/* xdelta 3 - delta compression tools and library
 * Copyright (C) 2002, 2006, 2007.  Joshua P. MacDonald
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

/* For demonstration purposes only.
 */

#ifndef _XDELTA3_FGK_h_
#define _XDELTA3_FGK_h_

/* An implementation of the FGK algorithm described by D.E. Knuth in
 * "Dynamic Huffman Coding" in Journal of Algorithms 6. */

/* A 32bit counter (fgk_weight) is used as the frequency counter for
 * nodes in the huffman tree.  TODO: Need oto test for overflow and/or
 * reset stats. */

typedef struct _fgk_stream fgk_stream;
typedef struct _fgk_node   fgk_node;
typedef struct _fgk_block  fgk_block;
typedef unsigned int       fgk_bit;
typedef uint32_t           fgk_weight;

struct _fgk_block {
  union {
    fgk_node  *un_leader;
    fgk_block *un_freeptr;
  } un;
};

#define block_leader  un.un_leader
#define block_freeptr un.un_freeptr

/* The code can also support fixed huffman encoding/decoding. */
#define IS_ADAPTIVE 1

/* weight is a count of the number of times this element has been seen
 * in the current encoding/decoding.  parent, right_child, and
 * left_child are pointers defining the tree structure.  right and
 * left point to neighbors in an ordered sequence of weights.  The
 * left child of a node is always guaranteed to have weight not
 * greater than its sibling.  fgk_blockLeader points to the element
 * with the same weight as itself which is closest to the next
 * increasing weight block.  */
struct _fgk_node
{
  fgk_weight  weight;
  fgk_node   *parent;
  fgk_node   *left_child;
  fgk_node   *right_child;
  fgk_node   *left;
  fgk_node   *right;
  fgk_block  *my_block;
};

/* alphabet_size is the a count of the number of possible leaves in
 * the huffman tree.  The number of total nodes counting internal
 * nodes is ((2 * alphabet_size) - 1).  zero_freq_count is the number
 * of elements remaining which have zero frequency.  zero_freq_exp and
 * zero_freq_rem satisfy the equation zero_freq_count =
 * 2^zero_freq_exp + zero_freq_rem.  root_node is the root of the
 * tree, which is initialized to a node with zero frequency and
 * contains the 0th such element.  free_node contains a pointer to the
 * next available fgk_node space.  alphabet contains all the elements
 * and is indexed by N.  remaining_zeros points to the head of the
 * list of zeros.  */
struct _fgk_stream
{
  usize_t alphabet_size;
  usize_t zero_freq_count;
  usize_t zero_freq_exp;
  usize_t zero_freq_rem;
  usize_t coded_depth;

  usize_t total_nodes;
  usize_t total_blocks;

  fgk_bit *coded_bits;

  fgk_block *block_array;
  fgk_block *free_block;

  fgk_node *decode_ptr;
  fgk_node *remaining_zeros;
  fgk_node *alphabet;
  fgk_node *root_node;
  fgk_node *free_node;
};

/*********************************************************************/
/*                             Encoder                               */
/*********************************************************************/

static fgk_stream*     fgk_alloc           (xd3_stream *stream /*, usize_t alphabet_size */);
static int             fgk_init            (xd3_stream *stream,
					    fgk_stream *h, 
					    int is_encode);
static int             fgk_encode_data     (fgk_stream *h,
					    usize_t    n);
static inline fgk_bit  fgk_get_encoded_bit (fgk_stream *h);

static int             xd3_encode_fgk      (xd3_stream  *stream,
					    fgk_stream  *sec_stream,
					    xd3_output  *input,
					    xd3_output  *output,
					    xd3_sec_cfg *cfg);

/*********************************************************************/
/* 			       Decoder                               */
/*********************************************************************/

static inline int      fgk_decode_bit      (fgk_stream *h,
					    fgk_bit     b);
static int             fgk_decode_data     (fgk_stream *h);
static void            fgk_destroy         (xd3_stream *stream,
					    fgk_stream *h);

static int             xd3_decode_fgk      (xd3_stream     *stream,
					    fgk_stream     *sec_stream,
					    const uint8_t **input,
					    const uint8_t  *const input_end,
					    uint8_t       **output,
					    const uint8_t  *const output_end);

/*********************************************************************/
/* 			       Private                               */
/*********************************************************************/

static unsigned int fgk_find_nth_zero        (fgk_stream *h, usize_t n);
static usize_t      fgk_nth_zero             (fgk_stream *h, usize_t n);
static void         fgk_update_tree          (fgk_stream *h, usize_t n);
static fgk_node*    fgk_increase_zero_weight (fgk_stream *h, usize_t n);
static void         fgk_eliminate_zero       (fgk_stream* h, fgk_node *node);
static void         fgk_move_right           (fgk_stream *h, fgk_node *node);
static void         fgk_promote              (fgk_stream *h, fgk_node *node);
static void         fgk_init_node            (fgk_node *node, usize_t i, usize_t size);
static fgk_block*   fgk_make_block           (fgk_stream *h, fgk_node *l);
static void         fgk_free_block           (fgk_stream *h, fgk_block *b);
static void         fgk_factor_remaining     (fgk_stream *h);
static inline void  fgk_swap_ptrs            (fgk_node **one, fgk_node **two);

/*********************************************************************/
/* 			    Basic Routines                           */
/*********************************************************************/

/* returns an initialized huffman encoder for an alphabet with the
 * given size.  returns NULL if enough memory cannot be allocated */
static fgk_stream* fgk_alloc (xd3_stream *stream /*, int alphabet_size0 */)
{
  usize_t alphabet_size0 = ALPHABET_SIZE;
  fgk_stream *h;

  if ((h = (fgk_stream*) xd3_alloc (stream, 1, sizeof (fgk_stream))) == NULL)
    {
      return NULL;
    }

  h->total_nodes  = (2 * alphabet_size0) - 1;
  h->total_blocks = (2 * h->total_nodes);
  h->alphabet     = (fgk_node*)  xd3_alloc (stream, h->total_nodes,    sizeof (fgk_node));
  h->block_array  = (fgk_block*) xd3_alloc (stream, h->total_blocks,   sizeof (fgk_block));
  h->coded_bits   = (fgk_bit*)   xd3_alloc (stream, alphabet_size0, sizeof (fgk_bit));

  if (h->coded_bits  == NULL ||
      h->alphabet    == NULL ||
      h->block_array == NULL)
    {
      fgk_destroy (stream, h);
      return NULL;
    }

  h->alphabet_size   = alphabet_size0;

  return h;
}

static int fgk_init (xd3_stream *stream, fgk_stream *h, int is_encode)
{
  usize_t ui;
  ssize_t si;

  h->root_node       = h->alphabet;
  h->decode_ptr      = h->root_node;
  h->free_node       = h->alphabet + h->alphabet_size;
  h->remaining_zeros = h->alphabet;
  h->coded_depth     = 0;
  h->zero_freq_count = h->alphabet_size + 2;

  /* after two calls to factor_remaining, zero_freq_count == alphabet_size */
  fgk_factor_remaining(h); /* set ZFE and ZFR */
  fgk_factor_remaining(h); /* set ZFDB according to prev state */

  IF_DEBUG (memset (h->alphabet, 0, sizeof (h->alphabet[0]) * h->total_nodes));

  for (ui = 0; ui < h->total_blocks-1; ui += 1)
    {
      h->block_array[ui].block_freeptr = &h->block_array[ui + 1];
    }

  h->block_array[h->total_blocks - 1].block_freeptr = NULL;
  h->free_block = h->block_array;

  /* Zero frequency nodes are inserted in the first alphabet_size
   * positions, with Value, weight, and a pointer to the next zero
   * frequency node.  */
  for (si = h->alphabet_size - 1; si >= 0; si -= 1)
    {
      fgk_init_node (h->alphabet + si, (usize_t) si, h->alphabet_size);
    }

  return 0;
}

static void fgk_swap_ptrs(fgk_node **one, fgk_node **two)
{
  fgk_node *tmp = *one;
  *one = *two;
  *two = tmp;
}

/* Takes huffman transmitter h and n, the nth elt in the alphabet, and
 * returns the number of required to encode n. */
static int fgk_encode_data (fgk_stream* h, usize_t n)
{
  fgk_node *target_ptr = h->alphabet + n;

  XD3_ASSERT (n < h->alphabet_size);

  h->coded_depth = 0;

  /* First encode the binary representation of the nth remaining
   * zero frequency element in reverse such that bit, which will be
   * encoded from h->coded_depth down to 0 will arrive in increasing
   * order following the tree path.  If there is only one left, it
   * is not neccesary to encode these bits. */
  if (IS_ADAPTIVE && target_ptr->weight == 0)
    {
      unsigned int where, shift;
      int bits;

      where = fgk_find_nth_zero(h, n);
      shift = 1;

      if (h->zero_freq_rem == 0)
	{
	  bits = h->zero_freq_exp;
	}
      else
	{
	  bits = h->zero_freq_exp + 1;
	}

      while (bits > 0)
	{
	  h->coded_bits[h->coded_depth++] = (shift & where) && 1;

	  bits   -= 1;
	  shift <<= 1;
	};

      target_ptr = h->remaining_zeros;
    }

  /* The path from root to node is filled into coded_bits in reverse so
   * that it is encoded in the right order */
  while (target_ptr != h->root_node)
    {
      h->coded_bits[h->coded_depth++] = (target_ptr->parent->right_child == target_ptr);

      target_ptr = target_ptr->parent;
    }

  if (IS_ADAPTIVE)
    {
      fgk_update_tree(h, n);
    }

  return h->coded_depth;
}

/* Should be called as many times as fgk_encode_data returns.
 */
static inline fgk_bit fgk_get_encoded_bit (fgk_stream *h)
{
  XD3_ASSERT (h->coded_depth > 0);

  return h->coded_bits[--h->coded_depth];
}

/* This procedure updates the tree after alphabet[n] has been encoded
 * or decoded.
 */
static void fgk_update_tree (fgk_stream *h, usize_t n)
{
  fgk_node *incr_node;

  if (h->alphabet[n].weight == 0)
    {
      incr_node = fgk_increase_zero_weight (h, n);
    }
  else
    {
      incr_node = h->alphabet + n;
    }

  while (incr_node != h->root_node)
    {
      fgk_move_right (h, incr_node);
      fgk_promote    (h, incr_node);
      incr_node->weight += 1;   /* incr the parent */
      incr_node = incr_node->parent; /* repeat */
    }

  h->root_node->weight += 1;
}

static void fgk_move_right (fgk_stream *h, fgk_node *move_fwd)
{
  fgk_node **fwd_par_ptr, **back_par_ptr;
  fgk_node *move_back, *tmp;

  move_back = move_fwd->my_block->block_leader;

  if (move_fwd         == move_back ||
      move_fwd->parent == move_back ||
      move_fwd->weight == 0)
    {
      return;
    }

  move_back->right->left = move_fwd;

  if (move_fwd->left)
    {
      move_fwd->left->right = move_back;
    }

  tmp = move_fwd->right;
  move_fwd->right = move_back->right;

  if (tmp == move_back)
    {
      move_back->right = move_fwd;
    }
  else
    {
      tmp->left = move_back;
      move_back->right = tmp;
    }

  tmp = move_back->left;
  move_back->left = move_fwd->left;

  if (tmp == move_fwd)
    {
      move_fwd->left = move_back;
    }
  else
    {
      tmp->right = move_fwd;
      move_fwd->left = tmp;
    }

  if (move_fwd->parent->right_child == move_fwd)
    {
      fwd_par_ptr = &move_fwd->parent->right_child;
    }
  else
    {
      fwd_par_ptr = &move_fwd->parent->left_child;
    }

  if (move_back->parent->right_child == move_back)
    {
      back_par_ptr = &move_back->parent->right_child;
    }
  else
    {
      back_par_ptr = &move_back->parent->left_child;
    }

  fgk_swap_ptrs (&move_fwd->parent, &move_back->parent);
  fgk_swap_ptrs (fwd_par_ptr, back_par_ptr);

  move_fwd->my_block->block_leader = move_fwd;
}

/* Shifts node, the leader of its block, into the next block. */
static void fgk_promote (fgk_stream *h, fgk_node *node)
{
  fgk_node *my_left, *my_right;
  fgk_block *cur_block;

  my_right  = node->right;
  my_left   = node->left;
  cur_block = node->my_block;

  if (node->weight == 0)
    {
      return;
    }

  /* if left is right child, parent of remaining zeros case (?), means parent
   * has same weight as right child. */
  if (my_left == node->right_child &&
      node->left_child &&
      node->left_child->weight == 0)
    {
      XD3_ASSERT (node->left_child == h->remaining_zeros);
      XD3_ASSERT (node->right_child->weight == (node->weight+1)); /* child weight was already incremented */
      
      if (node->weight == (my_right->weight - 1) && my_right != h->root_node)
	{
	  fgk_free_block (h, cur_block);
	  node->my_block    = my_right->my_block;
	  my_left->my_block = my_right->my_block;
	}

      return;
    }

  if (my_left == h->remaining_zeros)
    {
      return;
    }

  /* true if not the leftmost node */
  if (my_left->my_block == cur_block)
    {
      my_left->my_block->block_leader = my_left;
    }
  else
    {
      fgk_free_block (h, cur_block);
    }

  /* node->parent != my_right */
  if ((node->weight == (my_right->weight - 1)) && (my_right != h->root_node))
    {
      node->my_block = my_right->my_block;
    }
  else
    {
      node->my_block = fgk_make_block (h, node);
    }
}

/* When an element is seen the first time this is called to remove it from the list of
 * zero weight elements and introduce a new internal node to the tree.  */
static fgk_node* fgk_increase_zero_weight (fgk_stream *h, usize_t n)
{
  fgk_node *this_zero, *new_internal, *zero_ptr;

  this_zero = h->alphabet + n;

  if (h->zero_freq_count == 1)
    {
      /* this is the last one */
      this_zero->right_child = NULL;

      if (this_zero->right->weight == 1)
	{
	  this_zero->my_block = this_zero->right->my_block;
	}
      else
	{
	  this_zero->my_block = fgk_make_block (h, this_zero);
	}

      h->remaining_zeros = NULL;

      return this_zero;
    }

  zero_ptr = h->remaining_zeros;

  new_internal = h->free_node++;

  new_internal->parent      = zero_ptr->parent;
  new_internal->right       = zero_ptr->right;
  new_internal->weight      = 0;
  new_internal->right_child = this_zero;
  new_internal->left        = this_zero;

  if (h->remaining_zeros == h->root_node)
    {
      /* This is the first element to be coded */
      h->root_node           = new_internal;
      this_zero->my_block    = fgk_make_block (h, this_zero);
      new_internal->my_block = fgk_make_block (h, new_internal);
    }
  else
    {
      new_internal->right->left = new_internal;

      if (zero_ptr->parent->right_child == zero_ptr)
	{
	  zero_ptr->parent->right_child = new_internal;
	}
      else
	{
	  zero_ptr->parent->left_child = new_internal;
	}

      if (new_internal->right->weight == 1)
	{
	  new_internal->my_block = new_internal->right->my_block;
	}
      else
	{
	  new_internal->my_block = fgk_make_block (h, new_internal);
	}

      this_zero->my_block = new_internal->my_block;
    }

  fgk_eliminate_zero (h, this_zero);

  new_internal->left_child = h->remaining_zeros;

  this_zero->right       = new_internal;
  this_zero->left        = h->remaining_zeros;
  this_zero->parent      = new_internal;
  this_zero->left_child  = NULL;
  this_zero->right_child = NULL;

  h->remaining_zeros->parent = new_internal;
  h->remaining_zeros->right  = this_zero;

  return this_zero;
}

/* When a zero frequency element is encoded, it is followed by the
 * binary representation of the index into the remaining elements.
 * Sets a cache to the element before it so that it can be removed
 * without calling this procedure again.  */
static unsigned int fgk_find_nth_zero (fgk_stream* h, usize_t n)
{
  fgk_node *target_ptr = h->alphabet + n;
  fgk_node *head_ptr = h->remaining_zeros;
  unsigned int idx = 0;

  while (target_ptr != head_ptr)
    {
      head_ptr = head_ptr->right_child;
      idx += 1;
    }

  return idx;
}

/* Splices node out of the list of zeros. */
static void fgk_eliminate_zero (fgk_stream* h, fgk_node *node)
{
  if (h->zero_freq_count == 1)
    {
      return;
    }

  fgk_factor_remaining(h);

  if (node->left_child == NULL)
    {
      h->remaining_zeros = h->remaining_zeros->right_child;
      h->remaining_zeros->left_child = NULL;
    }
  else if (node->right_child == NULL)
    {
      node->left_child->right_child = NULL;
    }
  else
    {
      node->right_child->left_child = node->left_child;
      node->left_child->right_child = node->right_child;
    }
}

static void fgk_init_node (fgk_node *node, usize_t i, usize_t size)
{
  if (i < size - 1)
    {
      node->right_child = node + 1;
    }
  else
    {
      node->right_child = NULL;
    }

  if (i >= 1)
    {
      node->left_child = node - 1;
    }
  else
    {
      node->left_child = NULL;
    }

  node->weight      = 0;
  node->parent      = NULL;
  node->right = NULL;
  node->left  = NULL;
  node->my_block    = NULL;
}

/* The data structure used is an array of blocks, which are unions of
 * free pointers and huffnode pointers.  free blocks are a linked list
 * of free blocks, the front of which is h->free_block.  The used
 * blocks are pointers to the head of each block.  */
static fgk_block* fgk_make_block (fgk_stream *h, fgk_node* lead)
{
  fgk_block *ret = h->free_block;

  XD3_ASSERT (h->free_block != NULL);

  h->free_block = h->free_block->block_freeptr;

  ret->block_leader = lead;

  return ret;
}

/* Restores the block to the front of the free list. */
static void fgk_free_block (fgk_stream *h, fgk_block *b)
{
  b->block_freeptr = h->free_block;
  h->free_block = b;
}

/* sets zero_freq_count, zero_freq_rem, and zero_freq_exp to satsity
 * the equation given above.  */
static void fgk_factor_remaining (fgk_stream *h)
{
  unsigned int i;

  i = (--h->zero_freq_count);
  h->zero_freq_exp = 0;

  while (i > 1)
    {
      h->zero_freq_exp += 1;
      i >>= 1;
    }

  i = 1 << h->zero_freq_exp;

  h->zero_freq_rem = h->zero_freq_count - i;
}

/* receives a bit at a time and returns true when a complete code has
 * been received.
 */
static inline int fgk_decode_bit (fgk_stream* h, fgk_bit b)
{
  XD3_ASSERT (b == 1 || b == 0);

  if (IS_ADAPTIVE && h->decode_ptr->weight == 0)
    {
      usize_t bitsreq;

      if (h->zero_freq_rem == 0)
	{
	  bitsreq = h->zero_freq_exp;
	}
      else
	{
	  bitsreq = h->zero_freq_exp + 1;
	}

      h->coded_bits[h->coded_depth] = b;
      h->coded_depth += 1;

      return h->coded_depth >= bitsreq;
    }
  else
    {
      if (b)
	{
	  h->decode_ptr = h->decode_ptr->right_child;
	}
      else
	{
	  h->decode_ptr = h->decode_ptr->left_child;
	}

      if (h->decode_ptr->left_child == NULL)
	{
	  /* If the weight is non-zero, finished. */
	  if (h->decode_ptr->weight != 0)
	    {
	      return 1;
	    }

	  /* zero_freq_count is dropping to 0, finished. */
	  return h->zero_freq_count == 1;
	}
      else
	{
	  return 0;
	}
    }
}

static usize_t fgk_nth_zero (fgk_stream* h, usize_t n)
{
  fgk_node *ret = h->remaining_zeros;

  /* ERROR: if during this loop (ret->right_child == NULL) then the
   * encoder's zero count is too high.  Could return an error code
   * now, but is probably unnecessary overhead, since the caller
   * should check integrity anyway. */
  for (; n != 0 && ret->right_child != NULL; n -= 1)
    {
      ret = ret->right_child;
    }

  return (usize_t)(ret - h->alphabet);
}

/* once fgk_decode_bit returns 1, this retrieves an index into the
 * alphabet otherwise this returns 0, indicating more bits are
 * required.
 */
static int fgk_decode_data (fgk_stream* h)
{
  usize_t elt = (usize_t)(h->decode_ptr - h->alphabet);

  if (IS_ADAPTIVE && h->decode_ptr->weight == 0) {
    usize_t i = 0;
    usize_t n = 0;

    if (h->coded_depth > 0) 
      {
	for (; i < h->coded_depth - 1; i += 1)
	  {
	    n |= h->coded_bits[i];
	    n <<= 1;
	  }
      }

    n |= h->coded_bits[i];
    elt = fgk_nth_zero(h, n);
  }

  h->coded_depth = 0;

  if (IS_ADAPTIVE)
    {
      fgk_update_tree(h, elt);
    }

  h->decode_ptr = h->root_node;

  return elt;
}

static void fgk_destroy (xd3_stream *stream,
			 fgk_stream *h)
{
  if (h != NULL)
    {
      xd3_free (stream, h->alphabet);
      xd3_free (stream, h->coded_bits);
      xd3_free (stream, h->block_array);
      xd3_free (stream, h);
    }
}

/*********************************************************************/
/* 			       Xdelta                                */
/*********************************************************************/

static int
xd3_encode_fgk (xd3_stream *stream, fgk_stream *sec_stream, xd3_output *input, xd3_output *output, xd3_sec_cfg *cfg)
{
  bit_state   bstate = BIT_STATE_ENCODE_INIT;
  xd3_output *cur_page;
  int ret;

  /* OPT: quit compression early if it looks bad */
  for (cur_page = input; cur_page; cur_page = cur_page->next_page)
    {
      const uint8_t *inp     = cur_page->base;
      const uint8_t *inp_max = inp + cur_page->next;

      while (inp < inp_max)
	{
	  usize_t bits = fgk_encode_data (sec_stream, *inp++);

	  while (bits--)
	    {
	      if ((ret = xd3_encode_bit (stream, & output, & bstate, fgk_get_encoded_bit (sec_stream)))) { return ret; }
	    }
	}
    }

  return xd3_flush_bits (stream, & output, & bstate);
}

static int
xd3_decode_fgk (xd3_stream     *stream,
		fgk_stream     *sec_stream,
		const uint8_t **input_pos,
		const uint8_t  *const input_max,
		uint8_t       **output_pos,
		const uint8_t  *const output_max)
{
  bit_state bstate;
  uint8_t *output = *output_pos;
  const uint8_t *input = *input_pos;

  for (;;)
    {
      if (input == input_max)
	{
	  stream->msg = "secondary decoder end of input";
	  return XD3_INTERNAL;
	}

      bstate.cur_byte = *input++;

      for (bstate.cur_mask = 1; bstate.cur_mask != 0x100; bstate.cur_mask <<= 1)
	{
	  int done = fgk_decode_bit (sec_stream, (bstate.cur_byte & bstate.cur_mask) ? 1U : 0U);

	  if (! done) { continue; }

	  *output++ = fgk_decode_data (sec_stream);

	  if (output == output_max)
	    {
	      /* During regression testing: */
	      IF_REGRESSION ({
		int ret;
		bstate.cur_mask <<= 1;
		if ((ret = xd3_test_clean_bits (stream, & bstate))) { return ret; }
	      });

	      (*output_pos) = output;
	      (*input_pos) = input;
	      return 0;
	    }
	}
    }
}

#endif /* _XDELTA3_FGK_ */