//===--- DeltaTree.cpp - B-Tree for Rewrite Delta tracking ----------------===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file implements the DeltaTree and related classes.
//
//===----------------------------------------------------------------------===//

#include "clang/Rewrite/DeltaTree.h"
#include "llvm/Support/Casting.h"
#include <cstring>
using namespace clang;
using llvm::cast;
using llvm::dyn_cast;

namespace {
  struct SourceDelta;
  class DeltaTreeNode;
  class DeltaTreeInteriorNode;
}

/// The DeltaTree class is a multiway search tree (BTree) structure with some
/// fancy features.  B-Trees are are generally more memory and cache efficient
/// than binary trees, because they store multiple keys/values in each node.
///
/// DeltaTree implements a key/value mapping from FileIndex to Delta, allowing
/// fast lookup by FileIndex.  However, an added (important) bonus is that it
/// can also efficiently tell us the full accumulated delta for a specific
/// file offset as well, without traversing the whole tree.
///
/// The nodes of the tree are made up of instances of two classes:
/// DeltaTreeNode and DeltaTreeInteriorNode.  The later subclasses the
/// former and adds children pointers.  Each node knows the full delta of all
/// entries (recursively) contained inside of it, which allows us to get the
/// full delta implied by a whole subtree in constant time.
  
namespace {
  /// SourceDelta - As code in the original input buffer is added and deleted,
  /// SourceDelta records are used to keep track of how the input SourceLocation
  /// object is mapped into the output buffer.
  struct SourceDelta {
    unsigned FileLoc;
    int Delta;
    
    static SourceDelta get(unsigned Loc, int D) {
      SourceDelta Delta;
      Delta.FileLoc = Loc;
      Delta.Delta = D;
      return Delta;
    }
  };
} // end anonymous namespace

namespace {
  /// DeltaTreeNode - The common part of all nodes.
  ///
  class DeltaTreeNode {
    friend class DeltaTreeInteriorNode;
    
    /// WidthFactor - This controls the number of K/V slots held in the BTree:
    /// how wide it is.  Each level of the BTree is guaranteed to have at least
    /// WidthFactor-1 K/V pairs (unless the whole tree is less full than that)
    /// and may have at most 2*WidthFactor-1 K/V pairs.
    enum { WidthFactor = 8 };
    
    /// Values - This tracks the SourceDelta's currently in this node.
    ///
    SourceDelta Values[2*WidthFactor-1];
    
    /// NumValuesUsed - This tracks the number of values this node currently
    /// holds.
    unsigned char NumValuesUsed;
    
    /// IsLeaf - This is true if this is a leaf of the btree.  If false, this is
    /// an interior node, and is actually an instance of DeltaTreeInteriorNode.
    bool IsLeaf;
    
    /// FullDelta - This is the full delta of all the values in this node and
    /// all children nodes.
    int FullDelta;
  public:
    DeltaTreeNode(bool isLeaf = true)
    : NumValuesUsed(0), IsLeaf(isLeaf), FullDelta(0) {}
    
    bool isLeaf() const { return IsLeaf; }
    int getFullDelta() const { return FullDelta; }
    bool isFull() const { return NumValuesUsed == 2*WidthFactor-1; }
    
    unsigned getNumValuesUsed() const { return NumValuesUsed; }
    const SourceDelta &getValue(unsigned i) const {
      assert(i < NumValuesUsed && "Invalid value #");
      return Values[i];
    }
    SourceDelta &getValue(unsigned i) {
      assert(i < NumValuesUsed && "Invalid value #");
      return Values[i];
    }
    
    /// AddDeltaNonFull - Add a delta to this tree and/or it's children, knowing
    /// that this node is not currently full.
    void AddDeltaNonFull(unsigned FileIndex, int Delta);
    
    /// RecomputeFullDeltaLocally - Recompute the FullDelta field by doing a
    /// local walk over our contained deltas.
    void RecomputeFullDeltaLocally();
    
    void Destroy();
    
    static inline bool classof(const DeltaTreeNode *) { return true; }
  };
} // end anonymous namespace

namespace {
  /// DeltaTreeInteriorNode - When isLeaf = false, a node has child pointers.
  /// This class tracks them.
  class DeltaTreeInteriorNode : public DeltaTreeNode {
    DeltaTreeNode *Children[2*WidthFactor];
    ~DeltaTreeInteriorNode() {
      for (unsigned i = 0, e = NumValuesUsed+1; i != e; ++i)
        Children[i]->Destroy();
    }
    friend class DeltaTreeNode;
  public:
    DeltaTreeInteriorNode() : DeltaTreeNode(false /*nonleaf*/) {}
    
    DeltaTreeInteriorNode(DeltaTreeNode *FirstChild)
    : DeltaTreeNode(false /*nonleaf*/) {
      FullDelta = FirstChild->FullDelta;
      Children[0] = FirstChild;
    }
    
    const DeltaTreeNode *getChild(unsigned i) const {
      assert(i < getNumValuesUsed()+1 && "Invalid child");
      return Children[i];
    }
    DeltaTreeNode *getChild(unsigned i) {
      assert(i < getNumValuesUsed()+1 && "Invalid child");
      return Children[i];
    }
    
    static inline bool classof(const DeltaTreeInteriorNode *) { return true; }
    static inline bool classof(const DeltaTreeNode *N) { return !N->isLeaf(); }
  private:
    void SplitChild(unsigned ChildNo);
  };
}


/// Destroy - A 'virtual' destructor.
void DeltaTreeNode::Destroy() {
  if (isLeaf())
    delete this;
  else
    delete cast<DeltaTreeInteriorNode>(this);
}

/// RecomputeFullDeltaLocally - Recompute the FullDelta field by doing a
/// local walk over our contained deltas.
void DeltaTreeNode::RecomputeFullDeltaLocally() {
  int NewFullDelta = 0;
  for (unsigned i = 0, e = getNumValuesUsed(); i != e; ++i)
    NewFullDelta += Values[i].Delta;
  if (DeltaTreeInteriorNode *IN = dyn_cast<DeltaTreeInteriorNode>(this))
    for (unsigned i = 0, e = getNumValuesUsed()+1; i != e; ++i)
      NewFullDelta += IN->getChild(i)->getFullDelta();
  FullDelta = NewFullDelta;
}


/// AddDeltaNonFull - Add a delta to this tree and/or it's children, knowing
/// that this node is not currently full.
void DeltaTreeNode::AddDeltaNonFull(unsigned FileIndex, int Delta) {
  assert(!isFull() && "AddDeltaNonFull on a full tree?");
  
  // Maintain full delta for this node.
  FullDelta += Delta;
  
  // Find the insertion point, the first delta whose index is >= FileIndex.
  unsigned i = 0, e = getNumValuesUsed();
  while (i != e && FileIndex > getValue(i).FileLoc)
    ++i;
  
  // If we found an a record for exactly this file index, just merge this
  // value into the preexisting record and finish early.
  if (i != e && getValue(i).FileLoc == FileIndex) {
    // NOTE: Delta could drop to zero here.  This means that the next delta
    // entry is useless and could be removed.  Supporting erases is
    // significantly more complex though, so we just leave an entry with
    // Delta=0 in the tree.
    Values[i].Delta += Delta;
    return;
  }
  
  if (DeltaTreeInteriorNode *IN = dyn_cast<DeltaTreeInteriorNode>(this)) {
    // Insertion into an interior node propagates the value down to a child.
    DeltaTreeNode *Child = IN->getChild(i);
    
    // If the child tree is full, split it, pulling an element up into our
    // node.
    if (Child->isFull()) {
      IN->SplitChild(i);
      SourceDelta &MedianVal = getValue(i);
      
      // If the median value we pulled up is exactly our insert position, add
      // the delta and return.
      if (MedianVal.FileLoc == FileIndex) {
        MedianVal.Delta += Delta;
        return;
      }
      
      // If the median value pulled up is less than our current search point,
      // include those deltas and search down the RHS now.
      if (MedianVal.FileLoc < FileIndex)
        Child = IN->getChild(i+1);
    }
    
    Child->AddDeltaNonFull(FileIndex, Delta);
  } else {
    // For an insertion into a non-full leaf node, just insert the value in
    // its sorted position.  This requires moving later values over.
    if (i != e)
      memmove(&Values[i+1], &Values[i], sizeof(Values[0])*(e-i));
    Values[i] = SourceDelta::get(FileIndex, Delta);
    ++NumValuesUsed;
  }
}

/// SplitChild - At this point, we know that the current node is not full and
/// that the specified child of this node is.  Split the child in half at its
/// median, propagating one value up into us.  Child may be either an interior
/// or leaf node.
void DeltaTreeInteriorNode::SplitChild(unsigned ChildNo) {
  DeltaTreeNode *Child = getChild(ChildNo);
  assert(!isFull() && Child->isFull() && "Inconsistent constraints");
  
  // Since the child is full, it contains 2*WidthFactor-1 values.  We move
  // the first 'WidthFactor-1' values to the LHS child (which we leave in the
  // original child), propagate one value up into us, and move the last
  // 'WidthFactor-1' values into thew RHS child.
  
  // Create the new child node.
  DeltaTreeNode *NewNode;
  if (DeltaTreeInteriorNode *CIN = dyn_cast<DeltaTreeInteriorNode>(Child)) {
    // If the child is an interior node, also move over 'WidthFactor' grand
    // children into the new node.
    NewNode = new DeltaTreeInteriorNode();
    memcpy(&((DeltaTreeInteriorNode*)NewNode)->Children[0],
           &CIN->Children[WidthFactor],
           WidthFactor*sizeof(CIN->Children[0]));
  } else {
    // Just create the child node.
    NewNode = new DeltaTreeNode();
  }
  
  // Move over the last 'WidthFactor-1' values from Child to NewNode.
  memcpy(&NewNode->Values[0], &Child->Values[WidthFactor],
         (WidthFactor-1)*sizeof(Child->Values[0]));
  
  // Decrease the number of values in the two children.
  NewNode->NumValuesUsed = Child->NumValuesUsed = WidthFactor-1;
  
  // Recompute the two children's full delta.  Our delta hasn't changed, but
  // their delta has.
  NewNode->RecomputeFullDeltaLocally();
  Child->RecomputeFullDeltaLocally();
  
  // Now that we have two nodes and a new element, insert the median value
  // into ourself by moving all the later values/children down, then inserting
  // the new one.
  if (getNumValuesUsed() != ChildNo)
    memmove(&Children[ChildNo+2], &Children[ChildNo+1], 
            (getNumValuesUsed()-ChildNo)*sizeof(Children[0]));
  Children[ChildNo+1] = NewNode;
  
  if (getNumValuesUsed() != ChildNo)
    memmove(&Values[ChildNo+1], &Values[ChildNo],
            (getNumValuesUsed()-ChildNo)*sizeof(Values[0]));
  Values[ChildNo] = Child->Values[WidthFactor-1];
  ++NumValuesUsed;
}


//===----------------------------------------------------------------------===//
//                        DeltaTree Implementation
//===----------------------------------------------------------------------===//

//#define VERIFY_TREE

#ifdef VERIFY_TREE
/// VerifyTree - Walk the btree performing assertions on various properties to
/// verify consistency.  This is useful for debugging new changes to the tree.
static void VerifyTree(const DeltaTreeNode *N) {
  const DeltaTreeInteriorNode *IN = dyn_cast<DeltaTreeInteriorNode>(N);
  if (IN == 0) {
    // Verify leaves, just ensure that FullDelta matches up and the elements
    // are in proper order.
    int FullDelta = 0;
    for (unsigned i = 0, e = N->getNumValuesUsed(); i != e; ++i) {
      if (i)
        assert(N->getValue(i-1).FileLoc < N->getValue(i).FileLoc);
      FullDelta += N->getValue(i).Delta;
    }
    assert(FullDelta == N->getFullDelta());
    return;
  }
  
  // Verify interior nodes: Ensure that FullDelta matches up and the
  // elements are in proper order and the children are in proper order.
  int FullDelta = 0;
  for (unsigned i = 0, e = IN->getNumValuesUsed(); i != e; ++i) {
    const SourceDelta &IVal = N->getValue(i);
    const DeltaTreeNode *IChild = IN->getChild(i);
    if (i)
      assert(IN->getValue(i-1).FileLoc < IVal.FileLoc);
    FullDelta += IVal.Delta;
    FullDelta += IChild->getFullDelta();
    
    // The largest value in child #i should be smaller than FileLoc.
    assert(IChild->getValue(IChild->getNumValuesUsed()-1).FileLoc <
           IVal.FileLoc);
    
    // The smallest value in child #i+1 should be larger than FileLoc.
    assert(IN->getChild(i+1)->getValue(0).FileLoc > IVal.FileLoc);
    VerifyTree(IChild);
  }
  
  FullDelta += IN->getChild(IN->getNumValuesUsed())->getFullDelta();
  
  assert(FullDelta == N->getFullDelta());
}
#endif  // VERIFY_TREE

static DeltaTreeNode *getRoot(void *Root) {
  return (DeltaTreeNode*)Root;
}

DeltaTree::DeltaTree() {
  Root = new DeltaTreeNode();
}
DeltaTree::DeltaTree(const DeltaTree &RHS) {
  // Currently we only support copying when the RHS is empty.
  assert(getRoot(RHS.Root)->getNumValuesUsed() == 0 &&
         "Can only copy empty tree");
  Root = new DeltaTreeNode();
}

DeltaTree::~DeltaTree() {
  getRoot(Root)->Destroy();
}

/// getDeltaAt - Return the accumulated delta at the specified file offset.
/// This includes all insertions or delections that occurred *before* the
/// specified file index.
int DeltaTree::getDeltaAt(unsigned FileIndex) const {
  const DeltaTreeNode *Node = getRoot(Root);
  
  int Result = 0;
  
  // Walk down the tree.
  while (1) {
    // For all nodes, include any local deltas before the specified file
    // index by summing them up directly.  Keep track of how many were
    // included.
    unsigned NumValsGreater = 0;
    for (unsigned e = Node->getNumValuesUsed(); NumValsGreater != e;
         ++NumValsGreater) {
      const SourceDelta &Val = Node->getValue(NumValsGreater);
      
      if (Val.FileLoc >= FileIndex)
        break;
      Result += Val.Delta;
    }
    
    // If we have an interior node, include information about children and
    // recurse.  Otherwise, if we have a leaf, we're done.
    const DeltaTreeInteriorNode *IN = dyn_cast<DeltaTreeInteriorNode>(Node);
    if (!IN) return Result;
    
    // Include any children to the left of the values we skipped, all of
    // their deltas should be included as well.
    for (unsigned i = 0; i != NumValsGreater; ++i)
      Result += IN->getChild(i)->getFullDelta();
    
    // If we found exactly the value we were looking for, break off the
    // search early.  There is no need to search the RHS of the value for
    // partial results.
    if (NumValsGreater != Node->getNumValuesUsed() &&
        Node->getValue(NumValsGreater).FileLoc == FileIndex)
      return Result;
    
    // Otherwise, traverse down the tree.  The selected subtree may be
    // partially included in the range.
    Node = IN->getChild(NumValsGreater);
  }
  // NOT REACHED.
}


/// AddDelta - When a change is made that shifts around the text buffer,
/// this method is used to record that info.  It inserts a delta of 'Delta'
/// into the current DeltaTree at offset FileIndex.
void DeltaTree::AddDelta(unsigned FileIndex, int Delta) {
  assert(Delta && "Adding a noop?");
  
  // If the root is full, create a new dummy (non-empty) interior node that
  // points to it, allowing the old root to be split.
  if (getRoot(Root)->isFull())
    Root = new DeltaTreeInteriorNode(getRoot(Root));
  
  getRoot(Root)->AddDeltaNonFull(FileIndex, Delta);
  
#ifdef VERIFY_TREE
  VerifyTree(Root);
#endif
}