From b9ffe96f553ee29f48d2cbb9f517d5685fa39b1e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Wojciech=20Fr=C4=85cz?= <fraczwojciech@gmail.com>
Date: Sat, 11 Feb 2017 23:58:33 +0100
Subject: [PATCH 1/7] Working all Invoice and Product tests

---
 .../java/pl/edu/agh/mwo/invoice/Invoice.java  | 35 +++++++++++++++----
 .../edu/agh/mwo/invoice/product/Product.java  | 16 ++++++---
 2 files changed, 40 insertions(+), 11 deletions(-)

diff --git a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
index 56fe02359..8599ebb76 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
@@ -1,30 +1,51 @@
 package pl.edu.agh.mwo.invoice;
 
 import java.math.BigDecimal;
-import java.util.Collection;
+import java.util.HashMap;
+import java.util.Iterator;
+import java.util.Map;
 
 import pl.edu.agh.mwo.invoice.product.Product;
 
 public class Invoice {
-    private Collection<Product> products;
+    private Map<Product, Integer> products = new HashMap<Product, Integer>();
 
     public void addProduct(Product product) {
-        // TODO: implement
+        this.products.put(product, 1);
     }
 
     public void addProduct(Product product, Integer quantity) {
-        // TODO: implement
+        if (quantity <= 0) {
+            throw new IllegalArgumentException();
+        }
+        this.products.put(product, quantity);
     }
 
     public BigDecimal getSubtotal() {
-        return null;
+        return getTotal().subtract(getTax());
     }
 
     public BigDecimal getTax() {
-        return null;
+        BigDecimal totalTax = new BigDecimal(0);
+        Iterator<Map.Entry<Product, Integer>> it = products.entrySet().iterator();
+        while (it.hasNext()) {
+            Map.Entry<Product, Integer> pair = it.next();
+            BigDecimal productTax = pair.getKey().getTaxOnly();
+            BigDecimal quantity = new BigDecimal(pair.getValue());
+            totalTax = totalTax.add(productTax.multiply(quantity));
+        }
+        return totalTax;
     }
 
     public BigDecimal getTotal() {
-        return null;
+        BigDecimal total = new BigDecimal(0);
+        Iterator<Map.Entry<Product, Integer>> it = products.entrySet().iterator();
+        while (it.hasNext()) {
+            Map.Entry<Product, Integer> pair = it.next();
+            BigDecimal productPriceWithTax = pair.getKey().getPriceWithTax();
+            BigDecimal quantity = new BigDecimal(pair.getValue());
+            total = total.add(productPriceWithTax.multiply(quantity));
+        }
+        return total;
     }
 }
diff --git a/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java b/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
index 318de9ac9..b73269d75 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
@@ -10,24 +10,32 @@ public abstract class Product {
     private final BigDecimal taxPercent;
 
     protected Product(String name, BigDecimal price, BigDecimal tax) {
+        if (name == null || name.equals("") || price == null || tax == null || tax.compareTo(new BigDecimal(0)) < 0
+                || price.compareTo(new BigDecimal(0)) < 0) {
+            throw new IllegalArgumentException();
+        }
         this.name = name;
         this.price = price;
         this.taxPercent = tax;
     }
 
     public String getName() {
-        return null;
+        return name;
     }
 
     public BigDecimal getPrice() {
-        return null;
+        return price;
     }
 
     public BigDecimal getTaxPercent() {
-        return null;
+        return taxPercent;
     }
 
     public BigDecimal getPriceWithTax() {
-        return null;
+        return price.add(getTaxOnly());
+    }
+
+    public BigDecimal getTaxOnly() {
+        return price.multiply(taxPercent);
     }
 }

From fbb07dceb4407153fa266d69c832f48798da7a49 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Wojciech=20Fr=C4=85cz?= <fraczwojciech@gmail.com>
Date: Fri, 24 Feb 2017 23:32:19 +0100
Subject: [PATCH 2/7] Simplify invoice implementation

---
 .../java/pl/edu/agh/mwo/invoice/Invoice.java  | 43 ++++++++-----------
 .../edu/agh/mwo/invoice/product/Product.java  |  6 +--
 .../pl/edu/agh/mwo/invoice/InvoiceTest.java   | 22 +++++-----
 3 files changed, 30 insertions(+), 41 deletions(-)

diff --git a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
index 8599ebb76..72f4048d5 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
@@ -2,7 +2,6 @@
 
 import java.math.BigDecimal;
 import java.util.HashMap;
-import java.util.Iterator;
 import java.util.Map;
 
 import pl.edu.agh.mwo.invoice.product.Product;
@@ -11,41 +10,35 @@ public class Invoice {
     private Map<Product, Integer> products = new HashMap<Product, Integer>();
 
     public void addProduct(Product product) {
-        this.products.put(product, 1);
+        addProduct(product, 1);
     }
 
     public void addProduct(Product product, Integer quantity) {
-        if (quantity <= 0) {
+        if (product == null || quantity <= 0) {
             throw new IllegalArgumentException();
         }
-        this.products.put(product, quantity);
+        products.put(product, quantity);
     }
 
-    public BigDecimal getSubtotal() {
-        return getTotal().subtract(getTax());
+    public BigDecimal getNetTotal() {
+        BigDecimal totalNet = BigDecimal.ZERO;
+        for (Product product : products.keySet()) {
+            BigDecimal quantity = new BigDecimal(products.get(product));
+            totalNet = totalNet.add(product.getPrice().multiply(quantity));
+        }
+        return totalNet;
     }
 
-    public BigDecimal getTax() {
-        BigDecimal totalTax = new BigDecimal(0);
-        Iterator<Map.Entry<Product, Integer>> it = products.entrySet().iterator();
-        while (it.hasNext()) {
-            Map.Entry<Product, Integer> pair = it.next();
-            BigDecimal productTax = pair.getKey().getTaxOnly();
-            BigDecimal quantity = new BigDecimal(pair.getValue());
-            totalTax = totalTax.add(productTax.multiply(quantity));
-        }
-        return totalTax;
+    public BigDecimal getTaxTotal() {
+        return getGrossTotal().subtract(getNetTotal());
     }
 
-    public BigDecimal getTotal() {
-        BigDecimal total = new BigDecimal(0);
-        Iterator<Map.Entry<Product, Integer>> it = products.entrySet().iterator();
-        while (it.hasNext()) {
-            Map.Entry<Product, Integer> pair = it.next();
-            BigDecimal productPriceWithTax = pair.getKey().getPriceWithTax();
-            BigDecimal quantity = new BigDecimal(pair.getValue());
-            total = total.add(productPriceWithTax.multiply(quantity));
+    public BigDecimal getGrossTotal() {
+        BigDecimal totalGross = BigDecimal.ZERO;
+        for (Product product : products.keySet()) {
+            BigDecimal quantity = new BigDecimal(products.get(product));
+            totalGross = totalGross.add(product.getPriceWithTax().multiply(quantity));
         }
-        return total;
+        return totalGross;
     }
 }
diff --git a/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java b/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
index b73269d75..cd0f86a48 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
@@ -32,10 +32,6 @@ public BigDecimal getTaxPercent() {
     }
 
     public BigDecimal getPriceWithTax() {
-        return price.add(getTaxOnly());
-    }
-
-    public BigDecimal getTaxOnly() {
-        return price.multiply(taxPercent);
+        return price.multiply(taxPercent).add(price);
     }
 }
diff --git a/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java b/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
index 7f4b6f795..50513171c 100644
--- a/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
+++ b/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
@@ -23,17 +23,17 @@ public void createEmptyInvoiceForTheTest() {
 
     @Test
     public void testEmptyInvoiceHasEmptySubtotal() {
-        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getSubtotal()));
+        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getNetTotal()));
     }
 
     @Test
     public void testEmptyInvoiceHasEmptyTaxAmount() {
-        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getTax()));
+        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getTaxTotal()));
     }
 
     @Test
     public void testEmptyInvoiceHasEmptyTotal() {
-        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getTotal()));
+        Assert.assertThat(BigDecimal.ZERO, Matchers.comparesEqualTo(invoice.getGrossTotal()));
     }
 
     @Test
@@ -42,21 +42,21 @@ public void testInvoiceSubtotalWithTwoDifferentProducts() {
         Product apples = new TaxFreeProduct("Owoce", new BigDecimal("10"));
         invoice.addProduct(onions);
         invoice.addProduct(apples);
-        Assert.assertThat(new BigDecimal("20"), Matchers.comparesEqualTo(invoice.getSubtotal()));
+        Assert.assertThat(new BigDecimal("20"), Matchers.comparesEqualTo(invoice.getNetTotal()));
     }
 
     @Test
     public void testInvoiceSubtotalWithManySameProducts() {
         Product onions = new TaxFreeProduct("Warzywa", BigDecimal.valueOf(10));
         invoice.addProduct(onions, 100);
-        Assert.assertThat(new BigDecimal("1000"), Matchers.comparesEqualTo(invoice.getSubtotal()));
+        Assert.assertThat(new BigDecimal("1000"), Matchers.comparesEqualTo(invoice.getNetTotal()));
     }
 
     @Test
     public void testInvoiceHasTheSameSubtotalAndTotalIfTaxIsZero() {
         Product taxFreeProduct = new TaxFreeProduct("Warzywa", new BigDecimal("199.99"));
         invoice.addProduct(taxFreeProduct);
-        Assert.assertThat(invoice.getTotal(), Matchers.comparesEqualTo(invoice.getSubtotal()));
+        Assert.assertThat(invoice.getNetTotal(), Matchers.comparesEqualTo(invoice.getGrossTotal()));
     }
 
     @Test
@@ -64,7 +64,7 @@ public void testInvoiceHasProperSubtotalForManyProducts() {
         invoice.addProduct(new TaxFreeProduct("Owoce", new BigDecimal("200")));
         invoice.addProduct(new DairyProduct("Maslanka", new BigDecimal("100")));
         invoice.addProduct(new OtherProduct("Wino", new BigDecimal("10")));
-        Assert.assertThat(new BigDecimal("310"), Matchers.comparesEqualTo(invoice.getSubtotal()));
+        Assert.assertThat(new BigDecimal("310"), Matchers.comparesEqualTo(invoice.getNetTotal()));
     }
 
     @Test
@@ -75,7 +75,7 @@ public void testInvoiceHasProperTaxValueForManyProduct() {
         invoice.addProduct(new DairyProduct("Kefir", new BigDecimal("100")));
         // tax: 2.30
         invoice.addProduct(new OtherProduct("Piwko", new BigDecimal("10")));
-        Assert.assertThat(new BigDecimal("10.30"), Matchers.comparesEqualTo(invoice.getTax()));
+        Assert.assertThat(new BigDecimal("10.30"), Matchers.comparesEqualTo(invoice.getTaxTotal()));
     }
 
     @Test
@@ -86,7 +86,7 @@ public void testInvoiceHasProperTotalValueForManyProduct() {
         invoice.addProduct(new DairyProduct("Maslo", new BigDecimal("100")));
         // price with tax: 12.30
         invoice.addProduct(new OtherProduct("Chipsy", new BigDecimal("10")));
-        Assert.assertThat(new BigDecimal("320.30"), Matchers.comparesEqualTo(invoice.getTotal()));
+        Assert.assertThat(new BigDecimal("320.30"), Matchers.comparesEqualTo(invoice.getGrossTotal()));
     }
 
     @Test
@@ -97,7 +97,7 @@ public void testInvoiceHasPropoerSubtotalWithQuantityMoreThanOne() {
         invoice.addProduct(new DairyProduct("Kozi Serek", new BigDecimal("10")), 3);
         // 1000x pinezka - price: 10
         invoice.addProduct(new OtherProduct("Pinezka", new BigDecimal("0.01")), 1000);
-        Assert.assertThat(new BigDecimal("50"), Matchers.comparesEqualTo(invoice.getSubtotal()));
+        Assert.assertThat(new BigDecimal("50"), Matchers.comparesEqualTo(invoice.getNetTotal()));
     }
 
     @Test
@@ -108,7 +108,7 @@ public void testInvoiceHasPropoerTotalWithQuantityMoreThanOne() {
         invoice.addProduct(new DairyProduct("Chedar", new BigDecimal("10")), 3);
         // 1000x pinezka - price with tax: 12.30
         invoice.addProduct(new OtherProduct("Pinezka", new BigDecimal("0.01")), 1000);
-        Assert.assertThat(new BigDecimal("54.70"), Matchers.comparesEqualTo(invoice.getTotal()));
+        Assert.assertThat(new BigDecimal("54.70"), Matchers.comparesEqualTo(invoice.getGrossTotal()));
     }
 
     @Test(expected = IllegalArgumentException.class)

From c0197fd952e72a1b77469e59d3222174584b90a4 Mon Sep 17 00:00:00 2001
From: MajowyLas <aniamaywald@gmail.com>
Date: Sat, 9 May 2026 14:42:31 +0200
Subject: [PATCH 3/7] Add CI workflow for Java Invoice project

---
 .github/workflows/github-actions.yml | 15 +++++++++++++++
 1 file changed, 15 insertions(+)
 create mode 100644 .github/workflows/github-actions.yml

diff --git a/.github/workflows/github-actions.yml b/.github/workflows/github-actions.yml
new file mode 100644
index 000000000..560118517
--- /dev/null
+++ b/.github/workflows/github-actions.yml
@@ -0,0 +1,15 @@
+name: CI for Java Invoice
+on: [push]
+jobs:
+  test:
+    name: Unit tests
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up JDK
+        uses: actions/setup-java@v2
+        with:
+          java-version: '17'
+          distribution: 'adopt'
+      - name: Test
+        run: mvn test

From c54986887e35d66d6f2c00b02ed6b5233d7bdd52 Mon Sep 17 00:00:00 2001
From: Anna Maywald <aniamaywald@gmail.com>
Date: Sat, 9 May 2026 16:25:25 +0200
Subject: [PATCH 4/7] added checklist.xmls, added checkist to github actions,
 amended Product.java

---
 .github/workflows/github-actions.yml          |   3 +
 checkstyle.xml                                | 298 ++++++++++++++++++
 pom.xml                                       |  21 ++
 .../edu/agh/mwo/invoice/product/Product.java  |   8 +-
 4 files changed, 328 insertions(+), 2 deletions(-)
 create mode 100644 checkstyle.xml

diff --git a/.github/workflows/github-actions.yml b/.github/workflows/github-actions.yml
index 560118517..b477d81d3 100644
--- a/.github/workflows/github-actions.yml
+++ b/.github/workflows/github-actions.yml
@@ -13,3 +13,6 @@ jobs:
           distribution: 'adopt'
       - name: Test
         run: mvn test
+      - name: Checkstyle
+        run: mvn checkstyle:check
+
diff --git a/checkstyle.xml b/checkstyle.xml
new file mode 100644
index 000000000..fbcd05132
--- /dev/null
+++ b/checkstyle.xml
@@ -0,0 +1,298 @@
+<?xml version="1.0"?>
+<!--
+These rules are based on the
+https://github.com/checkstyle/checkstyle/blob/master/src/main/resources/google_checks.xml
+but without javadoc requirements and with severity set to error.
+-->
+<!DOCTYPE module PUBLIC
+        "-//Checkstyle//DTD Checkstyle Configuration 1.3//EN"
+        "https://checkstyle.org/dtds/configuration_1_3.dtd">
+<module name="Checker">
+    <property name="charset" value="UTF-8"/>
+
+    <property name="severity" value="error"/>
+
+    <property name="fileExtensions" value="java, properties, xml"/>
+
+    <module name="FileTabCharacter">
+        <property name="eachLine" value="true"/>
+    </module>
+
+    <module name="LineLength">
+        <property name="fileExtensions" value="java"/>
+        <property name="max" value="100"/>
+    </module>
+
+    <module name="TreeWalker">
+        <module name="MagicNumber"/>
+        <module name="OuterTypeFilename"/>
+        <module name="IllegalTokenText">
+            <property name="tokens" value="STRING_LITERAL, CHAR_LITERAL"/>
+            <property name="format"
+                      value="\\u00(09|0(a|A)|0(c|C)|0(d|D)|22|27|5(C|c))|\\(0(10|11|12|14|15|42|47)|134)"/>
+            <property name="message"
+                      value="Consider using special escape sequence instead of octal value or Unicode escaped value."/>
+        </module>
+        <module name="AvoidEscapedUnicodeCharacters">
+            <property name="allowEscapesForControlCharacters" value="true"/>
+            <property name="allowByTailComment" value="true"/>
+            <property name="allowNonPrintableEscapes" value="true"/>
+        </module>
+        <module name="AvoidStarImport"/>
+        <module name="OneTopLevelClass"/>
+        <module name="NoLineWrap">
+            <property name="tokens" value="PACKAGE_DEF, IMPORT, STATIC_IMPORT"/>
+        </module>
+        <module name="EmptyBlock">
+            <property name="option" value="TEXT"/>
+            <property name="tokens"
+                      value="LITERAL_TRY, LITERAL_FINALLY, LITERAL_IF, LITERAL_ELSE, LITERAL_SWITCH"/>
+        </module>
+        <module name="NeedBraces">
+            <property name="tokens"
+                      value="LITERAL_DO, LITERAL_ELSE, LITERAL_FOR, LITERAL_IF, LITERAL_WHILE"/>
+        </module>
+        <module name="LeftCurly">
+            <property name="tokens"
+                      value="ANNOTATION_DEF, CLASS_DEF, CTOR_DEF, ENUM_CONSTANT_DEF, ENUM_DEF,
+                    INTERFACE_DEF, LAMBDA, LITERAL_CASE, LITERAL_CATCH, LITERAL_DEFAULT,
+                    LITERAL_DO, LITERAL_ELSE, LITERAL_FINALLY, LITERAL_FOR, LITERAL_IF,
+                    LITERAL_SWITCH, LITERAL_SYNCHRONIZED, LITERAL_TRY, LITERAL_WHILE, METHOD_DEF,
+                    OBJBLOCK, STATIC_INIT"/>
+        </module>
+        <module name="RightCurly">
+            <property name="id" value="RightCurlySame"/>
+            <property name="tokens"
+                      value="LITERAL_TRY, LITERAL_CATCH, LITERAL_FINALLY, LITERAL_IF, LITERAL_ELSE,
+                    LITERAL_DO"/>
+        </module>
+        <module name="RightCurly">
+            <property name="id" value="RightCurlyAlone"/>
+            <property name="option" value="alone"/>
+            <property name="tokens"
+                      value="CLASS_DEF, METHOD_DEF, CTOR_DEF, LITERAL_FOR, LITERAL_WHILE, STATIC_INIT,
+                    INSTANCE_INIT, ANNOTATION_DEF, ENUM_DEF"/>
+        </module>
+        <module name="SuppressionXpathSingleFilter">
+            <!-- suppresion is required till https://github.com/checkstyle/checkstyle/issues/7541 -->
+            <property name="id" value="RightCurlyAlone"/>
+            <property name="query" value="//RCURLY[parent::SLIST[count(./*)=1]
+                                                 or preceding-sibling::*[last()][self::LCURLY]]"/>
+        </module>
+        <module name="WhitespaceAfter">
+            <property name="tokens"
+                      value="COMMA, SEMI, TYPECAST, LITERAL_IF, LITERAL_ELSE,
+                    LITERAL_WHILE, LITERAL_DO, LITERAL_FOR, DO_WHILE"/>
+        </module>
+        <module name="WhitespaceAround">
+            <property name="allowEmptyConstructors" value="true"/>
+            <property name="allowEmptyLambdas" value="true"/>
+            <property name="allowEmptyMethods" value="true"/>
+            <property name="allowEmptyTypes" value="true"/>
+            <property name="allowEmptyLoops" value="true"/>
+            <property name="tokens"
+                      value="ASSIGN, BAND, BAND_ASSIGN, BOR, BOR_ASSIGN, BSR, BSR_ASSIGN, BXOR,
+                    BXOR_ASSIGN, COLON, DIV, DIV_ASSIGN, DO_WHILE, EQUAL, GE, GT, LAMBDA, LAND,
+                    LCURLY, LE, LITERAL_CATCH, LITERAL_DO, LITERAL_ELSE, LITERAL_FINALLY,
+                    LITERAL_FOR, LITERAL_IF, LITERAL_RETURN, LITERAL_SWITCH, LITERAL_SYNCHRONIZED,
+                     LITERAL_TRY, LITERAL_WHILE, LOR, LT, MINUS, MINUS_ASSIGN, MOD, MOD_ASSIGN,
+                     NOT_EQUAL, PLUS, PLUS_ASSIGN, QUESTION, RCURLY, SL, SLIST, SL_ASSIGN, SR,
+                     SR_ASSIGN, STAR, STAR_ASSIGN, LITERAL_ASSERT, TYPE_EXTENSION_AND"/>
+            <message key="ws.notFollowed"
+                     value="WhitespaceAround: ''{0}'' is not followed by whitespace. Empty blocks may only be represented as '{}' when not part of a multi-block statement (4.1.3)"/>
+            <message key="ws.notPreceded"
+                     value="WhitespaceAround: ''{0}'' is not preceded with whitespace."/>
+        </module>
+        <module name="OneStatementPerLine"/>
+        <module name="MultipleVariableDeclarations"/>
+        <module name="ArrayTypeStyle"/>
+        <module name="MissingSwitchDefault"/>
+        <module name="FallThrough"/>
+        <module name="UpperEll"/>
+        <module name="ModifierOrder"/>
+        <module name="EmptyLineSeparator">
+            <property name="tokens"
+                      value="PACKAGE_DEF, IMPORT, STATIC_IMPORT, CLASS_DEF, INTERFACE_DEF, ENUM_DEF,
+                    STATIC_INIT, INSTANCE_INIT, METHOD_DEF, CTOR_DEF, VARIABLE_DEF"/>
+            <property name="allowNoEmptyLineBetweenFields" value="true"/>
+        </module>
+        <module name="SeparatorWrap">
+            <property name="id" value="SeparatorWrapDot"/>
+            <property name="tokens" value="DOT"/>
+            <property name="option" value="nl"/>
+        </module>
+        <module name="SeparatorWrap">
+            <property name="id" value="SeparatorWrapComma"/>
+            <property name="tokens" value="COMMA"/>
+            <property name="option" value="EOL"/>
+        </module>
+        <module name="SeparatorWrap">
+            <!-- ELLIPSIS is EOL until https://github.com/google/styleguide/issues/258 -->
+            <property name="id" value="SeparatorWrapEllipsis"/>
+            <property name="tokens" value="ELLIPSIS"/>
+            <property name="option" value="EOL"/>
+        </module>
+        <module name="SeparatorWrap">
+            <!-- ARRAY_DECLARATOR is EOL until https://github.com/google/styleguide/issues/259 -->
+            <property name="id" value="SeparatorWrapArrayDeclarator"/>
+            <property name="tokens" value="ARRAY_DECLARATOR"/>
+            <property name="option" value="EOL"/>
+        </module>
+        <module name="SeparatorWrap">
+            <property name="id" value="SeparatorWrapMethodRef"/>
+            <property name="tokens" value="METHOD_REF"/>
+            <property name="option" value="nl"/>
+        </module>
+        <module name="PackageName">
+            <property name="format" value="^[a-z]+(\.[a-z][a-z0-9]*)*$"/>
+            <message key="name.invalidPattern"
+                     value="Package name ''{0}'' must match pattern ''{1}''."/>
+        </module>
+        <module name="TypeName">
+            <property name="tokens" value="CLASS_DEF, INTERFACE_DEF, ENUM_DEF, ANNOTATION_DEF"/>
+            <message key="name.invalidPattern"
+                     value="Type name ''{0}'' must match pattern ''{1}''."/>
+        </module>
+        <module name="MemberName">
+            <property name="format" value="^[a-z][a-z0-9][a-zA-Z0-9]*$"/>
+            <message key="name.invalidPattern"
+                     value="Member name ''{0}'' must match pattern ''{1}''."/>
+        </module>
+        <module name="ParameterName">
+            <property name="format" value="^[a-z]([a-z0-9][a-zA-Z0-9]*)?$"/>
+            <message key="name.invalidPattern"
+                     value="Parameter name ''{0}'' must match pattern ''{1}''."/>
+        </module>
+        <module name="LambdaParameterName">
+            <property name="format" value="^[a-z]([a-z0-9][a-zA-Z0-9]*)?$"/>
+            <message key="name.invalidPattern"
+                     value="Lambda parameter name ''{0}'' must match pattern ''{1}''."/>
+        </module>
+        <module name="CatchParameterName">
+            <property name="format" value="^[a-z]([a-z0-9][a-zA-Z0-9]*)?$"/>
+            <message key="name.invalidPattern"
+                     value="Catch parameter name ''{0}'' must match pattern ''{1}''."/>
+        </module>
+        <module name="LocalVariableName">
+            <property name="format" value="^[a-z]([a-z0-9][a-zA-Z0-9]*)?$"/>
+            <message key="name.invalidPattern"
+                     value="Local variable name ''{0}'' must match pattern ''{1}''."/>
+        </module>
+        <module name="ClassTypeParameterName">
+            <property name="format" value="(^[A-Z][0-9]?)$|([A-Z][a-zA-Z0-9]*[T]$)"/>
+            <message key="name.invalidPattern"
+                     value="Class type name ''{0}'' must match pattern ''{1}''."/>
+        </module>
+        <module name="MethodTypeParameterName">
+            <property name="format" value="(^[A-Z][0-9]?)$|([A-Z][a-zA-Z0-9]*[T]$)"/>
+            <message key="name.invalidPattern"
+                     value="Method type name ''{0}'' must match pattern ''{1}''."/>
+        </module>
+        <module name="InterfaceTypeParameterName">
+            <property name="format" value="(^[A-Z][0-9]?)$|([A-Z][a-zA-Z0-9]*[T]$)"/>
+            <message key="name.invalidPattern"
+                     value="Interface type name ''{0}'' must match pattern ''{1}''."/>
+        </module>
+        <module name="NoFinalizer"/>
+        <module name="GenericWhitespace">
+            <message key="ws.followed"
+                     value="GenericWhitespace ''{0}'' is followed by whitespace."/>
+            <message key="ws.preceded"
+                     value="GenericWhitespace ''{0}'' is preceded with whitespace."/>
+            <message key="ws.illegalFollow"
+                     value="GenericWhitespace ''{0}'' should followed by whitespace."/>
+            <message key="ws.notPreceded"
+                     value="GenericWhitespace ''{0}'' is not preceded with whitespace."/>
+        </module>
+        <module name="Indentation">
+            <property name="basicOffset" value="4"/>
+            <property name="braceAdjustment" value="0"/>
+            <property name="caseIndent" value="4"/>
+            <property name="throwsIndent" value="4"/>
+            <property name="lineWrappingIndentation" value="4"/>
+            <property name="arrayInitIndent" value="4"/>
+        </module>
+        <module name="AbbreviationAsWordInName">
+            <property name="ignoreFinal" value="false"/>
+            <property name="allowedAbbreviationLength" value="1"/>
+            <property name="tokens"
+                      value="CLASS_DEF, INTERFACE_DEF, ENUM_DEF, ANNOTATION_DEF, ANNOTATION_FIELD_DEF,
+                    PARAMETER_DEF, VARIABLE_DEF, METHOD_DEF"/>
+        </module>
+        <module name="OverloadMethodsDeclarationOrder"/>
+        <module name="VariableDeclarationUsageDistance"/>
+        <module name="MethodParamPad">
+            <property name="tokens"
+                      value="CTOR_DEF, LITERAL_NEW, METHOD_CALL, METHOD_DEF,
+                    SUPER_CTOR_CALL, ENUM_CONSTANT_DEF"/>
+        </module>
+        <module name="NoWhitespaceBefore">
+            <property name="tokens"
+                      value="COMMA, SEMI, POST_INC, POST_DEC, DOT, ELLIPSIS, METHOD_REF"/>
+            <property name="allowLineBreaks" value="true"/>
+        </module>
+        <module name="ParenPad">
+            <property name="tokens"
+                      value="ANNOTATION, ANNOTATION_FIELD_DEF, CTOR_CALL, CTOR_DEF, DOT, ENUM_CONSTANT_DEF,
+                    EXPR, LITERAL_CATCH, LITERAL_DO, LITERAL_FOR, LITERAL_IF, LITERAL_NEW,
+                    LITERAL_SWITCH, LITERAL_SYNCHRONIZED, LITERAL_WHILE, METHOD_CALL,
+                    METHOD_DEF, QUESTION, RESOURCE_SPECIFICATION, SUPER_CTOR_CALL, LAMBDA"/>
+        </module>
+        <module name="OperatorWrap">
+            <property name="option" value="NL"/>
+            <property name="tokens"
+                      value="BAND, BOR, BSR, BXOR, DIV, EQUAL, GE, GT, LAND, LE, LITERAL_INSTANCEOF, LOR,
+                    LT, MINUS, MOD, NOT_EQUAL, PLUS, QUESTION, SL, SR, STAR, METHOD_REF "/>
+        </module>
+        <module name="AnnotationLocation">
+            <property name="id" value="AnnotationLocationMostCases"/>
+            <property name="tokens"
+                      value="CLASS_DEF, INTERFACE_DEF, ENUM_DEF, METHOD_DEF, CTOR_DEF"/>
+        </module>
+        <module name="AnnotationLocation">
+            <property name="id" value="AnnotationLocationVariables"/>
+            <property name="tokens" value="VARIABLE_DEF"/>
+            <property name="allowSamelineMultipleAnnotations" value="true"/>
+        </module>
+        <module name="NonEmptyAtclauseDescription"/>
+        <module name="InvalidJavadocPosition"/>
+        <module name="JavadocTagContinuationIndentation"/>
+        <module name="SummaryJavadoc">
+            <property name="forbiddenSummaryFragments"
+                      value="^@return the *|^This method returns |^A [{]@code [a-zA-Z0-9]+[}]( is a )"/>
+        </module>
+        <module name="JavadocParagraph"/>
+        <module name="AtclauseOrder">
+            <property name="tagOrder" value="@param, @return, @throws, @deprecated"/>
+            <property name="target"
+                      value="CLASS_DEF, INTERFACE_DEF, ENUM_DEF, METHOD_DEF, CTOR_DEF, VARIABLE_DEF"/>
+        </module>
+        <module name="JavadocMethod">
+            <property name="accessModifiers" value="public"/>
+            <property name="allowMissingParamTags" value="true"/>
+            <property name="allowMissingReturnTag" value="true"/>
+            <property name="allowedAnnotations" value="Override, Test"/>
+            <property name="tokens" value="METHOD_DEF, CTOR_DEF, ANNOTATION_FIELD_DEF"/>
+        </module>
+        <module name="MethodName">
+            <property name="format" value="^[a-z][a-z0-9][a-zA-Z0-9_]*$"/>
+            <message key="name.invalidPattern"
+                     value="Method name ''{0}'' must match pattern ''{1}''."/>
+        </module>
+        <module name="SingleLineJavadoc">
+            <property name="ignoreInlineTags" value="false"/>
+        </module>
+        <module name="EmptyCatchBlock">
+            <property name="exceptionVariableName" value="expected"/>
+        </module>
+        <module name="CommentsIndentation">
+            <property name="tokens" value="SINGLE_LINE_COMMENT, BLOCK_COMMENT_BEGIN"/>
+        </module>
+        <!-- https://checkstyle.org/config_filters.html#SuppressionXpathFilter -->
+        <module name="SuppressionXpathFilter">
+            <property name="file" value="${org.checkstyle.google.suppressionxpathfilter.config}"
+                      default="checkstyle-xpath-suppressions.xml"/>
+            <property name="optional" value="true"/>
+        </module>
+    </module>
+</module>
\ No newline at end of file
diff --git a/pom.xml b/pom.xml
index 2d40c3e8a..03c23ac83 100644
--- a/pom.xml
+++ b/pom.xml
@@ -25,6 +25,27 @@
                     <target>17</target>
                 </configuration>
             </plugin>
+            <plugin>
+
+                <groupId>org.apache.maven.plugins</groupId>
+
+                <artifactId>maven-checkstyle-plugin</artifactId>
+
+                <version>3.6.0</version>
+
+                <configuration>
+
+                    <configLocation>checkstyle.xml</configLocation>
+
+                    <consoleOutput>true</consoleOutput>
+
+                    <failsOnError>true</failsOnError>
+
+                </configuration>
+
+            </plugin>
+
+
         </plugins>
     </build>
 
diff --git a/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java b/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
index cd0f86a48..48168bd76 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
@@ -10,9 +10,13 @@ public abstract class Product {
     private final BigDecimal taxPercent;
 
     protected Product(String name, BigDecimal price, BigDecimal tax) {
-        if (name == null || name.equals("") || price == null || tax == null || tax.compareTo(new BigDecimal(0)) < 0
+        if (name == null
+                || name.equals("")
+                || price == null
+                || tax == null
+                || tax.compareTo(new BigDecimal(0)) < 0
                 || price.compareTo(new BigDecimal(0)) < 0) {
-            throw new IllegalArgumentException();
+            throw new IllegalArgumentException("Invalid product data");
         }
         this.name = name;
         this.price = price;

From 5e6d0b4284122cd7a7491cd6f0f1a77d3470f3eb Mon Sep 17 00:00:00 2001
From: Anna Maywald <aniamaywald@gmail.com>
Date: Sat, 9 May 2026 16:54:41 +0200
Subject: [PATCH 5/7] Add invoice number with auto-increment counter

---
 .../java/pl/edu/agh/mwo/invoice/Invoice.java  | 23 +++++++++++++++++++
 .../pl/edu/agh/mwo/invoice/InvoiceTest.java   | 23 +++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
index 72f4048d5..88c146a23 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
@@ -7,8 +7,22 @@
 import pl.edu.agh.mwo.invoice.product.Product;
 
 public class Invoice {
+
+    private static int nextInvoiceNumber = 1;
+    private final int invoiceNumber;
+
     private Map<Product, Integer> products = new HashMap<Product, Integer>();
 
+
+    public Invoice() {
+        this.invoiceNumber = nextInvoiceNumber;
+        nextInvoiceNumber++;
+    }
+
+    public static int getInvoiceNumber() {
+        return nextInvoiceNumber;
+    }
+
     public void addProduct(Product product) {
         addProduct(product, 1);
     }
@@ -41,4 +55,13 @@ public BigDecimal getGrossTotal() {
         }
         return totalGross;
     }
+
+    public int generateInvoiceNumber() {
+        int invoiceNumber = 0;
+        for (Product product : products.keySet()) {
+            invoiceNumber = invoiceNumber + 1;
+            products.put(product, invoiceNumber);
+        }
+        return invoiceNumber;
+    }
 }
diff --git a/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java b/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
index 50513171c..d1f046399 100644
--- a/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
+++ b/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
@@ -125,4 +125,27 @@ public void testInvoiceWithNegativeQuantity() {
     public void testAddingNullProduct() {
         invoice.addProduct(null);
     }
+
+    @Test
+    public void testInvoiceHasNumberGreaterThan0 () {
+        Invoice invoice = new Invoice();
+        int number = invoice.getInvoiceNumber();
+        Assert.assertThat(number, Matchers.greaterThan(0));
+    }
+
+    @Test
+    public void testTwoInvoicesHaveDifferentNumber() {
+        int number1 = new Invoice().getInvoiceNumber();
+        int number2 = new Invoice().getInvoiceNumber();
+        Assert.assertNotEquals(number1, number2);
+    }
+
+    @Test
+    public void testInvoiceNumberDoesNotChange() {
+        Invoice invoice = new Invoice();
+        int firstCheck = invoice.getInvoiceNumber();
+        int secondCheck = invoice.getInvoiceNumber();
+        Assert.assertEquals(firstCheck, secondCheck);
+
+    }
 }

From a1e17b0e017a7f4952ea81d4b16194fa7cae1f24 Mon Sep 17 00:00:00 2001
From: Anna Maywald <aniamaywald@gmail.com>
Date: Sat, 9 May 2026 17:20:11 +0200
Subject: [PATCH 6/7] Add printInvoice method with header, products, position
 count

---
 .../java/pl/edu/agh/mwo/invoice/Invoice.java  | 31 +++++++++++-----
 .../pl/edu/agh/mwo/invoice/InvoiceTest.java   | 36 +++++++++++++++++++
 2 files changed, 59 insertions(+), 8 deletions(-)

diff --git a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
index 88c146a23..097c8478c 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
@@ -19,8 +19,8 @@ public Invoice() {
         nextInvoiceNumber++;
     }
 
-    public static int getInvoiceNumber() {
-        return nextInvoiceNumber;
+    public int getInvoiceNumber() {
+        return invoiceNumber;
     }
 
     public void addProduct(Product product) {
@@ -56,12 +56,27 @@ public BigDecimal getGrossTotal() {
         return totalGross;
     }
 
-    public int generateInvoiceNumber() {
-        int invoiceNumber = 0;
+
+    public String printInvoice() {
+        if (products.isEmpty()) {
+            throw new IllegalStateException();
+        }
+
+        StringBuilder builder = new StringBuilder();
+        builder.append("Faktura nr ").append(invoiceNumber).append("\n");
+
         for (Product product : products.keySet()) {
-            invoiceNumber = invoiceNumber + 1;
-            products.put(product, invoiceNumber);
+            Integer quantity = products.get(product);
+            builder.append(product.getName())
+                    .append("\t")
+                    .append(quantity)
+                    .append("\t")
+                    .append(product.getPriceWithTax())
+                    .append("\n");
         }
-        return invoiceNumber;
+
+        builder.append("Liczba pozycji: ").append(products.size());
+        return builder.toString();
     }
-}
+
+}
\ No newline at end of file
diff --git a/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java b/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
index d1f046399..abe965455 100644
--- a/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
+++ b/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
@@ -148,4 +148,40 @@ public void testInvoiceNumberDoesNotChange() {
         Assert.assertEquals(firstCheck, secondCheck);
 
     }
+    @Test
+    public void testPrintInvoiceContainsInvoiceNumber() {
+        Invoice invoice = new Invoice();
+        invoice.addProduct(new OtherProduct("Chleb", new BigDecimal("3.00")));
+        String result = invoice.printInvoice();
+        Assert.assertTrue(result.contains("Faktura nr " + invoice.getInvoiceNumber()));
+    }
+
+
+    @Test
+    public void testPrintInvoiceContainsProductNames() {
+        Invoice invoice = new Invoice();
+        invoice.addProduct(new OtherProduct("Chleb", new BigDecimal("3.00")), 2);
+        invoice.addProduct(new DairyProduct("Mleko", new BigDecimal("4.00")), 1);
+        String result = invoice.printInvoice();
+        Assert.assertTrue(result.contains("Chleb"));
+        Assert.assertTrue(result.contains("Mleko"));
+    }
+
+
+    @Test
+    public void testPrintInvoiceEndsWithPositionCount() {
+        Invoice invoice = new Invoice();
+        invoice.addProduct(new OtherProduct("A", new BigDecimal("1.00")));
+        invoice.addProduct(new OtherProduct("B", new BigDecimal("2.00")));
+        invoice.addProduct(new DairyProduct("C", new BigDecimal("3.00")));
+        String result = invoice.printInvoice();
+        Assert.assertTrue(result.contains("Liczba pozycji: 3"));
+
+    }
+
+    @Test(expected = IllegalStateException.class)
+    public void testPrintInvoiceForEmptyInvoiceThrowsException() {
+        Invoice invoice = new Invoice();
+        invoice.printInvoice();
+    }
 }

From 8ea22749cf9196dce2ce2e36a2c04b4bc3d6fe23 Mon Sep 17 00:00:00 2001
From: Anna Maywald <aniamaywald@gmail.com>
Date: Sat, 9 May 2026 17:27:23 +0200
Subject: [PATCH 7/7] Merge duplicate products by name and price

---
 .../java/pl/edu/agh/mwo/invoice/Invoice.java  |  7 ++++-
 .../edu/agh/mwo/invoice/product/Product.java  | 17 ++++++++++++
 .../pl/edu/agh/mwo/invoice/InvoiceTest.java   | 27 +++++++++++++++++++
 3 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
index 097c8478c..87ab080f0 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/Invoice.java
@@ -30,8 +30,13 @@ public void addProduct(Product product) {
     public void addProduct(Product product, Integer quantity) {
         if (product == null || quantity <= 0) {
             throw new IllegalArgumentException();
+
+        }
+        if (products.containsKey(product)) {
+            products.put(product, products.get(product) + quantity);
+        } else {
+            products.put(product, quantity);
         }
-        products.put(product, quantity);
     }
 
     public BigDecimal getNetTotal() {
diff --git a/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java b/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
index 48168bd76..5951f7d3f 100644
--- a/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
+++ b/src/main/java/pl/edu/agh/mwo/invoice/product/Product.java
@@ -38,4 +38,21 @@ public BigDecimal getTaxPercent() {
     public BigDecimal getPriceWithTax() {
         return price.multiply(taxPercent).add(price);
     }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (this == obj) {
+            return true;
+        }
+        if (obj == null || getClass() != obj.getClass()) {
+            return false;
+        }
+        Product other = (Product) obj;
+        return name.equals(other.name) && price.compareTo(other.price) == 0;
+    }
+
+    @Override
+    public int hashCode() {
+        return java.util.Objects.hash(name, price);
+    }
 }
diff --git a/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java b/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
index abe965455..7c350935c 100644
--- a/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
+++ b/src/test/java/pl/edu/agh/mwo/invoice/InvoiceTest.java
@@ -184,4 +184,31 @@ public void testPrintInvoiceForEmptyInvoiceThrowsException() {
         Invoice invoice = new Invoice();
         invoice.printInvoice();
     }
+
+    @Test
+    public void testInvoiceMergesDuplicateProductsByName() {
+        Invoice invoice = new Invoice();
+        invoice.addProduct(new OtherProduct("Chleb", new BigDecimal("3.00")), 2);
+        invoice.addProduct(new OtherProduct("Chleb", new BigDecimal("3.00")), 3);
+        Assert.assertEquals(new BigDecimal("18.45"),
+                invoice.getGrossTotal().setScale(2, java.math.RoundingMode.HALF_UP));
+    }
+
+    @Test
+    public void testInvoiceWithDuplicateProductHasOnlyOnePosition() {
+        Invoice invoice = new Invoice();
+        invoice.addProduct(new OtherProduct("Chleb", new BigDecimal("3.00")), 2);
+        invoice.addProduct(new OtherProduct("Chleb", new BigDecimal("3.00")), 3);
+        String result = invoice.printInvoice();
+        Assert.assertTrue(result.contains("Liczba pozycji: 1"));
+    }
+
+    @Test
+    public void testInvoiceTreatsDifferentPricesAsSeparateProducts() {
+        Invoice invoice = new Invoice();
+        invoice.addProduct(new OtherProduct("Chleb", new BigDecimal("3.00")), 2);
+        invoice.addProduct(new OtherProduct("Chleb", new BigDecimal("2.50")), 3);
+        String result = invoice.printInvoice();
+        Assert.assertTrue(result.contains("Liczba pozycji: 2"));
+    }
 }