1 files changed, 98 insertions, 0 deletions
diff --git a/src/content/presenters/NavigationPresenter.ts b/src/content/presenters/NavigationPresenter.ts
new file mode 100644
index 0000000..66110e5
--- /dev/null
+++ b/src/content/presenters/NavigationPresenter.ts
@@ -0,0 +1,98 @@
+export default interface NavigationPresenter {
+  openHistoryPrev(): void;
+
+  openHistoryNext(): void;
+
+  openLinkPrev(): void;
+
+  openLinkNext(): void;
+
+  openParent(): void;
+
+  openRoot(): void;
+
+  // eslint-disable-next-line semi
+}
+
+const REL_PATTERN: {[key: string]: RegExp} = {
+  prev: /^(?:prev(?:ious)?|older)\b|\u2039|\u2190|\xab|\u226a|<</i,
+  next: /^(?:next|newer)\b|\u203a|\u2192|\xbb|\u226b|>>/i,
+};
+
+// Return the last element in the document matching the supplied selector
+// and the optional filter, or null if there are no matches.
+// eslint-disable-next-line func-style
+function selectLast<E extends Element>(
+  selector: string,
+  filter?: (e: E) => boolean,
+): E | null {
+  let nodes = Array.from(
+    window.document.querySelectorAll(selector) as NodeListOf<E>
+  );
+
+  if (filter) {
+    nodes = nodes.filter(filter);
+  }
+  return nodes.length ? nodes[nodes.length - 1] : null;
+}
+
+export class NavigationPresenterImpl implements NavigationPresenter {
+  openHistoryPrev(): void {
+    window.history.back();
+  }
+
+  openHistoryNext(): void {
+    window.history.forward();
+  }
+
+  openLinkPrev(): void {
+    this.linkRel('prev');
+  }
+
+  openLinkNext(): void {
+    this.linkRel('next');
+  }
+
+  openParent(): void {
+    const loc = window.location;
+    if (loc.hash !== '') {
+      loc.hash = '';
+      return;
+    } else if (loc.search !== '') {
+      loc.search = '';
+      return;
+    }
+
+    const basenamePattern = /\/[^/]+$/;
+    const lastDirPattern = /\/[^/]+\/$/;
+    if (basenamePattern.test(loc.pathname)) {
+      loc.pathname = loc.pathname.replace(basenamePattern, '/');
+    } else if (lastDirPattern.test(loc.pathname)) {
+      loc.pathname = loc.pathname.replace(lastDirPattern, '/');
+    }
+  }
+
+  openRoot(): void {
+    window.location.href = window.location.origin;
+  }
+
+  // Code common to linkPrev and linkNext which navigates to the specified page.
+  private linkRel(rel: 'prev' | 'next'): void {
+    let link = selectLast<HTMLLinkElement>(`link[rel~=${rel}][href]`);
+    if (link) {
+      window.location.href = link.href;
+      return;
+    }
+
+    const pattern = REL_PATTERN[rel];
+
+    let a = selectLast<HTMLAnchorElement>(`a[rel~=${rel}][href]`) ||
+    // `innerText` is much slower than `textContent`, but produces much better
+    // (i.e. less unexpected) results
+    selectLast('a[href]', lnk => pattern.test(lnk.innerText));
+
+    if (a) {
+      a.click();
+    }
+  }
+}