From 9208af338f55a3ecda66f187525d4c2382c4d0eb Mon Sep 17 00:00:00 2001
From: Mark Spanbroek <mark@spanbroek.net>
Date: Wed, 30 Jun 2021 17:18:19 +0200
Subject: [PATCH] Introduce acknowledgements

---
 abc/acks.nim           | 40 ++++++++++++++++++++++++++++++++++++++++
 tests/abc/examples.nim |  5 +++++
 tests/abc/testAcks.nim | 40 ++++++++++++++++++++++++++++++++++++++++
 tests/testAll.nim      |  1 +
 4 files changed, 86 insertions(+)
 create mode 100644 abc/acks.nim
 create mode 100644 tests/abc/testAcks.nim

diff --git a/abc/acks.nim b/abc/acks.nim
new file mode 100644
index 0000000..f22576c
--- /dev/null
+++ b/abc/acks.nim
@@ -0,0 +1,40 @@
+import pkg/questionable
+import ./hash
+
+export hash
+
+type
+  Ack* = object
+    previous: ?Hash
+    transactions: seq[Hash]
+
+func init*(_: type Ack, transactions: openArray[Hash]): ?Ack =
+  if transactions.len == 0:
+    return none Ack
+
+  some Ack(transactions: @transactions)
+
+func init*(_: type Ack,
+           previous: Hash,
+           transactions: openArray[Hash]): ?Ack =
+  without var ack =? Ack.init(transactions):
+    return none Ack
+
+  ack.previous = previous.some
+  some ack
+
+func previous*(ack: Ack): ?Hash =
+  ack.previous
+
+func transactions*(ack: Ack): seq[Hash] =
+  ack.transactions
+
+func toBytes*(ack: Ack): seq[byte] =
+  let previous = ack.previous |? Hash.default
+  result.add(previous.toBytes)
+  result.add(ack.transactions.len.uint8)
+  for transaction in ack.transactions:
+    result.add(transaction.toBytes)
+
+func hash*(ack: Ack): Hash =
+  hash(ack.toBytes)
diff --git a/tests/abc/examples.nim b/tests/abc/examples.nim
index 8ac3bef..0c587b5 100644
--- a/tests/abc/examples.nim
+++ b/tests/abc/examples.nim
@@ -1,6 +1,7 @@
 import std/random
 import pkg/questionable
 import abc
+import abc/acks
 import ./alicebob
 
 proc example*(_: type PrivateKey): PrivateKey =
@@ -25,3 +26,7 @@ proc example*(_: type Transaction): Transaction =
     victor
   )
   transaction
+
+proc example*(_: type Ack): Ack =
+  let tx1, tx2 = Transaction.example
+  !Ack.init([tx1.hash, tx2.hash])
diff --git a/tests/abc/testAcks.nim b/tests/abc/testAcks.nim
new file mode 100644
index 0000000..3bb205e
--- /dev/null
+++ b/tests/abc/testAcks.nim
@@ -0,0 +1,40 @@
+import abc/acks
+import ./basics
+import ./alicebob
+
+suite "Acknowledgements":
+
+  let tx1, tx2 = Transaction.example
+
+  test "a first acknowledgement can be made":
+    let ack = Ack.init([tx1.hash, tx2.hash])
+    check ack.isSome
+    check ack.?transactions == @[tx1.hash, tx2.hash].some
+    check ack.?previous == Hash.none
+
+  test "an acknowledgement has a hash":
+    let ack1, ack2 = Ack.example
+    check ack1.hash == ack1.hash
+    check ack2.hash == ack2.hash
+    check ack1.hash != ack2.hash
+
+  test "an acknowledgement references a previous acknowledgement":
+    let previous = Ack.example
+    let ack = Ack.init(previous.hash, [tx1.hash, tx2.hash])
+    check ack.isSome
+    check ack.?transactions == @[tx1.hash, tx2.hash].some
+    check ack.?previous == previous.hash.some
+
+  test "an acknowledgement can be converted to bytes":
+    let previous = Ack.example
+    let ack = !Ack.init(previous.hash, [tx1.hash, tx2.hash])
+    var expected: seq[byte]
+    expected.add(previous.hash.toBytes)
+    expected.add(2) # amount of transactions
+    expected.add(tx1.hash.toBytes)
+    expected.add(tx2.hash.toBytes)
+    check ack.toBytes == expected
+
+  test "an acknowledgement must contain at least one transaction":
+    let previous = Ack.example
+    check Ack.init(previous.hash, []).isNone
diff --git a/tests/testAll.nim b/tests/testAll.nim
index 3f93f98..a24f3d6 100644
--- a/tests/testAll.nim
+++ b/tests/testAll.nim
@@ -1,3 +1,4 @@
+import abc/testAcks
 import abc/testKeys
 import abc/testTransactions
 import abc/testTxStore