/*
 * 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> /* strlen () */

#include <event2/buffer.h>
#include <event2/event.h>

#include "transmission.h"
#include "bandwidth.h"
#include "cache.h"
#include "inout.h" /* tr_ioFindFileLocation () */
#include "list.h"
#include "peer-mgr.h"
#include "torrent.h"
#include "trevent.h" /* tr_runInEventThread () */
#include "utils.h"
#include "web.h"
#include "webseed.h"

struct tr_webseed_task
{
  bool                 dead;
  struct evbuffer    * content;
  struct tr_webseed  * webseed;
  tr_session         * session;
  tr_block_index_t     block;
  tr_piece_index_t     piece_index;
  uint32_t             piece_offset;
  uint32_t             length;
  tr_block_index_t     blocks_done;
  uint32_t             block_size;
  struct tr_web_task * web_task;
  long                 response_code;
};

struct tr_webseed
{
  tr_peer              parent;
  tr_bandwidth         bandwidth;
  tr_session         * session;
  tr_peer_callback     callback;
  void               * callback_data;
  tr_list            * tasks;
  struct event       * timer;
  char               * base_url;
  size_t               base_url_len;
  int                  torrent_id;
  int                  consecutive_failures;
  int                  retry_tickcount;
  int                  retry_challenge;
  int                  idle_connections;
  int                  active_transfers;
  char              ** file_urls;
};

enum
{
  TR_IDLE_TIMER_MSEC = 2000,

  FAILURE_RETRY_INTERVAL = 150,

  MAX_CONSECUTIVE_FAILURES = 5,

  MAX_WEBSEED_CONNECTIONS = 4
};

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

static void
publish (tr_webseed * w, tr_peer_event * e)
{
    if (w->callback != NULL)
        w->callback (&w->parent, e, w->callback_data);
}

static void
fire_client_got_rejs (tr_torrent        * tor,
                      tr_webseed        * w,
                      tr_block_index_t    block,
                      tr_block_index_t    count)
{
  tr_block_index_t i;
  tr_peer_event e = TR_PEER_EVENT_INIT;
  e.eventType = TR_PEER_CLIENT_GOT_REJ;
  tr_torrentGetBlockLocation (tor, block, &e.pieceIndex, &e.offset, &e.length);
  for (i = 1; i <= count; i++)
    {
      if (i == count)
        e.length = tr_torBlockCountBytes (tor, block + count - 1);
      publish (w, &e);
      e.offset += e.length;
    }
}

static void
fire_client_got_blocks (tr_torrent        * tor,
                        tr_webseed        * w,
                        tr_block_index_t    block,
                        tr_block_index_t    count)
{
  tr_block_index_t i;
  tr_peer_event e = TR_PEER_EVENT_INIT;
  e.eventType = TR_PEER_CLIENT_GOT_BLOCK;
  tr_torrentGetBlockLocation (tor, block, &e.pieceIndex, &e.offset, &e.length);
  for (i = 1; i <= count; i++)
    {
      if (i == count)
        e.length = tr_torBlockCountBytes (tor, block + count - 1);
      publish (w, &e);
      e.offset += e.length;
    }
}

static void
fire_client_got_piece_data (tr_webseed * w, uint32_t length)
{
  tr_peer_event e = TR_PEER_EVENT_INIT;
  e.eventType = TR_PEER_CLIENT_GOT_PIECE_DATA;
  e.length = length;
  publish (w, &e);
}

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

struct write_block_data
{
  tr_session         * session;
  int                  torrent_id;
  struct tr_webseed  * webseed;
  struct evbuffer    * content;
  tr_piece_index_t     piece_index;
  tr_block_index_t     block_index;
  tr_block_index_t     count;
  uint32_t             block_offset;
};

static void
write_block_func (void * vdata)
{
  struct write_block_data * data = vdata;
  struct tr_webseed * w = data->webseed;
  struct evbuffer * buf = data->content;
  struct tr_torrent * tor;

  tor = tr_torrentFindFromId (data->session, data->torrent_id);
  if (tor != NULL)
    {
      const uint32_t block_size = tor->blockSize;
      uint32_t len = evbuffer_get_length (buf);
      const uint32_t offset_end = data->block_offset + len;
      tr_cache * cache = data->session->cache;
      const tr_piece_index_t piece = data->piece_index;

      while (len > 0)
        {
          const uint32_t bytes_this_pass = MIN (len, block_size);
          tr_cacheWriteBlock (cache, tor, piece, offset_end - len, bytes_this_pass, buf);
          len -= bytes_this_pass;
        }

      fire_client_got_blocks (tor, w, data->block_index, data->count);
    }

  evbuffer_free (buf);
  tr_free (data);
}

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

struct connection_succeeded_data
{
  struct tr_webseed  * webseed;
  char               * real_url;
  tr_piece_index_t     piece_index;
  uint32_t             piece_offset;
};

static void
connection_succeeded (void * vdata)
{
  tr_torrent * tor;
  struct connection_succeeded_data * data = vdata;
  struct tr_webseed * w = data->webseed;

  if (++w->active_transfers >= w->retry_challenge && w->retry_challenge)
    /* the server seems to be accepting more connections now */
    w->consecutive_failures = w->retry_tickcount = w->retry_challenge = 0;

  if (data->real_url && (tor = tr_torrentFindFromId (w->session, w->torrent_id)))
    {
      uint64_t file_offset;
      tr_file_index_t file_index;

      tr_ioFindFileLocation (tor, data->piece_index, data->piece_offset,
                             &file_index, &file_offset);
      tr_free (w->file_urls[file_index]);
      w->file_urls[file_index] = data->real_url;
      data->real_url = NULL;
    }

  tr_free (data->real_url);
  tr_free (data);
}

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

static void
on_content_changed (struct evbuffer                * buf,
                    const struct evbuffer_cb_info  * info,
                    void                           * vtask)
{
  const size_t n_added = info->n_added;
  struct tr_webseed_task * task = vtask;
  tr_session * session = task->session;

  tr_sessionLock (session);

  if (!task->dead && (n_added>0))
    {
      uint32_t len;
      struct tr_webseed * w = task->webseed;

      tr_bandwidthUsed (&w->bandwidth, TR_DOWN, n_added, true, tr_time_msec ());
      fire_client_got_piece_data (w, n_added);
      len = evbuffer_get_length (buf);

      if (!task->response_code)
        {
          tr_webGetTaskInfo (task->web_task, TR_WEB_GET_CODE, &task->response_code);

          if (task->response_code == 206)
            {
              const char * url;
              struct connection_succeeded_data * data;

              url = NULL;
              tr_webGetTaskInfo (task->web_task, TR_WEB_GET_REAL_URL, &url);

              data = tr_new (struct connection_succeeded_data, 1);
              data->webseed = w;
              data->real_url = tr_strdup (url);
              data->piece_index = task->piece_index;
              data->piece_offset = task->piece_offset + (task->blocks_done * task->block_size) + (len - 1);

              /* processing this uses a tr_torrent pointer,
                 so push the work to the libevent thread... */
              tr_runInEventThread (w->session, connection_succeeded, data);
            }
        }

      if ((task->response_code == 206) && (len >= task->block_size))
        {
          /* once we've got at least one full block, save it */

          struct write_block_data * data;
          const uint32_t block_size = task->block_size;
          const tr_block_index_t completed = len / block_size;

          data = tr_new (struct write_block_data, 1);
          data->webseed = task->webseed;
          data->piece_index = task->piece_index;
          data->block_index = task->block + task->blocks_done;
          data->count = completed;
          data->block_offset = task->piece_offset + task->blocks_done * block_size;
          data->content = evbuffer_new ();
          data->torrent_id = w->torrent_id;
          data->session = w->session;

          /* we don't use locking on this evbuffer so we must copy out the data
             that will be needed when writing the block in a different thread */
          evbuffer_remove_buffer (task->content, data->content,
                                  block_size * completed);
  
          tr_runInEventThread (w->session, write_block_func, data);
          task->blocks_done += completed;
        }
    }

  tr_sessionUnlock (session);
}

static void task_request_next_chunk (struct tr_webseed_task * task);

static void
on_idle (tr_webseed * w)
{
  int want;
  int running_tasks = tr_list_size (w->tasks);
  tr_torrent * tor = tr_torrentFindFromId (w->session, w->torrent_id);

  if (w->consecutive_failures >= MAX_CONSECUTIVE_FAILURES)
    {
      want = w->idle_connections;

      if (w->retry_tickcount >= FAILURE_RETRY_INTERVAL)
        {
          /* some time has passed since our connection attempts failed. try again */
          ++want;
          /* if this challenge is fulfilled we will reset consecutive_failures */
          w->retry_challenge = running_tasks + want;
        }
    }
  else
    {
      want = MAX_WEBSEED_CONNECTIONS - running_tasks;
      w->retry_challenge = running_tasks + w->idle_connections + 1;
    }

  if (tor && tor->isRunning && !tr_torrentIsSeed (tor) && (want > 0))
    {
      int i;
      int got = 0;
      tr_block_index_t * blocks = NULL;

      blocks = tr_new (tr_block_index_t, want*2);
      tr_peerMgrGetNextRequests (tor, &w->parent, want, blocks, &got, true);

      w->idle_connections -= MIN (w->idle_connections, got);
      if (w->retry_tickcount >= FAILURE_RETRY_INTERVAL && got == want)
        w->retry_tickcount = 0;

      for (i=0; i<got; ++i)
        {
          const tr_block_index_t b = blocks[i*2];
          const tr_block_index_t be = blocks[i*2+1];
          struct tr_webseed_task * task;

          task = tr_new0 (struct tr_webseed_task, 1);
          task->session = tor->session;
          task->webseed = w;
          task->block = b;
          task->piece_index = tr_torBlockPiece (tor, b);
          task->piece_offset = (tor->blockSize * b) - (tor->info.pieceSize * task->piece_index);
          task->length = (be - b) * tor->blockSize + tr_torBlockCountBytes (tor, be);
          task->blocks_done = 0;
          task->response_code = 0;
          task->block_size = tor->blockSize;
          task->content = evbuffer_new ();
          evbuffer_add_cb (task->content, on_content_changed, task);
          tr_list_append (&w->tasks, task);
          task_request_next_chunk (task);
        }

      tr_free (blocks);
    }
}


static void
web_response_func (tr_session    * session,
                   bool            did_connect UNUSED,
                   bool            did_timeout UNUSED,
                   long            response_code,
                   const void    * response UNUSED,
                   size_t          response_byte_count UNUSED,
                   void          * vtask)
{
  tr_webseed * w;
  tr_torrent * tor;
  struct tr_webseed_task * t = vtask;
  const int success = (response_code == 206);

  if (t->dead)
    {
      evbuffer_free (t->content);
      tr_free (t);
      return;
    }

  w = t->webseed;
  tor = tr_torrentFindFromId (session, w->torrent_id);
  if (tor != NULL)
    {
      /* active_transfers was only increased if the connection was successful */
      if (t->response_code == 206)
        --w->active_transfers;

      if (!success)
        {
          const tr_block_index_t blocks_remain = (t->length + tor->blockSize - 1)
                                                   / tor->blockSize - t->blocks_done;

          if (blocks_remain)
            fire_client_got_rejs (tor, w, t->block + t->blocks_done, blocks_remain);

          if (t->blocks_done)
            ++w->idle_connections;
          else if (++w->consecutive_failures >= MAX_CONSECUTIVE_FAILURES && !w->retry_tickcount)
            /* now wait a while until retrying to establish a connection */
            ++w->retry_tickcount;

          tr_list_remove_data (&w->tasks, t);
          evbuffer_free (t->content);
          tr_free (t);
        }
        else
        {
          const uint32_t bytes_done = t->blocks_done * tor->blockSize;
          const uint32_t buf_len = evbuffer_get_length (t->content);

          if (bytes_done + buf_len < t->length)
            {
              /* request finished successfully but there's still data missing. that
                 means we've reached the end of a file and need to request the next one */
              t->response_code = 0;
              task_request_next_chunk (t);
            }
            else
            {
              if (buf_len)
                {
                  /* on_content_changed () will not write a block if it is smaller than
                     the torrent's block size, i.e. the torrent's very last block */
                  tr_cacheWriteBlock (session->cache, tor,
                                      t->piece_index, t->piece_offset + bytes_done,
                                      buf_len, t->content);

                  fire_client_got_blocks (tor, t->webseed,
                                          t->block + t->blocks_done, 1);
                }

              ++w->idle_connections;

              tr_list_remove_data (&w->tasks, t);
              evbuffer_free (t->content);
              tr_free (t);

              on_idle (w);
            }
        }
    }
}

static struct evbuffer *
make_url (tr_webseed * w, const tr_file * file)
{
  struct evbuffer * buf = evbuffer_new ();

  evbuffer_add (buf, w->base_url, w->base_url_len);

  /* if url ends with a '/', add the torrent name */
  if (w->base_url[w->base_url_len - 1] == '/' && file->name)
    tr_http_escape (buf, file->name, strlen (file->name), false);

  return buf;
}

static void
task_request_next_chunk (struct tr_webseed_task * t)
{
  tr_webseed * w = t->webseed;
  tr_torrent * tor = tr_torrentFindFromId (w->session, w->torrent_id);
  if (tor != NULL)
    {
      char range[64];
      char ** urls = t->webseed->file_urls;

      const tr_info * inf = tr_torrentInfo (tor);
      const uint64_t remain = t->length - t->blocks_done * tor->blockSize
                            - evbuffer_get_length (t->content);

      const uint64_t total_offset = tr_pieceOffset (tor, t->piece_index,
                                                         t->piece_offset,
                                                         t->length - remain);
      const tr_piece_index_t step_piece = total_offset / inf->pieceSize;
      const uint64_t step_piece_offset = total_offset - (inf->pieceSize * step_piece);

      tr_file_index_t file_index;
      const tr_file * file;
      uint64_t file_offset;
      uint64_t this_pass;

      tr_ioFindFileLocation (tor, step_piece, step_piece_offset,
                             &file_index, &file_offset);
      file = &inf->files[file_index];
      this_pass = MIN (remain, file->length - file_offset);

      if (!urls[file_index])
        urls[file_index] = evbuffer_free_to_str (make_url (t->webseed, file));

      tr_snprintf (range, sizeof range, "%"PRIu64"-%"PRIu64,
                   file_offset, file_offset + this_pass - 1);

      t->web_task = tr_webRunWebseed (tor, urls[file_index], range,
                                      web_response_func, t, t->content);
    }
}

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

static void
webseed_timer_func (evutil_socket_t foo UNUSED, short bar UNUSED, void * vw)
{
  tr_webseed * w = vw;

  if (w->retry_tickcount)
    ++w->retry_tickcount;

  on_idle (w);

  tr_timerAddMsec (w->timer, TR_IDLE_TIMER_MSEC);
}

/***
****  tr_peer virtual functions
***/

static bool
webseed_is_transferring_pieces (const tr_peer * peer,
                                uint64_t        now,
                                tr_direction    direction,
                                unsigned int  * setme_Bps)
{
  unsigned int Bps = 0;
  bool is_active = false;

  if (direction == TR_DOWN)
    {
      const tr_webseed * w = (const tr_webseed *) peer;
      is_active = w->tasks != NULL;
      Bps = tr_bandwidthGetPieceSpeed_Bps (&w->bandwidth, now, direction);
    }

  if (setme_Bps != NULL)
    *setme_Bps = Bps;

  return is_active;
}

static void
webseed_destruct (tr_peer * peer)
{
  tr_list * l;
  tr_webseed * w = (tr_webseed *) peer;

  /* flag all the pending tasks as dead */
  for (l=w->tasks; l!=NULL; l=l->next)
    {
      struct tr_webseed_task * task = l->data;
      task->dead = true;
    }
  tr_list_free (&w->tasks, NULL);

  /* if we have an array of file URLs, free it */
  if (w->file_urls != NULL)
    {
      tr_file_index_t i;
      tr_torrent * tor = tr_torrentFindFromId (w->session, w->torrent_id);
      const tr_info * inf = tr_torrentInfo (tor);

      for (i=0; i<inf->fileCount; ++i)
        tr_free (w->file_urls[i]);
      tr_free (w->file_urls);
    }

  /* webseed destruct */
  event_free (w->timer);
  tr_bandwidthDestruct (&w->bandwidth);
  tr_free (w->base_url);

  /* parent class destruct */
  tr_peerDestruct (&w->parent);
}

static const struct tr_peer_virtual_funcs my_funcs =
{
  .destruct = webseed_destruct,
  .is_transferring_pieces = webseed_is_transferring_pieces
};

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

tr_webseed*
tr_webseedNew (struct tr_torrent  * tor,
               const char         * url,
               tr_peer_callback     callback,
               void               * callback_data)
{
  tr_webseed * w = tr_new0 (tr_webseed, 1);
  tr_peer * peer = &w->parent;
  const tr_info * inf = tr_torrentInfo (tor);

  /* construct parent class */
  tr_peerConstruct (peer, tor);
  peer->client = TR_KEY_webseeds;
  peer->funcs = &my_funcs;
  tr_bitfieldSetHasAll (&peer->have);
  tr_peerUpdateProgress (tor, peer);

  w->torrent_id = tr_torrentId (tor);
  w->session = tor->session;
  w->base_url_len = strlen (url);
  w->base_url = tr_strndup (url, w->base_url_len);
  w->callback = callback;
  w->callback_data = callback_data;
  w->file_urls = tr_new0 (char *, inf->fileCount);
  //tr_rcConstruct (&w->download_rate);
  tr_bandwidthConstruct (&w->bandwidth, tor->session, &tor->bandwidth);
  w->timer = evtimer_new (w->session->event_base, webseed_timer_func, w);
  tr_timerAddMsec (w->timer, TR_IDLE_TIMER_MSEC);
  return w;
}