s = new ShardingTest( "find_and_modify_sharded" , 2 , 2);

s.adminCommand( { enablesharding : "test" } );
db = s.getDB( "test" );
primary = s.getServer( "test" ).getDB( "test" );
secondary = s.getOther( primary ).getDB( "test" );

numObjs = 20;

s.adminCommand( { shardcollection : "test.stuff"  , key : {_id:1} } );

// pre-split the collection so to avoid interference from balancer
s.adminCommand( { split: "test.stuff" , middle : { _id : numObjs/2 } } );
s.adminCommand( { movechunk : "test.stuff" , find : { _id : numObjs/2 } , to : secondary.getMongo().name } ) ;

for (var i=0; i < numObjs; i++){
    db.stuff.insert({_id: i});
}
db.getLastError()

// put two docs in each chunk (avoid the split in 0, since there are no docs less than 0)
for (var i=2; i < numObjs; i+=2){
    if (i == numObjs/2)
        continue;
    s.adminCommand( { split: "test.stuff"  , middle : {_id: i} } );
}

s.printChunks();
assert.eq( numObjs/2, s.config.chunks.count(), "split failed" );
assert.eq( numObjs/4, s.config.chunks.count({ shard: "shard0000" }) );
assert.eq( numObjs/4, s.config.chunks.count({ shard: "shard0001" }) ); 

// update
for (var i=0; i < numObjs; i++){
    assert.eq(db.stuff.count({b:1}), i, "2 A");

    var out = db.stuff.findAndModify({query: {_id:i, b:null}, update: {$set: {b:1}}});
    assert.eq(out._id, i, "2 E");

    assert.eq(db.stuff.count({b:1}), i+1, "2 B");
}

// remove
for (var i=0; i < numObjs; i++){
    assert.eq(db.stuff.count(), numObjs - i, "3 A");
    assert.eq(db.stuff.count({_id: i}), 1, "3 B");

    var out = db.stuff.findAndModify({remove: true, query: {_id:i}});

    assert.eq(db.stuff.count(), numObjs - i - 1, "3 C");
    assert.eq(db.stuff.count({_id: i}), 0, "3 D");
    assert.eq(out._id, i, "3 E");
}

s.stop();
