//===--- SymbolID.h ----------------------------------------------*- C++-*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_TOOLS_EXTRA_CLANGD_INDEX_SYMBOLID_H
#define LLVM_CLANG_TOOLS_EXTRA_CLANGD_INDEX_SYMBOLID_H

#include "llvm/ADT/Hashing.h"
#include "llvm/ADT/StringRef.h"
#include "llvm/Support/Error.h"
#include "llvm/Support/raw_ostream.h"
#include <array>
#include <cstddef>
#include <cstdint>
#include <string>

namespace clang {
namespace clangd {

// The class identifies a particular C++ symbol (class, function, method, etc).
//
// As USRs (Unified Symbol Resolution) could be large, especially for functions
// with long type arguments, SymbolID is using truncated SHA1(USR) values to
// guarantee the uniqueness of symbols while using a relatively small amount of
// memory (vs storing USRs directly).
//
// SymbolID can be used as key in the symbol indexes to lookup the symbol.
class SymbolID {
public:
  SymbolID() = default;
  explicit SymbolID(llvm::StringRef USR);

  bool operator==(const SymbolID &Sym) const {
    return HashValue == Sym.HashValue;
  }
  bool operator!=(const SymbolID &Sym) const { return !(*this == Sym); }
  bool operator<(const SymbolID &Sym) const {
    // Avoid lexicographic compare which requires swapping bytes or even memcmp!
    return llvm::bit_cast<IntTy>(HashValue) <
           llvm::bit_cast<IntTy>(Sym.HashValue);
  }

  // The stored hash is truncated to RawSize bytes.
  // This trades off memory against the number of symbols we can handle.
  constexpr static size_t RawSize = 8;
  llvm::StringRef raw() const;
  static SymbolID fromRaw(llvm::StringRef);

  // Returns a hex encoded string.
  std::string str() const;
  static llvm::Expected<SymbolID> fromStr(llvm::StringRef);

  bool isNull() const { return *this == SymbolID(); }
  explicit operator bool() const { return !isNull(); }

private:
  using IntTy = uint64_t;
  static_assert(sizeof(IntTy) == RawSize);
  std::array<uint8_t, RawSize> HashValue{};
};

inline llvm::hash_code hash_value(const SymbolID &ID) {
  // We already have a good hash, just return the first bytes.
  static_assert(sizeof(size_t) <= SymbolID::RawSize,
                "size_t longer than SHA1!");
  size_t Result;
  memcpy(&Result, ID.raw().data(), sizeof(size_t));
  return llvm::hash_code(Result);
}

// Write SymbolID into the given stream. SymbolID is encoded as ID.str().
llvm::raw_ostream &operator<<(llvm::raw_ostream &OS, const SymbolID &ID);

} // namespace clangd
} // namespace clang

namespace llvm {
// Support SymbolIDs as DenseMap keys.
template <> struct DenseMapInfo<clang::clangd::SymbolID> {
  static inline clang::clangd::SymbolID getEmptyKey() {
    static clang::clangd::SymbolID EmptyKey("EMPTYKEY");
    return EmptyKey;
  }
  static inline clang::clangd::SymbolID getTombstoneKey() {
    static clang::clangd::SymbolID TombstoneKey("TOMBSTONEKEY");
    return TombstoneKey;
  }
  static unsigned getHashValue(const clang::clangd::SymbolID &Sym) {
    return hash_value(Sym);
  }
  static bool isEqual(const clang::clangd::SymbolID &LHS,
                      const clang::clangd::SymbolID &RHS) {
    return LHS == RHS;
  }
};
} // namespace llvm

#endif // LLVM_CLANG_TOOLS_EXTRA_CLANGD_INDEX_SYMBOLID_H