28. Maven: pom.xml を1行ずつ読む

import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

// pom.xml の「書いていない値が埋まる」仕組みの模型(Maven の実装ではない)。
// 子 POM → 親 POM → その親 → Super POM の順にたどり、
//   (1) properties は子が親を上書きし、${X} は値に置き換える
//   (2) dependencies に version / scope が無ければ dependencyManagement から補う
//   (3) packaging が無ければ jar
//   (4) repositories は連鎖の全部を集める(central は Super POM の <repositories> にある)
// 値は、Boot 4.1.1 の雛形と親 POM に実際に書かれていたもの(effective-pom で確認)。
class Main {
    record Dep(String artifactId, String version, String scope) {}

    record Pom(String name, Map<String, String> properties, Map<String, String> managedVersions,
               List<Dep> dependencies, List<String> repositories, String packaging, Pom parent) {}

    // 親の連鎖を根(Super POM)まで並べる: [子, 親, 親の親, Super POM]
    static List<Pom> chain(Pom pom) {
        var list = new java.util.ArrayList<Pom>();
        for (Pom p = pom; p != null; p = p.parent()) list.add(p);
        return list;
    }

    // (1) properties: 根から順に重ね、子が後から上書きする
    static Map<String, String> effectiveProperties(Pom pom) {
        var chain = chain(pom);
        var merged = new LinkedHashMap<String, String>();
        for (int i = chain.size() - 1; i >= 0; i--) merged.putAll(chain.get(i).properties());
        // ${X} を値に置き換える(1段だけ。模型なので入れ子は扱わない)
        for (var e : merged.entrySet()) {
            String v = e.getValue();
            int s = v.indexOf("${");
            if (s >= 0) {
                String key = v.substring(s + 2, v.indexOf('}', s));
                e.setValue(v.replace("${" + key + "}", merged.getOrDefault(key, "?")));
            }
        }
        return merged;
    }

    // (2) dependencyManagement: 連鎖のどこかに版があれば、それで補う
    static String managedVersion(Pom pom, String artifactId) {
        for (Pom p : chain(pom)) {
            String v = p.managedVersions().get(artifactId);
            if (v != null) return v + "   (from " + p.name() + ")";
        }
        return "?? (no version anywhere in the chain)";
    }

    public static void main(String[] args) {
        // Super POM: すべての POM の土台。中央リポジトリの URL はここに書かれている
        Pom superPom = new Pom("Super POM", Map.of(), Map.of(), List.of(),
                List.of("central = https://repo.maven.apache.org/maven2"), null, null);
        // spring-boot-dependencies 4.1.1: 版の一覧表(BOM)。dependencyManagement だけを持つ
        Pom bom = new Pom("spring-boot-dependencies:4.1.1", Map.of(),
                Map.of("spring-boot-starter-webmvc", "4.1.1", "spring-boot-starter-webmvc-test", "4.1.1"),
                List.of(), List.of(), null, superPom);
        // spring-boot-starter-parent 4.1.1: 親 POM 14-17 行目に実際に書かれていた properties
        var parentProps = new LinkedHashMap<String, String>();   // 親 POM に書かれている順
        parentProps.put("java.version", "17");
        parentProps.put("resource.delimiter", "@");
        parentProps.put("maven.compiler.release", "${java.version}");
        parentProps.put("project.build.sourceEncoding", "UTF-8");
        Pom parent = new Pom("spring-boot-starter-parent:4.1.1", parentProps, Map.of(), List.of(), List.of(), null, bom);
        // 雛形の pom.xml: java.version だけ上書きし、依存 2 本には version を書いていない
        Pom demo = new Pom("com.example:demo:0.0.1-SNAPSHOT", Map.of("java.version", "25"), Map.of(),
                List.of(new Dep("spring-boot-starter-webmvc", null, null),
                        new Dep("spring-boot-starter-webmvc-test", null, "test")),
                List.of(), null, parent);

        System.out.println("## parent chain (child first)");
        for (Pom p : chain(demo)) System.out.println("   " + p.name());

        System.out.println();
        System.out.println("## (1) effective properties");
        effectiveProperties(demo).forEach((k, v) -> System.out.println("   " + k + " = " + v));

        System.out.println();
        System.out.println("## (2) effective dependencies");
        for (Dep d : demo.dependencies()) {
            String version = d.version() != null ? d.version() : managedVersion(demo, d.artifactId());
            String scope = d.scope() != null ? d.scope() : "compile (default when not specified)";
            System.out.println("   " + d.artifactId());
            System.out.println("      version: " + version);
            System.out.println("      scope  : " + scope);
        }

        System.out.println();
        System.out.println("## (3) effective packaging");
        String packaging = demo.packaging() != null ? demo.packaging() : "jar";
        System.out.println("   " + packaging + " (the pom wrote nothing; jar is the default)");

        System.out.println();
        System.out.println("## (4) effective repositories");
        for (Pom p : chain(demo)) for (String r : p.repositories()) System.out.println("   " + r + "   (from " + p.name() + ")");
    }
}

// 出力(JDK 22 で実行)
//   ## parent chain (child first)
//      com.example:demo:0.0.1-SNAPSHOT
//      spring-boot-starter-parent:4.1.1
//      spring-boot-dependencies:4.1.1
//      Super POM
//
//   ## (1) effective properties
//      java.version = 25
//      resource.delimiter = @
//      maven.compiler.release = 25
//      project.build.sourceEncoding = UTF-8
//
//   ## (2) effective dependencies
//      spring-boot-starter-webmvc
//         version: 4.1.1   (from spring-boot-dependencies:4.1.1)
//         scope  : compile (default when not specified)
//      spring-boot-starter-webmvc-test
//         version: 4.1.1   (from spring-boot-dependencies:4.1.1)
//         scope  : test
//
//   ## (3) effective packaging
//      jar (the pom wrote nothing; jar is the default)
//
//   ## (4) effective repositories
//      central = https://repo.maven.apache.org/maven2   (from Super POM)