lib/icu/Compare: add Windows implementation

Using CompareStringEx() and FindNLSStringEx().

Implements a missing piece for
https://github.com/MusicPlayerDaemon/MPD/issues/820

src/lib/icu/Compare.cxx

@@ -22,6 +22,11 @@
 #include "util/StringAPI.hxx"
 #include "config.h"
 
+#ifdef _WIN32
+#include "Win32.hxx"
+#include <windows.h>
+#endif
+
 #include <string.h>
 
 #ifdef HAVE_ICU_CASE_FOLD
@@ -29,6 +34,17 @@
 IcuCompare::IcuCompare(const char *_needle) noexcept
 	:needle(IcuCaseFold(_needle)) {}
 
+#elif defined(_WIN32)
+
+IcuCompare::IcuCompare(const char *_needle) noexcept
+	:needle(nullptr)
+{
+	try {
+		needle = MultiByteToWideChar(CP_UTF8, _needle);
+	} catch (...) {
+	}
+}
+
 #else
 
 IcuCompare::IcuCompare(const char *_needle) noexcept
@@ -41,6 +57,22 @@ IcuCompare::operator==(const char *haystack) const noexcept
 {
 #ifdef HAVE_ICU_CASE_FOLD
 	return StringIsEqual(IcuCaseFold(haystack).c_str(), needle.c_str());
+#elif defined(_WIN32)
+	if (needle.IsNull())
+		/* the MultiByteToWideChar() call in the constructor
+		   has failed, so let's always fail the comparison */
+		return false;
+
+	try {
+		auto w_haystack = MultiByteToWideChar(CP_UTF8, haystack);
+		return CompareStringEx(LOCALE_NAME_INVARIANT,
+				       NORM_IGNORECASE,
+				       w_haystack.c_str(), -1,
+				       needle.c_str(), -1,
+				       nullptr, nullptr, 0) == CSTR_EQUAL;
+	} catch (...) {
+		return false;
+	}
 #else
 	return strcasecmp(haystack, needle.c_str());
 #endif
@@ -52,6 +84,24 @@ IcuCompare::IsIn(const char *haystack) const noexcept
 #ifdef HAVE_ICU_CASE_FOLD
 	return StringFind(IcuCaseFold(haystack).c_str(),
 			  needle.c_str()) != nullptr;
+#elif defined(_WIN32)
+	if (needle.IsNull())
+		/* the MultiByteToWideChar() call in the constructor
+		   has failed, so let's always fail the comparison */
+		return false;
+
+	try {
+		auto w_haystack = MultiByteToWideChar(CP_UTF8, haystack);
+		return FindNLSStringEx(LOCALE_NAME_INVARIANT,
+				       FIND_FROMSTART|NORM_IGNORECASE,
+				       w_haystack.c_str(), -1,
+				       needle.c_str(), -1,
+				       nullptr,
+				       nullptr, nullptr, 0) >= 0;
+	} catch (...) {
+		/* MultiByteToWideChar() has failed */
+		return false;
+	}
 #elif defined(HAVE_STRCASESTR)
 	return strcasestr(haystack, needle.c_str()) != nullptr;
 #else

src/lib/icu/Compare.hxx

@@ -23,13 +23,23 @@
 #include "util/Compiler.h"
 #include "util/AllocatedString.hxx"
 
+#ifdef _WIN32
+#include <wchar.h>
+#endif
+
 /**
  * This class can compare one string ("needle") with lots of other
  * strings ("haystacks") efficiently, ignoring case.  With some
  * configurations, it can prepare a case-folded version of the needle.
  */
 class IcuCompare {
+#ifdef _WIN32
+	/* Windows API functions work with wchar_t strings, so let's
+	   cache the MultiByteToWideChar() result for performance */
+	AllocatedString<wchar_t> needle;
+#else
 	AllocatedString<> needle;
+#endif
 
 public:
 	IcuCompare():needle(nullptr) {}