/**
 * Basic integration tests for the $let expression.
 */
import {assertErrorCode} from "jstests/aggregation/extras/utils.js";

let coll = db.agg_expr_let;
coll.drop();
assert.commandWorked(coll.insert({zero: 0, one: 1, two: 2, three: 3, nested: {four: 4}}));

function testExpr(expression, output) {
    const res = coll.aggregate([{$project: {output: expression}}]).toArray();
    assert.eq(res.length, 1, tojson(res));
    assert.eq(res[0].output, output, tojson(res));

    // Test in group:
    const result = coll.aggregate({$group: {_id: 0, res: {$sum: expression}}}).toArray();
    assert.eq(result, [{_id: 0, res: output}]);
}

// Basic tests.
testExpr("$two", 2);
testExpr("$$CURRENT.two", 2);
testExpr("$$ROOT.two", 2);

// Using sub expressions.
testExpr({$add: ["$two", "$$CURRENT.three"]}, 5);
testExpr({$add: ["$$CURRENT.two", "$$ROOT.nested.four"]}, 6);

// Verify that the variables defined in $let work.
testExpr({$let: {vars: {a: 10}, in: "$$a"}}, 10);
testExpr({$let: {vars: {a: "$zero"}, in: "$$a"}}, 0);
testExpr({$let: {vars: {a: {$add: ["$one", "$two"]}, b: 10}, in: {$multiply: ["$$a", "$$b"]}}}, 30);

// Verify that the outer level variable works in inner level $let.
testExpr(
    {
        $let: {vars: {var1: 1}, in: {$let: {vars: {var2: "$$var1"}, in: {$sum: ["$$var1", "$$var2"]}}}},
    },
    2,
);

// Verify that the outer level variables get overwritten by inner level variables.
testExpr(
    {
        $let: {
            vars: {var1: "$one"},
            in: {$let: {vars: {var2: "$$var1", var1: 3}, in: {$sum: ["$$var2", "$$var1"]}}},
        },
    },
    4,
);

// $let changing CURRENT
testExpr({$let: {vars: {CURRENT: "$$ROOT.nested"}, in: {$multiply: ["$four", "$$ROOT.two"]}}}, 8);
testExpr(
    {
        $let: {
            vars: {CURRENT: "$$CURRENT.nested"}, // using original value of CURRENT
            in: {$multiply: ["$four", "$$ROOT.two"]},
        },
    },
    8,
);
testExpr(
    {
        $let: {
            vars: {CURRENT: "$nested"}, // same as last
            in: {$multiply: ["$four", "$$ROOT.two"]},
        },
    },
    8,
);
testExpr(
    {
        $let: {
            vars: {CURRENT: {$const: {ten: 10}}}, // "artificial" object
            in: {$multiply: ["$ten", "$$ROOT.two"]},
        },
    },
    20,
);
testExpr(
    {
        $let: {
            vars: {CURRENT: "$three"}, // sets current to the number 3 (not an object)
            in: {$multiply: ["$$CURRENT", "$$ROOT.two"]},
        },
    },
    6,
);

// Swapping with $let (ensures there is no ordering dependency in vars).
testExpr(
    {
        $let: {
            vars: {x: 6, y: 10},
            in: {
                $let: {
                    vars: {x: "$$y", y: "$$x"}, // now {x:10, y:6}
                    in: {$subtract: ["$$x", "$$y"]},
                },
            },
        },
    }, // Not commutative!
    4,
); // 10-6 not 6-10 or 6-6

// Unicode is allowed.
testExpr({$let: {vars: {"日本語": 10}, in: "$$日本語"}}, 10); // Japanese for "Japanese language".

// Can use ROOT and CURRENT directly with no subfield (SERVER-5916).
coll.drop();
coll.insert({_id: "obj"});
assert.eq(coll.aggregate({$project: {_id: 0, obj: "$$ROOT"}}).toArray(), [{obj: {_id: "obj"}}]);
assert.eq(coll.aggregate({$project: {_id: 0, obj: "$$CURRENT"}}).toArray(), [{obj: {_id: "obj"}}]);
assert.eq(coll.aggregate({$group: {_id: 0, objs: {$push: "$$ROOT"}}}).toArray(), [{_id: 0, objs: [{_id: "obj"}]}]);
assert.eq(coll.aggregate({$group: {_id: 0, objs: {$push: "$$CURRENT"}}}).toArray(), [{_id: 0, objs: [{_id: "obj"}]}]);

// Check name validity checks.
assertErrorCode(coll, {$project: {a: {$let: {vars: {ROOT: 1}, in: "$$ROOT"}}}}, ErrorCodes.FailedToParse);
assertErrorCode(coll, {$project: {a: {$let: {vars: {FOO: 1}, in: "$$FOO"}}}}, ErrorCodes.FailedToParse);
assertErrorCode(coll, {$project: {a: {$let: {vars: {_underbar: 1}, in: "$$FOO"}}}}, ErrorCodes.FailedToParse);
assertErrorCode(coll, {$project: {a: {$let: {vars: {"a.b": 1}, in: "$$FOO"}}}}, ErrorCodes.FailedToParse);
assertErrorCode(coll, {$project: {a: {$let: {vars: {"a b": 1}, in: "$$FOO"}}}}, ErrorCodes.FailedToParse);
assertErrorCode(coll, {$project: {a: "$$_underbar"}}, ErrorCodes.FailedToParse);
assertErrorCode(coll, {$project: {a: "$$with spaces"}}, ErrorCodes.FailedToParse);

// Verify that variables defined in '$let' cannot be used to initialize other variables.
assertErrorCode(coll, [{$project: {output: {$let: {vars: {var1: "$one", var2: "$$var1"}, in: "$$var1"}}}}], 17276);