From 47938d1a2cc7f3abb74b08c3c14c08c2786f58a3 Mon Sep 17 00:00:00 2001
From: Christopher Lam <christopher.lck@gmail.com>
Date: Wed, 11 Feb 2026 18:43:21 +0800
Subject: [PATCH] [gnc-date.cpp] gnc_date_interval_format localisable with ICU

---
 bindings/engine.i              |  3 ++
 libgnucash/engine/gnc-date.cpp | 67 ++++++++++++++++++++++++++++++++++
 libgnucash/engine/gnc-date.h   |  2 +
 3 files changed, 72 insertions(+)

diff --git a/bindings/engine.i b/bindings/engine.i
index 5b1d5b587c..8e9bce0d6e 100644
--- a/bindings/engine.i
+++ b/bindings/engine.i
@@ -116,6 +116,9 @@ engine-common.i */
 %newobject xaccTransGetPaymentAcctSplitList;
 %newobject xaccAccountGetSplitList;
 
+%newobject gnc_date_interval_format;
+gchar* gnc_date_interval_format (time64 from_date, time64 to_date);
+
 %include "engine-common.i"
 
 #if defined(SWIGGUILE)
diff --git a/libgnucash/engine/gnc-date.cpp b/libgnucash/engine/gnc-date.cpp
index 0f46cfcf87..cd5e64ba3f 100644
--- a/libgnucash/engine/gnc-date.cpp
+++ b/libgnucash/engine/gnc-date.cpp
@@ -45,6 +45,8 @@
 
 #include <cinttypes>
 #include <unicode/calendar.h>
+#include "unicode/dtitvfmt.h"
+#include "unicode/smpdtfmt.h"
 
 #include "gnc-date.h"
 #include "gnc-date-p.h"
@@ -613,6 +615,71 @@ qof_print_date (time64 t)
     return g_strdup (buff);
 }
 
+static icu::DateIntervalFormat*
+get_icu_date_interval_formatter ()
+{
+    static std::unique_ptr<icu::DateIntervalFormat> difmt;
+    if (!difmt)
+    {
+        auto locale = icu::Locale::getDefault();
+        UErrorCode status = U_ZERO_ERROR;
+        difmt.reset(icu::DateIntervalFormat::createInstance(UDAT_YEAR_NUM_MONTH_DAY, locale, status));
+        if (U_FAILURE(status))
+        {
+            PWARN ("icu::DateIntervalFormat::createInstance error %d", status);
+            return nullptr;
+        }
+    }
+    return difmt.get();
+}
+
+static gchar*
+icu_date_interval_format (time64 from_date, time64 to_date)
+{
+    auto difmt = get_icu_date_interval_formatter();
+    if (!difmt)
+        return nullptr;
+
+    if (from_date > to_date)
+        std::swap(from_date, to_date);
+
+    icu::DateInterval interval (from_date * 1000.0, to_date * 1000.0);
+    icu::UnicodeString result;
+    icu::FieldPosition fp;
+    UErrorCode status = U_ZERO_ERROR;
+    difmt->format (&interval, result, fp, status);
+    if (U_FAILURE(status))
+    {
+        PWARN("Error formatting interval: %d", status);
+        return nullptr;
+    }
+
+    std::string interval_string;
+    result.toUTF8String(interval_string);
+
+    return g_strdup (interval_string.c_str());
+}
+
+gchar*
+gnc_date_interval_format (time64 from_date, time64 to_date)
+{
+    gchar* rv = nullptr;
+
+    if (qof_date_format_get() == QOF_DATE_FORMAT_LOCALE)
+        rv = icu_date_interval_format (from_date, to_date);
+
+    // not using locale, or icu failure
+    if (!rv)
+    {
+        gchar from_buff[MAX_DATE_LENGTH+1], to_buff[MAX_DATE_LENGTH+1];
+        qof_print_date_buff (from_buff, MAX_DATE_LENGTH, from_date);
+        qof_print_date_buff (to_buff, MAX_DATE_LENGTH, to_date);
+        rv = g_strdup_printf (gettext("%s to %s"), from_buff, to_buff);
+    }
+
+    return rv;
+}
+
 /* ============================================================== */
 
 /* return the greatest integer <= a/b; works for b > 0 and positive or
diff --git a/libgnucash/engine/gnc-date.h b/libgnucash/engine/gnc-date.h
index d44bc2b289..3b4a50825e 100644
--- a/libgnucash/engine/gnc-date.h
+++ b/libgnucash/engine/gnc-date.h
@@ -482,6 +482,8 @@ size_t qof_print_gdate(char *buf, size_t bufflen, const GDate *gd);
 char * qof_print_date (time64 secs);
 
 
+gchar* gnc_date_interval_format (time64 from_date, time64 to_date);
+
 /* ------------------------------------------------------------------ */
 /* time printing utilities */