Add U mode to support Unicode input.

server/src/unicode/unicode_query.cpp

@@ -0,0 +1,67 @@
+#include "unicode/unicode_query.h"
+
+#include <algorithm>
+#include <cctype>
+#include <cstdint>
+#include <cstdio>
+#include <iterator>
+#include <utf8.h>
+
+namespace
+{
+bool IsHexChar(unsigned char ch)
+{
+    return std::isxdigit(ch) != 0;
+}
+
+bool IsUnicodeScalar(uint32_t codepoint)
+{
+    return codepoint <= 0x10FFFFu && (codepoint < 0xD800u || codepoint > 0xDFFFu);
+}
+
+std::string CodepointToUtf8(uint32_t codepoint)
+{
+    std::string utf8;
+    utf8::append(static_cast<utf8::utfchar32_t>(codepoint), std::back_inserter(utf8));
+    return utf8;
+}
+
+std::string FormatCodepointLabel(uint32_t codepoint)
+{
+    char buffer[16];
+    std::snprintf(buffer, sizeof(buffer), "U+%04X", codepoint);
+    return buffer;
+}
+} // namespace
+
+namespace UnicodeQuery
+{
+std::vector<WordItem> Query(const std::string &hex_part, int limit)
+{
+    std::vector<WordItem> results;
+    if (limit <= 0) return results;
+
+    size_t offset = 0;
+    if (!hex_part.empty() && hex_part.front() == '+') offset = 1;
+    if (offset >= hex_part.size()) return results;
+
+    const std::string hex = hex_part.substr(offset);
+    if (hex.empty() || hex.size() > 6) return results;
+    if (!std::all_of(hex.begin(), hex.end(), [](unsigned char ch) { return IsHexChar(ch); })) return results;
+
+    uint32_t codepoint = 0;
+    for (unsigned char ch : hex)
+    {
+        codepoint <<= 4;
+        if (ch >= '0' && ch <= '9') codepoint |= static_cast<uint32_t>(ch - '0');
+        else if (ch >= 'a' && ch <= 'f') codepoint |= static_cast<uint32_t>(ch - 'a' + 10);
+        else if (ch >= 'A' && ch <= 'F') codepoint |= static_cast<uint32_t>(ch - 'A' + 10);
+    }
+
+    if (!IsUnicodeScalar(codepoint)) return results;
+
+    results.emplace_back(FormatCodepointLabel(codepoint), CodepointToUtf8(codepoint), static_cast<int>(hex.size()),
+                         CandidateSource::Generated);
+    return results;
+}
+} // namespace UnicodeQuery