Limit array size Couchbase update query - couchbase

Question

i have got a couchbase n1ql update query:
UPDATE `store` document USE KEYS "test"
SET document = ARRAY_APPEND(ARRAY_REMOVE(document, "c"), "c")
this update will remove all occurences of the given "c" from the document and is then appending it to the end.
now i also want to limit the resulting array to a specific length, so the result never exeeds something like 50 array elements or so
since array slicing wont give a propper result, when the length of the array is less than the given slice, there is some more logic required.
i have tried the following:
UPDATE `store` document USE KEYS "test"
LET temp = ARRAY_APPEND(ARRAY_REMOVE(document, "c"), "c")
SET document = temp[-least(ARRAY_LENGTH(temp), 50):]
which fails, because "LET" is not part of the UPDATE syntax
is there any way to achieve limiting the stored array in size by using a single update statement?
EDIT:
with the selected answer and an additional case for new documents, i came up with this final solution:
MERGE INTO `store` document
USING (SELECT NULL) s ON KEY "test_x"
WHEN MATCHED THEN
UPDATE SET document = ARRAY_REVERSE(
ARRAY v FOR i:v IN ARRAY_REVERSE(
ARRAY_APPEND(ARRAY_REMOVE(document, "i"), "i")
) WHEN i < 3 END
)
WHEN NOT MATCHED THEN
INSERT ["i"]
RETURNING *

Answer 1

You can limit the length of an array using an indexed ARRAY operator, like this:
select array v for i:v in ["a", "b", "c", "d"] when i < 2 end
Result:
[
{
"$1": [
"a",
"b"
]
}
]

Answer 2

You can also use subquery expressions that are more flexible (like remove based on logical fields of objects) etc. If you need 50 elements give 49 because you are adding one more at the end.
UPDATE `store` AS document
USE KEYS "test"
SET document = ARRAY_APPEND((SELECT RAW d1 FROM document AS d1 WHERE d1 != "c" OFFSET ARRAY_LENGTH(document) - 49 LIMIT 49),"c");
https://docs.couchbase.com/server/6.0/n1ql/n1ql-language-reference/subqueries.html