/*
 * 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;

    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_data( tr_webseed * w, uint32_t length )
{
    tr_peer_event e = TR_PEER_EVENT_INIT;
    e.eventType = TR_PEER_CLIENT_GOT_DATA;
    e.length = length;
    e.wasPieceData = true;
    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_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_strdup( "webseed" );
    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 );
    }
}