/*
 * 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 <stdlib.h> /* qsort() */

#include <event2/buffer.h>

#include "transmission.h"
#include "cache.h"
#include "inout.h"
#include "peer-common.h" /* MAX_BLOCK_SIZE */
#include "ptrarray.h"
#include "torrent.h"
#include "utils.h"

#define MY_NAME "Cache"

#define dbgmsg( ... ) \
    do { \
        if( tr_deepLoggingIsActive( ) ) \
            tr_deepLog( __FILE__, __LINE__, MY_NAME, __VA_ARGS__ ); \
    } while( 0 )


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

struct cache_block
{
    tr_torrent * tor;

    tr_piece_index_t piece;
    uint32_t offset;
    uint32_t length;

    time_t time;
    tr_block_index_t block;

    struct evbuffer * evbuf;
};

struct tr_cache
{
    tr_ptrArray blocks;
    int max_blocks;
    size_t max_bytes;

    size_t disk_writes;
    size_t disk_write_bytes;
    size_t cache_writes;
    size_t cache_write_bytes;
};

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

struct run_info
{
  int       pos;
  int       rank;
  time_t    last_block_time;
  bool      is_multi_piece;
  bool      is_piece_done;
  unsigned  len;
};


/* return a count of how many contiguous blocks there are starting at this pos */
static int
getBlockRun( const tr_cache * cache, int pos, struct run_info * info )
{
    int i;
    const int n = tr_ptrArraySize( &cache->blocks );
    const struct cache_block ** blocks = (const struct cache_block**) tr_ptrArrayBase( &cache->blocks );
    const struct cache_block * ref = blocks[pos];
    tr_block_index_t block = ref->block;

    for( i=pos; i<n; ++i, ++block ) {
        const struct cache_block * b = blocks[i];
        if( b->block != block ) break;
        if( b->tor != ref->tor ) break;
//fprintf( stderr, "pos %d tor %d block %zu time %zu\n", i, b->tor->uniqueId, (size_t)b->block, (size_t)b->time );
    }

//fprintf( stderr, "run is %d long from [%d to %d)\n", (int)(i-pos), i, (int)pos );
    if( info != NULL ) {
        const struct cache_block * b = blocks[i-1];
        info->last_block_time = b->time;
        info->is_piece_done = tr_cpPieceIsComplete( &b->tor->completion, b->piece );
        info->is_multi_piece = b->piece != blocks[pos]->piece ? true : false;
        info->len = i - pos;
        info->pos = pos;
    }

    return i-pos;
}

/* higher rank comes before lower rank */
static int
compareRuns( const void * va, const void * vb )
{
    const struct run_info * a = va;
    const struct run_info * b = vb;
    return b->rank - a->rank;
}

enum
{
    MULTIFLAG   = 0x1000,
    DONEFLAG    = 0x2000,
    SESSIONFLAG = 0x4000
};
/* Calculte runs
 *   - Stale runs, runs sitting in cache for a long time or runs not growing, get priority.
 *     Returns number of runs.
 */
static int
calcRuns( tr_cache * cache, struct run_info * runs )
{
    const int n = tr_ptrArraySize( &cache->blocks );
    int i = 0, pos;
    const time_t now = tr_time();

    for( pos = 0; pos < n; pos += runs[i++].len )
    {
        int rank = getBlockRun( cache, pos, &runs[i] );

        /* This adds ~2 to the relative length of a run for every minute it has
         * languished in the cache. */
        rank += ( now - runs[i].last_block_time ) / 32;

        /* Flushing stale blocks should be a top priority as the probability of them
         * growing is very small, for blocks on piece boundaries, and nonexistant for
         * blocks inside pieces. */
        rank |= runs[i].is_piece_done ? DONEFLAG : 0;

        /* Move the multi piece runs higher */
        rank |= runs[i].is_multi_piece ? MULTIFLAG : 0;

        runs[i].rank = rank;
//fprintf(stderr,"block run at pos %d of length %d and age %ld adjusted +%d\n",runs[i].pos,runs[i].len,now-runs[i].last_block_time,rank-runs[i].len);
    }

    //fprintf( stderr, "%d block runs\n", i );
    qsort( runs, i, sizeof( struct run_info ), compareRuns );
    return i;
}

static int
flushContiguous( tr_cache * cache, int pos, int n )
{
    int i;
    int err = 0;
    uint8_t * buf = tr_new( uint8_t, n * MAX_BLOCK_SIZE );
    uint8_t * walk = buf;
    struct cache_block ** blocks = (struct cache_block**) tr_ptrArrayBase( &cache->blocks );

    struct cache_block * b = blocks[pos];
    tr_torrent * tor             = b->tor;
    const tr_piece_index_t piece = b->piece;
    const uint32_t offset        = b->offset;

    for( i=pos; i<pos+n; ++i ) {
        b = blocks[i];
        evbuffer_copyout( b->evbuf, walk, b->length );
        walk += b->length;
        evbuffer_free( b->evbuf );
        tr_free( b );
    }
    tr_ptrArrayErase( &cache->blocks, pos, pos+n );

    err = tr_ioWrite( tor, piece, offset, walk-buf, buf );
    tr_free( buf );

    ++cache->disk_writes;
    cache->disk_write_bytes += walk-buf;
    return err;
}

static int
flushRuns( tr_cache * cache, struct run_info * runs, int n )
{
    int i, j, err = 0;

    for( i = 0; !err && i < n; ++i )
    {
        err = flushContiguous( cache, runs[i].pos, runs[i].len );
        for( j = i + 1; j < n; ++j )
            if( runs[j].pos > runs[i].pos )
                runs[j].pos -= runs[i].len;
    }

    return err;
}

static int
cacheTrim( tr_cache * cache )
{
    int err = 0;

    if( tr_ptrArraySize( &cache->blocks ) > cache->max_blocks )
    {
        /* Amount of cache that should be removed by the flush. This influences how large
         * runs can grow as well as how often flushes will happen. */
        const int cacheCutoff = 1 + cache->max_blocks / 4;
        struct run_info * runs = tr_new( struct run_info, tr_ptrArraySize( &cache->blocks ) );
        int i = 0, j = 0;

        calcRuns( cache, runs );
        while( j < cacheCutoff )
            j += runs[i++].len;
        err = flushRuns( cache, runs, i );
        tr_free( runs );
    }

    return err;
}

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

static int
getMaxBlocks( int64_t max_bytes )
{
    return max_bytes / (double)MAX_BLOCK_SIZE;
}

int
tr_cacheSetLimit( tr_cache * cache, int64_t max_bytes )
{
    char buf[128];

    cache->max_bytes = max_bytes;
    cache->max_blocks = getMaxBlocks( max_bytes );

    tr_formatter_mem_B( buf, cache->max_bytes, sizeof( buf ) );
    tr_ndbg( MY_NAME, "Maximum cache size set to %s (%d blocks)", buf, cache->max_blocks );

    return cacheTrim( cache );
}

int64_t
tr_cacheGetLimit( const tr_cache * cache )
{
    return cache->max_bytes;
}

tr_cache *
tr_cacheNew( int64_t max_bytes )
{
    tr_cache * cache = tr_new0( tr_cache, 1 );
    cache->blocks = TR_PTR_ARRAY_INIT;
    cache->max_bytes = max_bytes;
    cache->max_blocks = getMaxBlocks( max_bytes );
    return cache;
}

void
tr_cacheFree( tr_cache * cache )
{
    assert( tr_ptrArrayEmpty( &cache->blocks ) );
    tr_ptrArrayDestruct( &cache->blocks, NULL );
    tr_free( cache );
}

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

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

    /* primary key: torrent id */
    if( a->tor->uniqueId != b->tor->uniqueId )
        return a->tor->uniqueId < b->tor->uniqueId ? -1 : 1;

    /* secondary key: block # */
    if( a->block != b->block )
        return a->block < b->block ? -1 : 1;

    /* they're equal */
    return 0;
}

static struct cache_block *
findBlock( tr_cache           * cache,
           tr_torrent         * torrent,
           tr_piece_index_t     piece,
           uint32_t             offset )
{
    struct cache_block key;
    key.tor = torrent;
    key.block = _tr_block( torrent, piece, offset );
    return tr_ptrArrayFindSorted( &cache->blocks, &key, cache_block_compare );
}

int
tr_cacheWriteBlock( tr_cache         * cache,
                    tr_torrent       * torrent,
                    tr_piece_index_t   piece,
                    uint32_t           offset,
                    uint32_t           length,
                    struct evbuffer  * writeme )
{
    struct cache_block * cb = findBlock( cache, torrent, piece, offset );

    if( cb == NULL )
    {
        cb = tr_new( struct cache_block, 1 );
        cb->tor = torrent;
        cb->piece = piece;
        cb->offset = offset;
        cb->length = length;
        cb->block = _tr_block( torrent, piece, offset );
        cb->evbuf = evbuffer_new( );
        tr_ptrArrayInsertSorted( &cache->blocks, cb, cache_block_compare );
    }

    cb->time = tr_time();

    assert( cb->length == length );
    evbuffer_drain( cb->evbuf, evbuffer_get_length( cb->evbuf ) );
    evbuffer_remove_buffer( writeme, cb->evbuf, cb->length );

    ++cache->cache_writes;
    cache->cache_write_bytes += cb->length;

    return cacheTrim( cache );
}

int
tr_cacheReadBlock( tr_cache         * cache,
                   tr_torrent       * torrent,
                   tr_piece_index_t   piece,
                   uint32_t           offset,
                   uint32_t           len,
                   uint8_t          * setme )
{
    int err = 0;
    struct cache_block * cb = findBlock( cache, torrent, piece, offset );

    if( cb )
        evbuffer_copyout( cb->evbuf, setme, len );
    else
        err = tr_ioRead( torrent, piece, offset, len, setme );

    return err;
}

int
tr_cachePrefetchBlock( tr_cache         * cache,
                       tr_torrent       * torrent,
                       tr_piece_index_t   piece,
                       uint32_t           offset,
                       uint32_t           len )
{
    int err = 0;
    struct cache_block * cb = findBlock( cache, torrent, piece, offset );

    if( cb == NULL )
        err = tr_ioPrefetch( torrent, piece, offset, len );

    return err;
}

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

static int
findBlockPos( tr_cache * cache, tr_torrent * torrent, tr_piece_index_t block )
{
    struct cache_block key;
    key.tor = torrent;
    key.block = block;
    return tr_ptrArrayLowerBound( &cache->blocks, &key, cache_block_compare, NULL );
}

int tr_cacheFlushDone( tr_cache * cache )
{
    int err = 0;

    if( tr_ptrArraySize( &cache->blocks ) > 0 )
    {
        struct run_info * runs = tr_new( struct run_info, tr_ptrArraySize( &cache->blocks ) );
        int i = 0, n;

        n = calcRuns( cache, runs );
        while( i < n && ( runs[i].is_piece_done || runs[i].is_multi_piece ) )
            runs[i++].rank |= SESSIONFLAG;
        err = flushRuns( cache, runs, i );
        tr_free( runs );
    }

    return err;
}

int
tr_cacheFlushFile( tr_cache * cache, tr_torrent * torrent, tr_file_index_t i )
{
    int pos;
    int err = 0;
    tr_block_index_t first;
    tr_block_index_t last;
    tr_torGetFileBlockRange( torrent, i, &first, &last );
    pos = findBlockPos( cache, torrent, first );
    dbgmsg( "flushing file %d from cache to disk: blocks [%zu...%zu]", (int)i, (size_t)first, (size_t)last );

    /* flush out all the blocks in that file */
    while( !err && ( pos < tr_ptrArraySize( &cache->blocks ) ) )
    {
        const struct cache_block * b = tr_ptrArrayNth( &cache->blocks, pos );
        if( b->tor != torrent ) break;
        if( ( b->block < first ) || ( b->block > last ) ) break;
        err = flushContiguous( cache, pos, getBlockRun( cache, pos, NULL ) );
    }

    return err;
}

int
tr_cacheFlushTorrent( tr_cache * cache, tr_torrent * torrent )
{
    int err = 0;
    const int pos = findBlockPos( cache, torrent, 0 );

    /* flush out all the blocks in that torrent */
    while( !err && ( pos < tr_ptrArraySize( &cache->blocks ) ) )
    {
        const struct cache_block * b = tr_ptrArrayNth( &cache->blocks, pos );
        if( b->tor != torrent ) break;
        err = flushContiguous( cache, pos, getBlockRun( cache, pos, NULL ) );
    }

    return err;
}