//===--- MacroDefinition.h - Swift Macro Definition -------------*- C++ -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// This provides the definition of a macro, which gives access to its
// implementation.
//
//===----------------------------------------------------------------------===//

#ifndef SWIFT_AST_MACRO_DEFINITION_H
#define SWIFT_AST_MACRO_DEFINITION_H

#include "llvm/ADT/PointerUnion.h"

namespace swift {

/// A reference to an external macro definition that is understood by ASTGen.
struct ExternalMacroDefinition {
  /// ASTGen's notion of an macro definition, which is opaque to the C++ part
  /// of the compiler.
  void *opaqueHandle = nullptr;
};

/// A reference to an external macro.
struct ExternalMacroReference {
  Identifier moduleName;
  Identifier macroTypeName;
};

/// Describes the known kinds of builtin macros.
enum class BuiltinMacroKind: uint8_t {
  /// #externalMacro, which references an external macro.
  ExternalMacro,
};

/// Provides the definition of a macro.
class MacroDefinition {
public:
    /// Describes how the macro is implemented.
  enum class Kind: uint8_t {
    /// The macro has a definition, but it is invalid, so the macro cannot be
    /// expanded.
    Invalid,

    /// The macro has no definition.
    Undefined,

    /// An externally-provided macro definition.
    External,

    /// A builtin macro definition, which has a separate builtin kind.
    Builtin,
  };

  Kind kind;

private:
  union Data {
    ExternalMacroReference external;
    BuiltinMacroKind builtin;

    Data() : builtin(BuiltinMacroKind::ExternalMacro) { }
  } data;

  MacroDefinition(Kind kind) : kind(kind) { }

  MacroDefinition(ExternalMacroReference external) : kind(Kind::External) {
    data.external = external;
  }

  MacroDefinition(BuiltinMacroKind builtinKind) : kind(Kind::Builtin) {
    data.builtin = builtinKind;
  }

public:
  static MacroDefinition forInvalid() {
    return MacroDefinition(Kind::Invalid);
  }

  static MacroDefinition forUndefined() {
    return MacroDefinition(Kind::Undefined);
  }

  static MacroDefinition forExternal(
      Identifier moduleName,
      Identifier macroTypeName
   ) {
    return MacroDefinition(ExternalMacroReference{moduleName, macroTypeName});
  }

  static MacroDefinition forBuiltin(BuiltinMacroKind builtinKind) {
    return MacroDefinition(builtinKind);
  }

  /// Retrieve the external macro being referenced.
  ExternalMacroReference getExternalMacro() const {
    assert(kind == Kind::External);
    return data.external;
  }

  /// Retrieve the builtin kind.
  BuiltinMacroKind getBuiltinKind() const {
    assert(kind == Kind::Builtin);
    return data.builtin;
  }

  operator Kind() const { return kind; }
};

}

#endif // SWIFT_AST_MACRO_DEFINITION_H