use std::io::Error;

#[derive(Debug, Clone)]
struct DBInfo {
    field_one: i8,
    field_two: i8
}

fn get_from_db(id: usize) -> Result<Vec<DBInfo>, Error> {
    // queries database
    Ok(vec![DBInfo{field_one: 1, field_two: 2}, DBInfo{field_one: 3, field_two: 4}])
}

fn get_from_cache(id: usize) -> Result<Vec<DBInfo>, Error> {
    // requests from cache
    Ok(vec![DBInfo{field_one: 1, field_two: 2}, DBInfo{field_one: 3, field_two: 4}])
}

fn cache_result(items: Vec<DBInfo>) -> Result<Vec<DBInfo>, Error> {
    // uses items here and returns it after
    Ok(items)
}

fn do_something(info: DBInfo){
    println!("DBInfo element: {:?}", info);
}

fn run(id: usize) -> Result<(), Error> {
    // Step 1:  Try to get a Vec<DBInfo> (serialized json) from cache
    // Step 2:  If cache returns Err, I have to query the db instead
    // Step 3:  Iterate over the Vec<DBInfo> and do_something with each element
    let result = get_from_cache(id).or_else(|_| cache_result(get_from_db(id)?));

    for element in result? {
        do_something(element)
    }

    Ok(())
}


fn main() { run(123).unwrap() }