bettercodepaul · bjoernwe · Jan 2, 2023 · Jan 2, 2023 · Jan 2, 2023 · Jan 2, 2023
diff --git 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
@@ -1,23 +1,47 @@
 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.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;
+
+
 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) {
 
-        // Your preparation code …
+        Path csvWeather = Path.of("./src/main/resources/de/bcxp/challenge/weather.csv");
+        DataSource<WeatherRecord> weatherDataSource = tryInitWeatherDataSource(csvWeather);
+        WeatherUi weatherUi = new WeatherUiCli();
 
-        String dayWithSmallestTempSpread = "Someday";     // Your day analysis function call …
-        System.out.printf("Day with smallest temperature spread: %s%n", dayWithSmallestTempSpread);
+        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);
     }
+
+    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/weather/WeatherStatsApp.java 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/data/DataSource.java b/src/main/java/de/bcxp/challenge/weather/data/DataSource.java
@@ -0,0 +1,6 @@
+package de.bcxp.challenge.weather.data;
+
+
+public interface DataSource<T> {
+    Iterable<T> getData();
+}
diff --git a/src/main/java/de/bcxp/challenge/weather/data/WeatherDataSourceCSV.java b/src/main/java/de/bcxp/challenge/weather/data/WeatherDataSourceCSV.java
@@ -0,0 +1,33 @@
+package de.bcxp.challenge.weather.data;
+
+import com.opencsv.bean.CsvToBeanBuilder;
+
+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 it will only be used in
+        // the main function in which the different dependencies are plugged together.
+        this.csvFileReader = new FileReader(csvPath.toString());
+    }
+
+    @Override
+    public Iterable<WeatherRecord> getData() {
+
+        CsvToBeanBuilder<WeatherRecord> beanBuilder = new CsvToBeanBuilder<>(this.csvFileReader);
+
+        return beanBuilder
+                .withOrderedResults(true)
+                .withType(WeatherRecord.class)
+                .build()
+                .parse();
+    }
+
+}
diff --git a/src/main/java/de/bcxp/challenge/weather/data/WeatherRecord.java b/src/main/java/de/bcxp/challenge/weather/data/WeatherRecord.java
@@ -0,0 +1,36 @@
+package de.bcxp.challenge.weather.data;
+
+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/main/java/de/bcxp/challenge/weather/stats/WeatherStats.java b/src/main/java/de/bcxp/challenge/weather/stats/WeatherStats.java
@@ -0,0 +1,25 @@
+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;
+
+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/main/java/de/bcxp/challenge/weather/ui/WeatherUi.java 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
@@ -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/AppTest.java b/src/test/java/de/bcxp/challenge/AppTest.java
diff --git a/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceCsvTest.java b/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceCsvTest.java
@@ -0,0 +1,61 @@
+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;
+
+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 CSV data source is instantiated with that path
+        // THEN a FileNotFoundException is thrown
+        Assertions.assertThrows(FileNotFoundException.class, () ->
+                new WeatherDataSourceCSV(invalidPath)
+        );
+
+    }
+
+
+    @Test
+    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");
+        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 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");
+        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/java/de/bcxp/challenge/weather/WeatherDataSourceTest.java b/src/test/java/de/bcxp/challenge/weather/WeatherDataSourceTest.java
@@ -0,0 +1,60 @@
+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;
+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());
+    }
+
+}