//===- DeclContextInternals.h - DeclContext Representation ------*- 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
//
//===----------------------------------------------------------------------===//
//
//  This file defines the data structures used in the implementation
//  of DeclContext.
//
//===----------------------------------------------------------------------===//

#ifndef LLVM_CLANG_AST_DECLCONTEXTINTERNALS_H
#define LLVM_CLANG_AST_DECLCONTEXTINTERNALS_H

#include "clang/AST/ASTContext.h"
#include "clang/AST/Decl.h"
#include "clang/AST/DeclBase.h"
#include "clang/AST/DeclCXX.h"
#include "clang/AST/DeclarationName.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/PointerUnion.h"
#include <cassert>

namespace clang {

class DependentDiagnostic;

/// An array of decls optimized for the common case of only containing
/// one entry.
class StoredDeclsList {
  using Decls = DeclListNode::Decls;

  /// A collection of declarations, with a flag to indicate if we have
  /// further external declarations.
  using DeclsAndHasExternalTy = llvm::PointerIntPair<Decls, 1, bool>;

  /// The stored data, which will be either a pointer to a NamedDecl,
  /// or a pointer to a list with a flag to indicate if there are further
  /// external declarations.
  DeclsAndHasExternalTy Data;

  template<typename Fn>
  void erase_if(Fn ShouldErase) {
    Decls List = Data.getPointer();
    if (!List)
      return;
    ASTContext &C = getASTContext();
    DeclListNode::Decls NewHead = nullptr;
    DeclListNode::Decls *NewLast = nullptr;
    DeclListNode::Decls *NewTail = &NewHead;
    while (true) {
      if (!ShouldErase(*DeclListNode::iterator(List))) {
        NewLast = NewTail;
        *NewTail = List;
        if (auto *Node = List.dyn_cast<DeclListNode*>()) {
          NewTail = &Node->Rest;
          List = Node->Rest;
        } else {
          break;
        }
      } else if (DeclListNode *N = List.dyn_cast<DeclListNode*>()) {
        List = N->Rest;
        C.DeallocateDeclListNode(N);
      } else {
        // We're discarding the last declaration in the list. The last node we
        // want to keep (if any) will be of the form DeclListNode(D, <rest>);
        // replace it with just D.
        if (NewLast) {
          DeclListNode *Node = NewLast->get<DeclListNode*>();
          *NewLast = Node->D;
          C.DeallocateDeclListNode(Node);
        }
        break;
      }
    }
    Data.setPointer(NewHead);

    assert(llvm::find_if(getLookupResult(), ShouldErase) ==
           getLookupResult().end() && "Still exists!");
  }

  void erase(NamedDecl *ND) {
    erase_if([ND](NamedDecl *D) { return D == ND; });
  }

public:
  StoredDeclsList() = default;

  StoredDeclsList(StoredDeclsList &&RHS) : Data(RHS.Data) {
    RHS.Data.setPointer(nullptr);
    RHS.Data.setInt(0);
  }

  void MaybeDeallocList() {
    if (isNull())
      return;
    // If this is a list-form, free the list.
    ASTContext &C = getASTContext();
    Decls List = Data.getPointer();
    while (DeclListNode *ToDealloc = List.dyn_cast<DeclListNode *>()) {
      List = ToDealloc->Rest;
      C.DeallocateDeclListNode(ToDealloc);
    }
  }

  ~StoredDeclsList() {
    MaybeDeallocList();
  }

  StoredDeclsList &operator=(StoredDeclsList &&RHS) {
    MaybeDeallocList();

    Data = RHS.Data;
    RHS.Data.setPointer(nullptr);
    RHS.Data.setInt(0);
    return *this;
  }

  bool isNull() const { return Data.getPointer().isNull(); }

  ASTContext &getASTContext() {
    assert(!isNull() && "No ASTContext.");
    if (NamedDecl *ND = getAsDecl())
      return ND->getASTContext();
    return getAsList()->D->getASTContext();
  }

  DeclsAndHasExternalTy getAsListAndHasExternal() const { return Data; }

  NamedDecl *getAsDecl() const {
    return getAsListAndHasExternal().getPointer().dyn_cast<NamedDecl *>();
  }

  DeclListNode *getAsList() const {
    return getAsListAndHasExternal().getPointer().dyn_cast<DeclListNode*>();
  }

  bool hasExternalDecls() const {
    return getAsListAndHasExternal().getInt();
  }

  void setHasExternalDecls() {
    Data.setInt(1);
  }

  void remove(NamedDecl *D) {
    assert(!isNull() && "removing from empty list");
    erase(D);
  }

  /// Remove any declarations which were imported from an external AST source.
  void removeExternalDecls() {
    erase_if([](NamedDecl *ND) { return ND->isFromASTFile(); });

    // Don't have any pending external decls any more.
    Data.setInt(0);
  }

  void replaceExternalDecls(ArrayRef<NamedDecl*> Decls) {
    // Remove all declarations that are either external or are replaced with
    // external declarations.
    erase_if([Decls](NamedDecl *ND) {
      if (ND->isFromASTFile())
        return true;
      for (NamedDecl *D : Decls)
        if (D->declarationReplaces(ND, /*IsKnownNewer=*/false))
          return true;
      return false;
    });

    // Don't have any pending external decls any more.
    Data.setInt(0);

    if (Decls.empty())
      return;

    // Convert Decls into a list, in order.
    ASTContext &C = Decls.front()->getASTContext();
    DeclListNode::Decls DeclsAsList = Decls.back();
    for (size_t I = Decls.size() - 1; I != 0; --I) {
      DeclListNode *Node = C.AllocateDeclListNode(Decls[I - 1]);
      Node->Rest = DeclsAsList;
      DeclsAsList = Node;
    }

    DeclListNode::Decls Head = Data.getPointer();
    if (Head.isNull()) {
      Data.setPointer(DeclsAsList);
      return;
    }

    // Find the end of the existing list.
    // FIXME: It would be possible to preserve information from erase_if to
    // avoid this rescan looking for the end of the list.
    DeclListNode::Decls *Tail = &Head;
    while (DeclListNode *Node = Tail->dyn_cast<DeclListNode *>())
      Tail = &Node->Rest;

    // Append the Decls.
    DeclListNode *Node = C.AllocateDeclListNode(Tail->get<NamedDecl *>());
    Node->Rest = DeclsAsList;
    *Tail = Node;
    Data.setPointer(Head);
  }

  /// Return an array of all the decls that this list represents.
  DeclContext::lookup_result getLookupResult() const {
    return DeclContext::lookup_result(Data.getPointer());
  }

  /// If this is a redeclaration of an existing decl, replace the old one with
  /// D. Otherwise, append D.
  void addOrReplaceDecl(NamedDecl *D) {
    const bool IsKnownNewer = true;

    if (isNull()) {
      Data.setPointer(D);
      return;
    }

    // Most decls only have one entry in their list, special case it.
    if (NamedDecl *OldD = getAsDecl()) {
      if (D->declarationReplaces(OldD, IsKnownNewer)) {
        Data.setPointer(D);
        return;
      }

      // Add D after OldD.
      ASTContext &C = D->getASTContext();
      DeclListNode *Node = C.AllocateDeclListNode(OldD);
      Node->Rest = D;
      Data.setPointer(Node);
      return;
    }

    // FIXME: Move the assert before the single decl case when we fix the
    // duplication coming from the ASTReader reading builtin types.
    assert(!llvm::is_contained(getLookupResult(), D) && "Already exists!");
    // Determine if this declaration is actually a redeclaration.
    for (DeclListNode *N = getAsList(); /*return in loop*/;
         N = N->Rest.dyn_cast<DeclListNode *>()) {
      if (D->declarationReplaces(N->D, IsKnownNewer)) {
        N->D = D;
        return;
      }
      if (auto *ND = N->Rest.dyn_cast<NamedDecl *>()) {
        if (D->declarationReplaces(ND, IsKnownNewer)) {
          N->Rest = D;
          return;
        }

        // Add D after ND.
        ASTContext &C = D->getASTContext();
        DeclListNode *Node = C.AllocateDeclListNode(ND);
        N->Rest = Node;
        Node->Rest = D;
        return;
      }
    }
  }

  /// Add a declaration to the list without checking if it replaces anything.
  void prependDeclNoReplace(NamedDecl *D) {
    if (isNull()) {
      Data.setPointer(D);
      return;
    }

    ASTContext &C = D->getASTContext();
    DeclListNode *Node = C.AllocateDeclListNode(D);
    Node->Rest = Data.getPointer();
    Data.setPointer(Node);
  }

  LLVM_DUMP_METHOD void dump() const {
    Decls D = Data.getPointer();
    if (!D) {
      llvm::errs() << "<null>\n";
      return;
    }

    while (true) {
      if (auto *Node = D.dyn_cast<DeclListNode*>()) {
        llvm::errs() << '[' << Node->D << "] -> ";
        D = Node->Rest;
      } else {
        llvm::errs() << '[' << D.get<NamedDecl*>() << "]\n";
        return;
      }
    }
  }
};

class StoredDeclsMap
    : public llvm::SmallDenseMap<DeclarationName, StoredDeclsList, 4> {
  friend class ASTContext; // walks the chain deleting these
  friend class DeclContext;

  llvm::PointerIntPair<StoredDeclsMap*, 1> Previous;
public:
  static void DestroyAll(StoredDeclsMap *Map, bool Dependent);
};

class DependentStoredDeclsMap : public StoredDeclsMap {
  friend class DeclContext; // iterates over diagnostics
  friend class DependentDiagnostic;

  DependentDiagnostic *FirstDiagnostic = nullptr;
public:
  DependentStoredDeclsMap() = default;
};

} // namespace clang

#endif // LLVM_CLANG_AST_DECLCONTEXTINTERNALS_H