Add bsv-20 futures contract (simple).

src/contracts/bsv20FuturesContractSimple.ts

@@ -0,0 +1,172 @@
+import { assert } from 'console'
+import { BSV20V2 } from 'scrypt-ord'
+import {
+    ByteString,
+    byteString2Int,
+    hash256,
+    method,
+    prop,
+    PubKey,
+    pubKey2Addr,
+    Sig,
+    slice,
+    SmartContract,
+    toByteString,
+    Utils,
+} from 'scrypt-ts'
+import { RabinPubKey, RabinSig, RabinVerifier } from 'scrypt-ts-lib'
+
+/**
+ * This is a simplistic implementation of a futures contract where two parties agree
+ * to trade a predetermined quantity of an asset (BSV-20 tokens) at a specified price at a future date.
+ * The contract requires the full amount to be exchanged. To mitigate risk, both parties are required
+ * to deposit collateral upon the contract's deployment.
+ */
+export class Bsv20FuturesContractSimple extends BSV20V2 {
+    @prop()
+    buyer: PubKey
+
+    @prop()
+    seller: PubKey
+
+    // Unit price of the asset.
+    @prop()
+    price: bigint
+
+    // Asset amount.
+    @prop()
+    amt: bigint
+
+    // Collateral amount.
+    @prop()
+    collateral: bigint
+
+    // Date at which the settlement can be carried out.
+    @prop()
+    settlementDate: bigint
+
+    // Deadline for settlement.
+    @prop()
+    deadline: bigint
+
+    @prop(true)
+    settlementInitiated: boolean
+
+    // Oracle is used to verify tokens origin.
+    @prop()
+    oraclePubKey: RabinPubKey
+
+    constructor(
+        id: ByteString,
+        sym: ByteString,
+        max: bigint,
+        dec: bigint,
+        buyer: PubKey,
+        seller: PubKey,
+        price: bigint,
+        amt: bigint,
+        collateral: bigint,
+        settlementDate: bigint,
+        deadline: bigint,
+        oraclePubKey: RabinPubKey
+    ) {
+        super(id, sym, max, dec)
+        this.init(...arguments)
+
+        this.buyer = buyer
+        this.seller = seller
+        this.price = price
+        this.amt = amt
+        this.collateral = collateral
+        this.settlementDate = settlementDate
+        this.deadline = deadline
+        this.settlementInitiated = false
+        this.oraclePubKey = oraclePubKey
+    }
+
+    @method()
+    public initiateSettlement(sigBuyer: Sig) {
+        // Check settlement date is reached.
+        assert(
+            this.timeLock(this.settlementDate),
+            'settlement date not yet reached'
+        )
+
+        // Check buyer signature.
+        assert(this.checkSig(sigBuyer, this.buyer), 'buyer sig invalid')
+
+        // Toggle settlementInitiated flag.
+        this.settlementInitiated = true
+
+        // Ensure buyer deposits full amount and propagate contract.
+        let outputs = this.buildStateOutput(
+            this.ctx.utxo.value + this.amt * this.price
+        )
+        outputs += this.buildChangeOutput()
+        assert(hash256(outputs) == this.ctx.hashOutputs, 'hashOutputs mismatch')
+    }
+
+    @method()
+    public settle(sigSeller: Sig, oracleMsg: ByteString, oracleSig: RabinSig) {
+        // Check if settlement is initiated.
+        assert(this.settlementInitiated, 'settlement not initiated')
+
+        // Check seller signature
+        assert(this.checkSig(sigSeller, this.seller), 'seller sig invalid')
+
+        // Check oracle signature.
+        assert(
+            RabinVerifier.verifySig(oracleMsg, oracleSig, this.oraclePubKey),
+            'oracle sig verify failed'
+        )
+
+        // Check that we're unlocking the UTXO specified in the oracles message.
+        assert(
+            slice(this.prevouts, 36n, 72n) == slice(oracleMsg, 0n, 36n),
+            'second input is not spending specified ordinal UTXO'
+        )
+
+        // Get token amount held by the UTXO from oracle message.
+        const utxoTokenAmt = byteString2Int(slice(oracleMsg, 36n, 44n))
+
+        // Check token amount is correct.
+        assert(utxoTokenAmt == this.amt, 'invalid token amount')
+
+        // Ensure contract pays total amount to seller. Also include their collateral.
+        let outputs = Utils.buildAddressOutput(
+            pubKey2Addr(this.seller),
+            this.amt * this.price + this.collateral
+        )
+
+        // Ensure seller sends assets to buyer.
+        outputs += BSV20V2.buildTransferOutput(
+            pubKey2Addr(this.buyer),
+            this.id,
+            this.amt
+        )
+
+        // Also return buyers collateral.
+        outputs += Utils.buildAddressOutput(
+            pubKey2Addr(this.buyer),
+            this.collateral
+        )
+
+        assert(hash256(outputs) == this.ctx.hashOutputs, 'hashOutputs mismatch')
+    }
+
+    @method()
+    public withdraw(sig: Sig) {
+        // Check deadline is reached.
+        assert(this.timeLock(this.deadline), 'deadline not yet reached')
+
+        // If settlement is initiated, pay out total amount to buyer.
+        // If not, pay out to seller.
+        const dest = this.settlementInitiated ? this.buyer : this.seller
+        let outputs = Utils.buildAddressOutput(
+            pubKey2Addr(dest),
+            this.ctx.utxo.value
+        )
+        outputs += this.buildChangeOutput()
+        assert(hash256(outputs) == this.ctx.hashOutputs, 'hashOutputs mismatch')
+    }
+}