module main

struct Decoder {
    json string
}

pub fn decode[T](val string) !T {
    mut decoder := Decoder{
        json: val
    }

    mut result := T{}
    decoder.decode_value(mut &result)!
    return result
}

fn (mut decoder Decoder) decode_value[T](mut val T) ! {
    $if T.unaliased_typ is $array {
        mut array_element := create_array_element(val)

        decoder.decode_value(mut array_element)!

        val << array_element

        assert val.len == 1
        assert val[0] == array_element
    } $else $if T.unaliased_typ is $map {
        mut map_value := create_map_value(val)

        decoder.decode_value(mut map_value)!

        val['key'] = map_value

        assert val.len == 1
        assert val['key'] == map_value
    }
}

fn create_array_element[T](array []T) T {
    return T{}
}

fn create_map_value[K, V](map_ map[K]V) V {
    return V{}
}

fn test_main() {
    assert decode[[]int]('[1, 2, 3]')! == [0]
    assert decode[[]string]('["1", "2", "3"]')! == ['']
    assert decode[map[string]int]('{"a": 1}')! == {
        'key': 0
    }
    assert decode[map[string]string]('{"val": "2"}')! == {
        'key': ''
    }
}