//========= Copyright Valve Corporation, All rights reserved. ============//
//
// Purpose:
//
// $NoKeywords: $
//=============================================================================//

#include "tier0/platform.h"
#include "tier0/dbg.h"
#include "tier1/diff.h"
#include "mathlib/mathlib.h"

// memdbgon must be the last include file in a .cpp file!!!
#include "tier0/memdbgon.h"


// format of diff output:
// 0NN (N=1..127)  copy next N literaly
//
// 1NN (N=1..127) ofs (-128..127) copy next N bytes from original, changin offset by N bytes from
// last copy end
// 100 N ofs(-32768..32767) copy next N, with larger delta offset
// 00 NNNN(1..65535) ofs(-32768..32767) big copy from old
// 80 00 NN NN NN big raw copy
//
// available codes (could be used for additonal compression ops)
// long offset form whose offset could have fit in short offset

// note - this algorithm uses storage equal to 8* the old buffer size. 64k=.5mb


#define MIN_MATCH_LEN 8
#define ACCEPTABLE_MATCH_LEN 4096

struct BlockPtr
{
  BlockPtr *Next;
  uint8 const *dataptr;
};

template<class T,class V> static inline void AddToHead(T * & head, V * node)
{
   node->Next=head;
   head=node;
}  

void Fail(char const *msg)
{
	Assert(0);
}

void ApplyDiffs(uint8 const *OldBlock, uint8 const *DiffList,
                int OldSize, int DiffListSize, int &ResultListSize,uint8 *Output,uint32 OutSize)
{
  uint8 const *copy_src=OldBlock;
  uint8 const *end_of_diff_list=DiffList+DiffListSize;
  uint8 const *obuf=Output;
  while(DiffList<end_of_diff_list)
  {
    //  printf("dptr=%x ",DiffList-d);
    uint8 op=*(DiffList++);
    if (op==0)
    {
      uint16 copy_sz=DiffList[0]+256*DiffList[1];
      int copy_ofs=DiffList[2]+DiffList[3]*256;
      if (copy_ofs>32767)
        copy_ofs|=0xffff0000;
    //    printf("long cp from %x to %x len=%d\n", copy_src+copy_ofs-OldBlock,Output-obuf,copy_sz);
      
      memcpy(Output,copy_src+copy_ofs,copy_sz);
      Output+=copy_sz;
      copy_src=copy_src+copy_ofs+copy_sz;
      DiffList+=4;
    }
    else
    {
      if (op & 0x80)
      {
        int copy_sz=op & 0x7f;
        int copy_ofs;
        if (copy_sz==0)
        {
          copy_sz=DiffList[0];
          if (copy_sz==0)
          {
            // big raw copy
            copy_sz=DiffList[1]+256*DiffList[2]+65536*DiffList[3];
            memcpy(Output,DiffList+4,copy_sz);
    //          printf("big rawcopy to %x len=%d\n", Output-obuf,copy_sz);
            
            DiffList+=copy_sz+4;
            Output+=copy_sz;
          }
          else
          {
            copy_ofs=DiffList[1]+(DiffList[2]*256);
            if (copy_ofs>32767)
              copy_ofs|=0xffff0000;
    //          printf("long ofs cp from %x to %x len=%d\n", copy_src+copy_ofs-OldBlock,Output-obuf,copy_sz);
            
            memcpy(Output,copy_src+copy_ofs,copy_sz);
            Output+=copy_sz;
            copy_src=copy_src+copy_ofs+copy_sz;
            DiffList+=3;
          }
        }
        else
        {
          copy_ofs=DiffList[0];
          if (copy_ofs>127)
            copy_ofs|=0xffffff80;
    //        printf("cp from %x to %x len=%d\n", copy_src+copy_ofs-OldBlock,Output-obuf,copy_sz);
          
          memcpy(Output,copy_src+copy_ofs,copy_sz);
          Output+=copy_sz;
          copy_src=copy_src+copy_ofs+copy_sz;
          DiffList++;
        }
      }
      else
      {
    //      printf("raw copy %d to %x\n",op & 127,Output-obuf);
        memcpy(Output,DiffList,op & 127);
        Output+=op & 127;
        DiffList+=(op & 127);
      }
    }
  }
  ResultListSize=Output-obuf;
  
}

static void CopyPending(int len, uint8 const *rawbytes,uint8 * &outbuf, uint8 const *limit)
{
//    printf("copy raw len=%d\n",len);
  if (len<128)
  {
    if (limit-outbuf < len+1)
      Fail("diff buffer overrun");
    *(outbuf++)=len;
    memcpy(outbuf,rawbytes,len);
    outbuf+=len;
  }
  else
  {
    if (limit-outbuf < len+5)
      Fail("diff buffer overrun");
    *(outbuf++)=0x80;
    *(outbuf++)=0x00;
    *(outbuf++)=(len & 255);
    *(outbuf++)=((len>>8) & 255);
    *(outbuf++)=((len>>16) & 255);
    memcpy(outbuf,rawbytes,len);
    outbuf+=len;
  }
}

static uint32 hasher(uint8 const *mdata)
{
  // attempt to scramble the bits of h1 and h2 together
  uint32 ret=0;
  for(int i=0;i<MIN_MATCH_LEN;i++)
  {
    ret=ret<<4;
    ret+=(*mdata++);
  }
  return ret;
}

int FindDiffsForLargeFiles(uint8 const *NewBlock, uint8 const *OldBlock,
                            int NewSize, int OldSize, int &DiffListSize,uint8 *Output,
                            uint32 OutSize,
                            int hashsize)
{
  
  int ret=0;
  if (OldSize!=NewSize)
    ret=1;
  // first, build the hash table
  BlockPtr **HashedMatches=new BlockPtr* [hashsize];
  memset(HashedMatches,0,sizeof(HashedMatches[0])*hashsize);
  BlockPtr *Blocks=0;
  if (OldSize)
    Blocks=new BlockPtr[OldSize];
  BlockPtr *FreeList=Blocks;
  // now, build the hash table
  uint8 const *walk=OldBlock;
  if (OldBlock && OldSize)
    while(walk<OldBlock+OldSize-MIN_MATCH_LEN)
    {
      uint32 hash1=hasher(walk);
      hash1 &=(hashsize-1);
      BlockPtr *newnode=FreeList;
      FreeList++;
      newnode->dataptr=walk;
      AddToHead(HashedMatches[hash1],newnode);
      walk++;
    }
  else
    ret=1;
  // now, we have the hash table which may be used to search. begin the output step
  int pending_raw_len=0;
  walk=NewBlock;
  uint8 *outbuf=Output;
  uint8 const *lastmatchend=OldBlock;
  while(walk<NewBlock+NewSize)
  {
    int longest=0;
    BlockPtr *longest_block=0;
    if (walk<NewBlock+NewSize-MIN_MATCH_LEN)
    {
      // check for a match
      uint32 hash1=hasher(walk);
      hash1 &= (hashsize-1);
      // now, find the longest match in the hash table. If we find one >MIN_MATCH_LEN, take it
      for(BlockPtr *b=HashedMatches[hash1];b;b=b->Next)
      {
        // find the match length
        int match_of=b->dataptr-lastmatchend;
        if ((match_of>-32768) && (match_of<32767))
        {
          int max_mlength=min(65535,OldBlock+OldSize-b->dataptr);
          max_mlength=min(max_mlength,NewBlock+NewSize-walk);
          int i;
		  for(i=0;i<max_mlength;i++)
            if (walk[i]!=b->dataptr[i])
              break;
          if ((i>MIN_MATCH_LEN) && (i>longest))
          {
            longest=i;
            longest_block=b;
            if (longest>ACCEPTABLE_MATCH_LEN)
              break;
          }
        }
      }
    }
    // now, we have a match maybe
    if (longest_block)
    {      
      if (pending_raw_len)                                  // must output
      {
        ret=1;
        CopyPending(pending_raw_len,walk-pending_raw_len,outbuf,Output+OutSize);
        pending_raw_len=0;
      }
      // now, output copy block
      int match_of=longest_block->dataptr-lastmatchend;
      int nremaining=OutSize-(outbuf-Output);
      
      if (match_of)
        ret=1;
//        printf("copy from %x to %x len=%d\n", match_of,outbuf-Output,longest);
      if (longest>127)
      {
        // use really long encoding
        if (nremaining<5)
          Fail("diff buff needs increase");
        *(outbuf++)=00;
        *(outbuf++)=(longest & 255);
        *(outbuf++)=((longest>>8) & 255);
        *(outbuf++)=(match_of & 255);
        *(outbuf++)=((match_of>>8) & 255);
        
      }
      else
      {
        if ((match_of>=-128) && (match_of<128))
        {
          if (nremaining<2)
            Fail("diff buff needs increase");
          *(outbuf++)=128+longest;
          *(outbuf++)=(match_of&255);
        }
        else
        {
          // use long encoding
          if (nremaining<4)
            Fail("diff buff needs increase");
          *(outbuf++)=0x80;          
          *(outbuf++)=longest;
          *(outbuf++)=(match_of & 255);
          *(outbuf++)=((match_of>>8) & 255);
        }
      }
      lastmatchend=longest_block->dataptr+longest;
      walk+=longest;
    }
    else
    {
      walk++;
      pending_raw_len++;
    }
  }
  // now, flush pending raw copy
  if (pending_raw_len)                                  // must output
  {
    ret=1;
    CopyPending(pending_raw_len,walk-pending_raw_len,outbuf,Output+OutSize);
    pending_raw_len=0;
  }
  delete[] HashedMatches;
  if (Blocks)
    delete[] Blocks;
  DiffListSize=outbuf-Output;
  return ret;
}


int FindDiffs(uint8 const *NewBlock, uint8 const *OldBlock,
               int NewSize, int OldSize, int &DiffListSize,uint8 *Output,uint32 OutSize)
{
  
  int ret=0;
  if (OldSize!=NewSize)
    ret=1;
  // first, build the hash table
  BlockPtr *HashedMatches[65536];
  memset(HashedMatches,0,sizeof(HashedMatches));
  BlockPtr *Blocks=0;
  if (OldSize)
    Blocks=new BlockPtr[OldSize];
  BlockPtr *FreeList=Blocks;
  // now, build the hash table
  uint8 const *walk=OldBlock;
  if (OldBlock && OldSize)
    while(walk<OldBlock+OldSize-MIN_MATCH_LEN)
    {
      uint16 hash1=*((uint16 const *) walk)+*((uint16 const *) walk+2);
      BlockPtr *newnode=FreeList;
      FreeList++;
      newnode->dataptr=walk;
      AddToHead(HashedMatches[hash1],newnode);
      walk++;
    }
  else
    ret=1;
  // now, we have the hash table which may be used to search. begin the output step
  int pending_raw_len=0;
  walk=NewBlock;
  uint8 *outbuf=Output;
  uint8 const *lastmatchend=OldBlock;
  while(walk<NewBlock+NewSize)
  {
    int longest=0;
    BlockPtr *longest_block=0;
    if (walk<NewBlock+NewSize-MIN_MATCH_LEN)
    {
      // check for a match
      uint16 hash1=*((uint16 const *) walk)+*((uint16 const *) walk+2);
      // now, find the longest match in the hash table. If we find one >MIN_MATCH_LEN, take it
      for(BlockPtr *b=HashedMatches[hash1];b;b=b->Next)
      {
        // find the match length
        int match_of=b->dataptr-lastmatchend;
        if ((match_of>-32768) && (match_of<32767))
        {
          int max_mlength=min(65535,OldBlock+OldSize-b->dataptr);
          max_mlength=min(max_mlength,NewBlock+NewSize-walk);
          int i;
		  for(i=0;i<max_mlength;i++)
            if (walk[i]!=b->dataptr[i])
              break;
          if ((i>MIN_MATCH_LEN) && (i>longest))
          {
            longest=i;
            longest_block=b;
          }
        }
      }
    }
    // now, we have a match maybe
    if (longest_block)
    {
      if (pending_raw_len)                                  // must output
      {
        ret=1;
        CopyPending(pending_raw_len,walk-pending_raw_len,outbuf,Output+OutSize);
        pending_raw_len=0;
      }
      // now, output copy block
      int match_of=longest_block->dataptr-lastmatchend;
      int nremaining=OutSize-(outbuf-Output);
      if (match_of)
        ret=1;
      if (longest>127)
      {
        // use really long encoding
        if (nremaining<5)
          Fail("diff buff needs increase");
        *(outbuf++)=00;
        *(outbuf++)=(longest & 255);
        *(outbuf++)=((longest>>8) & 255);
        *(outbuf++)=(match_of & 255);
        *(outbuf++)=((match_of>>8) & 255);
      }
      else
      {
        if ((match_of>=-128) && (match_of<128))
        {
          if (nremaining<2)
            Fail("diff buff needs increase");
          *(outbuf++)=128+longest;
          *(outbuf++)=(match_of&255);
        }
        else
        {
          // use long encoding
          if (nremaining<4)
            Fail("diff buff needs increase");
          *(outbuf++)=0x80;
          *(outbuf++)=longest;
          *(outbuf++)=(match_of & 255);
          *(outbuf++)=((match_of>>8) & 255);
        }
      }
      lastmatchend=longest_block->dataptr+longest;
      walk+=longest;
    }
    else
    {
      walk++;
      pending_raw_len++;
    }
  }
  // now, flush pending raw copy
  if (pending_raw_len)                                  // must output
  {
    ret=1;
    CopyPending(pending_raw_len,walk-pending_raw_len,outbuf,Output+OutSize);
    pending_raw_len=0;
  }
  if (Blocks)
    delete[] Blocks;
  DiffListSize=outbuf-Output;
  return ret;
}


int FindDiffsLowMemory(uint8 const *NewBlock, uint8 const *OldBlock,
                        int NewSize, int OldSize, int &DiffListSize,uint8 *Output,uint32 OutSize)
{
  
  int ret=0;
  if (OldSize!=NewSize)
    ret=1;
  uint8 const *old_data_hash[256];
  memset(old_data_hash,0,sizeof(old_data_hash));
  int pending_raw_len=0;
  uint8 const *walk=NewBlock;
  uint8 const *oldptr=OldBlock;
  uint8 *outbuf=Output;
  uint8 const *lastmatchend=OldBlock;
  while(walk<NewBlock+NewSize)
  {
    while( (oldptr-OldBlock<walk-NewBlock+40) && (oldptr-OldBlock<OldSize-MIN_MATCH_LEN))
    {
      uint16 hash1=(oldptr[0]+oldptr[1]+oldptr[2]+oldptr[3]) & (NELEMS(old_data_hash)-1);
      old_data_hash[hash1]=oldptr;
      oldptr++;
    }
    int longest=0;
    uint8 const *longest_block=0;
    if (walk<NewBlock+NewSize-MIN_MATCH_LEN)
    {
      // check for a match
      uint16 hash1=(walk[0]+walk[1]+walk[2]+walk[3]) & (NELEMS(old_data_hash)-1);
      if (old_data_hash[hash1])
      {
        int max_bytes_to_compare=min(NewBlock+NewSize-walk,OldBlock+OldSize-old_data_hash[hash1]);
        int nmatches;
		for(nmatches=0;nmatches<max_bytes_to_compare;nmatches++)
          if (walk[nmatches]!=old_data_hash[hash1][nmatches])
            break;
        if (nmatches>MIN_MATCH_LEN)
        {
          longest_block=old_data_hash[hash1];
          longest=nmatches;
        }
      }
    }
    // now, we have a match maybe
    if (longest_block)
    {
      if (pending_raw_len)                                  // must output
      {
        ret=1;
        CopyPending(pending_raw_len,walk-pending_raw_len,outbuf,Output+OutSize);
        pending_raw_len=0;
      }
      // now, output copy block
      int match_of=longest_block-lastmatchend;
      int nremaining=OutSize-(outbuf-Output);
      if (match_of)
        ret=1;
      if (longest>127)
      {
        // use really long encoding
        if (nremaining<5)
          Fail("diff buff needs increase");
        *(outbuf++)=00;
        *(outbuf++)=(longest & 255);
        *(outbuf++)=((longest>>8) & 255);
        *(outbuf++)=(match_of & 255);
        *(outbuf++)=((match_of>>8) & 255);
      }
      else
      {
        if ((match_of>=-128) && (match_of<128))
        {
          if (nremaining<2)
            Fail("diff buff needs increase");
          *(outbuf++)=128+longest;
          *(outbuf++)=(match_of&255);
        }
        else
        {
          // use long encoding
          if (nremaining<4)
            Fail("diff buff needs increase");
          *(outbuf++)=0x80;
          *(outbuf++)=longest;
          *(outbuf++)=(match_of & 255);
          *(outbuf++)=((match_of>>8) & 255);
        }
      }
      lastmatchend=longest_block+longest;
      walk+=longest;
    }
    else
    {
      walk++;
      pending_raw_len++;
    }
  }
  // now, flush pending raw copy
  if (pending_raw_len)                                  // must output
  {
    ret=1;
    CopyPending(pending_raw_len,walk-pending_raw_len,outbuf,Output+OutSize);
    pending_raw_len=0;
  }
  DiffListSize=outbuf-Output;
  return ret;
}