//===--- ExternalASTSource.h - Abstract External AST Interface --*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
//  This file defines the ExternalASTSource interface, which enables
//  construction of AST nodes from some external source.x
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_CLANG_AST_EXTERNAL_AST_SOURCE_H
#define LLVM_CLANG_AST_EXTERNAL_AST_SOURCE_H

#include "clang/AST/DeclarationName.h"
#include "clang/AST/Type.h"
#include "llvm/ADT/SmallVector.h"
#include <cassert>
namespace clang {

class ASTConsumer;
class Decl;
class DeclContext;
class ExternalSemaSource; // layering violation required for downcasting
class Stmt;

/// \brief The deserialized representation of a set of declarations
/// with the same name that are visible in a given context.
struct VisibleDeclaration {
  /// \brief The name of the declarations.
  DeclarationName Name;

  /// \brief The ID numbers of all of the declarations with this name. 
  ///
  /// These declarations have not necessarily been de-serialized.
  llvm::SmallVector<unsigned, 4> Declarations;
};

/// \brief Abstract interface for external sources of AST nodes.
///
/// External AST sources provide AST nodes constructed from some
/// external source, such as a precompiled header. External AST
/// sources can resolve types and declarations from abstract IDs into
/// actual type and declaration nodes, and read parts of declaration
/// contexts.
class ExternalASTSource {
  /// \brief Whether this AST source also provides information for
  /// semantic analysis.
  bool SemaSource;

  friend class ExternalSemaSource;

public:
  ExternalASTSource() : SemaSource(false) { }

  virtual ~ExternalASTSource();

  /// \brief Resolve a type ID into a type, potentially building a new
  /// type.
  virtual QualType GetType(uint32_t ID) = 0;

  /// \brief Resolve a declaration ID into a declaration, potentially
  /// building a new declaration.
  virtual Decl *GetDecl(uint32_t ID) = 0;

  /// \brief Resolve the offset of a statement in the decl stream into a
  /// statement.
  ///
  /// This operation will read a new statement from the external
  /// source each time it is called, and is meant to be used via a
  /// LazyOffsetPtr.
  virtual Stmt *GetDeclStmt(uint64_t Offset) = 0;

  /// \brief Read all of the declarations lexically stored in a
  /// declaration context.
  ///
  /// \param DC The declaration context whose declarations will be
  /// read.
  ///
  /// \param Decls Vector that will contain the declarations loaded
  /// from the external source. The caller is responsible for merging
  /// these declarations with any declarations already stored in the
  /// declaration context.
  ///
  /// \returns true if there was an error while reading the
  /// declarations for this declaration context.
  virtual bool ReadDeclsLexicallyInContext(DeclContext *DC,
                                  llvm::SmallVectorImpl<uint32_t> &Decls) = 0;

  /// \brief Read all of the declarations visible from a declaration
  /// context.
  ///
  /// \param DC The declaration context whose visible declarations
  /// will be read.
  ///
  /// \param Decls A vector of visible declaration structures,
  /// providing the mapping from each name visible in the declaration
  /// context to the declaration IDs of declarations with that name.
  ///
  /// \returns true if there was an error while reading the
  /// declarations for this declaration context.
  virtual bool ReadDeclsVisibleInContext(DeclContext *DC,
                       llvm::SmallVectorImpl<VisibleDeclaration> & Decls) = 0;

  /// \brief Function that will be invoked when we begin parsing a new
  /// translation unit involving this external AST source.
  virtual void StartTranslationUnit(ASTConsumer *Consumer) { }

  /// \brief Print any statistics that have been gathered regarding
  /// the external AST source.
  virtual void PrintStats();
};

/// \brief A lazy pointer to an AST node (of base type T) that resides
/// within an external AST source.
///
/// The AST node is identified within the external AST source by a
/// 63-bit offset, and can be retrieved via an operation on the
/// external AST source itself.
template<typename T, T* (ExternalASTSource::*Get)(uint64_t Offset)>
struct LazyOffsetPtr {
  /// \brief Either a pointer to an AST node or the offset within the
  /// external AST source where the AST node can be found.
  ///
  /// If the low bit is clear, a pointer to the AST node. If the low
  /// bit is set, the upper 63 bits are the offset.
  mutable uint64_t Ptr;

public:
  LazyOffsetPtr() : Ptr(0) { }

  explicit LazyOffsetPtr(T *Ptr) : Ptr(reinterpret_cast<uint64_t>(Ptr)) { }
  explicit LazyOffsetPtr(uint64_t Offset) : Ptr((Offset << 1) | 0x01) {
    assert((Offset << 1 >> 1) == Offset && "Offsets must require < 63 bits");
    if (Offset == 0)
      Ptr = 0;
  }

  LazyOffsetPtr &operator=(T *Ptr) {
    this->Ptr = reinterpret_cast<uint64_t>(Ptr);
    return *this;
  }
  
  LazyOffsetPtr &operator=(uint64_t Offset) {
    assert((Offset << 1 >> 1) == Offset && "Offsets must require < 63 bits");
    if (Offset == 0)
      Ptr = 0;
    else
      Ptr = (Offset << 1) | 0x01;

    return *this;
  }

  /// \brief Whether this pointer is non-NULL.
  ///
  /// This operation does not require the AST node to be deserialized.
  operator bool() const { return Ptr != 0; }

  /// \brief Whether this pointer is currently stored as an offset.
  bool isOffset() const { return Ptr & 0x01; }

  /// \brief Retrieve the pointer to the AST node that this lazy pointer
  ///
  /// \param Source the external AST source.
  ///
  /// \returns a pointer to the AST node.
  T* get(ExternalASTSource *Source) const {
    if (isOffset()) {
      assert(Source && 
             "Cannot deserialize a lazy pointer without an AST source");
      Ptr = reinterpret_cast<uint64_t>((Source->*Get)(Ptr >> 1));
    }
    return reinterpret_cast<T*>(Ptr);
  }
};

/// \brief A lazy pointer to a statement.
typedef LazyOffsetPtr<Stmt, &ExternalASTSource::GetDeclStmt> LazyDeclStmtPtr;

} // end namespace clang

#endif // LLVM_CLANG_AST_EXTERNAL_AST_SOURCE_H