From 5661469aee5d980b95de7e29f74e21f6bfa7558d Mon Sep 17 00:00:00 2001
From: Mark Spanbroek <mark@spanbroek.net>
Date: Mon, 28 Jun 2021 15:04:50 +0200
Subject: [PATCH] Transactions

---
 abc.nimble                 |  1 +
 abc/transactions.nim       | 52 ++++++++++++++++++++++++++++++++++++++
 tests/examples.nim         |  6 +++++
 tests/testTransactions.nim | 42 ++++++++++++++++++++++++++++++
 4 files changed, 101 insertions(+)
 create mode 100644 abc/transactions.nim
 create mode 100644 tests/testTransactions.nim

diff --git a/abc.nimble b/abc.nimble
index 376c973..1d917bb 100644
--- a/abc.nimble
+++ b/abc.nimble
@@ -6,4 +6,5 @@ license = "MIT"
 requires "questionable >= 0.10.0 & < 0.11.0"
 requires "https://github.com/markspanbroek/nim-blscurve#fix-nimble"
 requires "nimcrypto"
+requires "stint"
 requires "stew"
diff --git a/abc/transactions.nim b/abc/transactions.nim
new file mode 100644
index 0000000..df2cba3
--- /dev/null
+++ b/abc/transactions.nim
@@ -0,0 +1,52 @@
+import pkg/nimcrypto
+import pkg/stint
+import ./keys
+
+export stint
+export keys
+
+type
+  Transaction* = object
+    inputs: seq[TxInput]
+    outputs: seq[TxOutput]
+    signature: Signature
+  TxInput* = tuple
+    txHash: TxHash
+    owner: PublicKey
+  TxOutput* = tuple
+    owner: PublicKey
+    amount: UInt256
+  TxHash* = distinct MDigest[256]
+
+func `==`*(a, b: TxHash): bool {.borrow.}
+
+func init*(_: type Transaction,
+           inputs: openArray[TxInput],
+           outputs: openArray[TxOutput]): Transaction =
+  Transaction(inputs: @inputs, outputs: @outputs)
+
+func init*(_: type Transaction,
+           outputs: openArray[TxOutput]): Transaction =
+  Transaction.init([], outputs)
+
+func inputs*(transaction: Transaction): seq[TxInput] =
+  transaction.inputs
+
+func outputs*(transaction: Transaction): seq[TxOutput] =
+  transaction.outputs
+
+func toBytes*(hash: TxHash): array[32, byte] =
+  MDigest[256](hash).data
+
+func toBytes*(transaction: Transaction): seq[byte] =
+  result.add(transaction.inputs.len.uint8)
+  for (txHash, owner) in transaction.inputs:
+    result.add(txHash.toBytes)
+    result.add(owner.toBytes)
+  result.add(transaction.outputs.len.uint8)
+  for (owner, amount) in transaction.outputs:
+    result.add(owner.toBytes)
+    result.add(amount.toBytes)
+
+func hash*(transaction: Transaction): TxHash =
+  TxHash(sha256.digest(transaction.toBytes))
diff --git a/tests/examples.nim b/tests/examples.nim
index f8baff3..ebe3854 100644
--- a/tests/examples.nim
+++ b/tests/examples.nim
@@ -1,7 +1,13 @@
 import abc/keys
+import abc/transactions
 
 proc example*(_: type PrivateKey): PrivateKey =
   PrivateKey.random
 
 proc example*(_: type PublicKey): PublicKey =
   PrivateKey.example.toPublicKey
+
+proc example*(_: type Transaction): Transaction =
+  let alice, bob = PublicKey.example
+  let genesis = Transaction.init({alice: 32.u256, bob: 10.u256})
+  Transaction.init({genesis.hash: alice}, {alice: 2.u256, bob: 30.u256})
diff --git a/tests/testTransactions.nim b/tests/testTransactions.nim
new file mode 100644
index 0000000..ffd83aa
--- /dev/null
+++ b/tests/testTransactions.nim
@@ -0,0 +1,42 @@
+import std/unittest
+import abc/transactions
+import ./examples
+
+suite "Transactions":
+
+  let alice, bob = PublicKey.example
+
+  test "a genesis transaction can be made":
+    let genesis = Transaction.init({alice: 32.u256, bob: 10.u256})
+
+  test "a transaction has a hash":
+    let transaction1, transaction2 = Transaction.example
+    check transaction1.hash == transaction1.hash
+    check transaction2.hash == transaction2.hash
+    check transaction1.hash != transaction2.hash
+
+  test "a transaction references outputs from other transactions":
+    let genesis = Transaction.init({alice: 32.u256, bob: 10.u256})
+    let transaction = Transaction.init(
+      {genesis.hash: alice},
+      {alice: 2.u256, bob: 30.u256}
+    )
+    check transaction.inputs.len == 1
+    check transaction.outputs.len == 2
+
+  test "a transaction can be converted to bytes":
+    let genesis = Transaction.init({alice: 32.u256, bob: 10.u256})
+    let transaction = Transaction.init(
+      {genesis.hash: alice},
+      {alice: 2.u256, bob: 30.u256}
+    )
+    var expected: seq[byte]
+    expected.add(1) # amount of inputs
+    expected.add(genesis.hash.toBytes)
+    expected.add(alice.toBytes)
+    expected.add(2) # amount of outputs
+    expected.add(alice.toBytes)
+    expected.add(2.u256.toBytes)
+    expected.add(bob.toBytes)
+    expected.add(30.u256.toBytes)
+    check transaction.toBytes == expected