pub fn compile_admin(
    settings: &Settings,
    administration: &crate::settings::Administration,
    directory: Option<&Path>,
) -> Result<Option<Arc<ServerConfig>>> {
    if !administration.tls {
        return Ok(None);
    }
    let directory = directory.context("administration TLS requires a certificate directory")?;
    settings.policy.validate()?;
    let key = if let Some(id) = administration.certificate_id.as_deref() {
        let certificate = settings
            .certificates
            .iter()
            .find(|certificate| certificate.id == id)
            .context("administration certificate id is unknown")?;
        Arc::new(load_pair(
            directory,
            &certificate.cert_file,
            &certificate.key_file,
        )?)
    } else {
        Arc::new(load_pair(directory, "default.pem", "default.key")?)
    };
    #[derive(Debug)]
    struct Fixed(Arc<CertifiedKey>);
    impl ResolvesServerCert for Fixed {
        fn resolve(&self, _: ClientHello<'_>) -> Option<Arc<CertifiedKey>> {
            Some(self.0.clone())
        }
    }
    Ok(Some(server_config(
        Arc::new(Fixed(key)),
        &settings.policy,
        true,
    )?))
}
fn write_new(path: &Path, bytes: &[u8]) -> Result<()> {
    let mut options = OpenOptions::new();
    options.write(true).create_new(true);
    #[cfg(unix)]
    {
        use std::os::unix::fs::OpenOptionsExt;
        options.mode(0o600).custom_flags(libc::O_NOFOLLOW);
    }
    let mut file = options.open(path)?;
    file.write_all(bytes)?;
    file.sync_all()?;
    Ok(())
}
fn store_pair(directory: &Path, name: &str, cert: &[u8], key: &[u8]) -> Result<()> {
    safe_name(name)?;
    let cert_path = directory.join(format!("{name}.pem"));
    let key_path = directory.join(format!("{name}.key"));
    ensure!(
        !cert_path.try_exists()? && !key_path.try_exists()?,
        "certificate files already exist; use a new name for safe rotation"
    );
    parse_pair(cert, key)?;
    write_new(&key_path, key)?;
    if let Err(error) = write_new(&cert_path, cert) {
        let _ = fs::remove_file(&key_path);
        return Err(error);
    }
    #[cfg(unix)]
    std::fs::File::open(directory)?.sync_all()?;
    Ok(())
}
fn generate_locked(directory: &Path, name: &str, hosts: Vec<String>) -> Result<()> {
    ensure!(!hosts.is_empty(), "provide at least one certificate SAN");
    let hosts = hosts
        .into_iter()
        .map(|host| {
            if host.parse::<std::net::IpAddr>().is_ok() {
                Ok(host)
            } else {
                normalize_host_pattern(&host)
            }
        })
        .collect::<Result<Vec<_>>>()?;
    let rcgen::CertifiedKey { cert, signing_key } = rcgen::generate_simple_self_signed(hosts)?;
    let key = Zeroizing::new(signing_key.serialize_pem());
    store_pair(directory, name, cert.pem().as_bytes(), key.as_bytes())
}
pub fn initialize_default(directory: &Path) -> Result<()> {
    crate::auth::prepare_directory(directory)?;
    let _lock = crate::auth::lock_directory(directory)?;
    let cert = directory.join("default.pem").try_exists()?;
    let key = directory.join("default.key").try_exists()?;
    ensure!(
        cert == key,
        "incomplete default certificate pair; restore both default.pem and default.key"
    );
    if !cert {
        generate_locked(
            directory,
            "default",
            vec![
                "localhost".into(),
                "demo.localhost".into(),
                "127.0.0.1".into(),
                "::1".into(),
            ],
        )?;
    }
    load_pair(directory, "default.pem", "default.key")?;
    Ok(())
}
pub fn generate(directory: &Path, name: &str, hosts: Vec<String>) -> Result<()> {
    ensure!(
        name != "default",
        "the default certificate is managed at startup; use another name"
    );
    crate::auth::prepare_directory(directory)?;
    let _lock = crate::auth::lock_directory(directory)?;
    generate_locked(directory, name, hosts)
}
pub fn import(directory: &Path, name: &str, cert: PathBuf, key: PathBuf) -> Result<()> {
    ensure!(
        name != "default",
        "use a named certificate and configure default_certificate instead"
    );
    crate::auth::prepare_directory(directory)?;
    let _lock = crate::auth::lock_directory(directory)?;
    store_pair(
        directory,
        name,
        &read_pem(&cert, false)?,
        &read_pem(&key, true)?,
    )
}

#[derive(Debug, PartialEq, Eq)]
pub enum ExternalPairDeployment {
    Unchanged {
        covered_hosts: Vec<String>,
    },
    Staged {
        cert_file: String,
        key_file: String,
        covered_hosts: Vec<String>,
    },
}

fn external_generation_pair(certificate_id: &str, cert_file: &str, key_file: &str) -> bool {
    let prefix = format!("external-{certificate_id}-");
    let Some(cert_stem) = cert_file.strip_suffix(".pem") else {
        return false;
    };
    let Some(key_stem) = key_file.strip_suffix(".key") else {
        return false;
    };
    cert_stem == key_stem && cert_stem.starts_with(&prefix)
}

pub fn reconcile_external_pair(
    directory: &Path,
    certificate_id: &str,
    current_pair: Option<(&str, &str)>,
    certificate: &[u8],
    key: &[u8],
) -> Result<ExternalPairDeployment> {
    ensure!(
        crate::config::valid_id(certificate_id),
        "invalid certificate id"
    );
    ensure!(
        certificate.len() <= MAX_PEM as usize && key.len() <= MAX_PEM as usize,
        "each PEM input is limited to 128 KiB"
    );
    parse_pair(certificate, key)?;
    let covered_hosts = certificate_dns_names(certificate)?;
    crate::auth::prepare_directory(directory)?;
    let _lock = crate::auth::lock_directory(directory)?;

    if let Some((cert_file, key_file)) = current_pair {
        if external_generation_pair(certificate_id, cert_file, key_file) {
            let current_certificate = read_pem(&directory.join(cert_file), false);
            let current_key = read_pem(&directory.join(key_file), true);
            if let (Ok(current_certificate), Ok(current_key)) = (current_certificate, current_key) {
                if current_certificate.as_slice() == certificate && current_key.as_slice() == key {
                    return Ok(ExternalPairDeployment::Unchanged { covered_hosts });
                }
            }
        }
    }

    let name = format!(
        "external-{}-{:032x}",
        certificate_id,
        rand::random::<u128>()
    );
    store_pair(directory, &name, certificate, key)?;
    Ok(ExternalPairDeployment::Staged {
        cert_file: format!("{name}.pem"),
        key_file: format!("{name}.key"),
        covered_hosts,
    })
}

pub fn stage_external_pair(
    directory: &Path,
    certificate_id: &str,
    certificate: &[u8],
    key: &[u8],
) -> Result<(String, String, Vec<String>)> {
    match reconcile_external_pair(directory, certificate_id, None, certificate, key)? {
        ExternalPairDeployment::Staged {
            cert_file,
            key_file,
            covered_hosts,
        } => Ok((cert_file, key_file, covered_hosts)),
        ExternalPairDeployment::Unchanged { .. } => {
            unreachable!("reconcile without a current pair always stages")
        }
    }
}

pub fn remove_external_pair(directory: &Path, cert_file: &str, key_file: &str) -> Result<()> {
    safe_name(cert_file)?;
    safe_name(key_file)?;
    ensure!(
        cert_file.starts_with("external-")
            && cert_file.ends_with(".pem")
            && key_file.starts_with("external-")
            && key_file.ends_with(".key"),
        "refusing to remove non-external certificate files"
    );
    for file in [cert_file, key_file] {
        match fs::remove_file(directory.join(file)) {
            Ok(()) => {}
            Err(error) if error.kind() == io::ErrorKind::NotFound => {}
            Err(error) => return Err(error.into()),
        }
    }
    #[cfg(unix)]
    std::fs::File::open(directory)?.sync_all()?;
    Ok(())
}

pub fn for_all_frontends(
    settings: &Settings,
    vhosts: &[crate::vhost::Vhost],
    redirects: &[crate::redirect::Host],
    not_found_hosts: &[crate::not_found::Host],
) -> Result<Settings> {
    let mut result = settings.clone();
    let certificate_ids: std::collections::HashSet<_> =
        result.certificates.iter().map(|c| c.id.clone()).collect();
    let mut assignments = std::collections::HashMap::<String, String>::new();
    let mut assign = |hosts: &[String], id: &str, owner: &str| -> Result<()> {
        ensure!(
            certificate_ids.contains(id),
            "{owner} references unknown certificate id"
        );
        for host in hosts {
            if let Some(old) = assignments.insert(host.clone(), id.to_owned()) {
                ensure!(
                    old == id,
                    "same hostname cannot select different TLS certificates"
                );
            }
        }
        Ok(())
    };
    for vhost in vhosts {
        if let Some(id) = &vhost.certificate_id {
            let hosts = vhost.routing_hosts()?;
            assign(&hosts, id, "vhost")?;
            if vhost.allow_certificate_mismatch {
                for host in hosts {
                    result.forced_mismatches.insert((id.clone(), host));
                }
            }
        }
    }
    for redirect in redirects {
        if let Some(id) = &redirect.certificate_id {
            assign(&redirect.frontend.hosts, id, "redirect")?;
        }
    }
    for host in not_found_hosts {
        if let Some(id) = &host.certificate_id {
            assign(&host.frontend.hosts, id, "404 host")?;
        }
    }
    for cert in &mut result.certificates {
        cert.hosts.retain(|host| {
            !assignments.contains_key(host.to_ascii_lowercase().trim_end_matches('.'))
        });
        for (host, id) in &assignments {
            if id == &cert.id {
                cert.hosts.push(host.clone());
            }
        }
        cert.hosts.sort();
        cert.hosts.dedup();
    }
    Ok(result)
}

pub fn for_frontends(
    settings: &Settings,
    vhosts: &[crate::vhost::Vhost],
    redirects: &[crate::redirect::Host],
) -> Result<Settings> {
    for_all_frontends(settings, vhosts, redirects, &[])
}

pub fn for_vhosts(settings: &Settings, vhosts: &[crate::vhost::Vhost]) -> Result<Settings> {
    for_frontends(settings, vhosts, &[])
}
pub fn upload(
    directory: &Path,
    certificate: &[u8],
    key: &[u8],
    hosts: Vec<String>,
) -> Result<Certificate> {
    ensure!(
        certificate.len() <= MAX_PEM as usize && key.len() <= MAX_PEM as usize,
        "each PEM input is limited to 128 KiB"
    );
    ensure!(!hosts.is_empty(), "provide at least one vhost name");
    let certified = parse_pair(certificate, key)?;
    let covered_hosts = certificate_dns_names(certificate)?;
    let mut resolver = ResolvesServerCertUsingSni::new();
    for host in &hosts {
        let host = normalize_host_pattern(host)?;
        let validation_name = host
            .strip_prefix("*.")
            .map(|base| format!("rustproxy-wildcard-check.{base}"))
            .unwrap_or_else(|| host.clone());
        resolver
            .add(&validation_name, certified.clone())
            .context("certificate does not cover vhost name")?;
    }
    crate::auth::prepare_directory(directory)?;
    let _lock = crate::auth::lock_directory(directory)?;
    let staged = fs::read_dir(directory)?
        .filter_map(|e| e.ok())
        .filter(|e| {
            e.file_name().to_string_lossy().starts_with("upload-")
                && e.path().extension().is_some_and(|x| x == "key")
        })
        .count();
    ensure!(
        staged < 128,
        "upload storage limit reached; remove unused upload-* pairs locally"
    );
    let id = format!("upload-{:032x}", rand::random::<u128>());
    store_pair(directory, &id, certificate, key)?;
    Ok(Certificate {
        issuer: None,
        cert_file: format!("{id}.pem"),
        key_file: format!("{id}.key"),
        id,
        covered_hosts,
        hosts: Vec::new(),
    })
}
pub fn validate_acme(
    directory: &Path,
    id: String,
    cert_file: String,
    key_file: String,
    domains: &[String],
) -> Result<Certificate> {
    ensure!(crate::config::valid_id(&id), "invalid ACME certificate id");
    ensure!(
        cert_file.starts_with("acme-") && key_file.starts_with("acme-"),
        "invalid ACME output name"
    );
    ensure!(!domains.is_empty(), "ACME requires at least one domain");
    let key = load_pair(directory, &cert_file, &key_file)?;
    let certificate_pem = read_pem(&directory.join(&cert_file), false)?;
    let covered_hosts = certificate_dns_names(&certificate_pem)?;
    let mut resolver = ResolvesServerCertUsingSni::new();
    for domain in domains {
        let domain = normalize_host_pattern(domain)?;
        let name = domain
            .strip_prefix("*.")
            .map(|d| format!("rustproxy-acme-check.{d}"))
            .unwrap_or_else(|| domain.clone());
        resolver
            .add(&normalize_host(&name)?, key.clone())
            .context("ACME certificate does not cover requested domain")?;
    }
    Ok(Certificate {
        issuer: None,
        id,
        covered_hosts,
        hosts: Vec::new(),
        cert_file,
        key_file,
    })
}