Add change incompatibility (#9)

* Readme modification
Grouping of errors by changes
Generation of a file by breaking dependency update

* Initial template

* Submit explanation with 100 lines

* Update generation process and add Change type

* Add first explanation version

* generate template for only one change

* Remove logs

* Adding base template for explanations

* Adding download jar functionality

* Adding first version of Explanation :)

* Adding Download.java :)

src/main/java/se/kth/breaking_changes/Download.java

@@ -0,0 +1,92 @@
+package se.kth.breaking_changes;
+
+import org.jsoup.Jsoup;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.nio.file.Path;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+import java.util.stream.Collectors;
+
+public class Download {
+
+    private static final Map<String, String> repositoryUrls = Map.of(
+            "mavenCentral", "https://repo1.maven.org/maven2/",
+            "jenkins", "https://repo.jenkins-ci.org/artifactory/releases/",
+            "jboss", "https://repository.jboss.org/nexus/content/repositories/thirdparty-releases/"
+    );
+
+    private Download() {
+    }
+
+    private static String getIndexPageOfRepository(String artifactUrl) throws IOException, InterruptedException {
+        HttpClient client = HttpClient.newHttpClient();
+        HttpRequest request =
+                HttpRequest.newBuilder().uri(URI.create(artifactUrl)).build();
+        HttpResponse<String> result = client.send(request, HttpResponse.BodyHandlers.ofString());
+
+        if (result.statusCode() != 200) {
+            return null;
+        }
+        return result.body();
+    }
+
+    private static String getArtifactUrl(String groupId, String artifactId, String version, String repositoryUrl) {
+        groupId = groupId.replace('.', '/');
+        return repositoryUrl + groupId + "/" + artifactId + "/" + version + "/";
+    }
+
+    private static String getUrlOfRequestedJar(String indexPageContent, String indexPageUrl) {
+        List<String> candidates = Jsoup.parse(indexPageContent).select("a").stream()
+                .map(e -> e.attr("href"))
+                .collect(Collectors.toList());
+
+        Optional<String> artifactJar = candidates.stream()
+                .filter(c -> c.endsWith(".jar"))
+                .filter(c -> !c.contains("sources"))
+                .filter(c -> !c.contains("javadoc"))
+                .filter(c -> !c.contains("tests"))
+                .filter(c -> !c.contains("test"))
+                .filter(c -> !c.contains("config"))
+                .findFirst();
+
+        if (artifactJar.isPresent()) {
+            String artifactJarName = artifactJar.get();
+            // java.net.URI has the worst APIs ever
+            if (artifactJarName.startsWith("https://") || artifactJarName.startsWith("http://")) {
+                return artifactJarName;
+            }
+            return indexPageUrl + artifactJarName;
+        } else {
+            System.err.println("Could not find jar for " + indexPageUrl);
+            return null;
+        }
+    }
+
+    public static File getJarFile(String groupId, String artifactId, String version, Path directory)
+            throws IOException, InterruptedException {
+        for (String repositoryUrl : repositoryUrls.values()) {
+            String url = getArtifactUrl(groupId, artifactId, version, repositoryUrl);
+            String indexPageContent = getIndexPageOfRepository(url);
+            if (indexPageContent != null) {
+                String jarUrl = getUrlOfRequestedJar(indexPageContent, url);
+                if (jarUrl != null) {
+                    HttpClient client = HttpClient.newHttpClient();
+                    HttpRequest request =
+                            HttpRequest.newBuilder().uri(URI.create(jarUrl)).build();
+
+                    final var resolve = directory.resolve(String.format("%s-%s", artifactId, version) + ".jar");
+                    HttpResponse<Path> result = client.send(request, HttpResponse.BodyHandlers.ofFile(resolve));
+                    return result.body().toFile();
+                }
+            }
+        }
+        return null;
+    }
+}