diff --git a/src/contracts/tictactoe.ts b/src/contracts/tictactoe.ts
index a143cf0..e86eaa5 100644
--- a/src/contracts/tictactoe.ts
+++ b/src/contracts/tictactoe.ts
@@ -1,207 +1,226 @@
 import {
-    prop, method, SmartContract, PubKey, FixedArray, assert, Sig, Utils, toByteString, hash160,
+    prop,
+    method,
+    SmartContract,
+    PubKey,
+    FixedArray,
+    assert,
+    Sig,
+    Utils,
+    toByteString,
+    hash160,
     hash256,
     fill,
     ContractTransaction,
     MethodCallOptions,
-    bsv
-} from "scrypt-ts";
-
-export class TicTacToe extends SmartContract {
+    bsv,
+  } from "scrypt-ts";
+
+  export enum Player {
+    EMPTY = 0,
+    ALICE = 1,
+    BOB = 2
+}
+  
+  export class TicTacToe extends SmartContract {
     @prop()
     alice: PubKey;
     @prop()
     bob: PubKey;
-
+  
     @prop(true)
     isAliceTurn: boolean;
-
+  
     @prop(true)
     board: FixedArray<bigint, 9>;
-
-    static readonly EMPTY: bigint = 0n;
-    static readonly ALICE: bigint = 1n;
-    static readonly BOB: bigint = 2n;
-
+  
+  
     constructor(alice: PubKey, bob: PubKey) {
-        super(...arguments)
-        this.alice = alice;
-        this.bob = bob;
-        this.isAliceTurn = true;
-        this.board = fill(TicTacToe.EMPTY, 9);
+      super(...arguments);
+      this.alice = alice;
+      this.bob = bob;
+      this.isAliceTurn = true;
+      this.board = fill(BigInt(Player.EMPTY), 9);
     }
-
+  
     @method()
     public move(n: bigint, sig: Sig) {
-        // check position `n`
-        assert(n >= 0n && n < 9n);
-        // check signature `sig`
-        let player: PubKey = this.isAliceTurn ? this.alice : this.bob;
-        assert(this.checkSig(sig, player), `checkSig failed, pubkey: ${player}`);
-        // update stateful properties to make the move
-        assert(this.board[Number(n)] === TicTacToe.EMPTY, `board at position ${n} is not empty: ${this.board[Number(n)]}`);
-        let play = this.isAliceTurn ? TicTacToe.ALICE : TicTacToe.BOB;
-        this.board[Number(n)] = play;
-        this.isAliceTurn = !this.isAliceTurn;
-        
-        // build the transation outputs
-        let outputs = toByteString('');
-        if (this.won(play)) {
-            outputs = Utils.buildPublicKeyHashOutput(hash160(player), this.ctx.utxo.value);
-        }
-        else if (this.full()) {
-            const halfAmount = this.ctx.utxo.value / 2n;
-            const aliceOutput = Utils.buildPublicKeyHashOutput(hash160(this.alice), halfAmount);
-            const bobOutput = Utils.buildPublicKeyHashOutput(hash160(this.bob), halfAmount);
-            outputs = aliceOutput + bobOutput;
-        }
-        else {
-            // build a output that contains latest contract state.
-            outputs = this.buildStateOutput(this.ctx.utxo.value);
-        }
-
-        if (this.changeAmount > 0n) {
-            outputs += this.buildChangeOutput();
-        }
-        // make sure the transaction contains the expected outputs built above
-        assert(this.ctx.hashOutputs === hash256(outputs), "check hashOutputs failed");
+      // check position `n`
+      assert(n >= 0n && n < 9n);
+      // check signature `sig`
+      let player: PubKey = this.isAliceTurn ? this.alice : this.bob;
+      assert(this.checkSig(sig, player), `checkSig failed, pubkey: ${player}`);
+      // update stateful properties to make the move
+      assert(
+        this.board[Number(n)] === BigInt(Player.EMPTY),
+        `board at position ${n} is not empty: ${this.board[Number(n)]}`
+      );
+      let play = this.isAliceTurn ? BigInt(Player.ALICE) : BigInt(Player.BOB);
+      this.board[Number(n)] = play;
+      this.isAliceTurn = !this.isAliceTurn;
+  
+      // build the transation outputs
+      let outputs = toByteString("");
+      if (this.won(play)) {
+        outputs = Utils.buildPublicKeyHashOutput(
+          hash160(player),
+          this.ctx.utxo.value
+        );
+      } else if (this.full()) {
+        const halfAmount = this.ctx.utxo.value / 2n;
+        const aliceOutput = Utils.buildPublicKeyHashOutput(
+          hash160(this.alice),
+          halfAmount
+        );
+        const bobOutput = Utils.buildPublicKeyHashOutput(
+          hash160(this.bob),
+          halfAmount
+        );
+        outputs = aliceOutput + bobOutput;
+      } else {
+        // build a output that contains latest contract state.
+        outputs = this.buildStateOutput(this.ctx.utxo.value);
+      }
+  
+      if (this.changeAmount > 0n) {
+        outputs += this.buildChangeOutput();
+      }
+      // make sure the transaction contains the expected outputs built above
+      assert(
+        this.ctx.hashOutputs === hash256(outputs),
+        "check hashOutputs failed"
+      );
     }
-
+  
     @method()
     won(play: bigint): boolean {
-        let lines: FixedArray<FixedArray<bigint, 3>, 8> = [
-            [0n, 1n, 2n],
-            [3n, 4n, 5n],
-            [6n, 7n, 8n],
-            [0n, 3n, 6n],
-            [1n, 4n, 7n],
-            [2n, 5n, 8n],
-            [0n, 4n, 8n],
-            [2n, 4n, 6n]
-        ];
-
-        let anyLine = false;
-
-        for (let i = 0; i < 8; i++) {
-            let line = true;
-            for (let j = 0; j < 3; j++) {
-                line = line && this.board[Number(lines[i][j])] === play;
-            }
-
-            anyLine = anyLine || line;
+      let lines: FixedArray<FixedArray<bigint, 3>, 8> = [
+        [0n, 1n, 2n],
+        [3n, 4n, 5n],
+        [6n, 7n, 8n],
+        [0n, 3n, 6n],
+        [1n, 4n, 7n],
+        [2n, 5n, 8n],
+        [0n, 4n, 8n],
+        [2n, 4n, 6n],
+      ];
+  
+      let anyLine = false;
+  
+      for (let i = 0; i < 8; i++) {
+        let line = true;
+        for (let j = 0; j < 3; j++) {
+          line = line && this.board[Number(lines[i][j])] === play;
         }
-
-        return anyLine;
+  
+        anyLine = anyLine || line;
+      }
+  
+      return anyLine;
     }
-
+  
     @method()
     full(): boolean {
-        let full = true;
-        for (let i = 0; i < 9; i++) {
-            full = full && this.board[i] !== TicTacToe.EMPTY;
-        }
-        return full;
+      let full = true;
+      for (let i = 0; i < 9; i++) {
+        full = full && this.board[i] !== BigInt(Player.EMPTY);
+      }
+      return full;
     }
-
+  
     static buildTxForMove(
-        current: TicTacToe,
-        options: MethodCallOptions<TicTacToe>,
-        n: bigint
+      current: TicTacToe,
+      options: MethodCallOptions<TicTacToe>,
+      n: bigint
     ): Promise<ContractTransaction> {
-        const play = current.isAliceTurn ? TicTacToe.ALICE : TicTacToe.BOB
-        const nextInstance = current.next()
-        nextInstance.board[Number(n)] = play
-        nextInstance.isAliceTurn = !current.isAliceTurn
-
-        const unsignedTx: bsv.Transaction = new bsv.Transaction().addInput(
-            current.buildContractInput(options.fromUTXO)
-        )
-
-        if (nextInstance.won(play)) {
-            const script = Utils.buildPublicKeyHashScript(
-                hash160(current.isAliceTurn ? current.alice : current.bob)
-            )
-            unsignedTx
-                .addOutput(
-                    new bsv.Transaction.Output({
-                        script: bsv.Script.fromHex(script),
-                        satoshis: current.balance,
-                    })
-                )
-            
-            if (options.changeAddress) {
-                unsignedTx.change(options.changeAddress)
-            }
-
-            return Promise.resolve({
-                tx: unsignedTx,
-                atInputIndex: 0,
-                nexts: [],
-            })
-        }
-
-        if (nextInstance.full()) {
-            const halfAmount = current.balance / 2
-
-            unsignedTx
-                .addOutput(
-                    new bsv.Transaction.Output({
-                        script: bsv.Script.fromHex(
-                            Utils.buildPublicKeyHashScript(
-                                hash160(current.alice)
-                            )
-                        ),
-                        satoshis: halfAmount,
-                    })
-                )
-                .addOutput(
-                    new bsv.Transaction.Output({
-                        script: bsv.Script.fromHex(
-                            Utils.buildPublicKeyHashScript(hash160(current.bob))
-                        ),
-                        satoshis: halfAmount,
-                    })
-                )
-
-            if (options.changeAddress) {
-                unsignedTx.change(options.changeAddress)
-            }
-
-            return Promise.resolve({
-                tx: unsignedTx,
-                atInputIndex: 0,
-                nexts: [],
-            })
+      const play = current.isAliceTurn ? BigInt(Player.ALICE) : BigInt(Player.BOB);
+      const nextInstance = current.next();
+      nextInstance.board[Number(n)] = play;
+      nextInstance.isAliceTurn = !current.isAliceTurn;
+  
+      const unsignedTx: bsv.Transaction = new bsv.Transaction().addInput(
+        current.buildContractInput(options.fromUTXO)
+      );
+  
+      if (nextInstance.won(play)) {
+        const script = Utils.buildPublicKeyHashScript(
+          hash160(current.isAliceTurn ? current.alice : current.bob)
+        );
+        unsignedTx.addOutput(
+          new bsv.Transaction.Output({
+            script: bsv.Script.fromHex(script),
+            satoshis: current.balance,
+          })
+        );
+  
+        if (options.changeAddress) {
+          unsignedTx.change(options.changeAddress);
         }
-
+  
+        return Promise.resolve({
+          tx: unsignedTx,
+          atInputIndex: 0,
+          nexts: [],
+        });
+      }
+  
+      if (nextInstance.full()) {
+        const halfAmount = current.balance / 2;
+  
         unsignedTx
-            .setOutput(0, () => {
-                return new bsv.Transaction.Output({
-                    script: nextInstance.lockingScript,
-                    satoshis: current.balance,
-                })
+          .addOutput(
+            new bsv.Transaction.Output({
+              script: bsv.Script.fromHex(
+                Utils.buildPublicKeyHashScript(hash160(current.alice))
+              ),
+              satoshis: halfAmount,
             })
-            
-            
+          )
+          .addOutput(
+            new bsv.Transaction.Output({
+              script: bsv.Script.fromHex(
+                Utils.buildPublicKeyHashScript(hash160(current.bob))
+              ),
+              satoshis: halfAmount,
+            })
+          );
+  
         if (options.changeAddress) {
-            unsignedTx.change(options.changeAddress)
+          unsignedTx.change(options.changeAddress);
         }
-        
-
-        const nexts = [
-            {
-                instance: nextInstance,
-                atOutputIndex: 0,
-                balance: current.balance,
-            },
-        ]
-
+  
         return Promise.resolve({
-            tx: unsignedTx,
-            atInputIndex: 0,
-            nexts,
-            next: nexts[0],
-        })
-
+          tx: unsignedTx,
+          atInputIndex: 0,
+          nexts: [],
+        });
+      }
+  
+      unsignedTx.setOutput(0, () => {
+        return new bsv.Transaction.Output({
+          script: nextInstance.lockingScript,
+          satoshis: current.balance,
+        });
+      });
+  
+      if (options.changeAddress) {
+        unsignedTx.change(options.changeAddress);
+      }
+  
+      const nexts = [
+        {
+          instance: nextInstance,
+          atOutputIndex: 0,
+          balance: current.balance,
+        },
+      ];
+  
+      return Promise.resolve({
+        tx: unsignedTx,
+        atInputIndex: 0,
+        nexts,
+        next: nexts[0],
+      });
     }
-}
\ No newline at end of file
+  }
+