1 files changed, 83 insertions, 0 deletions
diff --git a/src/content/navigates.ts b/src/content/navigates.ts
new file mode 100644
index 0000000..a2007a6
--- /dev/null
+++ b/src/content/navigates.ts
@@ -0,0 +1,83 @@
+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>(
+  win: Window,
+  selector: string,
+  filter?: (e: E) => boolean,
+): E | null {
+  let nodes = Array.from(
+    win.document.querySelectorAll(selector) as NodeListOf<E>
+  );
+
+  if (filter) {
+    nodes = nodes.filter(filter);
+  }
+  return nodes.length ? nodes[nodes.length - 1] : null;
+}
+
+const historyPrev = (win: Window): void => {
+  win.history.back();
+};
+
+const historyNext = (win: Window): void => {
+  win.history.forward();
+};
+
+// Code common to linkPrev and linkNext which navigates to the specified page.
+const linkRel = (win: Window, rel: string): void => {
+  let link = selectLast<HTMLLinkElement>(win, `link[rel~=${rel}][href]`);
+  if (link) {
+    win.location.href = link.href;
+    return;
+  }
+
+  const pattern = REL_PATTERN[rel];
+
+  let a = selectLast<HTMLAnchorElement>(win, `a[rel~=${rel}][href]`) ||
+    // `innerText` is much slower than `textContent`, but produces much better
+    // (i.e. less unexpected) results
+    selectLast(win, 'a[href]', lnk => pattern.test(lnk.innerText));
+
+  if (a) {
+    a.click();
+  }
+};
+
+const linkPrev = (win: Window): void => {
+  linkRel(win, 'prev');
+};
+
+const linkNext = (win: Window): void => {
+  linkRel(win, 'next');
+};
+
+const parent = (win: Window): void => {
+  const loc = win.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, '/');
+  }
+};
+
+const root = (win: Window): void => {
+  win.location.href = win.location.origin;
+};
+
+export { historyPrev, historyNext, linkPrev, linkNext, parent, root };