//===--- Quality.cpp --------------------------------------------*- C++-*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===---------------------------------------------------------------------===//
#include "Quality.h"
#include "index/Index.h"
#include "clang/AST/ASTContext.h"
#include "clang/Basic/CharInfo.h"
#include "clang/AST/DeclVisitor.h"
#include "clang/Basic/SourceManager.h"
#include "clang/Sema/CodeCompleteConsumer.h"
#include "llvm/Support/FormatVariadic.h"
#include "llvm/Support/MathExtras.h"
#include "llvm/Support/raw_ostream.h"

namespace clang {
namespace clangd {
using namespace llvm;
static bool IsReserved(StringRef Name) {
  // FIXME: Should we exclude _Bool and others recognized by the standard?
  return Name.size() >= 2 && Name[0] == '_' &&
         (isUppercase(Name[1]) || Name[1] == '_');
}

static bool hasDeclInMainFile(const Decl &D) {
  auto &SourceMgr = D.getASTContext().getSourceManager();
  for (auto *Redecl : D.redecls()) {
    auto Loc = SourceMgr.getSpellingLoc(Redecl->getLocation());
    if (SourceMgr.isWrittenInMainFile(Loc))
      return true;
  }
  return false;
}

static SymbolQualitySignals::SymbolCategory categorize(const NamedDecl &ND) {
  class Switch
      : public ConstDeclVisitor<Switch, SymbolQualitySignals::SymbolCategory> {
  public:
#define MAP(DeclType, Category)                                                \
  SymbolQualitySignals::SymbolCategory Visit##DeclType(const DeclType *) {     \
    return SymbolQualitySignals::Category;                                     \
  }
    MAP(NamespaceDecl, Namespace);
    MAP(NamespaceAliasDecl, Namespace);
    MAP(TypeDecl, Type);
    MAP(TypeAliasTemplateDecl, Type);
    MAP(ClassTemplateDecl, Type);
    MAP(ValueDecl, Variable);
    MAP(VarTemplateDecl, Variable);
    MAP(FunctionDecl, Function);
    MAP(FunctionTemplateDecl, Function);
    MAP(Decl, Unknown);
#undef MAP
  };
  return Switch().Visit(&ND);
}

static SymbolQualitySignals::SymbolCategory
categorize(const index::SymbolInfo &D) {
  switch (D.Kind) {
    case index::SymbolKind::Namespace:
    case index::SymbolKind::NamespaceAlias:
      return SymbolQualitySignals::Namespace;
    case index::SymbolKind::Macro:
      return SymbolQualitySignals::Macro;
    case index::SymbolKind::Enum:
    case index::SymbolKind::Struct:
    case index::SymbolKind::Class:
    case index::SymbolKind::Protocol:
    case index::SymbolKind::Extension:
    case index::SymbolKind::Union:
    case index::SymbolKind::TypeAlias:
      return SymbolQualitySignals::Type;
    case index::SymbolKind::Function:
    case index::SymbolKind::ClassMethod:
    case index::SymbolKind::InstanceMethod:
    case index::SymbolKind::StaticMethod:
    case index::SymbolKind::InstanceProperty:
    case index::SymbolKind::ClassProperty:
    case index::SymbolKind::StaticProperty:
    case index::SymbolKind::Constructor:
    case index::SymbolKind::Destructor:
    case index::SymbolKind::ConversionFunction:
      return SymbolQualitySignals::Function;
    case index::SymbolKind::Variable:
    case index::SymbolKind::Field:
    case index::SymbolKind::EnumConstant:
    case index::SymbolKind::Parameter:
      return SymbolQualitySignals::Variable;
    case index::SymbolKind::Using:
    case index::SymbolKind::Module:
    case index::SymbolKind::Unknown:
      return SymbolQualitySignals::Unknown;
  }
  llvm_unreachable("Unknown index::SymbolKind");
}

void SymbolQualitySignals::merge(const CodeCompletionResult &SemaCCResult) {
  if (SemaCCResult.Availability == CXAvailability_Deprecated)
    Deprecated = true;

  if (SemaCCResult.Declaration)
    Category = categorize(*SemaCCResult.Declaration);
  else if (SemaCCResult.Kind == CodeCompletionResult::RK_Macro)
    Category = Macro;

  if (SemaCCResult.Declaration) {
    if (auto *ID = SemaCCResult.Declaration->getIdentifier())
      ReservedName = ReservedName || IsReserved(ID->getName());
  } else if (SemaCCResult.Kind == CodeCompletionResult::RK_Macro)
    ReservedName = ReservedName || IsReserved(SemaCCResult.Macro->getName());
}

void SymbolQualitySignals::merge(const Symbol &IndexResult) {
  References = std::max(IndexResult.References, References);
  Category = categorize(IndexResult.SymInfo);
  ReservedName = ReservedName || IsReserved(IndexResult.Name);
}

float SymbolQualitySignals::evaluate() const {
  float Score = 1;

  // This avoids a sharp gradient for tail symbols, and also neatly avoids the
  // question of whether 0 references means a bad symbol or missing data.
  if (References >= 3)
    Score *= std::log(References);

  if (Deprecated)
    Score *= 0.1f;
  if (ReservedName)
    Score *= 0.1f;

  switch (Category) {
    case Type:
    case Function:
    case Variable:
      Score *= 1.1f;
      break;
    case Namespace:
      Score *= 0.8f;
      break;
    case Macro:
      Score *= 0.2f;
      break;
    case Unknown:
      break;
  }

  return Score;
}

raw_ostream &operator<<(raw_ostream &OS, const SymbolQualitySignals &S) {
  OS << formatv("=== Symbol quality: {0}\n", S.evaluate());
  OS << formatv("\tReferences: {0}\n", S.References);
  OS << formatv("\tDeprecated: {0}\n", S.Deprecated);
  OS << formatv("\tReserved name: {0}\n", S.ReservedName);
  OS << formatv("\tCategory: {0}\n", static_cast<int>(S.Category));
  return OS;
}

static SymbolRelevanceSignals::AccessibleScope
ComputeScope(const NamedDecl &D) {
  bool InClass = false;
  for (const DeclContext *DC = D.getDeclContext(); !DC->isFileContext();
       DC = DC->getParent()) {
    if (DC->isFunctionOrMethod())
      return SymbolRelevanceSignals::FunctionScope;
    InClass = InClass || DC->isRecord();
  }
  if (InClass)
    return SymbolRelevanceSignals::ClassScope;
  // This threshold could be tweaked, e.g. to treat module-visible as global.
  if (D.getLinkageInternal() < ExternalLinkage)
    return SymbolRelevanceSignals::FileScope;
  return SymbolRelevanceSignals::GlobalScope;
}

void SymbolRelevanceSignals::merge(const Symbol &IndexResult) {
  // FIXME: Index results always assumed to be at global scope. If Scope becomes
  // relevant to non-completion requests, we should recognize class members etc.
}

void SymbolRelevanceSignals::merge(const CodeCompletionResult &SemaCCResult) {
  if (SemaCCResult.Availability == CXAvailability_NotAvailable ||
      SemaCCResult.Availability == CXAvailability_NotAccessible)
    Forbidden = true;

  if (SemaCCResult.Declaration) {
    // We boost things that have decls in the main file.
    // The real proximity scores would be more general when we have them.
    float DeclProximity =
        hasDeclInMainFile(*SemaCCResult.Declaration) ? 1.0 : 0.0;
    ProximityScore = std::max(DeclProximity, ProximityScore);
  }

  // Declarations are scoped, others (like macros) are assumed global.
  if (SemaCCResult.Declaration)
    Scope = std::min(Scope, ComputeScope(*SemaCCResult.Declaration));
}

float SymbolRelevanceSignals::evaluate() const {
  float Score = 1;

  if (Forbidden)
    return 0;

  Score *= NameMatch;

  // Proximity scores are [0,1] and we translate them into a multiplier in the
  // range from 1 to 2.
  Score *= 1 + ProximityScore;

  // Symbols like local variables may only be referenced within their scope.
  // Conversely if we're in that scope, it's likely we'll reference them.
  if (Query == CodeComplete) {
    // The narrower the scope where a symbol is visible, the more likely it is
    // to be relevant when it is available.
    switch (Scope) {
    case GlobalScope:
      break;
    case FileScope:
      Score *= 1.5;
      break;
    case ClassScope:
      Score *= 2;
      break;
    case FunctionScope:
      Score *= 4;
      break;
    }
  }

  return Score;
}
raw_ostream &operator<<(raw_ostream &OS, const SymbolRelevanceSignals &S) {
  OS << formatv("=== Symbol relevance: {0}\n", S.evaluate());
  OS << formatv("\tName match: {0}\n", S.NameMatch);
  OS << formatv("\tForbidden: {0}\n", S.Forbidden);
  OS << formatv("\tProximity: {0}\n", S.ProximityScore);
  OS << formatv("\tQuery type: {0}\n", static_cast<int>(S.Query));
  OS << formatv("\tScope: {0}\n", static_cast<int>(S.Scope));
  return OS;
}

float evaluateSymbolAndRelevance(float SymbolQuality, float SymbolRelevance) {
  return SymbolQuality * SymbolRelevance;
}

// Produces an integer that sorts in the same order as F.
// That is: a < b <==> encodeFloat(a) < encodeFloat(b).
static uint32_t encodeFloat(float F) {
  static_assert(std::numeric_limits<float>::is_iec559, "");
  constexpr uint32_t TopBit = ~(~uint32_t{0} >> 1);

  // Get the bits of the float. Endianness is the same as for integers.
  uint32_t U = FloatToBits(F);
  // IEEE 754 floats compare like sign-magnitude integers.
  if (U & TopBit)    // Negative float.
    return 0 - U;    // Map onto the low half of integers, order reversed.
  return U + TopBit; // Positive floats map onto the high half of integers.
}

std::string sortText(float Score, llvm::StringRef Name) {
  // We convert -Score to an integer, and hex-encode for readability.
  // Example: [0.5, "foo"] -> "41000000foo"
  std::string S;
  llvm::raw_string_ostream OS(S);
  write_hex(OS, encodeFloat(-Score), llvm::HexPrintStyle::Lower,
            /*Width=*/2 * sizeof(Score));
  OS << Name;
  OS.flush();
  return S;
}

} // namespace clangd
} // namespace clang