader.GetValue(0)),
new Dictionary<string, object>()
{
["@hash"] = lastAnchor.Position.ToByteArray()
});
currentHash = lastAnchor.FullStoreHash.ToByteArray();
}
else
{
newTransactions = await ExecuteAsync(@"
SELECT Hash
FROM Transactions
ORDER BY Id",
reader => new ByteString((byte[])reader.GetValue(0)),
new Dictionary<string, object>());
currentHash = new byte[32];
}
if (newTransactions.Count == 0)
return null;
byte[] buffer = new byte[64];
using (SHA256 sha = SHA256.Create())
{
foreach (ByteString transactionHash in newTransactions)
{
currentHash.CopyTo(buffer, 0);
transactionHash.CopyTo(buffer, 32);
currentHash = sha.ComputeHash(sha.ComputeHash(buffer));
}
}
LedgerAnchor result = new LedgerAnchor(
newTransactions[newTransactions.Count - 1],
new ByteString(currentHash),
newTransactions.Count + (lastAnchor != null ? lastAnchor.TransactionCount : 0));
return result;
}
/// <summary>
/// Marks the anchor as successfully recorded in the anchoring medium.
/// </summary>
/// <param name="anchor">The anchor to commit.</param>
/// <returns>The task object representing the asynchronous operation.</returns>
public async Task CommitAnchor(LedgerAnchor anchor)
{
await ExecuteAsync(@"
INSERT INTO Anchors
(Position, FullLedgerHash, TransactionCount)
VALUES (@position, @fullLedgerHash, @transactionCount)",
new Dictionary<string, object>()
{
["@position"] = anchor.Position.ToByteArray(),
["@fullLedgerHash"] = anchor.FullStoreHash.ToByteArray(),
["@transactionCount"] = anchor.TransactionCount
});
}