From c6f6e3a835df0c28cd78dd1cb6408c6cba6c221f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn?= <bjoernwe@users.noreply.github.com>
Date: Mon, 2 Jan 2023 18:06:08 +0100
Subject: [PATCH 1/7] Add WeatherDataSource

---
 pom.xml                                       | 13 ++++-
 src/main/java/de/bcxp/challenge/App.java      | 33 +++++++++--
 .../de/bcxp/challenge/data/DataSource.java    |  6 ++
 .../data/weather/WeatherDataSourceCSV.java    | 33 +++++++++++
 .../challenge/data/weather/WeatherRecord.java | 36 ++++++++++++
 src/test/java/de/bcxp/challenge/AppTest.java  | 25 --------
 .../weather/WeatherDataSourceCsvTest.java     | 27 +++++++++
 .../data/weather/WeatherDataSourceEnum.java   |  6 ++
 .../weather/WeatherDataSourceFactory.java     | 38 +++++++++++++
 .../data/weather/WeatherDataSourceMock.java   | 19 +++++++
 .../data/weather/WeatherDataSourceTest.java   | 57 +++++++++++++++++++
 src/test/resources/challenge/weather.csv      |  4 ++
 12 files changed, 265 insertions(+), 32 deletions(-)
 create mode 100644 src/main/java/de/bcxp/challenge/data/DataSource.java
 create mode 100644 src/main/java/de/bcxp/challenge/data/weather/WeatherDataSourceCSV.java
 create mode 100644 src/main/java/de/bcxp/challenge/data/weather/WeatherRecord.java
 delete mode 100644 src/test/java/de/bcxp/challenge/AppTest.java
 create mode 100644 src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceCsvTest.java
 create mode 100644 src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceEnum.java
 create mode 100644 src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceFactory.java
 create mode 100644 src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceMock.java
 create mode 100644 src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceTest.java
 create mode 100644 src/test/resources/challenge/weather.csv

diff --git a/pom.xml b/pom.xml
index 6187768..9f06a86 100644
--- a/pom.xml
+++ b/pom.xml
@@ -35,10 +35,21 @@
     </properties>
 
     <dependencies>
+        <dependency>
+            <groupId>com.opencsv</groupId>
+            <artifactId>opencsv</artifactId>
+            <version>5.7.1</version>
+        </dependency>
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter-engine</artifactId>
-            <version>5.8.0-M1</version>
+            <version>5.9.0</version>
+            <scope>test</scope>
+        </dependency>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-params</artifactId>
+            <version>5.9.0</version>
             <scope>test</scope>
         </dependency>
     </dependencies>
diff --git a/src/main/java/de/bcxp/challenge/App.java b/src/main/java/de/bcxp/challenge/App.java
index a6c1150..b21f9a4 100644
--- a/src/main/java/de/bcxp/challenge/App.java
+++ b/src/main/java/de/bcxp/challenge/App.java
@@ -1,23 +1,44 @@
 package de.bcxp.challenge;
 
-/**
- * The entry class for your solution. This class is only aimed as starting point and not intended as baseline for your software
- * design. Read: create your own classes and packages as appropriate.
- */
+import de.bcxp.challenge.data.DataSource;
+import de.bcxp.challenge.data.weather.WeatherDataSourceCSV;
+import de.bcxp.challenge.data.weather.WeatherRecord;
+
+import java.io.FileNotFoundException;
+import java.nio.file.Path;
+
+
 public final class App {
 
+    private static final int EXIT_ERROR_DATA_WEATHER = 1;
+
     /**
      * This is the main entry method of your program.
      * @param args The CLI arguments passed
      */
     public static void main(String... args) {
 
-        // Your preparation code …
+        DataSource<WeatherRecord> weatherDataSource = tryInitWeatherDataSource(
+                Path.of("./src/main/resources/de/bcxp/challenge/weather.csv")
+        );
 
-        String dayWithSmallestTempSpread = "Someday";     // Your day analysis function call …
+        int dayWithSmallestTempSpread = -1;
         System.out.printf("Day with smallest temperature spread: %s%n", dayWithSmallestTempSpread);
 
         String countryWithHighestPopulationDensity = "Some country"; // Your population density analysis function call …
         System.out.printf("Country with highest population density: %s%n", countryWithHighestPopulationDensity);
     }
+
+    private static DataSource<WeatherRecord> tryInitWeatherDataSource(Path csvPath) {
+
+        try {
+            return new WeatherDataSourceCSV(csvPath);
+        } catch (FileNotFoundException e) {
+            System.out.printf("Error: CSV file for weather data not found: %s%n", csvPath);
+            System.exit(EXIT_ERROR_DATA_WEATHER);
+        }
+
+        return null;
+    }
+
 }
diff --git a/src/main/java/de/bcxp/challenge/data/DataSource.java b/src/main/java/de/bcxp/challenge/data/DataSource.java
new file mode 100644
index 0000000..8d44722
--- /dev/null
+++ b/src/main/java/de/bcxp/challenge/data/DataSource.java
@@ -0,0 +1,6 @@
+package de.bcxp.challenge.data;
+
+
+public interface DataSource<T> {
+    Iterable<T> getData();
+}
diff --git a/src/main/java/de/bcxp/challenge/data/weather/WeatherDataSourceCSV.java b/src/main/java/de/bcxp/challenge/data/weather/WeatherDataSourceCSV.java
new file mode 100644
index 0000000..d8595fe
--- /dev/null
+++ b/src/main/java/de/bcxp/challenge/data/weather/WeatherDataSourceCSV.java
@@ -0,0 +1,33 @@
+package de.bcxp.challenge.data.weather;
+
+import com.opencsv.bean.CsvToBeanBuilder;
+import de.bcxp.challenge.data.DataSource;
+
+import java.io.FileNotFoundException;
+import java.io.FileReader;
+import java.nio.file.Path;
+
+public class WeatherDataSourceCSV implements DataSource<WeatherRecord> {
+
+    private final FileReader csvFileReader;
+
+    public WeatherDataSourceCSV(Path csvPath) throws FileNotFoundException {
+        // FileNotFoundException is an exception type that is clearly specific to a file-based implementation of the
+        // DataSource interface. Usually we should avoid throwing implementation-specific exceptions that are not
+        // defined by the interface. But for the constructor it's okay under the assumption that the data source will
+        // be initialized in a "dirty main" function and then injected into the application.
+        this.csvFileReader = new FileReader(csvPath.toString());
+    }
+
+    @Override
+    public Iterable<WeatherRecord> getData() {
+
+        CsvToBeanBuilder<WeatherRecord> beanBuilder = new CsvToBeanBuilder<>(this.csvFileReader);
+
+        return beanBuilder
+                .withType(WeatherRecord.class)
+                .build()
+                .parse();
+    }
+
+}
diff --git a/src/main/java/de/bcxp/challenge/data/weather/WeatherRecord.java b/src/main/java/de/bcxp/challenge/data/weather/WeatherRecord.java
new file mode 100644
index 0000000..1997604
--- /dev/null
+++ b/src/main/java/de/bcxp/challenge/data/weather/WeatherRecord.java
@@ -0,0 +1,36 @@
+package de.bcxp.challenge.data.weather;
+
+import com.opencsv.bean.CsvBindByName;
+
+public class WeatherRecord {
+
+        @CsvBindByName(column = "Day", required = true)
+        private int day;
+
+        @CsvBindByName(column = "MxT", required = true)
+        private int mxt;
+
+        @CsvBindByName(column = "MnT", required = true)
+        private int mnt;
+
+        public WeatherRecord() {}  // openCSV needs this constructor when reading weather records from file
+
+        public WeatherRecord(int day, int mxt, int mnt) {
+                this.day = day;
+                this.mxt = mxt;
+                this.mnt = mnt;
+        }
+
+        public int getDay() {
+                return day;
+        }
+
+        public int getMxT() {
+                return mxt;
+        }
+
+        public int getMnT() {
+                return mnt;
+        }
+
+}
diff --git a/src/test/java/de/bcxp/challenge/AppTest.java b/src/test/java/de/bcxp/challenge/AppTest.java
deleted file mode 100644
index e7b400c..0000000
--- a/src/test/java/de/bcxp/challenge/AppTest.java
+++ /dev/null
@@ -1,25 +0,0 @@
-package de.bcxp.challenge;
-
-import org.junit.jupiter.api.BeforeEach;
-import org.junit.jupiter.api.Test;
-
-import static org.junit.jupiter.api.Assertions.assertEquals;
-
-/**
- * Example JUnit 5 test case.
- */
-class AppTest {
-
-    private String successLabel = "not successful";
-
-    @BeforeEach
-    void setUp() {
-        successLabel = "successful";
-    }
-
-    @Test
-    void aPointlessTest() {
-        assertEquals("successful", successLabel, "My expectations were not met");
-    }
-
-}
\ No newline at end of file
diff --git a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceCsvTest.java b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceCsvTest.java
new file mode 100644
index 0000000..1c46e40
--- /dev/null
+++ b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceCsvTest.java
@@ -0,0 +1,27 @@
+package de.bcxp.challenge.data.weather;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.io.FileNotFoundException;
+import java.nio.file.Path;
+
+public class WeatherDataSourceCsvTest {
+
+    @Test
+    public void testInvalidPathThrowsException() {
+
+        // GIVEN an invalid path to CSV file
+        Path invalidPath = Path.of("./INVALID/PATH.csv");
+
+        // WHEN a CsvDataSource is instantiated with the wrong path
+        Exception exception = Assertions.assertThrows(FileNotFoundException.class, () ->
+                new WeatherDataSourceCSV(invalidPath)
+        );
+
+        // THEN an exception is thrown
+        Assertions.assertEquals(FileNotFoundException.class, exception.getClass());
+
+    }
+
+}
diff --git a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceEnum.java b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceEnum.java
new file mode 100644
index 0000000..f630a86
--- /dev/null
+++ b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceEnum.java
@@ -0,0 +1,6 @@
+package de.bcxp.challenge.data.weather;
+
+public enum WeatherDataSourceEnum {
+    MOCK,
+    CSV,
+}
diff --git a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceFactory.java b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceFactory.java
new file mode 100644
index 0000000..97e4e5f
--- /dev/null
+++ b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceFactory.java
@@ -0,0 +1,38 @@
+package de.bcxp.challenge.data.weather;
+
+import de.bcxp.challenge.data.DataSource;
+
+import java.io.FileNotFoundException;
+import java.nio.file.Path;
+import java.util.ArrayList;
+
+public class WeatherDataSourceFactory {
+
+    public static DataSource<WeatherRecord> newInstance(WeatherDataSourceEnum dataSourceEnum) throws FileNotFoundException {
+
+        if (dataSourceEnum == WeatherDataSourceEnum.MOCK) {
+            return newMock();
+        } else if (dataSourceEnum == WeatherDataSourceEnum.CSV) {
+            return newCsv();
+        }
+
+        return null;
+    }
+
+    private static DataSource<WeatherRecord> newMock() {
+
+        ArrayList<WeatherRecord> records = new ArrayList<>();
+
+        records.add(new WeatherRecord(1, 88, 59));
+        records.add(new WeatherRecord(2, 79, 63));
+        records.add(new WeatherRecord(3, 77, 55));
+
+        return new WeatherDataSourceMock(records);
+    }
+
+    private static DataSource<WeatherRecord> newCsv() throws FileNotFoundException {
+        Path csvPath = Path.of("./src/test/resources/challenge/weather.csv");
+        return new WeatherDataSourceCSV(csvPath);
+    }
+
+}
diff --git a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceMock.java b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceMock.java
new file mode 100644
index 0000000..f059051
--- /dev/null
+++ b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceMock.java
@@ -0,0 +1,19 @@
+package de.bcxp.challenge.data.weather;
+
+
+import de.bcxp.challenge.data.DataSource;
+
+public class WeatherDataSourceMock implements DataSource<WeatherRecord> {
+
+    private final Iterable<WeatherRecord> records;
+
+    public WeatherDataSourceMock(Iterable<WeatherRecord> mockRecords) {
+        this.records = mockRecords;
+    }
+
+    @Override
+    public Iterable<WeatherRecord> getData() {
+        return this.records;
+    }
+
+}
diff --git a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceTest.java b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceTest.java
new file mode 100644
index 0000000..a2306ba
--- /dev/null
+++ b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceTest.java
@@ -0,0 +1,57 @@
+package de.bcxp.challenge.data.weather;
+
+import de.bcxp.challenge.data.DataSource;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.EnumSource;
+
+import java.io.FileNotFoundException;
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+
+public class WeatherDataSourceTest {
+
+    @ParameterizedTest
+    @EnumSource(WeatherDataSourceEnum.class)  // Run test for all DataSource implementations (as listed in the enum)
+    void testAllWeatherDataSourcesReturnPlausibleWeatherRecords(WeatherDataSourceEnum dataSourceEnum) throws FileNotFoundException {
+
+        // GIVEN a data source for weather records
+        DataSource<WeatherRecord> dataSource = WeatherDataSourceFactory.newInstance(dataSourceEnum);
+        assertNotNull(dataSource);
+
+        // WHEN data is read into a list
+        List<WeatherRecord> records = new ArrayList<>();
+        dataSource.getData().forEach(records::add);
+
+        // THEN there are three plausible weather records
+        for (int i = 0; i < 3; i++) {
+            WeatherRecord record = records.get(i);
+            assertEquals(i+1, record.getDay());
+            assert(record.getMxT() >= record.getMnT());
+        }
+
+    }
+
+    @ParameterizedTest
+    @EnumSource(WeatherDataSourceEnum.class)  // Run test for all DataSource implementations (as listed in the enum)
+    void testDataSourcesReturnKnownMockData(WeatherDataSourceEnum dataSourceEnum) throws FileNotFoundException {
+
+        // GIVEN a data source for weather records
+        DataSource<WeatherRecord> dataSource = WeatherDataSourceFactory.newInstance(dataSourceEnum);
+        assertNotNull(dataSource);
+
+        // WHEN data is read into a list
+        List<WeatherRecord> records = new ArrayList<>();
+        dataSource.getData().forEach(records::add);
+
+        // THEN the weather records contain expected values (regression test)
+        assertEquals(88, records.get(0).getMxT());
+        assertEquals(79, records.get(1).getMxT());
+        assertEquals(63, records.get(1).getMnT());
+        assertEquals(55, records.get(2).getMnT());
+    }
+
+}
diff --git a/src/test/resources/challenge/weather.csv b/src/test/resources/challenge/weather.csv
new file mode 100644
index 0000000..2f6c771
--- /dev/null
+++ b/src/test/resources/challenge/weather.csv
@@ -0,0 +1,4 @@
+Day,MxT,MnT,AvT,AvDP,1HrP TPcpn,PDir,AvSp,Dir,MxS,SkyC,MxR,Mn,R AvSLP
+1,88,59,74,53.8,0,280,9.6,270,17,1.6,93,23,1004.5
+2,79,63,71,46.5,0,330,8.7,340,23,3.3,70,28,1004.5
+3,77,55,66,39.6,0,350,5,350,9,2.8,59,24,1016.8
\ No newline at end of file

From 26a1ee522985dd4c866f213def2fa459642eb5b7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn?= <bjoernwe@users.noreply.github.com>
Date: Mon, 2 Jan 2023 19:59:46 +0100
Subject: [PATCH 2/7] Add weather stats

---
 src/main/java/de/bcxp/challenge/App.java      |  9 ++--
 .../de/bcxp/challenge/stats/WeatherStats.java | 25 +++++++++
 .../weather/WeatherDataSourceFactory.java     |  9 +---
 .../data/weather/WeatherDataSourceMock.java   |  9 ++++
 .../challenge/stats/WeatherStatsTest.java     | 52 +++++++++++++++++++
 5 files changed, 92 insertions(+), 12 deletions(-)
 create mode 100644 src/main/java/de/bcxp/challenge/stats/WeatherStats.java
 create mode 100644 src/test/java/de/bcxp/challenge/stats/WeatherStatsTest.java

diff --git a/src/main/java/de/bcxp/challenge/App.java b/src/main/java/de/bcxp/challenge/App.java
index b21f9a4..2902f72 100644
--- a/src/main/java/de/bcxp/challenge/App.java
+++ b/src/main/java/de/bcxp/challenge/App.java
@@ -3,6 +3,7 @@
 import de.bcxp.challenge.data.DataSource;
 import de.bcxp.challenge.data.weather.WeatherDataSourceCSV;
 import de.bcxp.challenge.data.weather.WeatherRecord;
+import de.bcxp.challenge.stats.WeatherStats;
 
 import java.io.FileNotFoundException;
 import java.nio.file.Path;
@@ -18,12 +19,12 @@ public final class App {
      */
     public static void main(String... args) {
 
-        DataSource<WeatherRecord> weatherDataSource = tryInitWeatherDataSource(
+        Iterable<WeatherRecord> weatherData = tryInitWeatherDataSource(
                 Path.of("./src/main/resources/de/bcxp/challenge/weather.csv")
-        );
+        ).getData();
 
-        int dayWithSmallestTempSpread = -1;
-        System.out.printf("Day with smallest temperature spread: %s%n", dayWithSmallestTempSpread);
+        WeatherRecord recordWithSmallestTempSpread = WeatherStats.findMinTemperatureSpread(weatherData);
+        System.out.printf("Day with smallest temperature spread: %s%n", recordWithSmallestTempSpread.getDay());
 
         String countryWithHighestPopulationDensity = "Some country"; // Your population density analysis function call …
         System.out.printf("Country with highest population density: %s%n", countryWithHighestPopulationDensity);
diff --git a/src/main/java/de/bcxp/challenge/stats/WeatherStats.java b/src/main/java/de/bcxp/challenge/stats/WeatherStats.java
new file mode 100644
index 0000000..a6b3d4d
--- /dev/null
+++ b/src/main/java/de/bcxp/challenge/stats/WeatherStats.java
@@ -0,0 +1,25 @@
+package de.bcxp.challenge.stats;
+
+
+import de.bcxp.challenge.data.weather.WeatherRecord;
+
+import java.util.Comparator;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+public class WeatherStats {
+
+    public static WeatherRecord findMinTemperatureSpread(Iterable<WeatherRecord> records) {
+
+        Stream<WeatherRecord> recordStream = StreamSupport.stream(records.spliterator(), false);
+
+        return recordStream
+                .min(Comparator.comparing(WeatherStats::getMinMaxSpread))
+                .orElse(null);
+    }
+
+    private static int getMinMaxSpread(WeatherRecord indexedRecord) {
+        return indexedRecord.getMxT() - indexedRecord.getMnT();
+    }
+
+}
diff --git a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceFactory.java b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceFactory.java
index 97e4e5f..d5ff729 100644
--- a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceFactory.java
+++ b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceFactory.java
@@ -4,7 +4,6 @@
 
 import java.io.FileNotFoundException;
 import java.nio.file.Path;
-import java.util.ArrayList;
 
 public class WeatherDataSourceFactory {
 
@@ -20,13 +19,7 @@ public static DataSource<WeatherRecord> newInstance(WeatherDataSourceEnum dataSo
     }
 
     private static DataSource<WeatherRecord> newMock() {
-
-        ArrayList<WeatherRecord> records = new ArrayList<>();
-
-        records.add(new WeatherRecord(1, 88, 59));
-        records.add(new WeatherRecord(2, 79, 63));
-        records.add(new WeatherRecord(3, 77, 55));
-
+        Iterable<WeatherRecord> records = WeatherDataSourceMock.MOCK_RECORDS;
         return new WeatherDataSourceMock(records);
     }
 
diff --git a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceMock.java b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceMock.java
index f059051..8da6bf1 100644
--- a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceMock.java
+++ b/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceMock.java
@@ -3,8 +3,17 @@
 
 import de.bcxp.challenge.data.DataSource;
 
+import java.util.Arrays;
+import java.util.List;
+
 public class WeatherDataSourceMock implements DataSource<WeatherRecord> {
 
+    public static final List<WeatherRecord> MOCK_RECORDS = Arrays.asList(
+            new WeatherRecord(1, 88, 59),
+            new WeatherRecord(2, 79, 63),
+            new WeatherRecord(3, 77, 55)
+    );
+
     private final Iterable<WeatherRecord> records;
 
     public WeatherDataSourceMock(Iterable<WeatherRecord> mockRecords) {
diff --git a/src/test/java/de/bcxp/challenge/stats/WeatherStatsTest.java b/src/test/java/de/bcxp/challenge/stats/WeatherStatsTest.java
new file mode 100644
index 0000000..d4ad5f6
--- /dev/null
+++ b/src/test/java/de/bcxp/challenge/stats/WeatherStatsTest.java
@@ -0,0 +1,52 @@
+package de.bcxp.challenge.stats;
+
+
+import de.bcxp.challenge.data.weather.WeatherDataSourceMock;
+import de.bcxp.challenge.data.weather.WeatherRecord;
+import org.junit.jupiter.api.Test;
+
+import java.util.*;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+
+public class WeatherStatsTest {
+
+    @Test
+    void testMinSpreadForEmptyListIsNull() {
+
+        // GIVEN an empty list of weather records
+        Iterable<WeatherRecord> emptyRecords = new ArrayList<>();
+
+        // WHEN the record with minimum temperature spread is calculated
+        WeatherRecord minSpreadRecord = WeatherStats.findMinTemperatureSpread(emptyRecords);
+
+        // THEN the result is null
+        assertNull(minSpreadRecord);
+    }
+
+    @Test
+    void testMinimumTemperatureSpreadIsFound() {
+
+        // GIVEN weather records and their minimum temperature spread
+        List<WeatherRecord> records = WeatherDataSourceMock.MOCK_RECORDS;
+        WeatherRecord referenceMinSpreadRecord = records
+                .stream()
+                .min(
+                        Comparator.comparing(WeatherStatsTest::calcTemperatureSpread)
+                )
+                .orElse(null);
+
+        // WHEN the record with minimum temperature spread is calculated
+        WeatherRecord calculatedMinSpreadRecord = WeatherStats.findMinTemperatureSpread(records);
+
+        // THEN it corresponds to the reference minimum
+        assertNotNull(referenceMinSpreadRecord);
+        assertEquals(referenceMinSpreadRecord.getDay(), calculatedMinSpreadRecord.getDay());
+    }
+
+    private static int calcTemperatureSpread(WeatherRecord record) {
+        return record.getMxT() - record.getMnT();
+    }
+
+}

From 1fb3f7d45ab07e3c08e7119a26cdb147d503a952 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn?= <bjoernwe@users.noreply.github.com>
Date: Mon, 2 Jan 2023 20:27:50 +0100
Subject: [PATCH 3/7] Move files

---
 src/main/java/de/bcxp/challenge/App.java                  | 8 ++++----
 .../de/bcxp/challenge/{data => weather}/DataSource.java   | 2 +-
 .../{data => }/weather/WeatherDataSourceCSV.java          | 3 +--
 .../bcxp/challenge/{data => }/weather/WeatherRecord.java  | 2 +-
 .../bcxp/challenge/{stats => weather}/WeatherStats.java   | 4 +---
 .../{data => }/weather/WeatherDataSourceCsvTest.java      | 2 +-
 .../{data => }/weather/WeatherDataSourceTest.java         | 5 +++--
 .../challenge/{stats => weather}/WeatherStatsTest.java    | 5 ++---
 .../weather => weather/utils}/WeatherDataSourceEnum.java  | 2 +-
 .../utils}/WeatherDataSourceFactory.java                  | 6 ++++--
 .../weather => weather/utils}/WeatherDataSourceMock.java  | 5 +++--
 11 files changed, 22 insertions(+), 22 deletions(-)
 rename src/main/java/de/bcxp/challenge/{data => weather}/DataSource.java (64%)
 rename src/main/java/de/bcxp/challenge/{data => }/weather/WeatherDataSourceCSV.java (93%)
 rename src/main/java/de/bcxp/challenge/{data => }/weather/WeatherRecord.java (95%)
 rename src/main/java/de/bcxp/challenge/{stats => weather}/WeatherStats.java (87%)
 rename src/test/java/de/bcxp/challenge/{data => }/weather/WeatherDataSourceCsvTest.java (94%)
 rename src/test/java/de/bcxp/challenge/{data => }/weather/WeatherDataSourceTest.java (92%)
 rename src/test/java/de/bcxp/challenge/{stats => weather}/WeatherStatsTest.java (91%)
 rename src/test/java/de/bcxp/challenge/{data/weather => weather/utils}/WeatherDataSourceEnum.java (58%)
 rename src/test/java/de/bcxp/challenge/{data/weather => weather/utils}/WeatherDataSourceFactory.java (82%)
 rename src/test/java/de/bcxp/challenge/{data/weather => weather/utils}/WeatherDataSourceMock.java (81%)

diff --git a/src/main/java/de/bcxp/challenge/App.java b/src/main/java/de/bcxp/challenge/App.java
index 2902f72..f5224f2 100644
--- a/src/main/java/de/bcxp/challenge/App.java
+++ b/src/main/java/de/bcxp/challenge/App.java
@@ -1,9 +1,9 @@
 package de.bcxp.challenge;
 
-import de.bcxp.challenge.data.DataSource;
-import de.bcxp.challenge.data.weather.WeatherDataSourceCSV;
-import de.bcxp.challenge.data.weather.WeatherRecord;
-import de.bcxp.challenge.stats.WeatherStats;
+import de.bcxp.challenge.weather.DataSource;
+import de.bcxp.challenge.weather.WeatherDataSourceCSV;
+import de.bcxp.challenge.weather.WeatherRecord;
+import de.bcxp.challenge.weather.WeatherStats;
 
 import java.io.FileNotFoundException;
 import java.nio.file.Path;
diff --git a/src/main/java/de/bcxp/challenge/data/DataSource.java b/src/main/java/de/bcxp/challenge/weather/DataSource.java
similarity index 64%
rename from src/main/java/de/bcxp/challenge/data/DataSource.java
rename to src/main/java/de/bcxp/challenge/weather/DataSource.java
index 8d44722..9ab7789 100644
--- a/src/main/java/de/bcxp/challenge/data/DataSource.java
+++ b/src/main/java/de/bcxp/challenge/weather/DataSource.java
@@ -1,4 +1,4 @@
-package de.bcxp.challenge.data;
+package de.bcxp.challenge.weather;
 
 
 public interface DataSource<T> {
diff --git a/src/main/java/de/bcxp/challenge/data/weather/WeatherDataSourceCSV.java b/src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java
similarity index 93%
rename from src/main/java/de/bcxp/challenge/data/weather/WeatherDataSourceCSV.java
rename to src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java
index d8595fe..6536cfd 100644
--- a/src/main/java/de/bcxp/challenge/data/weather/WeatherDataSourceCSV.java
+++ b/src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java
@@ -1,7 +1,6 @@
-package de.bcxp.challenge.data.weather;
+package de.bcxp.challenge.weather;
 
 import com.opencsv.bean.CsvToBeanBuilder;
-import de.bcxp.challenge.data.DataSource;
 
 import java.io.FileNotFoundException;
 import java.io.FileReader;
diff --git a/src/main/java/de/bcxp/challenge/data/weather/WeatherRecord.java b/src/main/java/de/bcxp/challenge/weather/WeatherRecord.java
similarity index 95%
rename from src/main/java/de/bcxp/challenge/data/weather/WeatherRecord.java
rename to src/main/java/de/bcxp/challenge/weather/WeatherRecord.java
index 1997604..85a0e2f 100644
--- a/src/main/java/de/bcxp/challenge/data/weather/WeatherRecord.java
+++ b/src/main/java/de/bcxp/challenge/weather/WeatherRecord.java
@@ -1,4 +1,4 @@
-package de.bcxp.challenge.data.weather;
+package de.bcxp.challenge.weather;
 
 import com.opencsv.bean.CsvBindByName;
 
diff --git a/src/main/java/de/bcxp/challenge/stats/WeatherStats.java b/src/main/java/de/bcxp/challenge/weather/WeatherStats.java
similarity index 87%
rename from src/main/java/de/bcxp/challenge/stats/WeatherStats.java
rename to src/main/java/de/bcxp/challenge/weather/WeatherStats.java
index a6b3d4d..1a92a98 100644
--- a/src/main/java/de/bcxp/challenge/stats/WeatherStats.java
+++ b/src/main/java/de/bcxp/challenge/weather/WeatherStats.java
@@ -1,8 +1,6 @@
-package de.bcxp.challenge.stats;
+package de.bcxp.challenge.weather;
 
 
-import de.bcxp.challenge.data.weather.WeatherRecord;
-
 import java.util.Comparator;
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
diff --git a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceCsvTest.java b/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceCsvTest.java
similarity index 94%
rename from src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceCsvTest.java
rename to src/test/java/de/bcxp/challenge/weather/WeatherDataSourceCsvTest.java
index 1c46e40..aec87cd 100644
--- a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceCsvTest.java
+++ b/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceCsvTest.java
@@ -1,4 +1,4 @@
-package de.bcxp.challenge.data.weather;
+package de.bcxp.challenge.weather;
 
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
diff --git a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceTest.java b/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceTest.java
similarity index 92%
rename from src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceTest.java
rename to src/test/java/de/bcxp/challenge/weather/WeatherDataSourceTest.java
index a2306ba..6518f90 100644
--- a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceTest.java
+++ b/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceTest.java
@@ -1,6 +1,7 @@
-package de.bcxp.challenge.data.weather;
+package de.bcxp.challenge.weather;
 
-import de.bcxp.challenge.data.DataSource;
+import de.bcxp.challenge.weather.utils.WeatherDataSourceEnum;
+import de.bcxp.challenge.weather.utils.WeatherDataSourceFactory;
 import org.junit.jupiter.params.ParameterizedTest;
 import org.junit.jupiter.params.provider.EnumSource;
 
diff --git a/src/test/java/de/bcxp/challenge/stats/WeatherStatsTest.java b/src/test/java/de/bcxp/challenge/weather/WeatherStatsTest.java
similarity index 91%
rename from src/test/java/de/bcxp/challenge/stats/WeatherStatsTest.java
rename to src/test/java/de/bcxp/challenge/weather/WeatherStatsTest.java
index d4ad5f6..fa52b4a 100644
--- a/src/test/java/de/bcxp/challenge/stats/WeatherStatsTest.java
+++ b/src/test/java/de/bcxp/challenge/weather/WeatherStatsTest.java
@@ -1,8 +1,7 @@
-package de.bcxp.challenge.stats;
+package de.bcxp.challenge.weather;
 
 
-import de.bcxp.challenge.data.weather.WeatherDataSourceMock;
-import de.bcxp.challenge.data.weather.WeatherRecord;
+import de.bcxp.challenge.weather.utils.WeatherDataSourceMock;
 import org.junit.jupiter.api.Test;
 
 import java.util.*;
diff --git a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceEnum.java b/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceEnum.java
similarity index 58%
rename from src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceEnum.java
rename to src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceEnum.java
index f630a86..e488516 100644
--- a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceEnum.java
+++ b/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceEnum.java
@@ -1,4 +1,4 @@
-package de.bcxp.challenge.data.weather;
+package de.bcxp.challenge.weather.utils;
 
 public enum WeatherDataSourceEnum {
     MOCK,
diff --git a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceFactory.java b/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceFactory.java
similarity index 82%
rename from src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceFactory.java
rename to src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceFactory.java
index d5ff729..77ef6a9 100644
--- a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceFactory.java
+++ b/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceFactory.java
@@ -1,6 +1,8 @@
-package de.bcxp.challenge.data.weather;
+package de.bcxp.challenge.weather.utils;
 
-import de.bcxp.challenge.data.DataSource;
+import de.bcxp.challenge.weather.DataSource;
+import de.bcxp.challenge.weather.WeatherDataSourceCSV;
+import de.bcxp.challenge.weather.WeatherRecord;
 
 import java.io.FileNotFoundException;
 import java.nio.file.Path;
diff --git a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceMock.java b/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceMock.java
similarity index 81%
rename from src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceMock.java
rename to src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceMock.java
index 8da6bf1..0b811f3 100644
--- a/src/test/java/de/bcxp/challenge/data/weather/WeatherDataSourceMock.java
+++ b/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceMock.java
@@ -1,7 +1,8 @@
-package de.bcxp.challenge.data.weather;
+package de.bcxp.challenge.weather.utils;
 
 
-import de.bcxp.challenge.data.DataSource;
+import de.bcxp.challenge.weather.DataSource;
+import de.bcxp.challenge.weather.WeatherRecord;
 
 import java.util.Arrays;
 import java.util.List;

From f81bf3e7c71fc7a49f0c5e6757d582cb1a88e073 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn?= <bjoernwe@users.noreply.github.com>
Date: Mon, 2 Jan 2023 20:42:43 +0100
Subject: [PATCH 4/7] Update doc

---
 .../java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java b/src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java
index 6536cfd..5fff830 100644
--- a/src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java
+++ b/src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java
@@ -13,8 +13,9 @@ public class WeatherDataSourceCSV implements DataSource<WeatherRecord> {
     public WeatherDataSourceCSV(Path csvPath) throws FileNotFoundException {
         // FileNotFoundException is an exception type that is clearly specific to a file-based implementation of the
         // DataSource interface. Usually we should avoid throwing implementation-specific exceptions that are not
-        // defined by the interface. But for the constructor it's okay under the assumption that the data source will
-        // be initialized in a "dirty main" function and then injected into the application.
+        // defined by the interface. But for the constructor it's okay under the assumption that the only place that
+        // will use the implementation-specific constructor is the main function in which the different dependencies
+        // are plugged together.
         this.csvFileReader = new FileReader(csvPath.toString());
     }
 

From 9e684119750175c4ae99ca78404e49eabfccb607 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn?= <bjoernwe@users.noreply.github.com>
Date: Mon, 2 Jan 2023 21:00:55 +0100
Subject: [PATCH 5/7] Add tests for invalid inputs

---
 .../weather/WeatherDataSourceCSV.java         |  1 +
 .../weather/WeatherDataSourceCsvTest.java     | 39 +++++++++++++++++--
 .../resources/challenge/weather_empty.csv     |  0
 .../challenge/weather_with_float.csv          |  4 ++
 4 files changed, 40 insertions(+), 4 deletions(-)
 create mode 100644 src/test/resources/challenge/weather_empty.csv
 create mode 100644 src/test/resources/challenge/weather_with_float.csv

diff --git a/src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java b/src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java
index 5fff830..3c442e9 100644
--- a/src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java
+++ b/src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java
@@ -25,6 +25,7 @@ public Iterable<WeatherRecord> getData() {
         CsvToBeanBuilder<WeatherRecord> beanBuilder = new CsvToBeanBuilder<>(this.csvFileReader);
 
         return beanBuilder
+                .withOrderedResults(true)
                 .withType(WeatherRecord.class)
                 .build()
                 .parse();
diff --git a/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceCsvTest.java b/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceCsvTest.java
index aec87cd..a81a20f 100644
--- a/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceCsvTest.java
+++ b/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceCsvTest.java
@@ -14,14 +14,45 @@ public void testInvalidPathThrowsException() {
         // GIVEN an invalid path to CSV file
         Path invalidPath = Path.of("./INVALID/PATH.csv");
 
-        // WHEN a CsvDataSource is instantiated with the wrong path
-        Exception exception = Assertions.assertThrows(FileNotFoundException.class, () ->
+        // WHEN a CSV data source is instantiated with that path
+        // THEN a FileNotFoundException is thrown
+        Assertions.assertThrows(FileNotFoundException.class, () ->
                 new WeatherDataSourceCSV(invalidPath)
         );
 
-        // THEN an exception is thrown
-        Assertions.assertEquals(FileNotFoundException.class, exception.getClass());
+    }
+
+
+    @Test
+    public void testEmptyCsvResultsInRuntimeException() throws FileNotFoundException {
+
+        // GIVEN a data source for an empty CSV file
+        Path csvPath = Path.of("./src/test/resources/challenge/weather_empty.csv");
+        DataSource<WeatherRecord> dataSource = new WeatherDataSourceCSV(csvPath);
+
+        // WHEN data is requested
+        // THEN an RuntimeException is thrown
+        Exception exception = Assertions.assertThrows(RuntimeException.class, () ->
+                dataSource.getData()
+        );
 
+        // AND the error message is descriptive
+        assert(exception.getMessage().contains("Error capturing CSV header"));
+    }
+
+
+    @Test
+    public void testUnexpectedFloatValuesLeadToRuntimeException() throws FileNotFoundException {
+
+        // GIVEN a data source pointing to a CSV with float values instead of the expected integers
+        Path csvPath = Path.of("./src/test/resources/challenge/weather_with_float.csv");
+        DataSource<WeatherRecord> dataSource = new WeatherDataSourceCSV(csvPath);
+
+        // WHEN data is requested
+        // THEN an RuntimeException is thrown
+        Assertions.assertThrows(RuntimeException.class, () ->
+                dataSource.getData()
+        );
     }
 
 }
diff --git a/src/test/resources/challenge/weather_empty.csv b/src/test/resources/challenge/weather_empty.csv
new file mode 100644
index 0000000..e69de29
diff --git a/src/test/resources/challenge/weather_with_float.csv b/src/test/resources/challenge/weather_with_float.csv
new file mode 100644
index 0000000..9c5af26
--- /dev/null
+++ b/src/test/resources/challenge/weather_with_float.csv
@@ -0,0 +1,4 @@
+Day,MxT,MnT,AvT,AvDP,1HrP TPcpn,PDir,AvSp,Dir,MxS,SkyC,MxR,Mn,R AvSLP
+1.1,8.8,5.9,74,53.8,0,280,9.6,270,17,1.6,93,23,1004.5
+2.0,7.9,6.3,71,46.5,0,330,8.7,340,23,3.3,70,28,1004.5
+3.0,7.7,5.5,66,39.6,0,350,5,350,9,2.8,59,24,1016.8
\ No newline at end of file

From b4f558cca2c88951f8e0b45abe767a172f81fdb7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn?= <bjoernwe@users.noreply.github.com>
Date: Tue, 3 Jan 2023 12:31:05 +0100
Subject: [PATCH 6/7] Update comment

---
 .../challenge/weather/{ => data}/WeatherDataSourceCSV.java   | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)
 rename src/main/java/de/bcxp/challenge/weather/{ => data}/WeatherDataSourceCSV.java (84%)

diff --git a/src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java b/src/main/java/de/bcxp/challenge/weather/data/WeatherDataSourceCSV.java
similarity index 84%
rename from src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java
rename to src/main/java/de/bcxp/challenge/weather/data/WeatherDataSourceCSV.java
index 3c442e9..05b4f78 100644
--- a/src/main/java/de/bcxp/challenge/weather/WeatherDataSourceCSV.java
+++ b/src/main/java/de/bcxp/challenge/weather/data/WeatherDataSourceCSV.java
@@ -13,9 +13,8 @@ public class WeatherDataSourceCSV implements DataSource<WeatherRecord> {
     public WeatherDataSourceCSV(Path csvPath) throws FileNotFoundException {
         // FileNotFoundException is an exception type that is clearly specific to a file-based implementation of the
         // DataSource interface. Usually we should avoid throwing implementation-specific exceptions that are not
-        // defined by the interface. But for the constructor it's okay under the assumption that the only place that
-        // will use the implementation-specific constructor is the main function in which the different dependencies
-        // are plugged together.
+        // defined by the interface. But for the constructor it's okay under the assumption that it will only be used in
+        // the main function in which the different dependencies are plugged together.
         this.csvFileReader = new FileReader(csvPath.toString());
     }
 

From 8016687007fb034f06bad1c8bb8f8b55c742c46f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bj=C3=B6rn?= <bjoernwe@users.noreply.github.com>
Date: Tue, 3 Jan 2023 12:42:48 +0100
Subject: [PATCH 7/7] Add UI for weather

---
 src/main/java/de/bcxp/challenge/App.java      | 24 ++++----
 .../challenge/weather/WeatherStatsApp.java    | 38 ++++++++++++
 .../weather/{ => data}/DataSource.java        |  2 +-
 .../weather/data/WeatherDataSourceCSV.java    |  2 +-
 .../weather/{ => data}/WeatherRecord.java     |  2 +-
 .../weather/{ => stats}/WeatherStats.java     |  4 +-
 .../bcxp/challenge/weather/ui/WeatherUi.java  | 10 ++++
 .../challenge/weather/ui/WeatherUiCli.java    | 14 +++++
 .../weather/WeatherDataSourceCsvTest.java     |  7 ++-
 .../weather/WeatherDataSourceTest.java        |  2 +
 .../weather/WeatherStatsAppTest.java          | 33 +++++++++++
 .../challenge/weather/WeatherStatsTest.java   |  2 +
 .../challenge/weather/WeatherUiCliTest.java   | 59 +++++++++++++++++++
 .../utils/WeatherDataSourceFactory.java       |  6 +-
 .../weather/utils/WeatherDataSourceMock.java  |  4 +-
 .../weather/utils/WeatherUiMock.java          | 20 +++++++
 16 files changed, 207 insertions(+), 22 deletions(-)
 create mode 100644 src/main/java/de/bcxp/challenge/weather/WeatherStatsApp.java
 rename src/main/java/de/bcxp/challenge/weather/{ => data}/DataSource.java (61%)
 rename src/main/java/de/bcxp/challenge/weather/{ => data}/WeatherRecord.java (95%)
 rename src/main/java/de/bcxp/challenge/weather/{ => stats}/WeatherStats.java (86%)
 create mode 100644 src/main/java/de/bcxp/challenge/weather/ui/WeatherUi.java
 create mode 100644 src/main/java/de/bcxp/challenge/weather/ui/WeatherUiCli.java
 create mode 100644 src/test/java/de/bcxp/challenge/weather/WeatherStatsAppTest.java
 create mode 100644 src/test/java/de/bcxp/challenge/weather/WeatherUiCliTest.java
 create mode 100644 src/test/java/de/bcxp/challenge/weather/utils/WeatherUiMock.java

diff --git a/src/main/java/de/bcxp/challenge/App.java b/src/main/java/de/bcxp/challenge/App.java
index f5224f2..2a62585 100644
--- a/src/main/java/de/bcxp/challenge/App.java
+++ b/src/main/java/de/bcxp/challenge/App.java
@@ -1,9 +1,11 @@
 package de.bcxp.challenge;
 
-import de.bcxp.challenge.weather.DataSource;
-import de.bcxp.challenge.weather.WeatherDataSourceCSV;
-import de.bcxp.challenge.weather.WeatherRecord;
-import de.bcxp.challenge.weather.WeatherStats;
+import de.bcxp.challenge.weather.data.DataSource;
+import de.bcxp.challenge.weather.data.WeatherDataSourceCSV;
+import de.bcxp.challenge.weather.data.WeatherRecord;
+import de.bcxp.challenge.weather.WeatherStatsApp;
+import de.bcxp.challenge.weather.ui.WeatherUi;
+import de.bcxp.challenge.weather.ui.WeatherUiCli;
 
 import java.io.FileNotFoundException;
 import java.nio.file.Path;
@@ -14,17 +16,17 @@ public final class App {
     private static final int EXIT_ERROR_DATA_WEATHER = 1;
 
     /**
-     * This is the main entry method of your program.
-     * @param args The CLI arguments passed
+     * The app's main entry point assembles all dependencies and injects them into the core modules.
+     * @param args CLI arguments, currently not used
      */
     public static void main(String... args) {
 
-        Iterable<WeatherRecord> weatherData = tryInitWeatherDataSource(
-                Path.of("./src/main/resources/de/bcxp/challenge/weather.csv")
-        ).getData();
+        Path csvWeather = Path.of("./src/main/resources/de/bcxp/challenge/weather.csv");
+        DataSource<WeatherRecord> weatherDataSource = tryInitWeatherDataSource(csvWeather);
+        WeatherUi weatherUi = new WeatherUiCli();
 
-        WeatherRecord recordWithSmallestTempSpread = WeatherStats.findMinTemperatureSpread(weatherData);
-        System.out.printf("Day with smallest temperature spread: %s%n", recordWithSmallestTempSpread.getDay());
+        WeatherStatsApp weatherStatsApp = new WeatherStatsApp(weatherDataSource, weatherUi);
+        weatherStatsApp.run();
 
         String countryWithHighestPopulationDensity = "Some country"; // Your population density analysis function call …
         System.out.printf("Country with highest population density: %s%n", countryWithHighestPopulationDensity);
diff --git a/src/main/java/de/bcxp/challenge/weather/WeatherStatsApp.java b/src/main/java/de/bcxp/challenge/weather/WeatherStatsApp.java
new file mode 100644
index 0000000..2d631e7
--- /dev/null
+++ b/src/main/java/de/bcxp/challenge/weather/WeatherStatsApp.java
@@ -0,0 +1,38 @@
+package de.bcxp.challenge.weather;
+
+import de.bcxp.challenge.weather.data.DataSource;
+import de.bcxp.challenge.weather.data.WeatherRecord;
+import de.bcxp.challenge.weather.stats.WeatherStats;
+import de.bcxp.challenge.weather.ui.WeatherUi;
+
+
+public class WeatherStatsApp {
+
+    private final DataSource<WeatherRecord> dataSource;
+    private final WeatherUi weatherUi;
+
+    public WeatherStatsApp(DataSource<WeatherRecord> dataSource, WeatherUi weatherUi) {
+        this.dataSource = dataSource;
+        this.weatherUi = weatherUi;
+    }
+
+    /**
+     * Core business logic: Read data, calculate stats, display them.
+     */
+    public void run() {
+
+        try {
+
+            Iterable<WeatherRecord> data = this.dataSource.getData();
+            WeatherRecord minSpreadRecord = WeatherStats.findMinTemperatureSpread(data);
+            this.weatherUi.showMinTempSpread(minSpreadRecord);
+
+        } catch (Exception e) {
+            // There's not much error handling going on here. But this block is a good way to indicate that high-level
+            // error handling is part of the business logic and should probably go here.
+            System.out.printf("Error while calculating weather stats:%n%s%n", e);
+        }
+
+    }
+
+}
diff --git a/src/main/java/de/bcxp/challenge/weather/DataSource.java b/src/main/java/de/bcxp/challenge/weather/data/DataSource.java
similarity index 61%
rename from src/main/java/de/bcxp/challenge/weather/DataSource.java
rename to src/main/java/de/bcxp/challenge/weather/data/DataSource.java
index 9ab7789..98ae615 100644
--- a/src/main/java/de/bcxp/challenge/weather/DataSource.java
+++ b/src/main/java/de/bcxp/challenge/weather/data/DataSource.java
@@ -1,4 +1,4 @@
-package de.bcxp.challenge.weather;
+package de.bcxp.challenge.weather.data;
 
 
 public interface DataSource<T> {
diff --git a/src/main/java/de/bcxp/challenge/weather/data/WeatherDataSourceCSV.java b/src/main/java/de/bcxp/challenge/weather/data/WeatherDataSourceCSV.java
index 05b4f78..eead0c5 100644
--- a/src/main/java/de/bcxp/challenge/weather/data/WeatherDataSourceCSV.java
+++ b/src/main/java/de/bcxp/challenge/weather/data/WeatherDataSourceCSV.java
@@ -1,4 +1,4 @@
-package de.bcxp.challenge.weather;
+package de.bcxp.challenge.weather.data;
 
 import com.opencsv.bean.CsvToBeanBuilder;
 
diff --git a/src/main/java/de/bcxp/challenge/weather/WeatherRecord.java b/src/main/java/de/bcxp/challenge/weather/data/WeatherRecord.java
similarity index 95%
rename from src/main/java/de/bcxp/challenge/weather/WeatherRecord.java
rename to src/main/java/de/bcxp/challenge/weather/data/WeatherRecord.java
index 85a0e2f..aa59100 100644
--- a/src/main/java/de/bcxp/challenge/weather/WeatherRecord.java
+++ b/src/main/java/de/bcxp/challenge/weather/data/WeatherRecord.java
@@ -1,4 +1,4 @@
-package de.bcxp.challenge.weather;
+package de.bcxp.challenge.weather.data;
 
 import com.opencsv.bean.CsvBindByName;
 
diff --git a/src/main/java/de/bcxp/challenge/weather/WeatherStats.java b/src/main/java/de/bcxp/challenge/weather/stats/WeatherStats.java
similarity index 86%
rename from src/main/java/de/bcxp/challenge/weather/WeatherStats.java
rename to src/main/java/de/bcxp/challenge/weather/stats/WeatherStats.java
index 1a92a98..ff02ef9 100644
--- a/src/main/java/de/bcxp/challenge/weather/WeatherStats.java
+++ b/src/main/java/de/bcxp/challenge/weather/stats/WeatherStats.java
@@ -1,6 +1,8 @@
-package de.bcxp.challenge.weather;
+package de.bcxp.challenge.weather.stats;
 
 
+import de.bcxp.challenge.weather.data.WeatherRecord;
+
 import java.util.Comparator;
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
diff --git a/src/main/java/de/bcxp/challenge/weather/ui/WeatherUi.java b/src/main/java/de/bcxp/challenge/weather/ui/WeatherUi.java
new file mode 100644
index 0000000..520ec79
--- /dev/null
+++ b/src/main/java/de/bcxp/challenge/weather/ui/WeatherUi.java
@@ -0,0 +1,10 @@
+package de.bcxp.challenge.weather.ui;
+
+
+import de.bcxp.challenge.weather.data.WeatherRecord;
+
+public interface WeatherUi {
+
+    void showMinTempSpread(WeatherRecord weatherRecord);
+
+}
diff --git a/src/main/java/de/bcxp/challenge/weather/ui/WeatherUiCli.java b/src/main/java/de/bcxp/challenge/weather/ui/WeatherUiCli.java
new file mode 100644
index 0000000..387b551
--- /dev/null
+++ b/src/main/java/de/bcxp/challenge/weather/ui/WeatherUiCli.java
@@ -0,0 +1,14 @@
+package de.bcxp.challenge.weather.ui;
+
+
+import de.bcxp.challenge.weather.data.WeatherRecord;
+
+public class WeatherUiCli implements WeatherUi {
+
+    @Override
+    public void showMinTempSpread(WeatherRecord minSpreadRecord) {
+        String minSpreadDay = minSpreadRecord != null ? String.valueOf(minSpreadRecord.getDay()) : "[N/A]";
+        System.out.printf("Day with smallest temperature spread: %s%n", minSpreadDay);
+    }
+
+}
diff --git a/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceCsvTest.java b/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceCsvTest.java
index a81a20f..54c7948 100644
--- a/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceCsvTest.java
+++ b/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceCsvTest.java
@@ -1,5 +1,8 @@
 package de.bcxp.challenge.weather;
 
+import de.bcxp.challenge.weather.data.DataSource;
+import de.bcxp.challenge.weather.data.WeatherDataSourceCSV;
+import de.bcxp.challenge.weather.data.WeatherRecord;
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
 
@@ -24,7 +27,7 @@ public void testInvalidPathThrowsException() {
 
 
     @Test
-    public void testEmptyCsvResultsInRuntimeException() throws FileNotFoundException {
+    public void testEmptyCsvThrowsRuntimeException() throws FileNotFoundException {
 
         // GIVEN a data source for an empty CSV file
         Path csvPath = Path.of("./src/test/resources/challenge/weather_empty.csv");
@@ -42,7 +45,7 @@ public void testEmptyCsvResultsInRuntimeException() throws FileNotFoundException
 
 
     @Test
-    public void testUnexpectedFloatValuesLeadToRuntimeException() throws FileNotFoundException {
+    public void testUnexpectedFloatValuesThrowRuntimeException() throws FileNotFoundException {
 
         // GIVEN a data source pointing to a CSV with float values instead of the expected integers
         Path csvPath = Path.of("./src/test/resources/challenge/weather_with_float.csv");
diff --git a/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceTest.java b/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceTest.java
index 6518f90..b05c8f2 100644
--- a/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceTest.java
+++ b/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceTest.java
@@ -1,5 +1,7 @@
 package de.bcxp.challenge.weather;
 
+import de.bcxp.challenge.weather.data.DataSource;
+import de.bcxp.challenge.weather.data.WeatherRecord;
 import de.bcxp.challenge.weather.utils.WeatherDataSourceEnum;
 import de.bcxp.challenge.weather.utils.WeatherDataSourceFactory;
 import org.junit.jupiter.params.ParameterizedTest;
diff --git a/src/test/java/de/bcxp/challenge/weather/WeatherStatsAppTest.java b/src/test/java/de/bcxp/challenge/weather/WeatherStatsAppTest.java
new file mode 100644
index 0000000..f3bacab
--- /dev/null
+++ b/src/test/java/de/bcxp/challenge/weather/WeatherStatsAppTest.java
@@ -0,0 +1,33 @@
+package de.bcxp.challenge.weather;
+
+
+import de.bcxp.challenge.weather.data.DataSource;
+import de.bcxp.challenge.weather.data.WeatherRecord;
+import de.bcxp.challenge.weather.stats.WeatherStats;
+import de.bcxp.challenge.weather.utils.WeatherDataSourceMock;
+import de.bcxp.challenge.weather.utils.WeatherUiMock;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+
+public class WeatherStatsAppTest {
+
+    @Test
+    void testAppDisplaysDayWithMinTempSpread() {
+
+        // GIVEN a WeatherStatsApp
+        DataSource<WeatherRecord> dataSource = new WeatherDataSourceMock(WeatherDataSourceMock.MOCK_RECORDS);
+        WeatherUiMock ui = new WeatherUiMock();
+        WeatherStatsApp app = new WeatherStatsApp(dataSource, ui);
+
+        // WHEN the app runs
+        app.run();
+
+        // THEN it "displays" the weather record with minimum spread
+        WeatherRecord expectedRecord = WeatherStats.findMinTemperatureSpread(dataSource.getData());
+        assertEquals(1, ui.shownRecords.size());
+        assertEquals(expectedRecord, ui.shownRecords.get(0));
+    }
+
+}
diff --git a/src/test/java/de/bcxp/challenge/weather/WeatherStatsTest.java b/src/test/java/de/bcxp/challenge/weather/WeatherStatsTest.java
index fa52b4a..827a66b 100644
--- a/src/test/java/de/bcxp/challenge/weather/WeatherStatsTest.java
+++ b/src/test/java/de/bcxp/challenge/weather/WeatherStatsTest.java
@@ -1,6 +1,8 @@
 package de.bcxp.challenge.weather;
 
 
+import de.bcxp.challenge.weather.data.WeatherRecord;
+import de.bcxp.challenge.weather.stats.WeatherStats;
 import de.bcxp.challenge.weather.utils.WeatherDataSourceMock;
 import org.junit.jupiter.api.Test;
 
diff --git a/src/test/java/de/bcxp/challenge/weather/WeatherUiCliTest.java b/src/test/java/de/bcxp/challenge/weather/WeatherUiCliTest.java
new file mode 100644
index 0000000..9b47edd
--- /dev/null
+++ b/src/test/java/de/bcxp/challenge/weather/WeatherUiCliTest.java
@@ -0,0 +1,59 @@
+package de.bcxp.challenge.weather;
+
+
+import de.bcxp.challenge.weather.data.DataSource;
+import de.bcxp.challenge.weather.data.WeatherRecord;
+import de.bcxp.challenge.weather.ui.WeatherUi;
+import de.bcxp.challenge.weather.ui.WeatherUiCli;
+import de.bcxp.challenge.weather.utils.WeatherDataSourceMock;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayOutputStream;
+import java.io.PrintStream;
+
+public class WeatherUiCliTest {
+
+    private final ByteArrayOutputStream outContent = new ByteArrayOutputStream();
+    private final PrintStream originalOut = System.out;
+
+    @BeforeEach
+    void setUpStreams() {
+        System.setOut(new PrintStream(outContent));
+    }
+
+    @AfterEach
+    public void restoreStreams() {
+        System.setOut(originalOut);
+    }
+
+    @Test
+    void testRecordIsPrinted() {
+
+        // GIVEN a CLI user interface and a weather record
+        WeatherUi ui = new WeatherUiCli();
+        DataSource<WeatherRecord> dataSource = new WeatherDataSourceMock(WeatherDataSourceMock.MOCK_RECORDS);
+        WeatherRecord record = dataSource.getData().iterator().next();
+
+        // WHEN the record is shown in the UI
+        ui.showMinTempSpread(record);
+
+        // THEN it is printed to (mocked) stdout
+        assert(outContent.toString().contains("Day with smallest temperature spread: 1"));
+    }
+
+    @Test
+    void testNullRecordIsPrinted() {
+
+        // GIVEN a CLI user interface and a weather record
+        WeatherUi ui = new WeatherUiCli();
+
+        // WHEN the record is shown in the UI
+        ui.showMinTempSpread(null);
+
+        // THEN it is printed to (mocked) stdout
+        assert(outContent.toString().contains("Day with smallest temperature spread: [N/A]"));
+    }
+
+}
diff --git a/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceFactory.java b/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceFactory.java
index 77ef6a9..5863bdb 100644
--- a/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceFactory.java
+++ b/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceFactory.java
@@ -1,8 +1,8 @@
 package de.bcxp.challenge.weather.utils;
 
-import de.bcxp.challenge.weather.DataSource;
-import de.bcxp.challenge.weather.WeatherDataSourceCSV;
-import de.bcxp.challenge.weather.WeatherRecord;
+import de.bcxp.challenge.weather.data.DataSource;
+import de.bcxp.challenge.weather.data.WeatherDataSourceCSV;
+import de.bcxp.challenge.weather.data.WeatherRecord;
 
 import java.io.FileNotFoundException;
 import java.nio.file.Path;
diff --git a/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceMock.java b/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceMock.java
index 0b811f3..1b42daf 100644
--- a/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceMock.java
+++ b/src/test/java/de/bcxp/challenge/weather/utils/WeatherDataSourceMock.java
@@ -1,8 +1,8 @@
 package de.bcxp.challenge.weather.utils;
 
 
-import de.bcxp.challenge.weather.DataSource;
-import de.bcxp.challenge.weather.WeatherRecord;
+import de.bcxp.challenge.weather.data.DataSource;
+import de.bcxp.challenge.weather.data.WeatherRecord;
 
 import java.util.Arrays;
 import java.util.List;
diff --git a/src/test/java/de/bcxp/challenge/weather/utils/WeatherUiMock.java b/src/test/java/de/bcxp/challenge/weather/utils/WeatherUiMock.java
new file mode 100644
index 0000000..aea87cd
--- /dev/null
+++ b/src/test/java/de/bcxp/challenge/weather/utils/WeatherUiMock.java
@@ -0,0 +1,20 @@
+package de.bcxp.challenge.weather.utils;
+
+
+import de.bcxp.challenge.weather.data.WeatherRecord;
+import de.bcxp.challenge.weather.ui.WeatherUi;
+
+import java.util.ArrayList;
+import java.util.List;
+
+
+public class WeatherUiMock implements WeatherUi {
+
+    public List<WeatherRecord> shownRecords = new ArrayList<>();
+
+    @Override
+    public void showMinTempSpread(WeatherRecord weatherRecord) {
+        this.shownRecords.add(weatherRecord);
+    }
+
+}

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