Generate changelogs

GenerateChangelog.java

//usr/bin/env jbang "$0" "$@" ; exit $?

//DEPS com.google.code.gson:gson:2.8.6
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.URL;
import java.net.URLConnection;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.stream.Stream;

import com.google.gson.Gson;

/**
 * Generate changelog for a release. Requires
 * <a href="https://github.com/maxandersen/jbang">j'bang</a> to be installed.
 * <p>
 * Execute with:
 * <ul>
 * <li><code>jbang GenerateChangelog.java repo1/milestone/number1 repoN/milestone/numberN ...</code></li>
 * <li>eg. <code>jbang GenerateChangelog.java
 * https://github.com/eclipse/lemminx/milestone/14
 * https://github.com/eclipse/lemminx/milestone/13
 * 
 * </ul>
 * </p>
 */
public class GenerateChangelog {

  private static final Map<String, List<Issue>> labeledIssues = new LinkedHashMap<>();

  public static void main(String[] args) throws Exception {
    for (String repo : args) {
      String url = repo.replace("https://github.com/", "https://api.github.com/repos/")
                       .replace("/milestone/", "/issues?state=closed&milestone=");
      fillIssues(url);
    }
    // Performance
    generateIssues("performance -", labeledIssues.get("performance"));
    // enhancement
    generateIssues("enhancement -", labeledIssues.get("enhancement"));
    // Bug Fixes
    generateIssues("bug fix -", labeledIssues.get("bug"));
    // Performance
    generateIssues("build -", labeledIssues.get("build"));
    // Other
    generateIssues("other -", labeledIssues.get("other"));

    System.exit(0);
  }

  private static void generateIssues(String title, List<Issue> list) {
    if (list == null) {
      return;
    }
    for (Issue issue : list) {
      String url = issue.html_url;
      String number = url.substring(url.lastIndexOf("/") + 1);
      String line = " * " + title + " " + issue.title + ". See [#" + number + "](" + url + ").";
      generateLine(line);
    }
  }

  private static void generateLine(String line) {
    System.out.println(line);
  }

  private static void fillIssues(String url) throws Exception {
    int page = 1;
    boolean hasMore = true;
    do {
      String pageUrl = url+"&page="+(page++);
      System.out.println("Fetching issues from " + pageUrl);
      URL u = new URL(pageUrl);
      URLConnection connection = u.openConnection();
      try (InputStream in = connection.getInputStream()) {
        Reader reader = new InputStreamReader(in, "UTF-8");
        Issue[] issues = new Gson().fromJson(reader, Issue[].class);
        hasMore = issues.length == 30;
        Stream.of(issues).filter(Issue::isValid).forEach(i -> {
          labeledIssues.computeIfAbsent(i.getMainLabel(), k -> new ArrayList<>()).add(i);
        });
      }
    } while (hasMore);
  }

  static class Label {
    public String name;
  }

  static class Issue {
    private static String[] SIGNIFICANT_LABELS = { "build", "enhancement", "bug", "performance", "other" };
    String html_url;
    String title;
    Label[] labels;

    public String getMainLabel() {
      String mainLabel = findLabel(SIGNIFICANT_LABELS);
      return mainLabel == null ? "other" : mainLabel;
    }

    public String findLabel(String... names) {
      if (labels != null) {
        for (Label label : labels) {
          for (String name : names) {
            if (Objects.equals(label.name, name)) {
              return name;
            }
          }
        }
      }
      return null;
    }

    public boolean isValid() {
      return findLabel("invalid") == null;
    }
  }
}