How to correctly index jsonb arrays and the fields in array elements in postgreSQL - postgresql

Question

a have a simple table of purchases consisting of id and jsonb column, like this:
CREATE TABLE purchase (id SERIAL, products JSONB)
Then and index:
CREATE INDEX idx_purchase_products ON purchase USING GIN (products);
The sample data are like this:
INSERT INTO purchase VALUES (
1, jsonb('[
{
"country": 1,
"type": 1,
"size": 10,
"color": 3
}
]')
),
(
2, jsonb('[
{
"country": 1,
"type": 1,
"size": 10,
"color": 3
},
{
"country": 1,
"type": 2,
"size": 12,
"color": 4
},
{
"country": 2,
"type": 1,
"size": 12,
"color": 3
}
]')
),
(
3, jsonb('[
{
"country": 1,
"type": 1,
"size": 10,
"color": 3
}
]')
),
(
4, jsonb('[
{
"country": 1,
"type": 1,
"size": 10,
"color": 3
},
{
"country": 1,
"type": 2,
"size": 12,
"color": 4
},
{
"country": 2,
"type": 1,
"size": 12,
"color": 3
}
]')
);
And some scenarios of searching:
SELECT *
FROM purchase
WHERE products #> '[{"country": 1}]'
SELECT *
FROM purchase
WHERE products #> '[{"country": 1, "type": 1}]'
SELECT *
FROM purchase
WHERE products #> '[{"size": 12}]'
SELECT *
FROM purchase
WHERE products #> '[{"size": 12, "color": 4}]'
It is expected, that the customer could search for combinations:
country,
country + type
country + type + size
country + type + size + color
country + size
size + color
type + color
etc.
And there is a big chance, the list of 4 field (country, type, size, color) will grow in future to 7-10.
And of course we want also search combinations like this:
.. WHERE products #> '[{"country": 1}]' OR products #> '[{"color": 4}]' OR products #> '[{"type": 1, "size": 10}]'
Estimated size of the table purchase is 9-12 millions rows (depending on season).
Any idea how to implement the indexes to get the query result as fast as possible?