From d392c38a738e8c2c34a8edd472e5cd408088024b Mon Sep 17 00:00:00 2001
From: Timothy Flynn <trflynn89@pm.me>
Date: Tue, 3 Sep 2024 11:20:20 -0400
Subject: [PATCH] LibUnicode: Cache all created icu::TimeZone objects

This cache works exactly the same as the existing icu::Locale cache.
---
 .../Libraries/LibUnicode/DateTimeFormat.cpp   |  4 +--
 Userland/Libraries/LibUnicode/ICU.cpp         | 25 +++++++++++++++++++
 Userland/Libraries/LibUnicode/ICU.h           | 13 ++++++++++
 Userland/Libraries/LibUnicode/TimeZone.cpp    |  6 ++---
 Userland/Libraries/LibUnicode/TimeZone.h      |  4 +--
 5 files changed, 45 insertions(+), 7 deletions(-)

diff --git a/Userland/Libraries/LibUnicode/DateTimeFormat.cpp b/Userland/Libraries/LibUnicode/DateTimeFormat.cpp
index 841006a4bbd..ed486395b6f 100644
--- a/Userland/Libraries/LibUnicode/DateTimeFormat.cpp
+++ b/Userland/Libraries/LibUnicode/DateTimeFormat.cpp
@@ -622,9 +622,9 @@ static void apply_time_zone_to_formatter(icu::SimpleDateFormat& formatter, icu::
 {
     UErrorCode status = U_ZERO_ERROR;
 
-    auto* time_zone = icu::TimeZone::createTimeZone(icu_string(time_zone_identifier));
+    auto time_zone_data = TimeZoneData::for_time_zone(time_zone_identifier);
 
-    auto* calendar = icu::Calendar::createInstance(time_zone, locale, status);
+    auto* calendar = icu::Calendar::createInstance(time_zone_data->time_zone(), locale, status);
     VERIFY(icu_success(status));
 
     if (calendar->getDynamicClassID() == icu::GregorianCalendar::getStaticClassID()) {
diff --git a/Userland/Libraries/LibUnicode/ICU.cpp b/Userland/Libraries/LibUnicode/ICU.cpp
index fc63292ed6f..0b6cf867c29 100644
--- a/Userland/Libraries/LibUnicode/ICU.cpp
+++ b/Userland/Libraries/LibUnicode/ICU.cpp
@@ -17,6 +17,7 @@
 namespace Unicode {
 
 static HashMap<String, OwnPtr<LocaleData>> s_locale_cache;
+static HashMap<String, OwnPtr<TimeZoneData>> s_time_zone_cache;
 
 Optional<LocaleData&> LocaleData::for_locale(StringView locale)
 {
@@ -113,6 +114,30 @@ icu::TimeZoneNames& LocaleData::time_zone_names()
     return *m_time_zone_names;
 }
 
+Optional<TimeZoneData&> TimeZoneData::for_time_zone(StringView time_zone)
+{
+    auto time_zone_data = s_time_zone_cache.get(time_zone);
+
+    if (!time_zone_data.has_value()) {
+        time_zone_data = s_time_zone_cache.ensure(MUST(String::from_utf8(time_zone)), [&]() -> OwnPtr<TimeZoneData> {
+            auto icu_time_zone = adopt_own_if_nonnull(icu::TimeZone::createTimeZone(icu_string(time_zone)));
+            if (!icu_time_zone || *icu_time_zone == icu::TimeZone::getUnknown())
+                return nullptr;
+
+            return adopt_own(*new TimeZoneData { icu_time_zone.release_nonnull() });
+        });
+    }
+
+    if (time_zone_data.value())
+        return *time_zone_data.value();
+    return {};
+}
+
+TimeZoneData::TimeZoneData(NonnullOwnPtr<icu::TimeZone> time_zone)
+    : m_time_zone(move(time_zone))
+{
+}
+
 Vector<icu::UnicodeString> icu_string_list(ReadonlySpan<String> strings)
 {
     Vector<icu::UnicodeString> result;
diff --git a/Userland/Libraries/LibUnicode/ICU.h b/Userland/Libraries/LibUnicode/ICU.h
index c6af66b2ae2..a436a378a68 100644
--- a/Userland/Libraries/LibUnicode/ICU.h
+++ b/Userland/Libraries/LibUnicode/ICU.h
@@ -24,6 +24,7 @@ U_NAMESPACE_BEGIN
 class DateTimePatternGenerator;
 class LocaleDisplayNames;
 class NumberingSystem;
+class TimeZone;
 class TimeZoneNames;
 U_NAMESPACE_END
 
@@ -63,6 +64,18 @@ private:
     Optional<DigitalFormat> m_digital_format;
 };
 
+class TimeZoneData {
+public:
+    static Optional<TimeZoneData&> for_time_zone(StringView time_zone);
+
+    ALWAYS_INLINE icu::TimeZone& time_zone() { return *m_time_zone; }
+
+private:
+    explicit TimeZoneData(NonnullOwnPtr<icu::TimeZone>);
+
+    NonnullOwnPtr<icu::TimeZone> m_time_zone;
+};
+
 constexpr bool icu_success(UErrorCode code)
 {
     return static_cast<bool>(U_SUCCESS(code));
diff --git a/Userland/Libraries/LibUnicode/TimeZone.cpp b/Userland/Libraries/LibUnicode/TimeZone.cpp
index 817101a2e7c..382f37fce0e 100644
--- a/Userland/Libraries/LibUnicode/TimeZone.cpp
+++ b/Userland/Libraries/LibUnicode/TimeZone.cpp
@@ -131,14 +131,14 @@ Optional<TimeZoneOffset> time_zone_offset(StringView time_zone, UnixDateTime tim
 {
     UErrorCode status = U_ZERO_ERROR;
 
-    auto icu_time_zone = adopt_own_if_nonnull(icu::TimeZone::createTimeZone(icu_string(time_zone)));
-    if (!icu_time_zone || *icu_time_zone == icu::TimeZone::getUnknown())
+    auto time_zone_data = TimeZoneData::for_time_zone(time_zone);
+    if (!time_zone_data.has_value())
         return {};
 
     i32 raw_offset = 0;
     i32 dst_offset = 0;
 
-    icu_time_zone->getOffset(static_cast<UDate>(time.milliseconds_since_epoch()), 0, raw_offset, dst_offset, status);
+    time_zone_data->time_zone().getOffset(static_cast<UDate>(time.milliseconds_since_epoch()), 0, raw_offset, dst_offset, status);
     if (icu_failure(status))
         return {};
 
diff --git a/Userland/Libraries/LibUnicode/TimeZone.h b/Userland/Libraries/LibUnicode/TimeZone.h
index 4b8cbf8b958..518589d1fd7 100644
--- a/Userland/Libraries/LibUnicode/TimeZone.h
+++ b/Userland/Libraries/LibUnicode/TimeZone.h
@@ -4,13 +4,13 @@
  * SPDX-License-Identifier: BSD-2-Clause
  */
 
+#pragma once
+
 #include <AK/Optional.h>
 #include <AK/String.h>
 #include <AK/Time.h>
 #include <AK/Vector.h>
 
-#pragma once
-
 namespace Unicode {
 
 struct TimeZoneOffset {