use crate::keydata::SPKI_DER;

pub fn build_min_cert() -> Vec<u8> {
    let sig_alg = der_seq(&der_oid(&[0x2a]));

    let name = der_seq(&[]);

    let not_before = der_tlv(0x17, b"000101000000Z");
    let not_after = der_tlv(0x17, b"490101000000Z");
    let validity = der_seq(&[not_before, not_after].concat());

    let cert_spki = SPKI_DER.to_vec();
    let tbs = der_seq(
        &[
            der_int(&[1]),
            sig_alg.clone(),
            name.clone(),
            validity,
            name,
            cert_spki,
        ]
        .concat(),
    );

    let sig_bitstring = der_tlv(0x03, &[0x00]);

    der_seq(&[tbs, sig_alg, sig_bitstring].concat())
}

fn der_len(len: usize) -> Vec<u8> {
    if len < 0x80 {
        vec![len as u8]
    } else {
        let mut b = Vec::new();
        let mut l = len;
        while l > 0 {
            b.insert(0, (l & 0xff) as u8);
            l >>= 8;
        }
        let mut out = vec![0x80 | b.len() as u8];
        out.extend_from_slice(&b);
        out
    }
}
fn der_tlv(tag: u8, body: &[u8]) -> Vec<u8> {
    let mut out = vec![tag];
    out.extend_from_slice(&der_len(body.len()));
    out.extend_from_slice(body);
    out
}
fn der_seq(body: &[u8]) -> Vec<u8> {
    der_tlv(0x30, body)
}
fn der_oid(bytes: &[u8]) -> Vec<u8> {
    der_tlv(0x06, bytes)
}
fn der_int(bytes: &[u8]) -> Vec<u8> {
    let mut b = bytes.to_vec();
    if !b.is_empty() && b[0] & 0x80 != 0 {
        b.insert(0, 0x00);
    }
    der_tlv(0x02, &b)
}