/*
 * 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
{
    struct evbuffer    * content;
    struct tr_webseed  * webseed;
    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;
    bool                 is_stopping;
    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
webseed_free (struct tr_webseed * w)
{
    tr_torrent * tor = tr_torrentFindFromId (w->session, w->torrent_id);
    const tr_info * inf = tr_torrentInfo (tor);
    tr_file_index_t i;

    /* if we have an array of file URLs, free it */
    if (w->file_urls != NULL) {
        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 (tor, &w->parent);

    tr_free (w);
}

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

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
{
    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 (w->session, w->torrent_id);
    if (tor)
    {
        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 = w->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;
    }
}

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

static void
on_content_changed (struct evbuffer                * buf,
                    const struct evbuffer_cb_info  * info,
                    void                           * vtask)
{
    uint32_t len;
    const size_t n_added = info->n_added;
    struct tr_webseed_task * task = vtask;
    struct tr_webseed * w = task->webseed;

    if (n_added <= 0)
        return;

    if (!w->is_stopping)
    {
        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 ();

        /* 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;
    }
}

static void task_request_next_chunk (struct tr_webseed_task * task);

static bool
webseed_has_tasks (const tr_webseed * w)
{
    return w->tasks != NULL;
}


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

    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 (w->is_stopping && !webseed_has_tasks (w))
    {
        webseed_free (w);
    }
    else if (!w->is_stopping && tor
                             && tor->isRunning
                             && !tr_torrentIsSeed (tor)
                             && want)
    {
        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 = tr_new (struct tr_webseed_task, 1);
            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)
{
    struct tr_webseed_task * t = vtask;
    tr_webseed * w = t->webseed;
    tr_torrent * tor = tr_torrentFindFromId (session, w->torrent_id);
    const int success = (response_code == 206);

    if (tor)
    {
        /* 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_webRunWithBuffer (w->session, urls[file_index],
                                           range, NULL, web_response_func, t, t->content);
    }
}

bool
tr_webseedGetSpeed_Bps (const tr_webseed * w,
                        uint64_t           now,
                        unsigned int     * setme_Bps)
{
    const bool is_active = webseed_has_tasks (w);
    *setme_Bps = is_active ? tr_bandwidthGetPieceSpeed_Bps (&w->bandwidth, now, TR_DOWN) : 0;
    return is_active;
}

bool
tr_webseedIsActive (const tr_webseed * w)
{
    unsigned int Bps = 0;
    return tr_webseedGetSpeed_Bps (w, tr_time_msec (), &Bps) && (Bps > 0);
}

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

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_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);
    peer->peerIsChoked = true;
    peer->clientIsInterested = !tr_torrentIsSeed (tor);
    peer->client = TR_KEY_webseeds;
    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;
}

void
tr_webseedFree (tr_webseed * w)
{
    if (w)
    {
        if (webseed_has_tasks (w))
            w->is_stopping = true;
        else
            webseed_free (w);
    }
}