/*  RetroArch - A frontend for libretro.
 *  Copyright (C) 2010-2014 - Hans-Kristian Arntzen
 *  Copyright (C) 2011-2015 - Daniel De Matteis
 *  Copyright (C) 2014-2015 - Alfred Agrell
 *
 *  RetroArch 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 Found-
 *  ation, either version 3 of the License, or (at your option) any later version.
 *
 *  RetroArch 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 RetroArch.
 *  If not, see <http://www.gnu.org/licenses/>.
 */

#define __STDC_LIMIT_MACROS
#include "rewind.h"
#include "performance.h"
#include <stdlib.h>
#include <string.h>
#include <retro_inline.h>
#include "dynamic.h"
#include "general.h"
#include "msg_hash.h"

#ifndef UINT16_MAX
#define UINT16_MAX 0xffff
#endif

#ifndef UINT32_MAX
#define UINT32_MAX 0xffffffffu
#endif

#undef CPU_X86
#if defined(__x86_64__) || defined(__i386__) || defined(__i486__) || defined(__i686__)
#define CPU_X86
#endif

/* Other arches SIGBUS (usually) on unaligned accesses. */
#ifndef CPU_X86
#define NO_UNALIGNED_MEM
#endif

/* Format per frame (pseudocode): */
#if 0
size nextstart;
repeat {
   uint16 numchanged; /* everything is counted in units of uint16 */
   if (numchanged)
   {
      uint16 numunchanged; /* skip these before handling numchanged */
      uint16[numchanged] changeddata;
   }
   else
   {
      uint32 numunchanged;
      if (!numunchanged)
         break;
   }
}
size thisstart;
#endif

size_t state_manager_raw_maxsize(size_t uncomp)
{
   /* bytes covered by a compressed block */
   const int maxcblkcover = UINT16_MAX * sizeof(uint16_t);
   /* uncompressed size, rounded to 16 bits */
   size_t uncomp16        = (uncomp + sizeof(uint16_t) - 1) & ~sizeof(uint16_t);
   /* number of blocks */
   size_t maxcblks        = (uncomp + maxcblkcover - 1) / maxcblkcover;
   return uncomp16 + maxcblks * sizeof(uint16_t) * 2 /* two u16 overhead per block */ + sizeof(uint16_t) *
      3; /* three u16 to end it */
}

void *state_manager_raw_alloc(size_t len, uint16_t uniq)
{
   size_t  len16 = (len + sizeof(uint16_t) - 1) & ~sizeof(uint16_t);

   uint16_t *ret = (uint16_t*)calloc(len16 + sizeof(uint16_t) * 4 + 16, 1);

   /* Force in a different byte at the end, so we don't need to check 
    * bounds in the innermost loop (it's expensive).
    *
    * There is also a large amount of data that's the same, to stop 
    * the other scan.
    *
    * There is also some padding at the end. This is so we don't 
    * read outside the buffer end if we're reading in large blocks;
    *
    * It doesn't make any difference to us, but sacrificing 16 bytes to get 
    * Valgrind happy is worth it. */
   ret[len16/sizeof(uint16_t) + 3] = uniq;

   return ret;
}

#if __SSE2__
#if defined(__GNUC__)
static INLINE int compat_ctz(unsigned x)
{
   return __builtin_ctz(x);
}
#else

/* Only checks at nibble granularity, 
 * because that's what we need. */

static INLINE int compat_ctz(unsigned x)
{
   if (x & 0x000f)
      return 0;
   if (x & 0x00f0)
      return 4;
   if (x & 0x0f00)
      return 8;
   if (x & 0xf000)
      return 12;
   return 16;
}
#endif

#include <emmintrin.h>
/* There's no equivalent in libc, you'd think so ...
 * std::mismatch exists, but it's not optimized at all. */

static INLINE size_t find_change(const uint16_t *a, const uint16_t *b)
{
   const __m128i *a128 = (const __m128i*)a;
   const __m128i *b128 = (const __m128i*)b;
   
   for (;;)
   {
      __m128i v0    = _mm_loadu_si128(a128);
      __m128i v1    = _mm_loadu_si128(b128);
      __m128i c     = _mm_cmpeq_epi32(v0, v1);
      uint32_t mask = _mm_movemask_epi8(c);

      if (mask != 0xffff) /* Something has changed, figure out where. */
      {
         size_t ret = (((uint8_t*)a128 - (uint8_t*)a) |
               (compat_ctz(~mask))) >> 1;
         return ret | (a[ret] == b[ret]);
      }

      a128++;
      b128++;
   }
}
#else
static INLINE size_t find_change(const uint16_t *a, const uint16_t *b)
{
   const uint16_t *a_org = a;
#ifdef NO_UNALIGNED_MEM
   while (((uintptr_t)a & (sizeof(size_t) - 1)) && *a == *b)
   {
      a++;
      b++;
   }
   if (*a == *b)
#endif
   {
      const size_t *a_big = (const size_t*)a;
      const size_t *b_big = (const size_t*)b;
      
      while (*a_big == *b_big)
      {
         a_big++;
         b_big++;
      }
      a = (const uint16_t*)a_big;
      b = (const uint16_t*)b_big;
      
      while (*a == *b)
      {
         a++;
         b++;
      }
   }
   return a - a_org;
}
#endif

static INLINE size_t find_same(const uint16_t *a, const uint16_t *b)
{
   const uint16_t *a_org = a;
#ifdef NO_UNALIGNED_MEM
   if (((uintptr_t)a & (sizeof(uint32_t) - 1)) && *a != *b)
   {
      a++;
      b++;
   }
   if (*a != *b)
#endif
   {
      /* With this, it's random whether two consecutive identical
       * words are caught.
       *
       * Luckily, compression rate is the same for both cases, and 
       * three is always caught.
       *
       * (We prefer to miss two-word blocks, anyways; fewer iterations 
       * of the outer loop, as well as in the decompressor.) */
      const uint32_t *a_big = (const uint32_t*)a;
      const uint32_t *b_big = (const uint32_t*)b;
      
      while (*a_big != *b_big)
      {
         a_big++;
         b_big++;
      }
      a = (const uint16_t*)a_big;
      b = (const uint16_t*)b_big;
      
      if (a != a_org && a[-1] == b[-1])
      {
         a--;
         b--;
      }
   }
   return a - a_org;
}

size_t state_manager_raw_compress(const void *src,
      const void *dst, size_t len, void *patch)
{
   const uint16_t  *old16 = (const uint16_t*)src;
   const uint16_t  *new16 = (const uint16_t*)dst;
   uint16_t *compressed16 = (uint16_t*)patch;
   size_t          num16s = (len + sizeof(uint16_t) - 1) 
      / sizeof(uint16_t);
   
   while (num16s)
   {
      size_t i, changed;
      size_t skip = find_change(old16, new16);
   
      if (skip >= num16s)
         break;
   
      old16 += skip;
      new16 += skip;
      num16s -= skip;
   
      if (skip > UINT16_MAX)
      {
         if (skip > UINT32_MAX)
         {
            /* This will make it scan the entire thing again, 
             * but it only hits on 8GB unchanged data anyways,
             * and if you're doing that, you've got bigger problems. */
            skip = UINT32_MAX;
         }
         *compressed16++ = 0;
         *compressed16++ = skip;
         *compressed16++ = skip >> 16;
         skip = 0;
         continue;
      }
   
      changed = find_same(old16, new16);
      if (changed > UINT16_MAX)
         changed = UINT16_MAX;
   
      *compressed16++ = changed;
      *compressed16++ = skip;
   
      for (i = 0; i < changed; i++)
         compressed16[i] = old16[i];
   
      old16 += changed;
      new16 += changed;
      num16s -= changed;
      compressed16 += changed;
   }
   
   compressed16[0] = 0;
   compressed16[1] = 0;
   compressed16[2] = 0;
   
   return (uint8_t*)(compressed16+3) - (uint8_t*)patch;
}

void state_manager_raw_decompress(const void *patch,
      size_t patchlen, void *data, size_t datalen)
{
   uint16_t         *out16 = (uint16_t*)data;
   const uint16_t *patch16 = (const uint16_t*)patch;
   
   (void)patchlen;
   (void)datalen;
   
   for (;;)
   {
      uint16_t i;
      uint16_t numchanged = *(patch16++);

      if (numchanged)
      {
         out16 += *patch16++;

         /* We could do memcpy, but it seems that memcpy has a 
          * constant-per-call overhead that actually shows up.
          *
          * Our average size in here seems to be 8 or something.
          * Therefore, we do something with lower overhead. */
         for (i = 0; i < numchanged; i++)
            out16[i] = patch16[i];

         patch16 += numchanged;
         out16 += numchanged;
      }
      else
      {
         uint32_t numunchanged = patch16[0] | (patch16[1] << 16);

         if (!numunchanged)
            break;
         patch16 += 2;
         out16 += numunchanged;
      }
   }
}

/* The start offsets point to 'nextstart' of any given compressed frame.
 * Each uint16 is stored native endian; anything that claims any other 
 * endianness refers to the endianness of this specific item.
 * The uint32 is stored little endian.
 *
 * Each size value is stored native endian if alignment is not enforced; 
 * if it is, they're little endian.
 *
 * The start of the buffer contains a size pointing to the end of the 
 * buffer; the end points to its start.
 *
 * Wrapping is handled by returning to the start of the buffer if the 
 * compressed data could potentially hit the edge;
 *
 * if the compressed data could potentially overwrite the tail pointer, 
 * the tail retreats until it can no longer collide.
 *
 * This means that on average, ~2 * maxcompsize is 
 * unused at any given moment. */


/* These are called very few constant times per frame, 
 * keep it as simple as possible. */
static INLINE void write_size_t(void *ptr, size_t val)
{
   memcpy(ptr, &val, sizeof(val));
}

static INLINE size_t read_size_t(const void *ptr)
{
   size_t ret;

   memcpy(&ret, ptr, sizeof(ret));
   return ret;
}

struct state_manager
{
   uint8_t *data;
   size_t capacity;
   /* Reading and writing is done here here. */
   uint8_t *head;
   /* If head comes close to this, discard a frame. */
   uint8_t *tail;

   uint8_t *thisblock;
   uint8_t *nextblock;

   /* This one is rounded up from reset::blocksize. */
   size_t blocksize;

   /* size_t + (blocksize + 131071) / 131072 * 
    * (blocksize + u16 + u16) + u16 + u32 + size_t
    * (yes, the math is a bit ugly). */
   size_t maxcompsize;

   unsigned entries;
   bool thisblock_valid;
};

state_manager_t *state_manager_new(size_t state_size, size_t buffer_size)
{
   state_manager_t *state = (state_manager_t*)calloc(1, sizeof(*state));

   if (!state)
      return NULL;

   state->blocksize   = (state_size + sizeof(uint16_t) - 1) & ~sizeof(uint16_t);
   /* the compressed data is surrounded by pointers to the other side */
   state->maxcompsize = state_manager_raw_maxsize(state_size) + sizeof(size_t) * 2;
   state->data        = (uint8_t*)malloc(buffer_size);

   state->thisblock   = (uint8_t*)state_manager_raw_alloc(state_size, 0);
   state->nextblock   = (uint8_t*)state_manager_raw_alloc(state_size, 1);
   if (!state->data || !state->thisblock || !state->nextblock)
      goto error;

   state->capacity = buffer_size;

   state->head = state->data + sizeof(size_t);
   state->tail = state->data + sizeof(size_t);

   return state;

error:
   state_manager_free(state);
   return NULL;
}

void state_manager_free(state_manager_t *state)
{
   if (!state)
      return;

   free(state->data);
   free(state->thisblock);
   free(state->nextblock);
   free(state);
}

bool state_manager_pop(state_manager_t *state, const void **data)
{
   size_t start;
   uint8_t *out                 = NULL;
   const uint8_t *compressed    = NULL;

   *data = NULL;

   if (state->thisblock_valid)
   {
      state->thisblock_valid = false;
      state->entries--;
      *data = state->thisblock;
      return true;
   }

   if (state->head == state->tail)
      return false;

   start = read_size_t(state->head - sizeof(size_t));
   state->head = state->data + start;

   compressed = state->data + start + sizeof(size_t);
   out = state->thisblock;

   state_manager_raw_decompress(compressed, state->maxcompsize, out, state->blocksize);

   state->entries--;
   *data = state->thisblock;
   return true;
}

void state_manager_push_where(state_manager_t *state, void **data)
{
   /* We need to ensure we have an uncompressed copy of the last
    * pushed state, or we could end up applying a 'patch' to wrong 
    * savestate, and that'd blow up rather quickly. */

   if (!state->thisblock_valid) 
   {
      const void *ignored;
      if (state_manager_pop(state, &ignored))
      {
         state->thisblock_valid = true;
         state->entries++;
      }
   }
   
   *data = state->nextblock;
}

void state_manager_push_do(state_manager_t *state)
{
   uint8_t *swap = NULL;

   if (state->thisblock_valid)
   {
      const uint8_t *oldb, *newb;
      uint8_t *compressed;
      size_t headpos, tailpos, remaining;
      if (state->capacity < sizeof(size_t) + state->maxcompsize)
         return;

recheckcapacity:;

      headpos = state->head - state->data;
      tailpos = state->tail - state->data;
      remaining = (tailpos + state->capacity -
            sizeof(size_t) - headpos - 1) % state->capacity + 1;

      if (remaining <= state->maxcompsize)
      {
         state->tail = state->data + read_size_t(state->tail);
         state->entries--;
         goto recheckcapacity;
      }

      RARCH_PERFORMANCE_INIT(gen_deltas);
      RARCH_PERFORMANCE_START(gen_deltas);

      oldb = state->thisblock;
      newb = state->nextblock;
      compressed = state->head + sizeof(size_t);

      compressed += state_manager_raw_compress(oldb, newb, state->blocksize, compressed);

      if (compressed - state->data + state->maxcompsize > state->capacity)
      {
         compressed = state->data;
         if (state->tail == state->data + sizeof(size_t))
            state->tail = state->data + read_size_t(state->tail);
      }
      write_size_t(compressed, state->head-state->data);
      compressed += sizeof(size_t);
      write_size_t(state->head, compressed-state->data);
      state->head = compressed;

      RARCH_PERFORMANCE_STOP(gen_deltas);
   }
   else
      state->thisblock_valid = true;

   swap             = state->thisblock;
   state->thisblock = state->nextblock;
   state->nextblock = swap;

   state->entries++;
}

void state_manager_capacity(state_manager_t *state,
      unsigned *entries, size_t *bytes, bool *full)
{
   size_t headpos   = state->head - state->data;
   size_t tailpos   = state->tail - state->data;
   size_t remaining = (tailpos + state->capacity -
         sizeof(size_t) - headpos - 1) % state->capacity + 1;

   if (entries)
      *entries = state->entries;
   if (bytes)
      *bytes = state->capacity-remaining;
   if (full)
      *full = remaining <= state->maxcompsize * 2;
}

void init_rewind(void)
{
   void *state          = NULL;
   driver_t *driver     = driver_get_ptr();
   settings_t *settings = config_get_ptr();
   global_t *global     = global_get_ptr();

   (void)driver;

#ifdef HAVE_NETPLAY
   if (driver->netplay_data)
      return;
#endif

   if (!settings->rewind_enable || global->rewind.state)
      return;

   if (audio_driver_has_callback())
   {
      RARCH_ERR("%s.\n", msg_hash_to_str(MSG_REWIND_INIT_FAILED));
      return;
   }

   global->rewind.size = pretro_serialize_size();

   if (!global->rewind.size)
   {
      RARCH_ERR("%s.\n",
            msg_hash_to_str(MSG_REWIND_INIT_FAILED_THREADED_AUDIO));
      return;
   }

   RARCH_LOG("%s: %u MB\n",
         msg_hash_to_str(MSG_REWIND_INIT),
         (unsigned)(settings->rewind_buffer_size / 1000000));

   global->rewind.state = state_manager_new(global->rewind.size,
         settings->rewind_buffer_size);

   if (!global->rewind.state)
      RARCH_WARN("%s.\n", msg_hash_to_str(MSG_REWIND_INIT_FAILED));

   state_manager_push_where(global->rewind.state, &state);
   pretro_serialize(state, global->rewind.size);
   state_manager_push_do(global->rewind.state);
}