Add split-loop-with-lambda learning hour: draft, pre-factored exercise, solution

- Samman learning hour: 5/5/10/25/5 outline; pairs stop at extracted method taking the lambda as a parameter - exercise/java: pre-factored variant of the kata (Q1/Q4 dead branch stripped, dates as constant), approval test red/flaky by design - exercise/solution: collectExpectedWeather(LongFunction<Boolean>) + no-arg overload; deterministic approval test (all-sunny lambda) - rehearse-with-agent.md: rehearsal setup with qwen + java-refactoring-mcp
2026-09-27 13:30:00 +00:00
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+target/
+*.received.txt
+*.approved.txt
+.idea/
+*.iml
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+# IceCreamForecasting — Split Loop with Lambda (exercise)
+
+Pre-factored variant of [IceCreamForecasting-Refactoring-Kata](https://github.com/emilybache/IceCreamForecasting-Refactoring-Kata):
+the Q1/Q4 dead branch is stripped and the hardcoded dates are a constant now.
+Everything else — including the noise in the scoring loop — is untouched.
+
+## Task
+
+`longRangeForecast()` is hard to test: it calls `scorer`, and `Scorer`
+stands for an external weather service you must not call from a unit test.
+The rest of the method's inputs are only `DATES` and `ANCHOR_DATE`.
+
+Get it under test:
+
+1. First get any test running that calls `longRangeForecast()` —
+   it will fail or be flaky, because of the dependency on `Scorer`.
+2. Then use the **Split Loop with Lambda** mechanics (6 steps, on the handout)
+   so that the weather collection becomes an extracted method that takes the
+   weather-reading as a **lambda parameter**.
+3. Stop when you have an extracted method that takes the lambda as a parameter,
+   and a test that passes **without** touching `Scorer`.
+
+## Constraint
+
+Don't change `Scorer` and don't change the *behaviour* of
+`longRangeForecast()`. Compile early, compile often.
+
+## Debrief questions
+
+- At which step did plain **Split Loop** stop working, and why?
+  (Hint: what type did your introduced variable end up being?)
+- There are **two** calls to `scorer` in the weather loop.
+  What did you do with each one?
+- Could you delete either call without changing the forecast?
+  Try it. Why did that work?
+- Where would you take this next — more extraction, or moving the method
+  to another class where `Scorer` is unknown?
@@ -0,0 +1,31 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+
+    <groupId>codingdojo</groupId>
+    <artifactId>icecream-split-loop-lambda-exercise</artifactId>
+    <version>1.0.0</version>
+
+    <properties>
+        <maven.compiler.source>17</maven.compiler.source>
+        <maven.compiler.target>17</maven.compiler.target>
+        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter</artifactId>
+            <version>5.10.2</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>com.approvaltests</groupId>
+            <artifactId>approvaltests</artifactId>
+            <version>18.6.0</version>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+</project>
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+package codingdojo;
+
+public enum IceCream {
+    Strawberry,
+    Chocolate,
+    Vanilla;
+}
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+package codingdojo;
+
+import java.time.Instant;
+import java.time.temporal.ChronoUnit;
+import java.util.*;
+
+/**
+ * Pre-factored variant of LongRangeForecasts from
+ * https://github.com/emilybache/IceCreamForecasting-Refactoring-Kata
+ *
+ * Differences from the kata original (deliberate, for the learning hour):
+ * - The Q1/Q4 branch was removed. It was dead code anyway: the unconditional
+ *   loop right after it overwrites every value it sets. (Splitting loops
+ *   sometimes reveals things like this.)
+ * - The hardcoded list of interesting dates is now a constant, DATES, and the
+ *   anchor instant is ANCHOR_DATE. (Turning the dates into a parameter is a
+ *   *later* refactoring — not part of this exercise.)
+ *
+ * Your task: see README.md
+ */
+public class LongRangeForecasts {
+
+    private static final Instant ANCHOR_DATE = Instant.parse("2023-04-26T14:00:00.000-07:00");
+    private static final List<Instant> DATES = List.of(
+            Instant.parse("2023-05-01T14:00:00.000-07:00"),
+            Instant.parse("2023-05-18T14:00:00.000-07:00"),
+            Instant.parse("2023-06-05T14:00:00.000-07:00"),
+            Instant.parse("2023-06-23T14:00:00.000-07:00")
+    );
+
+    private final Scorer scorer = new Scorer();
+
+    public Map<IceCream, Integer> longRangeForecast() {
+
+        var result = new HashMap<IceCream, Integer>();
+        for (IceCream flavour : IceCream.values()) {
+            result.put(flavour, 0);
+        }
+        List<Boolean> expectedWeather = new ArrayList<>();
+        for (Instant interestingDate : DATES) {
+            scorer.updateSelection();
+            long daysForward = ChronoUnit.DAYS.between(ANCHOR_DATE, interestingDate);
+            Boolean weather = scorer.lookupWeather(daysForward);
+            expectedWeather.add(weather);
+        }
+
+        for (IceCream flavour : result.keySet()) {
+            result.put(flavour, result.get(flavour) + 10);
+            var sunnyHolidays = expectedWeather.stream().filter(s -> s).count();
+            if (sunnyHolidays > 2 && flavour == IceCream.Vanilla) {
+                result.put(flavour, result.get(flavour) + 5);
+            }
+            if (sunnyHolidays > 1 && expectedWeather.get(1)) {
+                result.put(flavour, result.get(flavour) + 2);
+            }
+        }
+        return result;
+    }
+}
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+package codingdojo;
+
+import java.util.Random;
+
+/**
+ * Trimmed version of the kata's Scorer: only the parts LongRangeForecasts uses.
+ * lookupWeather stands in for an API call to a weather service — in the real
+ * system this is the "unwanted dependency".
+ */
+public class Scorer {
+
+    public static IceCream flavour = null;
+
+    public int getScore() {
+        boolean sunnyToday = lookupWeather();
+        if (flavour == null) {
+            return -1;
+        }
+        switch (flavour) {
+            case Strawberry:
+                return sunnyToday ? 10 : 5;
+            case Chocolate:
+                return 6;
+            case Vanilla:
+                return sunnyToday ? 7 : 5;
+            default:
+                return -1;
+        }
+    }
+
+    public boolean lookupWeather() {
+        return new Random().nextBoolean();
+    }
+
+    public boolean lookupWeather(long daysForward) {
+        // placeholder implementation - real version would make API call to weather service
+        return new Random().nextBoolean();
+    }
+
+    public void updateSelection() {
+        // placeholder implementation - real version would use machine learning to predict sales
+        var score = getScore();
+        if (score > 5) {
+            var randomizer = new Random();
+            IceCream[] allFlavours = IceCream.values();
+            flavour = allFlavours[randomizer.nextInt(allFlavours.length)];
+        }
+    }
+}
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+package codingdojo;
+
+import org.approvaltests.Approvals;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Map;
+
+public class LongRangeForecastsTest {
+
+    @Test
+    void longRangeForecast() {
+        var actual = new LongRangeForecasts().longRangeForecast();
+        Approvals.verify(printIceCreamForecast(actual));
+    }
+
+    private static String printIceCreamForecast(Map<IceCream, Integer> actual) {
+        var printedResult = new StringBuilder();
+        printedResult.append("{");
+        var sortedKeys = new ArrayList<>(actual.keySet());
+        Collections.sort(sortedKeys);
+        for (IceCream key : sortedKeys) {
+            printedResult.append(key);
+            printedResult.append(":");
+            printedResult.append(actual.get(key));
+            printedResult.append(", ");
+        }
+        printedResult.append("}");
+        return printedResult.toString();
+    }
+}