Downloads (MacOS): show relative date

This is yet another thing that was computed server-side but can be
computed on the client side instead.

The logic for the approximate date difference was inspired by
https://github.com/rails/rails/blob/4136145819ab/actionview/lib/action_view/helpers/date_helper.rb#L29-L158
(because this was used indirectly in the Rails app, via the
`time_ago_in_words` function).

However, rather than reimplementing all of that complicated logic, let's
implement a vastly simpler yet still similar logic that imitates how
that Rails function handles year-long differencess: up to 25% longer a
time difference and we say "about X ago", up to 25% shorter and we say
"almost X ago", otherwise we say "over X ago".

Co-authored-by: Matthias Aßhauer <[email protected]>
Signed-off-by: Matthias Aßhauer <[email protected]>
Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

content/downloads/mac.html

@@ -28,7 +28,7 @@ <h3>Xcode</h3>
   <h3>Binary installer</h3>
   <p>Tim Harper provides an <a href="https://sourceforge.net/projects/git-osx-installer/">installer</a>
   for Git. The latest version is <a href="{{< site-param macos_installer.url >}}">{{< site-param macos_installer.version >}}</a>,
-  which was released on {{< site-param macos_installer.release_date >}}.
+  which was released <span id="relative-release-date"></span>on <span id="auto-download-date">{{< site-param macos_installer.release_date >}}</span>.
 
   <h3>Building from Source</h3>
   <p>If you prefer to build from source, you can find tarballs

static/js/application.js

@@ -248,6 +248,7 @@ var Downloads = {
     Downloads.observeGUIOSFilter();
     Downloads.observePopState();
     Downloads.filterGUIS();
+    Downloads.postProcessDownloadPage();
   },
 
   getOSFromQueryString: function() {
@@ -314,7 +315,35 @@ var Downloads = {
     onPopState(function() {
       Downloads.filterGUIS();
     });
-  }
+  },
+
+  // say how many days ago this version was released
+  postProcessReleaseDate: function(index, releaseDateString) {
+    const daysAgo = Math.floor((Date.now() - Date.parse($('#auto-download-date').html())) / 86400000);
+    if (daysAgo < 0) return releaseDateString; // leave unparseable content alone
+
+    const rest = (count, unit) => `${count} ${unit}${count > 1 ? "s" : ""} ago`;
+    let ago = rest(daysAgo, "day");
+
+    const handwave = (exact, unit) => {
+      const roundedDown = Math.floor(exact);
+      const fract = exact - roundedDown;
+      if (fract < 0.25) return `about ${rest(roundedDown, unit)}`;
+      if (fract < 0.75) return `over ${rest(roundedDown, unit)}`;
+      return `almost ${rest(roundedDown + 1, unit)}`;
+    }
+
+    if (daysAgo == 0) ago = "today";
+    else if (daysAgo == 1) ago = "yesterday";
+    // from here on out, we keep it only approximately exact
+    else if (daysAgo > 365 * 0.75) ago = handwave(daysAgo / 365.25, "year");
+    else if (daysAgo > 45) ago = handwave(daysAgo / 30.4, "month");
+    return `<strong>${ago}</strong>, `;
+  },
+
+  postProcessDownloadPage: function() {
+    $('#relative-release-date').html(Downloads.postProcessReleaseDate);
+  },
 }
 
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