// Part of the Carbon Language project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

#ifndef CARBON_TOOLCHAIN_SEM_IR_SINGLETON_INSTS_H_
#define CARBON_TOOLCHAIN_SEM_IR_SINGLETON_INSTS_H_

#include "toolchain/sem_ir/ids.h"
#include "toolchain/sem_ir/inst_kind.h"

namespace Carbon::SemIR {

// The canonical list of singleton kinds. The order of `TypeType` is
// significant because other singletons use it as a type.
static constexpr std::array SingletonInstKinds = {
    InstKind::TypeType,         InstKind::AutoType,
    InstKind::BoolType,         InstKind::BoundMethodType,
    InstKind::CharLiteralType,  InstKind::ErrorInst,
    InstKind::FloatLiteralType, InstKind::ImplWitnessTablePlaceholder,
    InstKind::InstType,         InstKind::IntLiteralType,
    InstKind::NamespaceType,    InstKind::SpecificFunctionType,
    InstKind::VtableType,       InstKind::WitnessType,
};

// Returns true if the InstKind is a singleton.
constexpr auto IsSingletonInstKind(InstKind kind) -> bool;

// Provides the TypeInstId for singleton instructions. These are exposed as
// `InstT::TypeInstId` in `typed_insts.h`.
template <InstKind::RawEnumType Kind>
  requires(IsSingletonInstKind(InstKind::Make(Kind)))
constexpr auto MakeSingletonTypeInstId() -> TypeInstId;

// Returns true if the InstId corresponds to a singleton inst.
constexpr auto IsSingletonInstId(InstId id) -> bool {
  return id.index >= 0 &&
         id.index < static_cast<int32_t>(SingletonInstKinds.size());
}

// Only implementation details are below.

namespace Internal {

// Returns the index for a singleton instruction, or -1 if it's not a singleton.
constexpr auto GetSingletonInstIndex(InstKind kind) -> int32_t {
  for (int32_t i = 0; i < static_cast<int32_t>(SingletonInstKinds.size());
       ++i) {
    if (SingletonInstKinds[i] == kind) {
      return i;
    }
  }
  return -1;
}

}  // namespace Internal

constexpr auto IsSingletonInstKind(InstKind kind) -> bool {
  return Internal::GetSingletonInstIndex(kind) >= 0;
}

template <InstKind::RawEnumType Kind>
  requires(IsSingletonInstKind(InstKind::Make(Kind)))
constexpr auto MakeSingletonTypeInstId() -> TypeInstId {
  auto index = Internal::GetSingletonInstIndex(InstKind::Make(Kind));
  return TypeInstId(index);
}

}  // namespace Carbon::SemIR

#endif  // CARBON_TOOLCHAIN_SEM_IR_SINGLETON_INSTS_H_
