3 files changed, 85 insertions, 15 deletions

diff --git a/src/common/settings.cpp b/src/common/settings.cpp
index 9ff3edabb..66dffc9bf 100644
--- a/src/common/settings.cpp
+++ b/src/common/settings.cpp
@@ -1,12 +1,16 @@
 // SPDX-FileCopyrightText: Copyright 2021 yuzu Emulator Project
 // SPDX-License-Identifier: GPL-2.0-or-later
 
+#if __cpp_lib_chrono >= 201907L
+#include <chrono>
+#endif
 #include <string_view>
 
 #include "common/assert.h"
 #include "common/fs/path_util.h"
 #include "common/logging/log.h"
 #include "common/settings.h"
+#include "common/time_zone.h"
 
 namespace Settings {
 
@@ -14,18 +18,23 @@ Values values;
 static bool configuring_global = true;
 
 std::string GetTimeZoneString() {
-    static constexpr std::array timezones{
-        "auto",      "default",   "CET", "CST6CDT", "Cuba",    "EET",    "Egypt",     "Eire",
-        "EST",       "EST5EDT",   "GB",  "GB-Eire", "GMT",     "GMT+0",  "GMT-0",     "GMT0",
-        "Greenwich", "Hongkong",  "HST", "Iceland", "Iran",    "Israel", "Jamaica",   "Japan",
-        "Kwajalein", "Libya",     "MET", "MST",     "MST7MDT", "Navajo", "NZ",        "NZ-CHAT",
-        "Poland",    "Portugal",  "PRC", "PST8PDT", "ROC",     "ROK",    "Singapore", "Turkey",
-        "UCT",       "Universal", "UTC", "W-SU",    "WET",     "Zulu",
-    };
-
     const auto time_zone_index = static_cast<std::size_t>(values.time_zone_index.GetValue());
-    ASSERT(time_zone_index < timezones.size());
-    return timezones[time_zone_index];
+    ASSERT(time_zone_index < Common::TimeZone::GetTimeZoneStrings().size());
+
+    std::string location_name;
+    if (time_zone_index == 0) { // Auto
+#if __cpp_lib_chrono >= 201907L
+        const struct std::chrono::tzdb& time_zone_data = std::chrono::get_tzdb();
+        const std::chrono::time_zone* current_zone = time_zone_data.current_zone();
+        std::string_view current_zone_name = current_zone->name();
+        location_name = current_zone_name;
+#else
+        location_name = Common::TimeZone::FindSystemTimeZone();
+#endif
+    } else {
+        location_name = Common::TimeZone::GetTimeZoneStrings()[time_zone_index];
+    }
+    return location_name;
 }
 
 void LogSettings() {
diff --git a/src/common/time_zone.cpp b/src/common/time_zone.cpp
index 126836b01..d8d7896c6 100644
--- a/src/common/time_zone.cpp
+++ b/src/common/time_zone.cpp
@@ -2,14 +2,33 @@
 // SPDX-License-Identifier: GPL-2.0-or-later
 
 #include <chrono>
+#include <exception>
 #include <iomanip>
 #include <sstream>
+#include <stdexcept>
+#include <fmt/chrono.h>
+#include <fmt/core.h>
 
 #include "common/logging/log.h"
+#include "common/settings.h"
 #include "common/time_zone.h"
 
 namespace Common::TimeZone {
 
+// Time zone strings
+constexpr std::array timezones{
+    "GMT",       "GMT",       "CET", "CST6CDT", "Cuba",    "EET",    "Egypt",     "Eire",
+    "EST",       "EST5EDT",   "GB",  "GB-Eire", "GMT",     "GMT+0",  "GMT-0",     "GMT0",
+    "Greenwich", "Hongkong",  "HST", "Iceland", "Iran",    "Israel", "Jamaica",   "Japan",
+    "Kwajalein", "Libya",     "MET", "MST",     "MST7MDT", "Navajo", "NZ",        "NZ-CHAT",
+    "Poland",    "Portugal",  "PRC", "PST8PDT", "ROC",     "ROK",    "Singapore", "Turkey",
+    "UCT",       "Universal", "UTC", "W-SU",    "WET",     "Zulu",
+};
+
+const std::array<const char*, 46>& GetTimeZoneStrings() {
+    return timezones;
+}
+
 std::string GetDefaultTimeZone() {
     return "GMT";
 }
@@ -18,10 +37,7 @@ static std::string GetOsTimeZoneOffset() {
     const std::time_t t{std::time(nullptr)};
     const std::tm tm{*std::localtime(&t)};
 
-    std::stringstream ss;
-    ss << std::put_time(&tm, "%z"); // Get the current timezone offset, e.g. "-400", as a string
-
-    return ss.str();
+    return fmt::format("{:%z}", tm);
 }
 
 static int ConvertOsTimeZoneOffsetToInt(const std::string& timezone) {
@@ -45,4 +61,43 @@ std::chrono::seconds GetCurrentOffsetSeconds() {
     return std::chrono::seconds{seconds};
 }
 
+// Key is [Hours * 100 + Minutes], multiplied by 100 if DST
+const static std::map<s64, const char*> off_timezones = {
+    {530, "Asia/Calcutta"},          {930, "Australia/Darwin"},     {845, "Australia/Eucla"},
+    {103000, "Australia/Adelaide"},  {1030, "Australia/Lord_Howe"}, {630, "Indian/Cocos"},
+    {1245, "Pacific/Chatham"},       {134500, "Pacific/Chatham"},   {-330, "Canada/Newfoundland"},
+    {-23000, "Canada/Newfoundland"}, {430, "Asia/Kabul"},           {330, "Asia/Tehran"},
+    {43000, "Asia/Tehran"},          {545, "Asia/Kathmandu"},       {-930, "Asia/Marquesas"},
+};
+
+std::string FindSystemTimeZone() {
+#if defined(MINGW)
+    // MinGW has broken strftime -- https://sourceforge.net/p/mingw-w64/bugs/793/
+    // e.g. fmt::format("{:%z}") -- returns "Eastern Daylight Time" when it should be "-0400"
+    return timezones[0];
+#else
+    const s64 seconds = static_cast<s64>(GetCurrentOffsetSeconds().count());
+
+    const s64 minutes = seconds / 60;
+    const s64 hours = minutes / 60;
+
+    const s64 minutes_off = minutes - hours * 60;
+
+    if (minutes_off != 0) {
+        const auto the_time = std::time(nullptr);
+        const struct std::tm& local = *std::localtime(&the_time);
+        const bool is_dst = local.tm_isdst != 0;
+
+        const s64 tz_index = (hours * 100 + minutes_off) * (is_dst ? 100 : 1);
+
+        try {
+            return off_timezones.at(tz_index);
+        } catch (std::out_of_range&) {
+            LOG_ERROR(Common, "Time zone {} not handled, defaulting to hour offset.", tz_index);
+        }
+    }
+    return fmt::format("Etc/GMT{:s}{:d}", hours > 0 ? "-" : "+", std::abs(hours));
+#endif
+}
+
 } // namespace Common::TimeZone
diff --git a/src/common/time_zone.h b/src/common/time_zone.h
index 99cae6ef2..f574d5c04 100644
--- a/src/common/time_zone.h
+++ b/src/common/time_zone.h
@@ -3,15 +3,21 @@
 
 #pragma once
 
+#include <array>
 #include <chrono>
 #include <string>
 
 namespace Common::TimeZone {
 
+[[nodiscard]] const std::array<const char*, 46>& GetTimeZoneStrings();
+
 /// Gets the default timezone, i.e. "GMT"
 [[nodiscard]] std::string GetDefaultTimeZone();
 
 /// Gets the offset of the current timezone (from the default), in seconds
 [[nodiscard]] std::chrono::seconds GetCurrentOffsetSeconds();
 
+/// Searches time zone offsets for the closest offset to the system time zone
+[[nodiscard]] std::string FindSystemTimeZone();
+
 } // namespace Common::TimeZone