// Tests for explaining the delete command.

var collName = "jstests_explain_delete";
var t = db[collName];
t.drop();

var explain;

/**
 * Verify that the explain command output 'explain' shows a DELETE stage with an nWouldDelete
 * value equal to 'nWouldDelete'.
 */
function checkNWouldDelete(explain, nWouldDelete) {
    printjson(explain);
    assert.commandWorked(explain);
    assert("executionStats" in explain);
    var executionStats = explain.executionStats;
    assert("executionStages" in executionStats);

    // If passed through mongos, then DELETE should be below the SINGLE_SHARD mongos stage.
    // Otherwise it is the root stage.
    var execStages = executionStats.executionStages;
    if ("SHARD_WRITE" === execStages.stage) {
        var deleteStage = execStages.shards[0].executionStages;
        assert.eq(deleteStage.stage, "DELETE");
        assert.eq(deleteStage.nWouldDelete, nWouldDelete);
    }
    else {
        assert.eq(execStages.stage, "DELETE");
        assert.eq(execStages.nWouldDelete, nWouldDelete);
    }
}

// Explain delete against an empty collection.
explain = db.runCommand({
    explain: {
        delete: collName,
        deletes: [
            {q: {a: 1}, limit: 0}
        ]
    }
});
checkNWouldDelete(explain, 0);

// Add an index but no data, and check that the explain still works.
t.ensureIndex({a: 1});
explain = db.runCommand({
    explain: {
        delete: collName,
        deletes: [
            {q: {a: 1}, limit: 0}
        ]
    }
});
checkNWouldDelete(explain, 0);

// Add some copies of the same document.
for (var i = 0; i < 10; i++) {
    t.insert({a: 1});
}
assert.eq(10, t.count());

// Run an explain which shows that all 10 documents *would* be deleted.
explain = db.runCommand({
    explain: {
        delete: collName,
        deletes: [
            {q: {a: 1}, limit: 0}
        ]
    }
});
checkNWouldDelete(explain, 10);

// Make sure all 10 documents are still there.
assert.eq(10, t.count());

// If we run the same thing without the explain, then all 10 docs should be deleted.
var deleteResult = db.runCommand({
    delete: collName,
    deletes: [
        {q: {a: 1}, limit: 0}
    ]
});
assert.commandWorked(deleteResult);
assert.eq(0, t.count());