use std::time::{SystemTime, UNIX_EPOCH, Duration};

const BASE62: &[u8] = b"0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";

fn to_base62(mut num: u64) -> String {
    let mut encoded = String::new();
    while num > 0 {
        encoded.insert(0, BASE62[(num % 62) as usize] as char);
        num /= 62;
    }
    encoded
}

fn generate_id() -> String {
    let epoch_start = UNIX_EPOCH + Duration::from_millis(1_577_836_800_000); // 2020-01-01
    let now = SystemTime::now().duration_since(epoch_start).unwrap().as_millis() as u64;
    
    let timestamp = now % 1_000_000_000_000; // Keep last 12 digits
    let random_num = rand::random::<u8>() % 100; // Random 2-digit number
    let final_num = timestamp * 100 + random_num as u64;

    let mut id = to_base62(final_num);
    while id.len() < 8 { id.insert(0, '0'); } // Ensure 8-char length

    id
}

fn main() {
    println!("{}", generate_id()); // Example output: "A1b2C3D4"
}