use std::{convert, ops::Index};

const B64TABLE: &str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789._";

fn b64(data: &[u8]) -> String {
    let binary: Vec<u8> = data
        .iter()
        .flat_map(|b| (0..8).rev().map(move |i| (b >> i) & 1))
        .collect();
    let mut chunks: Vec<Vec<u8>> = binary.chunks(6).map(|s| s.to_vec()).collect();
    let last = chunks.last_mut().unwrap();
    if last.len() < 6 {
        for _ in last.len()..6 {
            last.push(0);
        }
    }
    let decimal: Vec<u8> = chunks
        .iter()
        .map(|bits| bits.iter().fold(0, |acc, &bit| (acc << 1) | bit))
        .collect();
    let mut converted: Vec<String> = Vec::new();

    for dec in decimal {
        converted.push(B64TABLE.chars().nth(dec as usize).unwrap().to_string());
    }
    match data.len() % 3 {
        1 => {
            converted.push("--".to_string());
        }
        2 => {
            converted.push("-".to_string());
        }
        _ => {}
    }
    converted.join("")
}
pub fn compute_disc_id(first_track: u8, last_track: u8, leadout: u32, offsets: &[u32]) -> String {
    let mut toc = String::new();
    toc.push_str(&format!("{first_track:02X}{last_track:02X}{leadout:08X}"));
    for i in 0..99 {
        let offset = offsets.get(i).copied().unwrap_or(0);
        toc.push_str(&format!("{:08X}", offset));
    }
    toc
}
#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn known_example() {
        let first_track = 1;
        let last_track = 12;
        let leadout = 224556;
        let offsets = [
            150, 9078, 13528, 34182, 53768, 70987, 96424, 118425, 136793, 159514, 179777, 198006,
        ];
        assert_eq!(
            compute_disc_id(first_track, last_track, leadout, &offsets),
            "T_prJXQSrqbnH8OE.dgOKsHm5Uw-"
        );
    }
    #[test]
    fn base64() {
        assert_eq!(b64("Man".as_bytes()), "TWFu".to_string());
        assert_eq!(b64("M".as_bytes()), "TQ--".to_string());
        assert_eq!(b64("Ma".as_bytes()), "TWE-".to_string());
    }
}