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diff --git a/src/urls.js b/src/urls.js
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+// Code that deals with URLs (really the pathnames that get referenced all
+// throughout the gener8ted HTML). Most nota8ly here is generateURLs, which
+// is in charge of pre-gener8ting a complete network of template strings
+// which can really quickly take su8stitute parameters to link from any one
+// place to another; 8ut there are also a few other utilities, too.
+
+import * as path from 'node:path';
+
+import {withEntries} from '#sugar';
+
+export * from './url-spec.js';
+
+export function generateURLs(urlSpec) {
+  const getValueForFullKey = (obj, fullKey) => {
+    const [groupKey, subKey] = fullKey.split('.');
+    if (!groupKey || !subKey) {
+      throw new Error(`Expected group key and subkey (got ${fullKey})`);
+    }
+
+    if (!Object.hasOwn(obj, groupKey)) {
+      throw new Error(`Expected valid group key (got ${groupKey})`);
+    }
+
+    const group = obj[groupKey];
+
+    if (!Object.hasOwn(group, subKey)) {
+      throw new Error(`Expected valid subkey (got ${subKey} for group ${groupKey})`);
+    }
+
+    return {
+      value: group[subKey],
+      group,
+    };
+  };
+
+  // This should be called on values which are going to be passed to
+  // path.relative, because relative will resolve a leading slash as the root
+  // directory of the working device, which we aren't looking for here.
+  const trimLeadingSlash = (P) => (P.startsWith('/') ? P.slice(1) : P);
+
+  const generateTo = (fromPath, fromGroup) => {
+    const A = trimLeadingSlash(fromPath);
+
+    const rebasePrefix = '../'
+      .repeat((fromGroup.prefix || '').split('/').filter(Boolean).length);
+
+    const pathHelper = (toPath, toGroup) => {
+      let B = trimLeadingSlash(toPath);
+
+      let argIndex = 0;
+      B = B.replaceAll('<>', () => `<${argIndex++}>`);
+
+      if (toGroup.prefix !== fromGroup.prefix) {
+        // TODO: Handle differing domains in prefixes.
+        B = rebasePrefix + (toGroup.prefix || '') + B;
+      }
+
+      const suffix = toPath.endsWith('/') ? '/' : '';
+
+      return {
+        posix: path.posix.relative(A, B) + suffix,
+        device: path.relative(A, B) + suffix,
+      };
+    };
+
+    const groupSymbol = Symbol();
+
+    const groupHelper = (urlGroup) => ({
+      [groupSymbol]: urlGroup,
+      ...withEntries(urlGroup.paths, (entries) =>
+        entries.map(([key, path]) => [key, pathHelper(path, urlGroup)])
+      ),
+    });
+
+    const relative = withEntries(urlSpec, (entries) =>
+      entries.map(([key, urlGroup]) => [key, groupHelper(urlGroup)])
+    );
+
+    const toHelper =
+      ({device}) =>
+      (key, ...args) => {
+        const {
+          value: {
+            [device ? 'device' : 'posix']: template,
+          },
+        } = getValueForFullKey(relative, key);
+
+        let missing = 0;
+        let result = template.replaceAll(/<([0-9]+)>/g, (match, n) => {
+          if (n < args.length) {
+            const value = args[n];
+            if (device) {
+              return value;
+            } else {
+              let encoded = encodeURIComponent(value);
+              encoded = encoded.replaceAll('%2F', '/');
+              return encoded;
+            }
+          } else {
+            missing++;
+          }
+        });
+
+        if (missing) {
+          throw new Error(
+            `Expected ${missing + args.length} arguments, got ${
+              args.length
+            } (key ${key}, args [${args}])`
+          );
+        }
+
+        return result;
+      };
+
+    return {
+      to: toHelper({device: false}),
+      toDevice: toHelper({device: true}),
+    };
+  };
+
+  const generateFrom = () => {
+    const map = withEntries(
+      urlSpec,
+      (entries) => entries.map(([key, group]) => [
+        key,
+        withEntries(group.paths, (entries) =>
+          entries.map(([key, path]) => [key, generateTo(path, group)])
+        ),
+      ]));
+
+    const from = (key) => getValueForFullKey(map, key).value;
+
+    return {from, map};
+  };
+
+  return generateFrom();
+}
+
+const thumbnailHelper = (name) => (file) =>
+  file.replace(/\.(jpg|png)$/, name + '.jpg');
+
+export const thumb = {
+  large: thumbnailHelper('.large'),
+  medium: thumbnailHelper('.medium'),
+  small: thumbnailHelper('.small'),
+};
+
+// Makes the generally-used and wiki-specialized "to" page utility.
+// "to" returns a relative path from the current page to the target.
+export function getURLsFrom({
+  baseDirectory,
+  pagePath,
+  urls,
+}) {
+  const pageSubKey = pagePath[0];
+  const subdirectoryPrefix = getPageSubdirectoryPrefix({pagePath});
+
+  return (targetFullKey, ...args) => {
+    const [groupKey, subKey] = targetFullKey.split('.');
+    let from, to;
+
+    // When linking to *outside* the localized area of the site, we need to
+    // make sure the result is correctly relative to the 8ase directory.
+    if (
+      groupKey !== 'localized' &&
+      groupKey !== 'localizedDefaultLanguage' &&
+      baseDirectory
+    ) {
+      from = 'localizedWithBaseDirectory.' + pageSubKey;
+      to = targetFullKey;
+    } else if (groupKey === 'localizedDefaultLanguage' && baseDirectory) {
+      // Special case for specifically linking *from* a page with base
+      // directory *to* a page without! Used for the language switcher and
+      // hopefully nothing else oh god.
+      from = 'localizedWithBaseDirectory.' + pageSubKey;
+      to = 'localized.' + subKey;
+    } else if (groupKey === 'localizedDefaultLanguage') {
+      // Linking to the default, except surprise, we're already IN the default
+      // (no baseDirectory set).
+      from = 'localized.' + pageSubKey;
+      to = 'localized.' + subKey;
+    } else {
+      // If we're linking inside the localized area (or there just is no
+      // 8ase directory), the 8ase directory doesn't matter.
+      from = 'localized.' + pageSubKey;
+      to = targetFullKey;
+    }
+
+    return (
+      subdirectoryPrefix +
+      urls.from(from).to(to, ...args));
+  };
+}
+
+// Makes the generally-used and wiki-specialized "absoluteTo" page utility.
+// "absoluteTo" returns an absolute path, starting at site root (/) leading
+// to the target.
+export function getURLsFromRoot({
+  baseDirectory,
+  urls,
+}) {
+  const {to} = urls.from('shared.root');
+
+  return (targetFullKey, ...args) => {
+    const [groupKey, subKey] = targetFullKey.split('.');
+    return (
+      '/' +
+      (groupKey === 'localized' && baseDirectory
+        ? to(
+            'localizedWithBaseDirectory.' + subKey,
+            baseDirectory,
+            ...args
+          )
+        : to(targetFullKey, ...args))
+    );
+  };
+}
+
+export function getPagePathname({
+  baseDirectory,
+  device = false,
+  pagePath,
+  urls,
+}) {
+  const {[device ? 'toDevice' : 'to']: to} = urls.from('shared.root');
+
+  return (baseDirectory
+    ? to('localizedWithBaseDirectory.' + pagePath[0], baseDirectory, ...pagePath.slice(1))
+    : to('localized.' + pagePath[0], ...pagePath.slice(1)));
+}
+
+// Needed for the rare path arguments which themselves contains one or more
+// slashes, e.g. for listings, with arguments like 'albums/by-name'.
+export function getPageSubdirectoryPrefix({
+  pagePath,
+}) {
+  const timesNestedDeeply = (pagePath
+    .slice(1) // skip URL key, only check arguments
+    .join('/')
+    .split('/')
+    .length - 1);
+  return '../'.repeat(timesNestedDeeply);
+}