CP: check in a "childrens paper" contract that is sort of like commercial paper, but not really. Tests are incomplete.

src/contracts/ChildrensPaper.kt

@@ -0,0 +1,65 @@
+package contracts
+
+import core.*
+import java.security.PublicKey
+import java.time.Instant
+
+/**
+ * "Children's paper" is basically like commercial paper, but modelled by a non-expert and without any attention paid
+ * to the issuance aspect. It has a weird name to emphasise that it's not a prototype of real CP, as that's currently
+ * waiting for Jo/Ayoub to deliver full CP use case models. This file may be renamed later if it grows up and
+ * becomes real CP.
+ *
+ * Open issues:
+ *  - In this model, you cannot merge or split CP. Can you do this normally? We could model CP as a specialised form
+ *    of cash, or reuse some of the cash code?
+ *  - Currently cannot trade more than one piece of CP in a single transaction. This is probably going to be a common
+ *    issue: need to find a cleaner way to allow this. Does the single-execution-per-transaction model make sense?
+ */
+
+val CP_PROGRAM_ID = SecureHash.sha256("childrens-paper")
+
+data class ChildrensPaperState(
+    val issuance: InstitutionReference,
+    val owner: PublicKey,
+    val faceValue: Amount,
+    val maturityDate: Instant
+) : ContractState {
+    override val programRef = CP_PROGRAM_ID
+
+    fun withoutOwner() = copy(owner = NullPublicKey)
+}
+
+// TODO: Generalise the notion of an owned object into a superclass/supercontract. Consider composition vs inheritance.
+sealed class CPCommands : Command {
+    class MoveCommand : CPCommands()
+    class RedeemCommand : CPCommands()
+}
+
+object ChildrensPaper : Contract {
+    override fun verify(inStates: List<ContractState>, outStates: List<ContractState>, args: List<VerifiedSigned<Command>>, time: Instant) {
+        // There are two possible things that can be done with CP. The first is trading it. The second is redeeming it
+        // for cash on or after the maturity date.
+        val command = args.requireSingleCommand<CPCommands>()
+
+        // For now do not allow multiple pieces of CP to trade in a single transaction. Study this more!
+        val input = inStates.filterIsInstance<ChildrensPaperState>().single()
+        val output = outStates.filterIsInstance<ChildrensPaperState>().single()
+
+        when (command.value) {
+            is CPCommands.MoveCommand -> requireThat {
+                "the transaction is signed by the owner of the CP" by (command.signer == input.owner)
+                "the output state is the same as the input state except for owner" by (input.withoutOwner() == output.withoutOwner())
+            }
+
+            is CPCommands.RedeemCommand -> {
+                val received = outStates.sumCashBy(command.signer)
+                requireThat {
+                    "the paper must have matured" by (input.maturityDate < time)
+                    "the received amount equals the face value" by (received == input.faceValue)
+                }
+            }
+        }
+    }
+}
+

src/core/TestUtils.kt

@@ -26,6 +26,9 @@ val TEST_KEYS_TO_CORP_MAP: Map<PublicKey, Institution> = mapOf(
         MINI_CORP_KEY to MINI_CORP
 )
 
+// A dummy time at which we will be pretending test transactions are created.
+val TEST_TX_TIME = Instant.parse("2015-04-17T12:00:00.00Z")
+
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 //
 // DSL for building pseudo-transactions (not the same as the wire protocol) for testing purposes.
@@ -59,21 +62,33 @@ data class TransactionForTest(
 
     infix fun Contract.`fails requirement`(msg: String) {
         try {
-            verify(inStates, outStates, args, Instant.now())
+            verify(inStates, outStates, args, TEST_TX_TIME)
         } catch(e: Exception) {
             val m = e.message
             if (m == null)
                 fail("Threw exception without a message")
             else
-                if (!m.contains(msg)) throw AssertionError("Error was actually: $m")
+                if (!m.contains(msg)) throw AssertionError("Error was actually: $m", e)
         }
     }
 
     // which is uglier?? :)
     fun Contract.fails_requirement(msg: String) = this.`fails requirement`(msg)
 
-    fun Contract.accepts() {
+    fun Contract.accepts() = verify(inStates, outStates, args, TEST_TX_TIME)
-        verify(inStates, outStates, args, Instant.now())
+    fun Contract.rejects(withMessage: String? = null) {
+        val r = try {
+            accepts()
+            false
+        } catch (e: Exception) {
+            val m = e.message
+            if (m == null)
+                fail("Threw exception without a message")
+            else
+                if (withMessage != null && !m.contains(withMessage)) throw AssertionError("Error was actually: $m", e)
+            true
+        }
+        if (!r) throw AssertionError("Expected exception but didn't get one")
     }
 
     // Allow customisation of partial transactions.

src/core/Utils.kt

@@ -1,6 +1,7 @@
 package core
 
 import com.google.common.io.BaseEncoding
+import java.time.Duration
 import java.util.*
 
 /** A simple class that wraps a byte array and makes the equals/hashCode/toString methods work as you actually expect */
@@ -19,3 +20,8 @@ open class OpaqueBytes(val bits: ByteArray) {
 
     override fun toString() = "[" + BaseEncoding.base16().encode(bits) + "]"
 }
+
+val Int.days: Duration get() = Duration.ofDays(this.toLong())
+val Int.hours: Duration get() = Duration.ofHours(this.toLong())
+val Int.minutes: Duration get() = Duration.ofMinutes(this.toLong())
+val Int.seconds: Duration get() = Duration.ofSeconds(this.toLong())

tests/contracts/ChildrensPaperTests.kt

@@ -0,0 +1,39 @@
+package contracts
+
+import core.*
+import org.junit.Test
+
+// TODO: Finish this off.
+
+class ChildrensPaperTests {
+    val contract = ChildrensPaper
+
+    val PAPER_1 = ChildrensPaperState(
+            issuance = InstitutionReference(MEGA_CORP, OpaqueBytes.of(123)),
+            owner = DUMMY_PUBKEY_1,
+            faceValue = 1000.DOLLARS,
+            maturityDate = TEST_TX_TIME + 7.days
+    )
+    val PAPER_2 = PAPER_1.copy(owner = DUMMY_PUBKEY_2)
+
+    @Test
+    fun move() {
+        // One entity sells the paper to another (e.g. the issuer sells it to a first time buyer)
+        transaction {
+            input { PAPER_1 }
+            output { PAPER_2 }
+
+            contract.rejects()
+
+            transaction {
+                arg(DUMMY_PUBKEY_2) { CPCommands.MoveCommand() }
+                contract `fails requirement` "is signed by the owner"
+            }
+
+            transaction {
+                arg(DUMMY_PUBKEY_1) { CPCommands.MoveCommand() }
+                contract.accepts()
+            }
+        }
+    }
+}