From 3a0c9753916f3113307a4d24959fc9a1083c8ff2 Mon Sep 17 00:00:00 2001
From: Lucas Gass <lucas@bywatersolutions.com>
Date: Fri, 17 Oct 2025 12:50:56 +0000
Subject: [PATCH] Revert "Bug 31149: Use dayjs to parse dates"

This reverts commit ccb4bcf055a12c52f5744153d9bbce4f9f227364.

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
---
 .../prog/en/includes/calendar.inc             |  1 -
 koha-tmpl/intranet-tmpl/prog/js/calendar.js   | 45 +++++++++++++------
 2 files changed, 32 insertions(+), 14 deletions(-)

diff --git a/koha-tmpl/intranet-tmpl/prog/en/includes/calendar.inc b/koha-tmpl/intranet-tmpl/prog/en/includes/calendar.inc
index cd498a00c6..1437f2e157 100644
--- a/koha-tmpl/intranet-tmpl/prog/en/includes/calendar.inc
+++ b/koha-tmpl/intranet-tmpl/prog/en/includes/calendar.inc
@@ -37,7 +37,6 @@
         var flatpickr_timeformat = [% IF Koha.Preference('TimeFormat') == '12hr' %]false[% ELSE %]true[% END %];
     </script>
     <!-- / calendar.inc -->
-    [% Asset.js("lib/dayjs/dayjs.min.js") | $raw %]
     [% Asset.js("js/calendar.js") | $raw %]
     [% Asset.js("lib/flatpickr/flatpickr.min.js") | $raw %]
     [% Asset.js("lib/flatpickr/shortcut-buttons-flatpickr.min.js") | $raw %]
diff --git a/koha-tmpl/intranet-tmpl/prog/js/calendar.js b/koha-tmpl/intranet-tmpl/prog/js/calendar.js
index 80f0b04d99..e1637b2ba7 100644
--- a/koha-tmpl/intranet-tmpl/prog/js/calendar.js
+++ b/koha-tmpl/intranet-tmpl/prog/js/calendar.js
@@ -9,12 +9,29 @@ if (debug > 1) {
     );
 }
 
-function is_valid_date(dateText) {
-    return dayjs(
-        dateText,
-        get_dateformat_str(dateformat_pref).toUpperCase(),
-        true
-    ).isValid();
+function is_valid_date(date) {
+    // An empty string is considered as a valid date for convenient reasons.
+    if (date === "") return 1;
+    var dateformat = flatpickr_dateformat_string;
+    if (dateformat == "us") {
+        if (date.search(/^\d{2}\/\d{2}\/\d{4}($|\s)/) == -1) return 0;
+        dateformat = "m/d/Y";
+    } else if (dateformat == "metric") {
+        if (date.search(/^\d{2}\/\d{2}\/\d{4}($|\s)/) == -1) return 0;
+        dateformat = "d/m/Y";
+    } else if (dateformat == "iso") {
+        if (date.search(/^\d{4}-\d{2}-\d{2}($|\s)/) == -1) return 0;
+        dateformat = "Y-m-d";
+    } else if (dateformat == "dmydot") {
+        if (date.search(/^\d{2}\.\d{2}\.\d{4}($|\s)/) == -1) return 0;
+        dateformat = "d.m.Y";
+    }
+    try {
+        flatpickr.parseDate(date, dateformat);
+    } catch (e) {
+        return 0;
+    }
+    return 1;
 }
 
 function get_dateformat_str(dateformat) {
@@ -47,18 +64,20 @@ function Date_from_syspref(dstring) {
             "Date_from_syspref(" + dstring + ") splits to:\n" + dateX.join("\n")
         );
     }
-    let d = dayjs(
-        dstring,
-        get_dateformat_str(dateformat_pref).toUpperCase(),
-        true
-    );
-    if (!d.isValid()) {
+    if (dateformat_pref === "iso") {
+        return new Date(dateX[0], dateX[1] - 1, dateX[2]); // YYYY-MM-DD to (YYYY,m(0-11),d)
+    } else if (dateformat_pref === "us") {
+        return new Date(dateX[2], dateX[0] - 1, dateX[1]); // MM/DD/YYYY to (YYYY,m(0-11),d)
+    } else if (dateformat_pref === "metric") {
+        return new Date(dateX[2], dateX[1] - 1, dateX[0]); // DD/MM/YYYY to (YYYY,m(0-11),d)
+    } else if (dateformat_pref === "dmydot") {
+        return new Date(dateX[2], dateX[1] - 1, dateX[0]); // DD.MM.YYYY to (YYYY,m(0-11),d)
+    } else {
         if (debug > 0) {
             alert("KOHA ERROR - Unrecognized date format: " + dateformat_pref);
         }
         return 0;
     }
-    return d.toDate();
 }
 
 function DateTime_from_syspref(date_time) {