// Tests the behaviour of the $merge stage with whenMatched=[pipeline] and whenNotMatched=fail.
//
// Cannot implicitly shard accessed collections because a collection can be implictly created and
// exists when none is expected.
(function() {
"use strict";

load("jstests/aggregation/extras/utils.js");  // For assertArrayEq.
load("jstests/libs/fixture_helpers.js");      // For FixtureHelpers.isMongos.

const source = db[`${jsTest.name()}_source`];
source.drop();
const target = db[`${jsTest.name()}_target`];
target.drop();
const mergeStage = {
    $merge: {into: target.getName(), whenMatched: [{$addFields: {x: 2}}], whenNotMatched: "fail"}
};
const pipeline = [mergeStage];

// Test $merge when some documents in the source collection don't have a matching document in
// the target collection.
(function testMergeFailsIfMatchingDocumentNotFound() {
    // Single document without a match.
    assert.commandWorked(source.insert([{_id: 1, a: 1}, {_id: 2, a: 2}, {_id: 3, a: 3}]));
    assert.commandWorked(target.insert([{_id: 1, b: 1}, {_id: 3, b: 3}]));
    let error = assert.throws(() => source.aggregate(pipeline));
    assert.commandFailedWithCode(error, ErrorCodes.MergeStageNoMatchingDocument);
    // Since there is no way to guarantee the ordering of the writes performed by $merge, it
    // follows that the contents of the target collection will depend on when the write which
    // triggers the MergeStageNoMatchingDocument error executes. As such, we test that the
    // target collection contains some combination of its original documents and expected
    // updates. In particular, it should be the case that each document has fields '_id' and
    // 'b', but may or not have field 'x'. Additionally, 'b' should have the same value as
    // '_id' and if 'x' is present, it should be equal to 2.
    let checkOutputDocument = function(document) {
        const hasB = document.hasOwnProperty("b");
        const hasX = document.hasOwnProperty("x");
        assert(hasB, document);
        const value = document["b"];
        assert.eq(value, document['_id'], document);
        if (hasX)
            assert.eq(2, document['x'], document);
    };

    let result = target.find().toArray();
    assert.eq(result.length, 2, result);
    for (let elem of result) {
        checkOutputDocument(elem);
    }

    // Multiple documents without a match.
    assert(target.drop());
    assert.commandWorked(target.insert([{_id: 1, b: 1}]));
    error = assert.throws(() => source.aggregate(pipeline));
    assert.commandFailedWithCode(error, ErrorCodes.MergeStageNoMatchingDocument);
    result = target.find().toArray();
    assert.eq(result.length, 1, result);
    checkOutputDocument(result[0]);
})();

// Test $merge when all documents in the source collection have a matching document in the
// target collection.
(function testMergeWhenAllDocumentsHaveMatch() {
    // Source has a single element with a match in the target.
    assert(source.drop());
    assert(target.drop());
    assert.commandWorked(source.insert({_id: 3, a: 3}));
    assert.commandWorked(target.insert([{_id: 1, b: 1}, {_id: 3, b: 3}]));
    assert.doesNotThrow(() => source.aggregate(pipeline));
    assertArrayEq(
        {actual: target.find().toArray(), expected: [{_id: 1, b: 1}, {_id: 3, b: 3, x: 2}]});

    // Source has multiple documents with matches in the target.
    assert(target.drop());
    assert.commandWorked(source.insert([{_id: 1, a: 1}, {_id: 2, a: 2}]));
    assert.commandWorked(target.insert([{_id: 1, b: 1}, {_id: 2, b: 2}, {_id: 3, b: 3}]));
    assert.doesNotThrow(() => source.aggregate(pipeline));
    assertArrayEq({
        actual: target.find().toArray(),
        expected: [{_id: 1, b: 1, x: 2}, {_id: 2, b: 2, x: 2}, {_id: 3, b: 3, x: 2}]
    });
})();

// Test $merge when the source collection is empty. The target collection should not be
// modified.
(function testMergeWhenSourceIsEmpty() {
    assert.commandWorked(source.deleteMany({}));
    assert(target.drop());
    assert.commandWorked(target.insert([{_id: 1, b: 1}, {_id: 2, b: 2}]));
    assert.doesNotThrow(() => source.aggregate(pipeline));
    assertArrayEq({actual: target.find().toArray(), expected: [{_id: 1, b: 1}, {_id: 2, b: 2}]});
})();

// Test that variables referencing the fields in the source document can be specified in the
// 'let' argument and referenced in the update pipeline.
(function testMergeWithLetVariables() {
    assert(source.drop());
    assert(target.drop());
    assert.commandWorked(source.insert([{_id: 1, a: 1, b: 1}, {_id: 2, a: 2, b: 2}]));
    assert.commandWorked(target.insert([{_id: 1, c: 1}, {_id: 2, c: 2}]));

    assert.doesNotThrow(() => source.aggregate([{
        $merge: {
            into: target.getName(),
            let : {x: "$a", y: "$b"},
            whenMatched: [{$set: {z: {$add: ["$$x", "$$y"]}}}],
            whenNotMatched: "fail"
        }
    }]));
    assertArrayEq(
        {actual: target.find().toArray(), expected: [{_id: 1, c: 1, z: 2}, {_id: 2, c: 2, z: 4}]});
})();
}());