From a0d1e71ed56c75542545806be76127c48b1d9717 Mon Sep 17 00:00:00 2001
From: h7x4 <h7x4abk3g@protonmail.com>
Date: Sun, 5 Sep 2021 19:29:09 +0200
Subject: [PATCH] Implement calculator logic

---
 .../src/main/java/oysteikt/calc/Calc.java     | 20 ++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/oysteikt-calc/src/main/java/oysteikt/calc/Calc.java b/oysteikt-calc/src/main/java/oysteikt/calc/Calc.java
index cc90df3..6841127 100644
--- a/oysteikt-calc/src/main/java/oysteikt/calc/Calc.java
+++ b/oysteikt-calc/src/main/java/oysteikt/calc/Calc.java
@@ -74,8 +74,13 @@ public class Calc {
    * @throws IllegalStateException if the operand stack is empty
    */
   public double performOperation(UnaryOperator<Double> op) throws IllegalStateException {
-    // TODO
-    return 0.0;
+    // if (this.getOperandCount() == 0)
+    if (this.operandStack.isEmpty())
+      throw new IllegalStateException("Cannot perform operation " + op + " because of missing operands");
+
+    Double result = op.apply(this.popOperand());
+    this.pushOperand(result);
+    return result;
   }
 
   /**
@@ -103,7 +108,13 @@ public class Calc {
    * @throws IllegalStateException if the operand count is less than two
    */
   public void swap() {
+    if (this.getOperandCount() < 2)
+      throw new IllegalStateException("Not enough operands to swap");
 
+    Double x = this.popOperand();
+    Double y = this.popOperand();
+    this.pushOperand(x);
+    this.pushOperand(y);
   }
 
   /**
@@ -112,6 +123,9 @@ public class Calc {
    * @throws IllegalStateException if the operand stack is empty
    */
   public void dup() {
-    // TODO
+    if (this.operandStack.isEmpty())
+      throw new IllegalStateException("Cannot duplicate top operand because there are no operands left");
+
+    this.pushOperand(this.peekOperand());
   }
 }
\ No newline at end of file