[>] Create domain model (sealed types)

Author: nipafx

README.md

@@ -4,11 +4,24 @@ A repository for my live-coding talk [Modern Java in Action](https://nipafx.dev/
 
 ## Next
 
-Records:
-* `record ExternalPage(URI url, String content)`
-	* compact constructor checks all arguments
-	* `equals` with `instanceof`
-* `record GitHubPrPage(URI url, String content, Set<URI> links, int prNumber)`
-	* compact constructor checks all arguments
-	* additional constructor without `links`
-	* `equals` with `instanceof`
+Sealed types:
+* `sealed interface Page permits ErrorPage, SuccessfulPage` with `URI url()`
+* `sealed interface SuccessfulPage extends Page permits ExternalPage, GitHubPage` with `String content()`
+* `sealed interface GitHubPage extends SuccessfulPage permits GitHubIssuePage, GitHubPrPage` with `Set<Page> links()` and
+	```java
+	default Stream<Page> subtree() {
+		var subtree = new ArrayList<Page>(Set.of(this));
+		var upcomingPages = new LinkedHashSet<>(this.links());
+
+		while (!upcomingPages.isEmpty()) {
+			var nextPage = upcomingPages.removeFirst();
+			if (!subtree.contains(nextPage) && nextPage instanceof GitHubPage nextGhPage)
+				new LinkedHashSet<>(nextGhPage.links())
+						.reversed()
+						.forEach(upcomingPages::addFirst);
+			subtree.add(nextPage);
+		}
+
+		return subtree.stream();
+	}
+	```

src/main/java/dev/nipafx/demo/modern/page/ErrorPage.java

@@ -0,0 +1,27 @@
+package dev.nipafx.demo.modern.page;
+
+import java.net.URI;
+import java.util.Objects;
+
+import static java.util.Objects.requireNonNull;
+
+public record ErrorPage(URI url, Exception ex) {
+
+	public ErrorPage {
+		requireNonNull(url);
+		requireNonNull(ex);
+	}
+
+	@Override
+	public boolean equals(Object other) {
+		return other == this
+				|| other instanceof GitHubIssuePage page
+				&& this.url.equals(page.url());
+	}
+
+	@Override
+	public int hashCode() {
+		return Objects.hash(url);
+	}
+
+}

src/main/java/dev/nipafx/demo/modern/page/ExternalPage.java

@@ -0,0 +1,27 @@
+package dev.nipafx.demo.modern.page;
+
+import java.net.URI;
+import java.util.Objects;
+
+import static java.util.Objects.requireNonNull;
+
+public record ExternalPage(URI url, String content) {
+
+	public ExternalPage {
+		requireNonNull(url);
+		requireNonNull(content);
+	}
+
+	@Override
+	public boolean equals(Object other) {
+		return other == this
+				|| other instanceof GitHubIssuePage page
+				&& this.url.equals(page.url());
+	}
+
+	@Override
+	public int hashCode() {
+		return Objects.hash(url);
+	}
+
+}

src/main/java/dev/nipafx/demo/modern/page/GitHubIssuePage.java

@@ -0,0 +1,36 @@
+package dev.nipafx.demo.modern.page;
+
+import java.net.URI;
+import java.util.HashSet;
+import java.util.Objects;
+import java.util.Set;
+
+import static java.util.Objects.requireNonNull;
+
+public record GitHubIssuePage(URI url, String content, Set<URI> links, int issueNumber) {
+
+	public GitHubIssuePage {
+		requireNonNull(url);
+		requireNonNull(content);
+		links = Set.copyOf(links);
+		if (issueNumber <= 0)
+			throw new IllegalArgumentException("Issue number must be 1 or greater - was '%s' at '%s'.".formatted(issueNumber, url));
+	}
+
+	public GitHubIssuePage(URI url, String content, int issueNumber) {
+		this(url, content, new HashSet<>(), issueNumber);
+	}
+
+	@Override
+	public boolean equals(Object other) {
+		return other == this
+				|| other instanceof GitHubIssuePage page
+				&& this.url.equals(page.url());
+	}
+
+	@Override
+	public int hashCode() {
+		return Objects.hash(url);
+	}
+
+}

src/main/java/dev/nipafx/demo/modern/page/GitHubPrPage.java

@@ -0,0 +1,36 @@
+package dev.nipafx.demo.modern.page;
+
+import java.net.URI;
+import java.util.HashSet;
+import java.util.Objects;
+import java.util.Set;
+
+import static java.util.Objects.requireNonNull;
+
+public record GitHubPrPage(URI url, String content, Set<URI> links, int prNumber) {
+
+	public GitHubPrPage {
+		requireNonNull(url);
+		requireNonNull(content);
+		links = Set.copyOf(links);
+		if (prNumber <= 0)
+			throw new IllegalArgumentException("PR number must be 1 or greater - was '%s' at '%s'.".formatted(prNumber, url));
+	}
+
+	public GitHubPrPage(URI url, String content, int prNumber) {
+		this(url, content, new HashSet<>(), prNumber);
+	}
+
+	@Override
+	public boolean equals(Object other) {
+		return other == this
+				|| other instanceof GitHubPrPage page
+				&& this.url.equals(page.url());
+	}
+
+	@Override
+	public int hashCode() {
+		return Objects.hash(url);
+	}
+
+}