/**
 * Tests that cursors opened before a chunk is moved will not see the effects of the chunk
 * migration.
 */
(function() {
"use strict";
const dbName = "test";
const collName = jsTest.name();
const testNs = dbName + "." + collName;

const nDocs = 1000 * 10;
const st = new ShardingTest({shards: 2});
const coll = st.s0.getDB(dbName)[collName];
let bulk = coll.initializeUnorderedBulkOp();
for (let i = 0; i < nDocs; i++) {
    bulk.insert({_id: i});
}
assert.commandWorked(bulk.execute());

// Make sure we know which shard will host the data to begin.
st.ensurePrimaryShard(dbName, st.shard0.shardName);
assert.commandWorked(st.admin.runCommand({enableSharding: dbName}));
assert.commandWorked(st.admin.runCommand({shardCollection: testNs, key: {_id: 1}}));

// Open some cursors before migrating data.
// Ensure the cursor stage at the front of the pipeline does not buffer any data.
assert.commandWorked(
    st.shard0.adminCommand({setParameter: 1, internalDocumentSourceCursorBatchSizeBytes: 1}));
const getMoreBatchSize = 100;
const aggResponse = assert.commandWorked(
    coll.runCommand({aggregate: collName, pipeline: [], cursor: {batchSize: 0}}));
const aggCursor = new DBCommandCursor(coll.getDB(), aggResponse, getMoreBatchSize);

assert(st.adminCommand({split: testNs, middle: {_id: nDocs / 2}}));
assert(st.adminCommand({moveChunk: testNs, find: {_id: nDocs - 1}, to: st.shard1.shardName}));

assert.eq(aggCursor.itcount(),
          nDocs,
          "expected agg cursor to return all matching documents, even though some have migrated");

// Test the same behavior with the find command.
const findResponse = assert.commandWorked(
    coll.runCommand({find: collName, filter: {}, batchSize: getMoreBatchSize}));
const findCursor = new DBCommandCursor(coll.getDB(), findResponse, getMoreBatchSize);
assert(st.adminCommand({split: testNs, middle: {_id: nDocs / 4}}));
assert(st.adminCommand({moveChunk: testNs, find: {_id: 0}, to: st.shard1.shardName}));

assert.eq(findCursor.itcount(),
          nDocs,
          "expected find cursor to return all matching documents, even though some have migrated");
st.stop();
}());