/**
 * Tests that the cluster is balanced in parallel in one balancer round (standalone).
 */

(function() {
'use strict';

var st = new ShardingTest({shards: 4});
var config = st.s0.getDB('config');

assert.commandWorked(st.s0.adminCommand({enableSharding: 'TestDB'}));
st.ensurePrimaryShard('TestDB', st.shard0.shardName);

function prepareCollectionForBalance(collName) {
    assert.commandWorked(st.s0.adminCommand({shardCollection: collName, key: {Key: 1}}));

    var coll = st.s0.getCollection(collName);

    // Create 4 chunks initially and ensure they get balanced within 1 balancer round
    assert.commandWorked(coll.insert({Key: 1, Value: 'Test value 1'}));
    assert.commandWorked(coll.insert({Key: 10, Value: 'Test value 10'}));
    assert.commandWorked(coll.insert({Key: 20, Value: 'Test value 20'}));
    assert.commandWorked(coll.insert({Key: 30, Value: 'Test value 30'}));

    assert.commandWorked(st.splitAt(collName, {Key: 10}));
    assert.commandWorked(st.splitAt(collName, {Key: 20}));
    assert.commandWorked(st.splitAt(collName, {Key: 30}));

    // Move two of the chunks to st.shard1.shardName so we have option to do parallel balancing
    assert.commandWorked(st.moveChunk(collName, {Key: 20}, st.shard1.shardName));
    assert.commandWorked(st.moveChunk(collName, {Key: 30}, st.shard1.shardName));

    assert.eq(2, config.chunks.find({ns: collName, shard: st.shard0.shardName}).itcount());
    assert.eq(2, config.chunks.find({ns: collName, shard: st.shard1.shardName}).itcount());
}

function checkCollectionBalanced(collName) {
    assert.eq(1, config.chunks.find({ns: collName, shard: st.shard0.shardName}).itcount());
    assert.eq(1, config.chunks.find({ns: collName, shard: st.shard1.shardName}).itcount());
    assert.eq(1, config.chunks.find({ns: collName, shard: st.shard2.shardName}).itcount());
    assert.eq(1, config.chunks.find({ns: collName, shard: st.shard3.shardName}).itcount());
}

function countMoves(collName) {
    return config.changelog.find({what: 'moveChunk.start', ns: collName}).itcount();
}

prepareCollectionForBalance('TestDB.TestColl1');
prepareCollectionForBalance('TestDB.TestColl2');

// Count the moveChunk start attempts accurately and ensure that only the correct number of
// migrations are scheduled
const testColl1InitialMoves = countMoves('TestDB.TestColl1');
const testColl2InitialMoves = countMoves('TestDB.TestColl2');

st.startBalancer();
st.waitForBalancer(true, 60000);
st.waitForBalancer(true, 60000);
st.stopBalancer();

checkCollectionBalanced('TestDB.TestColl1');
checkCollectionBalanced('TestDB.TestColl2');

assert.eq(2, countMoves('TestDB.TestColl1') - testColl1InitialMoves);
assert.eq(2, countMoves('TestDB.TestColl2') - testColl2InitialMoves);

// Ensure there are no migration errors reported
assert.eq(0, config.changelog.find({what: 'moveChunk.error'}).itcount());

st.stop();
})();