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// Copyright Epic Games, Inc. All Rights Reserved.
#include <zenutil/suggest.h>
#include <zencore/string.h>
#if ZEN_WITH_TESTS
# include <zencore/testing.h>
# include <ostream> // needed for doctest to stringify std::string_view on CHECK failure
#endif
#include <algorithm>
namespace zen {
namespace {
constexpr size_t kMaxSuggestionInputLen = 64;
// Damerau-Levenshtein distance with case-insensitive ASCII comparison. Returns the
// raw edit count (insertions, deletions, substitutions, adjacent transpositions).
// Falls back to max(len) for pathologically long inputs so the scratch buffers can
// stay stack-allocated.
size_t ComputeEditDistance(std::string_view Source, std::string_view Target)
{
if (Source.size() > kMaxSuggestionInputLen || Target.size() > kMaxSuggestionInputLen)
{
return std::max(Source.size(), Target.size());
}
auto AsciiToLower = [](unsigned char Ch) -> unsigned char {
return (Ch >= 'A' && Ch <= 'Z') ? static_cast<unsigned char>(Ch + ('a' - 'A')) : Ch;
};
const size_t SourceLen = Source.size();
const size_t TargetLen = Target.size();
if (SourceLen == 0)
{
return TargetLen;
}
if (TargetLen == 0)
{
return SourceLen;
}
size_t Buf0[kMaxSuggestionInputLen + 1];
size_t Buf1[kMaxSuggestionInputLen + 1];
size_t Buf2[kMaxSuggestionInputLen + 1];
size_t* PrevPrev = Buf0;
size_t* Prev = Buf1;
size_t* Curr = Buf2;
for (size_t j = 0; j <= TargetLen; ++j)
{
Prev[j] = j;
}
for (size_t i = 1; i <= SourceLen; ++i)
{
Curr[0] = i;
for (size_t j = 1; j <= TargetLen; ++j)
{
const size_t Cost = (AsciiToLower(Source[i - 1]) == AsciiToLower(Target[j - 1])) ? 0 : 1;
Curr[j] = std::min({Prev[j] + 1, // deletion from Source
Curr[j - 1] + 1, // insertion into Source
Prev[j - 1] + Cost}); // substitution
if (i > 1 && j > 1 && AsciiToLower(Source[i - 1]) == AsciiToLower(Target[j - 2]) &&
AsciiToLower(Source[i - 2]) == AsciiToLower(Target[j - 1]))
{
Curr[j] = std::min(Curr[j], PrevPrev[j - 2] + 1); // transposition
}
}
// Rotate buffers: (PrevPrev, Prev, Curr) -> (Prev, Curr, PrevPrev)
size_t* Tmp = PrevPrev;
PrevPrev = Prev;
Prev = Curr;
Curr = Tmp;
}
return Prev[TargetLen];
}
} // namespace
std::vector<std::string_view>
SuggestSimilarCommands(std::string_view Typed, std::span<const std::string_view> Candidates)
{
constexpr size_t kMaxSuggestions = 5;
if (Typed.empty())
{
return {};
}
struct Scored
{
std::string_view Name;
size_t Distance;
};
std::vector<Scored> Ranked;
Ranked.reserve(Candidates.size());
for (std::string_view Name : Candidates)
{
size_t Distance = ComputeEditDistance(Typed, Name);
// Prefix bonus so short inputs ("ca") still surface longer commands ("cache")
// without us having to use a distance threshold that would admit unrelated matches.
if (Name.size() >= Typed.size() && StrCaseCompare(Name.substr(0, Typed.size()), Typed) == 0)
{
Distance = std::min<size_t>(Distance, 1);
}
Ranked.push_back({Name, Distance});
}
// Scale with typed length: very short inputs get a tighter bound so we don't
// flood the output with every short command that happens to be 2 edits away.
// Short inputs rely on the prefix bonus instead. Cap at 3 for longer strings
// since beyond that the suggestions stop being plausible.
const size_t MaxDistance = std::clamp<size_t>(Typed.size() / 2, 1, 3);
std::stable_sort(Ranked.begin(), Ranked.end(), [](const Scored& Lhs, const Scored& Rhs) { return Lhs.Distance < Rhs.Distance; });
std::vector<std::string_view> Result;
for (const Scored& Entry : Ranked)
{
if (Entry.Distance > MaxDistance)
{
break;
}
Result.push_back(Entry.Name);
if (Result.size() >= kMaxSuggestions)
{
break;
}
}
return Result;
}
#if ZEN_WITH_TESTS
void
suggest_forcelink()
{
}
TEST_SUITE_BEGIN("util.suggest");
TEST_CASE("transposition_is_distance_one")
{
// "stauts" -> "status" is a single adjacent transposition under Damerau-Levenshtein.
const std::string_view Candidates[] = {"status", "start", "stop"};
std::vector<std::string_view> Result = SuggestSimilarCommands("stauts", Candidates);
REQUIRE(!Result.empty());
CHECK(Result.front() == "status");
}
TEST_CASE("short_prefix_surfaces_longer_candidate")
{
// "ca" is raw distance 3 from "cache", outside the default threshold for a 2-char
// input. The prefix bonus is what brings it back into the result set.
const std::string_view Candidates[] = {"cache", "status", "version"};
std::vector<std::string_view> Result = SuggestSimilarCommands("ca", Candidates);
REQUIRE(!Result.empty());
CHECK(Result.front() == "cache");
}
TEST_CASE("gibberish_returns_no_suggestions")
{
// Nothing in the candidate set is plausibly close.
const std::string_view Candidates[] = {"cache", "status", "version"};
std::vector<std::string_view> Result = SuggestSimilarCommands("xyzzyqqqq", Candidates);
CHECK(Result.empty());
}
TEST_CASE("empty_input_returns_no_suggestions")
{
const std::string_view Candidates[] = {"cache", "status"};
std::vector<std::string_view> Result = SuggestSimilarCommands("", Candidates);
CHECK(Result.empty());
}
TEST_CASE("case_insensitive_match")
{
const std::string_view Candidates[] = {"cache", "status"};
std::vector<std::string_view> Result = SuggestSimilarCommands("STAUTS", Candidates);
REQUIRE(!Result.empty());
CHECK(Result.front() == "status");
}
TEST_CASE("substitution_within_threshold")
{
// "versoin" -> "version": one transposition. Within threshold for a 7-char input.
const std::string_view Candidates[] = {"version", "verify", "value"};
std::vector<std::string_view> Result = SuggestSimilarCommands("versoin", Candidates);
REQUIRE(!Result.empty());
CHECK(Result.front() == "version");
}
TEST_CASE("results_sorted_by_distance")
{
// "stats" is exact match; "stat" and "start" are both distance 1. Best-first ordering.
const std::string_view Candidates[] = {"start", "stat", "stats"};
std::vector<std::string_view> Result = SuggestSimilarCommands("stats", Candidates);
REQUIRE(Result.size() >= 1);
CHECK(Result.front() == "stats");
}
TEST_CASE("caps_at_five_results")
{
// Eight prefix-matching candidates; only the first five should survive the cap.
const std::string_view Candidates[] = {"ca1", "ca2", "ca3", "ca4", "ca5", "ca6", "ca7", "ca8"};
std::vector<std::string_view> Result = SuggestSimilarCommands("ca", Candidates);
CHECK(Result.size() == 5);
}
TEST_SUITE_END();
#endif // ZEN_WITH_TESTS
} // namespace zen
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