//===-- Redeclarable.h - Base for Decls that can be redeclared -*- 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 Redeclarable interface.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_AST_REDECLARABLE_H
#define LLVM_CLANG_AST_REDECLARABLE_H

#include "clang/AST/ExternalASTSource.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/Support/Casting.h"
#include <iterator>

namespace clang {

/// \brief Provides common interface for the Decls that can be redeclared.
template<typename decl_type>
class Redeclarable {
protected:
  class DeclLink {
    /// A pointer to a known latest declaration, either statically known or
    /// generationally updated as decls are added by an external source.
    typedef LazyGenerationalUpdatePtr<const Decl*, Decl*,
                                      &ExternalASTSource::CompleteRedeclChain>
                                          KnownLatest;

    typedef const ASTContext *UninitializedLatest;
    typedef Decl *Previous;

    /// A pointer to either an uninitialized latest declaration (where either
    /// we've not yet set the previous decl or there isn't one), or to a known
    /// previous declaration.
    typedef llvm::PointerUnion<Previous, UninitializedLatest> NotKnownLatest;

    mutable llvm::PointerUnion<NotKnownLatest, KnownLatest> Next;

  public:
    enum PreviousTag { PreviousLink };
    enum LatestTag { LatestLink };

    DeclLink(LatestTag, const ASTContext &Ctx)
        : Next(NotKnownLatest(&Ctx)) {}
    DeclLink(PreviousTag, decl_type *D)
        : Next(NotKnownLatest(Previous(D))) {}

    bool NextIsPrevious() const {
      return Next.is<NotKnownLatest>() &&
             // FIXME: 'template' is required on the next line due to an
             // apparent clang bug.
             Next.get<NotKnownLatest>().template is<Previous>();
    }

    bool NextIsLatest() const { return !NextIsPrevious(); }

    decl_type *getNext(const decl_type *D) const {
      if (Next.is<NotKnownLatest>()) {
        NotKnownLatest NKL = Next.get<NotKnownLatest>();
        if (NKL.is<Previous>())
          return static_cast<decl_type*>(NKL.get<Previous>());

        // Allocate the generational 'most recent' cache now, if needed.
        Next = KnownLatest(*NKL.get<UninitializedLatest>(),
                           const_cast<decl_type *>(D));
      }

      return static_cast<decl_type*>(Next.get<KnownLatest>().get(D));
    }

    void setPrevious(decl_type *D) {
      assert(NextIsPrevious() && "decl became non-canonical unexpectedly");
      Next = Previous(D);
    }

    void setLatest(decl_type *D) {
      assert(NextIsLatest() && "decl became canonical unexpectedly");
      if (Next.is<NotKnownLatest>()) {
        NotKnownLatest NKL = Next.get<NotKnownLatest>();
        Next = KnownLatest(*NKL.get<UninitializedLatest>(), D);
      } else {
        auto Latest = Next.get<KnownLatest>();
        Latest.set(D);
        Next = Latest;
      }
    }

    void markIncomplete() { Next.get<KnownLatest>().markIncomplete(); }
  };

  static DeclLink PreviousDeclLink(decl_type *D) {
    return DeclLink(DeclLink::PreviousLink, D);
  }

  static DeclLink LatestDeclLink(const ASTContext &Ctx) {
    return DeclLink(DeclLink::LatestLink, Ctx);
  }

  /// \brief Points to the next redeclaration in the chain.
  ///
  /// If NextIsPrevious() is true, this is a link to the previous declaration
  /// of this same Decl. If NextIsLatest() is true, this is the first
  /// declaration and Link points to the latest declaration. For example:
  ///
  ///  #1 int f(int x, int y = 1); // <pointer to #3, true>
  ///  #2 int f(int x = 0, int y); // <pointer to #1, false>
  ///  #3 int f(int x, int y) { return x + y; } // <pointer to #2, false>
  ///
  /// If there is only one declaration, it is <pointer to self, true>
  DeclLink RedeclLink;

  decl_type *getNextRedeclaration() const {
    return RedeclLink.getNext(static_cast<const decl_type *>(this));
  }

public:
  Redeclarable(const ASTContext &Ctx)
      : RedeclLink(LatestDeclLink(Ctx)) {}

  /// \brief Return the previous declaration of this declaration or NULL if this
  /// is the first declaration.
  decl_type *getPreviousDecl() {
    if (RedeclLink.NextIsPrevious())
      return getNextRedeclaration();
    return nullptr;
  }
  const decl_type *getPreviousDecl() const {
    return const_cast<decl_type *>(
                 static_cast<const decl_type*>(this))->getPreviousDecl();
  }

  /// \brief Return the first declaration of this declaration or itself if this
  /// is the only declaration.
  decl_type *getFirstDecl() {
    decl_type *D = static_cast<decl_type*>(this);
    while (D->getPreviousDecl())
      D = D->getPreviousDecl();
    return D;
  }

  /// \brief Return the first declaration of this declaration or itself if this
  /// is the only declaration.
  const decl_type *getFirstDecl() const {
    const decl_type *D = static_cast<const decl_type*>(this);
    while (D->getPreviousDecl())
      D = D->getPreviousDecl();
    return D;
  }

  /// \brief True if this is the first declaration in its redeclaration chain.
  bool isFirstDecl() const { return RedeclLink.NextIsLatest(); }

  /// \brief Returns the most recent (re)declaration of this declaration.
  decl_type *getMostRecentDecl() {
    return getFirstDecl()->getNextRedeclaration();
  }

  /// \brief Returns the most recent (re)declaration of this declaration.
  const decl_type *getMostRecentDecl() const {
    return getFirstDecl()->getNextRedeclaration();
  }

  /// \brief Set the previous declaration. If PrevDecl is NULL, set this as the
  /// first and only declaration.
  void setPreviousDecl(decl_type *PrevDecl);

  /// \brief Iterates through all the redeclarations of the same decl.
  class redecl_iterator {
    /// Current - The current declaration.
    decl_type *Current;
    decl_type *Starter;
    bool PassedFirst;

  public:
    typedef decl_type*                value_type;
    typedef decl_type*                reference;
    typedef decl_type*                pointer;
    typedef std::forward_iterator_tag iterator_category;
    typedef std::ptrdiff_t            difference_type;

    redecl_iterator() : Current(nullptr) { }
    explicit redecl_iterator(decl_type *C)
      : Current(C), Starter(C), PassedFirst(false) { }

    reference operator*() const { return Current; }
    pointer operator->() const { return Current; }

    redecl_iterator& operator++() {
      assert(Current && "Advancing while iterator has reached end");
      // Sanity check to avoid infinite loop on invalid redecl chain.
      if (Current->isFirstDecl()) {
        if (PassedFirst) {
          assert(0 && "Passed first decl twice, invalid redecl chain!");
          Current = nullptr;
          return *this;
        }
        PassedFirst = true;
      }

      // Get either previous decl or latest decl.
      decl_type *Next = Current->getNextRedeclaration();
      Current = (Next != Starter) ? Next : nullptr;
      return *this;
    }

    redecl_iterator operator++(int) {
      redecl_iterator tmp(*this);
      ++(*this);
      return tmp;
    }

    friend bool operator==(redecl_iterator x, redecl_iterator y) {
      return x.Current == y.Current;
    }
    friend bool operator!=(redecl_iterator x, redecl_iterator y) {
      return x.Current != y.Current;
    }
  };

  typedef llvm::iterator_range<redecl_iterator> redecl_range;

  /// \brief Returns an iterator range for all the redeclarations of the same
  /// decl. It will iterate at least once (when this decl is the only one).
  redecl_range redecls() const {
    return redecl_range(redecl_iterator(const_cast<decl_type *>(
                            static_cast<const decl_type *>(this))),
                        redecl_iterator());
  }

  redecl_iterator redecls_begin() const { return redecls().begin(); }
  redecl_iterator redecls_end() const { return redecls().end(); }

  friend class ASTDeclReader;
  friend class ASTDeclWriter;
};

/// \brief Get the primary declaration for a declaration from an AST file. That
/// will be the first-loaded declaration.
Decl *getPrimaryMergedDecl(Decl *D);

/// \brief Provides common interface for the Decls that cannot be redeclared,
/// but can be merged if the same declaration is brought in from multiple
/// modules.
template<typename decl_type>
class Mergeable {
public:
  Mergeable() {}

  /// \brief Return the first declaration of this declaration or itself if this
  /// is the only declaration.
  decl_type *getFirstDecl() {
    decl_type *D = static_cast<decl_type*>(this);
    if (!D->isFromASTFile())
      return D;
    return cast<decl_type>(getPrimaryMergedDecl(const_cast<decl_type*>(D)));
  }

  /// \brief Return the first declaration of this declaration or itself if this
  /// is the only declaration.
  const decl_type *getFirstDecl() const {
    const decl_type *D = static_cast<const decl_type*>(this);
    if (!D->isFromASTFile())
      return D;
    return cast<decl_type>(getPrimaryMergedDecl(const_cast<decl_type*>(D)));
  }

  /// \brief Returns true if this is the first declaration.
  bool isFirstDecl() const { return getFirstDecl() == this; }
};

}

#endif
