/*
 * This file Copyright (C) Mnemosyne LLC
 *
 * This file is licensed by the GPL version 2. Works owned by the
 * Transmission project are granted a special exemption to clause 2 (b)
 * so that the bulk of its code can remain under the MIT license.
 * This exemption does not extend to derived works not owned by
 * the Transmission project.
 *
 * $Id$
 */

#include <string.h> /* memcmp () */
#include <stdlib.h> /* free () */

#ifdef HAVE_POSIX_FADVISE
 #define _XOPEN_SOURCE 600
 #include <fcntl.h> /* posix_fadvise () */
#endif

#include <openssl/sha.h>

#include "transmission.h"
#include "completion.h"
#include "fdlimit.h"
#include "list.h"
#include "platform.h" /* tr_lock () */
#include "torrent.h"
#include "utils.h" /* tr_valloc (), tr_free () */
#include "verify.h"

/***
****
***/

enum
{
  MSEC_TO_SLEEP_PER_SECOND_DURING_VERIFY = 100
};

static bool
verifyTorrent (tr_torrent * tor, bool * stopFlag)
{
  time_t end;
  SHA_CTX sha;
  int fd = -1;
  int64_t filePos = 0;
  bool changed = 0;
  bool hadPiece = 0;
  time_t lastSleptAt = 0;
  uint32_t piecePos = 0;
  tr_file_index_t fileIndex = 0;
  tr_file_index_t prevFileIndex = !fileIndex;
  tr_piece_index_t pieceIndex = 0;
  const time_t begin = tr_time ();
  const size_t buflen = 1024 * 128; /* 128 KiB buffer */
  uint8_t * buffer = tr_valloc (buflen);

  SHA1_Init (&sha);

  tr_tordbg (tor, "%s", "verifying torrent...");
  tr_torrentSetChecked (tor, 0);
  while (!*stopFlag && (pieceIndex < tor->info.pieceCount))
    {
      uint32_t leftInPiece;
      uint32_t bytesThisPass;
      uint64_t leftInFile;
      const tr_file * file = &tor->info.files[fileIndex];

      /* if we're starting a new piece... */
      if (piecePos == 0)
        hadPiece = tr_cpPieceIsComplete (&tor->completion, pieceIndex);

      /* if we're starting a new file... */
      if (!filePos && (fd<0) && (fileIndex!=prevFileIndex))
        {
          char * filename = tr_torrentFindFile (tor, fileIndex);
          fd = filename == NULL ? -1 : tr_open_file_for_scanning (filename);
          tr_free (filename);
          prevFileIndex = fileIndex;
        }

      /* figure out how much we can read this pass */
      leftInPiece = tr_torPieceCountBytes (tor, pieceIndex) - piecePos;
      leftInFile = file->length - filePos;
      bytesThisPass = MIN (leftInFile, leftInPiece);
      bytesThisPass = MIN (bytesThisPass, buflen);

      /* read a bit */
      if (fd >= 0)
        {
          const ssize_t numRead = tr_pread (fd, buffer, bytesThisPass, filePos);
          if (numRead > 0)
            {
              bytesThisPass = (uint32_t)numRead;
              SHA1_Update (&sha, buffer, bytesThisPass);
#if defined HAVE_POSIX_FADVISE && defined POSIX_FADV_DONTNEED
              posix_fadvise (fd, filePos, bytesThisPass, POSIX_FADV_DONTNEED);
#endif
            }
        }

      /* move our offsets */
      leftInPiece -= bytesThisPass;
      leftInFile -= bytesThisPass;
      piecePos += bytesThisPass;
      filePos += bytesThisPass;

      /* if we're finishing a piece... */
      if (leftInPiece == 0)
        {
          time_t now;
          bool hasPiece;
          uint8_t hash[SHA_DIGEST_LENGTH];

          SHA1_Final (hash, &sha);
          hasPiece = !memcmp (hash, tor->info.pieces[pieceIndex].hash, SHA_DIGEST_LENGTH);

          if (hasPiece || hadPiece)
            {
              tr_torrentSetHasPiece (tor, pieceIndex, hasPiece);
              changed |= hasPiece != hadPiece;
            }

          tr_torrentSetPieceChecked (tor, pieceIndex);
          now = tr_time ();
          tor->anyDate = now;

          /* sleeping even just a few msec per second goes a long
           * way towards reducing IO load... */
          if (lastSleptAt != now)
            {
              lastSleptAt = now;
              tr_wait_msec (MSEC_TO_SLEEP_PER_SECOND_DURING_VERIFY);
            }

          SHA1_Init (&sha);
          pieceIndex++;
          piecePos = 0;
        }

      /* if we're finishing a file... */
      if (leftInFile == 0)
        {
          if (fd >= 0)
            {
              tr_close_file (fd);
              fd = -1;
            }
          fileIndex++;
          filePos = 0;
        }
    }

  /* cleanup */
  if (fd >= 0)
    tr_close_file (fd);
  free (buffer);

  /* stopwatch */
  end = tr_time ();
  tr_tordbg (tor, "Verification is done. It took %d seconds to verify %"PRIu64" bytes (%"PRIu64" bytes per second)",
             (int)(end-begin), tor->info.totalSize,
             (uint64_t)(tor->info.totalSize/ (1+ (end-begin))));

  return changed;
}

/***
****
***/

struct verify_node
{
  tr_torrent *         torrent;
  tr_verify_done_cb    verify_done_cb;
  uint64_t             current_size;
};

static void
fireCheckDone (tr_torrent * tor, tr_verify_done_cb verify_done_cb)
{
  assert (tr_isTorrent (tor));

  if (verify_done_cb)
    verify_done_cb (tor);
}

static struct verify_node currentNode;
static tr_list * verifyList = NULL;
static tr_thread * verifyThread = NULL;
static bool stopCurrent = false;

static tr_lock*
getVerifyLock (void)
{
  static tr_lock * lock = NULL;

  if (lock == NULL)
    lock = tr_lockNew ();

  return lock;
}

static void
verifyThreadFunc (void * unused UNUSED)
{
  for (;;)
    {
      int changed = 0;
      tr_torrent * tor;
      struct verify_node * node;

      tr_lockLock (getVerifyLock ());
      stopCurrent = false;
      node = (struct verify_node*) verifyList ? verifyList->data : NULL;
      if (node == NULL)
        {
          currentNode.torrent = NULL;
          break;
        }

      currentNode = *node;
      tor = currentNode.torrent;
      tr_list_remove_data (&verifyList, node);
      tr_free (node);
      tr_lockUnlock (getVerifyLock ());

      tr_torinf (tor, "%s", _("Verifying torrent"));
      tr_torrentSetVerifyState (tor, TR_VERIFY_NOW);
      changed = verifyTorrent (tor, &stopCurrent);
      tr_torrentSetVerifyState (tor, TR_VERIFY_NONE);
      assert (tr_isTorrent (tor));

      if (!stopCurrent)
        {
          if (changed)
            tr_torrentSetDirty (tor);
          fireCheckDone (tor, currentNode.verify_done_cb);
        }
    }

  verifyThread = NULL;
  tr_lockUnlock (getVerifyLock ());
}

static int
compareVerifyByPriorityAndSize (const void * va, const void * vb)
{
  const struct verify_node * a = va;
  const struct verify_node * b = vb;

  /* higher priority comes before lower priority */
  const tr_priority_t pa = tr_torrentGetPriority (a->torrent);
  const tr_priority_t pb = tr_torrentGetPriority (b->torrent);
  if (pa != pb)
    return pa > pb ? -1 : 1;

  /* smaller torrents come before larger ones because they verify faster */
  if (a->current_size < b->current_size)
    return -1;
  if (a->current_size > b->current_size)
    return  1;
  return 0;
}

void
tr_verifyAdd (tr_torrent * tor, tr_verify_done_cb verify_done_cb)
{
  struct verify_node * node;

  assert (tr_isTorrent (tor));
  tr_torinf (tor, "%s", _("Queued for verification"));

  node = tr_new (struct verify_node, 1);
  node->torrent = tor;
  node->verify_done_cb = verify_done_cb;
  node->current_size = tr_torrentGetCurrentSizeOnDisk (tor);

  tr_lockLock (getVerifyLock ());
  tr_torrentSetVerifyState (tor, TR_VERIFY_WAIT);
  tr_list_insert_sorted (&verifyList, node, compareVerifyByPriorityAndSize);
  if (verifyThread == NULL)
    verifyThread = tr_threadNew (verifyThreadFunc, NULL);
  tr_lockUnlock (getVerifyLock ());
}

static int
compareVerifyByTorrent (const void * va, const void * vb)
{
  const struct verify_node * a = va;
  const tr_torrent * b = vb;
  return a->torrent - b;
}

void
tr_verifyRemove (tr_torrent * tor)
{
  tr_lock * lock = getVerifyLock ();
  tr_lockLock (lock);

  assert (tr_isTorrent (tor));

  if (tor == currentNode.torrent)
    {
      stopCurrent = true;

      while (stopCurrent)
        {
          tr_lockUnlock (lock);
          tr_wait_msec (100);
          tr_lockLock (lock);
        }
    }
  else
    {
      tr_free (tr_list_remove (&verifyList, tor, compareVerifyByTorrent));
      tr_torrentSetVerifyState (tor, TR_VERIFY_NONE);
    }

  tr_lockUnlock (lock);
}

void
tr_verifyClose (tr_session * session UNUSED)
{
  tr_lockLock (getVerifyLock ());

  stopCurrent = true;
  tr_list_free (&verifyList, tr_free);

  tr_lockUnlock (getVerifyLock ());
}