Add dateformat "Locale" to pick current locale

libgnucash/engine/gnc-datetime.cpp

@@ -29,6 +29,11 @@
 #include <boost/date_time/local_time/local_time.hpp>
 #include <boost/locale.hpp>
 #include <boost/regex.hpp>
+#include <unicode/smpdtfmt.h>
+#include <unicode/locid.h>
+#include <unicode/udat.h>
+#include <unicode/parsepos.h>
+#include <unicode/calendar.h>
 #include <libintl.h>
 #include <locale.h>
 #include <map>
@@ -84,6 +89,10 @@ static constexpr auto ticks_per_second = INT64_C(1000000000);
  * without separators.
  */
 const std::vector<GncDateFormat> GncDate::c_formats ({
+    GncDateFormat {
+        N_("Locale"),
+        ""
+    },
     GncDateFormat {
         N_("y-m-d"),
         "(?:"                                   // either y-m-d
@@ -607,6 +616,53 @@ GncDateTimeImpl::timestamp()
     return str.substr(0, 8) + str.substr(9, 15);
 }
 
+static icu::Locale
+get_LCTIME_locale()
+{
+    const char* lc_time_locale = setlocale(LC_TIME, nullptr);
+
+    if (lc_time_locale == nullptr)
+        return icu::Locale::getDefault();
+
+    std::string localeStr(lc_time_locale);
+    size_t dotPos = localeStr.find('.');
+    if (dotPos != std::string::npos)
+        localeStr = localeStr.substr(0, dotPos);
+
+    return icu::Locale::createCanonical (localeStr.c_str());
+}
+
+static Date
+use_icu_parser (const std::string str)
+{
+    UErrorCode status = U_ZERO_ERROR;
+    icu::Locale locale = get_LCTIME_locale();
+
+    static std::unique_ptr<icu::DateFormat> formatter(icu::DateFormat::createDateInstance(icu::DateFormat::kDefault, locale));
+    if (formatter == nullptr)
+        throw std::invalid_argument ("Cannot create date formatter.");
+
+    static std::unique_ptr<icu::Calendar> calendar(icu::Calendar::createInstance(locale, status));
+    if (U_FAILURE(status))
+        throw std::invalid_argument("Cannot create calendar instance.");
+    calendar->setLenient (false);
+
+    icu::UnicodeString input = icu::UnicodeString::fromUTF8(str);
+    icu::ParsePosition parsePos;
+
+    UDate date = formatter->parse(input, parsePos);
+    if (parsePos.getErrorIndex() != -1 || parsePos.getIndex() != input.length())
+        throw std::invalid_argument ("Cannot parse string");
+
+    calendar->setTime(date, status);
+    if (U_FAILURE(status))
+        throw std::invalid_argument ("Cannot set calendar time");
+
+    return Date (calendar->get(UCAL_YEAR, status),
+                 calendar->get(UCAL_MONTH, status) + 1,
+                 calendar->get(UCAL_DATE, status));
+}
+
 /* Member function definitions for GncDateImpl.
  */
 GncDateImpl::GncDateImpl(const std::string str, const std::string fmt) :
@@ -617,6 +673,12 @@ GncDateImpl::GncDateImpl(const std::string str, const std::string fmt) :
     if (iter == GncDate::c_formats.cend())
         throw std::invalid_argument(N_("Unknown date format specifier passed as argument."));
 
+    if (iter->m_re == "")
+    {
+        m_greg = use_icu_parser (str);
+        return;
+    }
+
     boost::regex r(iter->m_re);
     boost::smatch what;
     if(!boost::regex_search(str, what, r))  // regex didn't find a match