/** @file

  A brief file description

  @section license License

  Licensed to the Apache Software Foundation (ASF) under one
  or more contributor license agreements.  See the NOTICE file
  distributed with this work for additional information
  regarding copyright ownership.  The ASF licenses this file
  to you under the Apache License, Version 2.0 (the
  "License"); you may not use this file except in compliance
  with the License.  You may obtain a copy of the License at

      http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
 */

#include "HuffmanCodec.h"
#include "tscore/ink_platform.h"
#include "tscore/ink_memory.h"
#include "tscore/ink_defs.h"

struct huffman_entry {
  uint32_t code_as_hex;
  uint32_t bit_len;
};

static const huffman_entry huffman_table[] = {
  {0x1ff8, 13},    {0x7fffd8, 23},   {0xfffffe2, 28}, {0xfffffe3, 28},  {0xfffffe4, 28}, {0xfffffe5, 28}, {0xfffffe6, 28},
  {0xfffffe7, 28}, {0xfffffe8, 28},  {0xffffea, 24},  {0x3ffffffc, 30}, {0xfffffe9, 28}, {0xfffffea, 28}, {0x3ffffffd, 30},
  {0xfffffeb, 28}, {0xfffffec, 28},  {0xfffffed, 28}, {0xfffffee, 28},  {0xfffffef, 28}, {0xffffff0, 28}, {0xffffff1, 28},
  {0xffffff2, 28}, {0x3ffffffe, 30}, {0xffffff3, 28}, {0xffffff4, 28},  {0xffffff5, 28}, {0xffffff6, 28}, {0xffffff7, 28},
  {0xffffff8, 28}, {0xffffff9, 28},  {0xffffffa, 28}, {0xffffffb, 28},  {0x14, 6},       {0x3f8, 10},     {0x3f9, 10},
  {0xffa, 12},     {0x1ff9, 13},     {0x15, 6},       {0xf8, 8},        {0x7fa, 11},     {0x3fa, 10},     {0x3fb, 10},
  {0xf9, 8},       {0x7fb, 11},      {0xfa, 8},       {0x16, 6},        {0x17, 6},       {0x18, 6},       {0x0, 5},
  {0x1, 5},        {0x2, 5},         {0x19, 6},       {0x1a, 6},        {0x1b, 6},       {0x1c, 6},       {0x1d, 6},
  {0x1e, 6},       {0x1f, 6},        {0x5c, 7},       {0xfb, 8},        {0x7ffc, 15},    {0x20, 6},       {0xffb, 12},
  {0x3fc, 10},     {0x1ffa, 13},     {0x21, 6},       {0x5d, 7},        {0x5e, 7},       {0x5f, 7},       {0x60, 7},
  {0x61, 7},       {0x62, 7},        {0x63, 7},       {0x64, 7},        {0x65, 7},       {0x66, 7},       {0x67, 7},
  {0x68, 7},       {0x69, 7},        {0x6a, 7},       {0x6b, 7},        {0x6c, 7},       {0x6d, 7},       {0x6e, 7},
  {0x6f, 7},       {0x70, 7},        {0x71, 7},       {0x72, 7},        {0xfc, 8},       {0x73, 7},       {0xfd, 8},
  {0x1ffb, 13},    {0x7fff0, 19},    {0x1ffc, 13},    {0x3ffc, 14},     {0x22, 6},       {0x7ffd, 15},    {0x3, 5},
  {0x23, 6},       {0x4, 5},         {0x24, 6},       {0x5, 5},         {0x25, 6},       {0x26, 6},       {0x27, 6},
  {0x6, 5},        {0x74, 7},        {0x75, 7},       {0x28, 6},        {0x29, 6},       {0x2a, 6},       {0x7, 5},
  {0x2b, 6},       {0x76, 7},        {0x2c, 6},       {0x8, 5},         {0x9, 5},        {0x2d, 6},       {0x77, 7},
  {0x78, 7},       {0x79, 7},        {0x7a, 7},       {0x7b, 7},        {0x7ffe, 15},    {0x7fc, 11},     {0x3ffd, 14},
  {0x1ffd, 13},    {0xffffffc, 28},  {0xfffe6, 20},   {0x3fffd2, 22},   {0xfffe7, 20},   {0xfffe8, 20},   {0x3fffd3, 22},
  {0x3fffd4, 22},  {0x3fffd5, 22},   {0x7fffd9, 23},  {0x3fffd6, 22},   {0x7fffda, 23},  {0x7fffdb, 23},  {0x7fffdc, 23},
  {0x7fffdd, 23},  {0x7fffde, 23},   {0xffffeb, 24},  {0x7fffdf, 23},   {0xffffec, 24},  {0xffffed, 24},  {0x3fffd7, 22},
  {0x7fffe0, 23},  {0xffffee, 24},   {0x7fffe1, 23},  {0x7fffe2, 23},   {0x7fffe3, 23},  {0x7fffe4, 23},  {0x1fffdc, 21},
  {0x3fffd8, 22},  {0x7fffe5, 23},   {0x3fffd9, 22},  {0x7fffe6, 23},   {0x7fffe7, 23},  {0xffffef, 24},  {0x3fffda, 22},
  {0x1fffdd, 21},  {0xfffe9, 20},    {0x3fffdb, 22},  {0x3fffdc, 22},   {0x7fffe8, 23},  {0x7fffe9, 23},  {0x1fffde, 21},
  {0x7fffea, 23},  {0x3fffdd, 22},   {0x3fffde, 22},  {0xfffff0, 24},   {0x1fffdf, 21},  {0x3fffdf, 22},  {0x7fffeb, 23},
  {0x7fffec, 23},  {0x1fffe0, 21},   {0x1fffe1, 21},  {0x3fffe0, 22},   {0x1fffe2, 21},  {0x7fffed, 23},  {0x3fffe1, 22},
  {0x7fffee, 23},  {0x7fffef, 23},   {0xfffea, 20},   {0x3fffe2, 22},   {0x3fffe3, 22},  {0x3fffe4, 22},  {0x7ffff0, 23},
  {0x3fffe5, 22},  {0x3fffe6, 22},   {0x7ffff1, 23},  {0x3ffffe0, 26},  {0x3ffffe1, 26}, {0xfffeb, 20},   {0x7fff1, 19},
  {0x3fffe7, 22},  {0x7ffff2, 23},   {0x3fffe8, 22},  {0x1ffffec, 25},  {0x3ffffe2, 26}, {0x3ffffe3, 26}, {0x3ffffe4, 26},
  {0x7ffffde, 27}, {0x7ffffdf, 27},  {0x3ffffe5, 26}, {0xfffff1, 24},   {0x1ffffed, 25}, {0x7fff2, 19},   {0x1fffe3, 21},
  {0x3ffffe6, 26}, {0x7ffffe0, 27},  {0x7ffffe1, 27}, {0x3ffffe7, 26},  {0x7ffffe2, 27}, {0xfffff2, 24},  {0x1fffe4, 21},
  {0x1fffe5, 21},  {0x3ffffe8, 26},  {0x3ffffe9, 26}, {0xffffffd, 28},  {0x7ffffe3, 27}, {0x7ffffe4, 27}, {0x7ffffe5, 27},
  {0xfffec, 20},   {0xfffff3, 24},   {0xfffed, 20},   {0x1fffe6, 21},   {0x3fffe9, 22},  {0x1fffe7, 21},  {0x1fffe8, 21},
  {0x7ffff3, 23},  {0x3fffea, 22},   {0x3fffeb, 22},  {0x1ffffee, 25},  {0x1ffffef, 25}, {0xfffff4, 24},  {0xfffff5, 24},
  {0x3ffffea, 26}, {0x7ffff4, 23},   {0x3ffffeb, 26}, {0x7ffffe6, 27},  {0x3ffffec, 26}, {0x3ffffed, 26}, {0x7ffffe7, 27},
  {0x7ffffe8, 27}, {0x7ffffe9, 27},  {0x7ffffea, 27}, {0x7ffffeb, 27},  {0xffffffe, 28}, {0x7ffffec, 27}, {0x7ffffed, 27},
  {0x7ffffee, 27}, {0x7ffffef, 27},  {0x7fffff0, 27}, {0x3ffffee, 26},  {0x3fffffff, 30}};

using Node = struct node {
  node *left, *right;
  char ascii_code;
  bool leaf_node;
};

Node *HUFFMAN_TREE_ROOT;

static Node *
make_huffman_tree_node()
{
  Node *n       = static_cast<Node *>(ats_malloc(sizeof(Node)));
  n->left       = nullptr;
  n->right      = nullptr;
  n->ascii_code = '\0';
  n->leaf_node  = false;
  return n;
}

static Node *
make_huffman_tree()
{
  Node *root = make_huffman_tree_node();

  // insert leafs for each ascii code
  for (unsigned i = 0; i < countof(huffman_table); i++) {
    uint32_t bit_len = huffman_table[i].bit_len;
    Node *current    = root;

    while (bit_len > 0) {
      if (huffman_table[i].code_as_hex & (1 << (bit_len - 1))) {
        if (!current->right) {
          current->right = make_huffman_tree_node();
        }
        current = current->right;
      } else {
        if (!current->left) {
          current->left = make_huffman_tree_node();
        }
        current = current->left;
      }
      bit_len--;
    }
    current->ascii_code = i;
    current->leaf_node  = true;
  }

  return root;
}

static void
free_huffman_tree(Node *node)
{
  if (node->left) {
    free_huffman_tree(node->left);
  }
  if (node->right) {
    free_huffman_tree(node->right);
  }

  ats_free(node);
}

void
hpack_huffman_init()
{
  if (!HUFFMAN_TREE_ROOT) {
    HUFFMAN_TREE_ROOT = make_huffman_tree();
  }
}

void
hpack_huffman_fin()
{
  if (HUFFMAN_TREE_ROOT) {
    free_huffman_tree(HUFFMAN_TREE_ROOT);
  }
}

#define MAX_HUFFMAN_CODE_LEN 30
#define EOS 0x3fffffff

int64_t
huffman_decode(char *dst_start, const uint8_t *src, uint32_t src_len)
{
  char *dst_end      = dst_start;
  uint8_t shift      = 7;
  Node *current      = HUFFMAN_TREE_ROOT;
  int nbits          = 0;
  uint32_t curr_bits = 0;

  while (src_len) {
    if (nbits > 0) {
      curr_bits <<= 1;
    }
    if (*src & (1 << shift)) {
      curr_bits |= 1;
      current = current->right;
    } else {
      current = current->left;
    }
    ++nbits;

    if (current->leaf_node == true) {
      if (curr_bits == EOS) {
        return -1;
      }
      nbits     = 0;
      curr_bits = 0;
      *dst_end  = current->ascii_code;
      ++dst_end;
      current = HUFFMAN_TREE_ROOT;
    }

    if (shift) {
      --shift;
    } else {
      shift = 7;
      ++src;
      --src_len;
    }

    if (nbits > MAX_HUFFMAN_CODE_LEN) {
      return -1;
    }
  }

  if (nbits > 7) {
    return -1;
  }

  // Padding bits must be a prefix of EOS
  uint8_t mask = (1 << nbits) - 1;
  if ((mask & curr_bits) != mask) {
    return -1;
  }

  return dst_end - dst_start;
}

uint8_t *
huffman_encode_append(uint8_t *dst, uint32_t src, int n = 0)
{
  for (int j = 3; j >= n; --j) {
    *dst++ = ((src >> (8 * j)) & 255);
  }
  return dst;
}

int64_t
huffman_encode(uint8_t *dst_start, const uint8_t *src, uint32_t src_len)
{
  uint8_t *dst = dst_start;
  // NOTE: The maximum length of Huffman Code is 30, thus using uint32_t as buffer.
  uint32_t buf         = 0;
  uint32_t remain_bits = 32;

  for (uint32_t i = 0; i < src_len; ++i) {
    const uint32_t hex     = huffman_table[src[i]].code_as_hex;
    const uint32_t bit_len = huffman_table[src[i]].bit_len;

    if (remain_bits > bit_len) {
      remain_bits = remain_bits - bit_len;
      buf |= hex << remain_bits;
    } else if (remain_bits == bit_len) {
      buf |= hex;
      dst         = huffman_encode_append(dst, buf);
      remain_bits = 32;
      buf         = 0;
    } else {
      buf |= hex >> (bit_len - remain_bits);
      dst         = huffman_encode_append(dst, buf);
      remain_bits = (32 - (bit_len - remain_bits));
      buf         = hex << remain_bits;
    }
  }

  dst = huffman_encode_append(dst, buf, remain_bits / 8);

  // NOTE: Add padding w/ EOS
  uint32_t pad_len = remain_bits % 8;
  if (pad_len) {
    *(dst - 1) |= 0xff >> (8 - pad_len);
  }

  return dst - dst_start;
}