From 70b14222ec6d4cddd0a48c0783037acf15838fd9 Mon Sep 17 00:00:00 2001
From: Chris Wolfgang <210299580+Chris-Wolfgang@users.noreply.github.com>
Date: Thu, 18 Jun 2026 22:39:29 -0400
Subject: [PATCH 1/3] docfx_project: add canonical versions.json stub

---
 docfx_project/versions.json | 1 +
 1 file changed, 1 insertion(+)
 create mode 100644 docfx_project/versions.json

diff --git a/docfx_project/versions.json b/docfx_project/versions.json
new file mode 100644
index 00000000..fe51488c
--- /dev/null
+++ b/docfx_project/versions.json
@@ -0,0 +1 @@
+[]

From 4120707aeee09dbd859cb8cbd5f89d5f2db44787 Mon Sep 17 00:00:00 2001
From: Chris Wolfgang <210299580+Chris-Wolfgang@users.noreply.github.com>
Date: Thu, 18 Jun 2026 22:39:30 -0400
Subject: [PATCH 2/3] docfx_project/public: add canonical version-picker.js

---
 docfx_project/public/version-picker.js | 205 +++++++++++++++++++++++++
 1 file changed, 205 insertions(+)
 create mode 100644 docfx_project/public/version-picker.js

diff --git a/docfx_project/public/version-picker.js b/docfx_project/public/version-picker.js
new file mode 100644
index 00000000..d5afe387
--- /dev/null
+++ b/docfx_project/public/version-picker.js
@@ -0,0 +1,205 @@
+// Version picker for Wolfgang.* DocFX sites.
+//
+// Reads versions.json from the site root and inserts a <select> dropdown
+// into the header navbar so readers can switch between published doc
+// versions. Falls back silently if versions.json is missing or malformed
+// — the page renders normally without a picker.
+//
+// Designed to live in the canonical repo-template's docfx_project/public/
+// directory and fan out unchanged to all downstream repos. The script
+// detects the repo segment from window.location.pathname so the same
+// file works on github.io and on `docfx build --serve` localhost.
+//
+// Canonical design + tracking lives at:
+//   https://github.com/Chris-Wolfgang/repo-template/issues/379
+(function () {
+    'use strict';
+
+    function init() {
+        // Compute where versions.json lives.
+        //  - On GitHub Pages (*.github.io): the first path segment is the
+        //    repo name, e.g. /DateTime-Extensions/... → /DateTime-Extensions/versions.json
+        //  - On localhost (`docfx build --serve`): just /versions.json
+        //  - On custom domain (CNAME): same as localhost — versions.json is
+        //    at the document root.
+        var pathSegments = window.location.pathname.split('/').filter(function (s) { return s.length > 0; });
+        var versionsUrl;
+        if (window.location.hostname.endsWith('.github.io') && pathSegments.length > 0) {
+            versionsUrl = '/' + pathSegments[0] + '/versions.json';
+        } else {
+            versionsUrl = '/versions.json';
+        }
+
+        // Use the browser's default caching policy: versions.json changes
+        // infrequently (only on a new release deploy) so forcing a network
+        // request on every page view is wasteful. The workflow emits the
+        // file with normal HTTP cache headers; the browser handles
+        // conditional revalidation correctly.
+        fetch(versionsUrl)
+            .then(function (r) { return r.ok ? r.json() : null; })
+            .then(function (data) {
+                if (!data || !Array.isArray(data) || data.length === 0) {
+                    return; // silent — no picker to show
+                }
+                renderPicker(data);
+            })
+            .catch(function () {
+                // silent — no picker, but the page is still usable
+            });
+    }
+
+    function renderPicker(versions) {
+        // Detect the currently-viewed version from the URL.
+        var currentVersion = 'latest';
+        var m = window.location.pathname.match(/\/versions\/([^\/]+)(?:\/|$)/);
+        if (m) {
+            currentVersion = m[1];
+        }
+
+        // If we're on /versions/latest/, resolve 'latest' to the concrete
+        // version it points to (matching the `latest` entry's url against
+        // the versioned entries). Without this resolution, the browser
+        // auto-selects the first option in the dropdown — which is usually
+        // the same concrete version 'latest' aliases — and picking that
+        // option doesn't fire `change`, leaving the user unable to navigate
+        // away from /versions/latest/ to the equivalent concrete-version
+        // URL via the picker.
+        if (currentVersion === 'latest') {
+            var latestEntry = null;
+            for (var i = 0; i < versions.length; i++) {
+                if (versions[i] && versions[i].version === 'latest') {
+                    latestEntry = versions[i];
+                    break;
+                }
+            }
+            if (latestEntry && latestEntry.url) {
+                for (var j = 0; j < versions.length; j++) {
+                    var v = versions[j];
+                    if (v && v.version !== 'latest' && v.url === latestEntry.url) {
+                        currentVersion = v.version;
+                        break;
+                    }
+                }
+            }
+        }
+
+        // Build the <select>.
+        var select = document.createElement('select');
+        select.className = 'wolfgang-version-picker';
+        select.setAttribute('aria-label', 'Documentation version');
+
+        // Light styling — neutral, follows theme colors.
+        //
+        // `color-scheme: light dark` tells the browser the element's
+        // popup can render in either color scheme; the browser then
+        // picks the right one based on the page's data-bs-theme / OS
+        // preference. Without this, the OS-rendered popup defaults to
+        // light mode and the option text ends up white-on-white in
+        // DocFX modern's dark theme.
+        select.style.cssText = [
+            'margin-left: 0.75rem',
+            'margin-right: 0.5rem',
+            'padding: 0.25rem 0.5rem',
+            'background: transparent',
+            'color: inherit',
+            'color-scheme: light dark',
+            'border: 1px solid currentColor',
+            'border-radius: 4px',
+            'font: inherit',
+            'cursor: pointer',
+            'opacity: 0.85'
+        ].join('; ');
+
+        var optionCount = 0;
+        versions.forEach(function (v) {
+            if (!v || !v.version || !v.url) return;
+            // Skip the "latest" alias — the highest-numbered v* entry
+            // already represents the latest release; surfacing both is
+            // redundant in the picker. versions.json keeps the "latest"
+            // entry so other consumers (links, scripts) can still
+            // resolve it.
+            if (v.version === 'latest') return;
+            var opt = document.createElement('option');
+            opt.value = v.url;
+            opt.textContent = v.version;
+            if (v.version === currentVersion) {
+                opt.selected = true;
+            }
+            // Explicit option styling so the OS-rendered popup is
+            // readable in both themes. Bootstrap variables (used by
+            // DocFX's modern template) flip automatically with
+            // data-bs-theme; the fallback values cover non-Bootstrap
+            // hosts.
+            opt.style.backgroundColor = 'var(--bs-body-bg, Canvas)';
+            opt.style.color = 'var(--bs-body-color, CanvasText)';
+            select.appendChild(opt);
+            optionCount++;
+        });
+
+        // No selectable versions (e.g. versions.json contained only the
+        // "latest" alias, or all entries were malformed) — don't insert
+        // an empty dropdown.
+        if (optionCount === 0) return;
+
+        select.addEventListener('change', function (e) {
+            var target = e.target.value;
+            if (!target) return;
+            // versions.json's `url` fields include the gh-pages repo prefix
+            // (e.g. /DateTime-Extensions/versions/v1.2.0/) because that's
+            // the correct absolute path on github.io. On localhost or on a
+            // CNAME-served custom domain, that prefix isn't a directory
+            // and the navigation 404s. Strip the first path segment when
+            // we're not on github.io so the URL becomes relative to the
+            // actual document root.
+            if (!window.location.hostname.endsWith('.github.io') && target.charAt(0) === '/') {
+                target = target.replace(/^\/[^\/]+\//, '/');
+            }
+            window.location.href = target;
+        });
+
+        // Insert into the DocFX modern-template navbar.
+        // Anchors are pairs of [selector, mode]:
+        //   - "before" inserts the picker as a sibling immediately before
+        //     the matched element (preferred for the theme toggle / nav
+        //     groups / search box — keeps the picker inline with them).
+        //   - "append" inserts the picker as the LAST child of the matched
+        //     element (used for the <header> fallback so the picker lands
+        //     INSIDE the header, not as a sibling under <html>).
+        // First match wins.
+        var anchors = [
+            ['header #mode', 'before'],
+            ['header .navbar-nav', 'before'],
+            ['header form[role="search"]', 'before'],
+            ['header nav', 'append'],
+            ['header', 'append']
+        ];
+        var inserted = false;
+        for (var i = 0; i < anchors.length; i++) {
+            var sel = anchors[i][0];
+            var mode = anchors[i][1];
+            var anchor = document.querySelector(sel);
+            if (!anchor) continue;
+            if (mode === 'before' && anchor.parentNode) {
+                anchor.parentNode.insertBefore(select, anchor);
+            } else {
+                anchor.appendChild(select);
+            }
+            inserted = true;
+            break;
+        }
+        if (!inserted) {
+            // Last-resort fallback — pin to top-right.
+            select.style.position = 'fixed';
+            select.style.top = '0.5rem';
+            select.style.right = '1rem';
+            select.style.zIndex = '1000';
+            document.body.appendChild(select);
+        }
+    }
+
+    if (document.readyState === 'loading') {
+        document.addEventListener('DOMContentLoaded', init);
+    } else {
+        init();
+    }
+})();

From 208bda99c48c4c7d17fd8cf459849588f968286c Mon Sep 17 00:00:00 2001
From: Chris Wolfgang <210299580+Chris-Wolfgang@users.noreply.github.com>
Date: Thu, 18 Jun 2026 22:39:32 -0400
Subject: [PATCH 3/3] docfx_project/docfx.json: add public/** + versions.json
 to resource.files

---
 docfx_project/docfx.json | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/docfx_project/docfx.json b/docfx_project/docfx.json
index 3559e29c..e8cef3d7 100644
--- a/docfx_project/docfx.json
+++ b/docfx_project/docfx.json
@@ -34,9 +34,11 @@
         "files": [
           "logo.svg",
           "apple-touch-icon.png",
-          "favicon.ico",
           "favicon.svg",
-          "images/**"
+          "favicon.ico",
+          "images/**",
+          "public/**",
+          "versions.json"
         ]
       }
     ],