Split Downloader into Downloader and Parser

src/main/java/com/europeanexchangerates/exchangeapi/exception/NoDataFromSource.java

@@ -0,0 +1,7 @@
+package com.europeanexchangerates.exchangeapi.exception;
+
+public class NoDataFromSource extends RuntimeException {
+    public NoDataFromSource(String message) {
+        super(message);
+    }
+}

src/main/java/com/europeanexchangerates/exchangeapi/provider/UrlCsvZipExchangeRateProvider.java

@@ -1,24 +1,50 @@
 package com.europeanexchangerates.exchangeapi.provider;
 
+import java.io.InputStream;
 import java.time.LocalDate;
 import java.util.TreeMap;
+import java.util.zip.ZipInputStream;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import com.europeanexchangerates.exchangeapi.dto.ExchangeRate;
-import com.europeanexchangerates.exchangeapi.util.DataDownloader;
-import com.europeanexchangerates.exchangeapi.util.UrlCsvZipDataDownloader;
+import com.europeanexchangerates.exchangeapi.exception.NoDataFromSource;
+import com.europeanexchangerates.exchangeapi.util.datadownloader.DataDownloader;
+import com.europeanexchangerates.exchangeapi.util.datadownloader.UrlCsvZipDataDownloader;
+import com.europeanexchangerates.exchangeapi.util.dataparser.CsvDataParser;
+import com.europeanexchangerates.exchangeapi.util.dataparser.DataParser;
 
 public class UrlCsvZipExchangeRateProvider implements ExchangeRateProvider {
     private DataDownloader downloader;
+    private DataParser parser;
+    private static final Logger LOGGER = LoggerFactory.getLogger(UrlCsvZipExchangeRateProvider.class);
 
     public UrlCsvZipExchangeRateProvider() {
         this.downloader = new UrlCsvZipDataDownloader();
+        this.parser = new CsvDataParser();
     }
 
-    public UrlCsvZipExchangeRateProvider(DataDownloader downloader) {
+    public UrlCsvZipExchangeRateProvider(DataDownloader downloader, DataParser parser) {
         this.downloader = downloader;
+        this.parser = parser;
     }
 
     public TreeMap<LocalDate, ExchangeRate> getExchangeRates() throws Exception {
-        return downloader.downloadData();
+        InputStream data = downloader.downloadData("https://www.ecb.europa.eu/stats/eurofxref/eurofxref-hist.zip");
+
+        // Only one CSV file is expected from the ZIP file.
+        if (((ZipInputStream) data).getNextEntry() == null) {
+            throw new NoDataFromSource("No files found from the zip file");
+        }
+        TreeMap<LocalDate, ExchangeRate> exchangeRates = parser.parseData(data);
+
+        // If the zip file has changed, skip the next files but log a warning.
+        // Ideally, alerts should be sent if running in a production environment.
+        if (((ZipInputStream) data).getNextEntry() != null) {
+            LOGGER.warn("The contents of the zip archive has changed. Please check the data source.");
+        }
+
+        return exchangeRates;
     }
 }

src/main/java/com/europeanexchangerates/exchangeapi/util/datadownloader/DataDownloader.java

@@ -0,0 +1,7 @@
+package com.europeanexchangerates.exchangeapi.util.datadownloader;
+
+import java.io.InputStream;
+
+public interface DataDownloader {
+    public InputStream downloadData(String url) throws Exception;
+}

src/main/java/com/europeanexchangerates/exchangeapi/util/datadownloader/UrlCsvZipDataDownloader.java

@@ -0,0 +1,13 @@
+package com.europeanexchangerates.exchangeapi.util.datadownloader;
+
+import java.io.InputStream;
+import java.net.URL;
+import java.util.zip.ZipInputStream;
+
+public class UrlCsvZipDataDownloader implements DataDownloader {
+    public InputStream downloadData(String url) throws Exception {
+        ZipInputStream zipInputStream = new ZipInputStream(
+                (new URL(url)).openStream());
+        return zipInputStream;
+    }
+}

src/main/java/com/europeanexchangerates/exchangeapi/util/dataparser/CsvDataParser.java

@@ -0,0 +1,39 @@
+package com.europeanexchangerates.exchangeapi.util.dataparser;
+
+import java.io.BufferedReader;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.math.BigDecimal;
+import java.time.LocalDate;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.TreeMap;
+
+import com.europeanexchangerates.exchangeapi.dto.ExchangeRate;
+
+public class CsvDataParser implements DataParser {
+    public TreeMap<LocalDate, ExchangeRate> parseData(InputStream inputStream) throws Exception {
+        TreeMap<LocalDate, ExchangeRate> exchangeRates = new TreeMap<>();
+        BufferedReader bufferedReader = new BufferedReader(
+                new InputStreamReader(inputStream));
+
+        // Iterate over each entry in the zip file
+        // Skip header line
+        String[] headers = bufferedReader.readLine().split(",");
+        String line;
+        while ((line = bufferedReader.readLine()) != null) {
+            String[] data = line.split(",");
+            LocalDate date = LocalDate.parse(data[0]);
+
+            Map<String, BigDecimal> rates = new HashMap<>();
+            for (int i = 1; i < headers.length; i++) {
+                if (!data[i].equals("N/A")) {
+                    rates.put(headers[i], new BigDecimal(data[i]));
+                }
+            }
+            exchangeRates.put(date, new ExchangeRate(rates));
+        }
+
+        return exchangeRates;
+    }
+}

src/main/java/com/europeanexchangerates/exchangeapi/util/dataparser/DataParser.java

@@ -0,0 +1,11 @@
+package com.europeanexchangerates.exchangeapi.util.dataparser;
+
+import java.io.InputStream;
+import java.time.LocalDate;
+import java.util.TreeMap;
+
+import com.europeanexchangerates.exchangeapi.dto.ExchangeRate;
+
+public interface DataParser {
+    public TreeMap<LocalDate, ExchangeRate> parseData(InputStream inputStream) throws Exception;
+}

src/test/java/com/europeanexchangerates/exchangeapi/util/CsvZipDataParserTest.java

@@ -0,0 +1,57 @@
+package com.europeanexchangerates.exchangeapi.util;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import com.europeanexchangerates.exchangeapi.dto.ExchangeRate;
+import com.europeanexchangerates.exchangeapi.util.dataparser.CsvDataParser;
+
+import java.io.ByteArrayInputStream;
+import java.io.InputStream;
+import java.math.BigDecimal;
+import java.time.LocalDate;
+import java.util.Map;
+import java.util.TreeMap;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class CsvZipDataParserTest {
+
+    @Mock
+    InputStream inputStream;
+
+    private CsvDataParser parser;
+
+    @BeforeEach
+    void setUp() {
+        MockitoAnnotations.openMocks(this);
+        parser = new CsvDataParser();
+    }
+
+    @Test
+    void parseData() throws Exception {
+        String testInput = "Date,USD,EUR\n" +
+                "2023-06-04,1.2100,0.8400\n" +
+                "2023-06-03,1.2200,0.8500\n";
+        InputStream inputStream = new ByteArrayInputStream(testInput.getBytes());
+
+        TreeMap<LocalDate, ExchangeRate> result = parser.parseData(inputStream);
+
+        assertEquals(new BigDecimal("1.2100"), result.get(LocalDate.of(2023, 6, 4)).getRates().get("USD"));
+        assertEquals(new BigDecimal("0.8400"), result.get(LocalDate.of(2023, 6, 4)).getRates().get("EUR"));
+        assertEquals(new BigDecimal("1.2200"), result.get(LocalDate.of(2023, 6, 3)).getRates().get("USD"));
+        assertEquals(new BigDecimal("0.8500"), result.get(LocalDate.of(2023, 6, 3)).getRates().get("EUR"));
+    }
+
+    @Test
+    void parseData_throwsExceptionForMalformedData() {
+        String testInput = "Date,USD,EUR\n" +
+                "2023-06-04,1.2100,\n" +
+                "2023-06-03,1.2200,0.8500\n";
+        InputStream inputStream = new ByteArrayInputStream(testInput.getBytes());
+
+        assertThrows(Exception.class, () -> parser.parseData(inputStream));
+    }
+}