Add staged quality increase behavior

Depending on the sellIn value, we can have a different rate of quality
increase. There always needs to be a default quality increase defined.
And then we need to define the stages at with the quality increase
changes.

Java/src/main/java/com/gildedrose/behavior/quality/QualityStage.java

@@ -0,0 +1,24 @@
+package com.gildedrose.behavior.quality;
+
+public class QualityStage {
+
+    private final int sellInCutoff;
+    private final int qualityIncrease;
+
+    private QualityStage(int sellInCutoff, int qualityIncrease) {
+        this.sellInCutoff = sellInCutoff;
+        this.qualityIncrease = qualityIncrease;
+    }
+
+    public static QualityStage of(int sellInCutoff, int qualityIncrease) {
+        return new QualityStage(sellInCutoff, qualityIncrease);
+    }
+
+    public int getSellInCutoff() {
+        return sellInCutoff;
+    }
+
+    public int getQualityIncrease() {
+        return qualityIncrease;
+    }
+}

Java/src/main/java/com/gildedrose/behavior/quality/StagedIncreasingQualityBehavior.java

@@ -0,0 +1,52 @@
+package com.gildedrose.behavior.quality;
+
+import com.gildedrose.Item;
+
+import java.util.Comparator;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class StagedIncreasingQualityBehavior implements QualityBehavior {
+
+    public static final int MAX_QUALITY_LEVEL = 50;
+    public static final int MIN_QUALITY_LEVEL = 0;
+    private final List<QualityStage> stages;
+    private final QualityStage defaultStage;
+
+
+    private StagedIncreasingQualityBehavior(List<QualityStage> stages, int defaultQualityIncrease) {
+        this.stages = getSortedQualityStages(stages);
+        this.defaultStage = QualityStage.of(0, defaultQualityIncrease);
+    }
+
+    public static StagedIncreasingQualityBehavior withStages(List<QualityStage> stages, int defaultQualityIncrease) {
+        return new StagedIncreasingQualityBehavior(stages, defaultQualityIncrease);
+    }
+
+    @Override
+    public void processQualityUpdate(Item item) {
+        increaseQuality(item);
+    }
+
+    private void increaseQuality(Item item) {
+        if (item.sellIn <= 0) {
+            item.quality = 0;
+        } else {
+            final QualityStage stage = findStage(item);
+            item.quality = limitQuality(item.quality + stage.getQualityIncrease());
+        }
+    }
+
+    private int limitQuality(int newQuality) {
+        return Math.max(MIN_QUALITY_LEVEL, Math.min(MAX_QUALITY_LEVEL, newQuality));
+    }
+
+    private QualityStage findStage(Item item) {
+        return stages.stream().filter(qualityStage -> qualityStage.getSellInCutoff() >= item.sellIn)
+                .findFirst().orElse(defaultStage);
+    }
+
+    private List<QualityStage> getSortedQualityStages(List<QualityStage> stagesUnsorted) {
+        return stagesUnsorted.stream().sorted(Comparator.comparingInt(QualityStage::getSellInCutoff)).collect(Collectors.toList());
+    }
+}

Java/src/test/java/com/gildedrose/behavior/quality/StagedIncreasingQualityBehaviorTest.java

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+package com.gildedrose.behavior.quality;
+
+import com.gildedrose.Item;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class StagedIncreasingQualityBehaviorTest {
+
+    private QualityBehavior stagedQualityBehavior;
+
+    private QualityStage stage1 = QualityStage.of(10, 2);
+    private QualityStage stage2 = QualityStage.of(5, 3);
+
+    @BeforeEach
+    public void setUp() throws Exception {
+        stagedQualityBehavior = StagedIncreasingQualityBehavior.withStages(new ArrayList<>(Arrays.asList(stage1, stage2)), 1);
+    }
+
+    @Test
+    void stagedIncrease() {
+        Item item = getItem(11, 1);
+        stagedQualityBehavior.processQualityUpdate(item);
+        assertEquals(2, item.quality);
+
+        item.sellIn = 10;
+        stagedQualityBehavior.processQualityUpdate(item);
+        assertEquals(4, item.quality);
+
+        item.sellIn = 6;
+        stagedQualityBehavior.processQualityUpdate(item);
+        assertEquals(6, item.quality);
+
+        item.sellIn = 5;
+        stagedQualityBehavior.processQualityUpdate(item);
+        assertEquals(9, item.quality);
+
+        item.sellIn = 1;
+        stagedQualityBehavior.processQualityUpdate(item);
+        assertEquals(12, item.quality);
+
+        item.sellIn = 0;
+        stagedQualityBehavior.processQualityUpdate(item);
+        assertEquals(0, item.quality);
+
+        item.sellIn = -10;
+        item.quality = 10;
+        stagedQualityBehavior.processQualityUpdate(item);
+        assertEquals(0, item.quality);
+    }
+
+    private Item getItem(int sellIn, int quality) {
+        return new Item("SomeItem", sellIn, quality);
+    }
+}