# The root-side copy of the cache facts the host's nix daemon and hive-priv use:
# the key a closure must be signed by, the netrc the pull token goes out in and
# the CA bundle that trusts the cache. The script runs as root on the hive host
# under the hive's own store identity and writes:
#
# - the key into `dir`, which only root can read;
# - the netrc at `netrcFile`, root 0600: the pull token's entry for `host` then
#   the entries of the host's own netrc (`hostNetrc`), as `netrc-file` is one path;
# - the CA bundle at `caBundleFile`, root 0644: the host's own bundle
#   (`baseBundle`) then the swarm's root (`swarmCa`), when the host holds it,
#   which the cache's certificate chains to; `ssl-cert-file` is one path too;
# - a nix.conf fragment at `confFile` that the host's nix.conf includes, with
#   `extra-substituters` (the cache's address), `extra-trusted-public-keys`,
#   `netrc-file` and `ssl-cert-file`. It holds no secret.
#
# Nothing is read from a file hive-c0re (unprivileged) writes: the key and the
# token come from the store. A store that holds no facts yet, or cannot be
# reached, leaves what is in `dir`, `netrcFile`, `caBundleFile` and `confFile`
# as they are. Nothing here removes a file.
#
# Pure function — NOT a NixOS module. Call it from a unit's `script`, with `bao`,
# `coreutils`, `gnugrep`, `systemd` on its `path` and the `BAO_*` client set:
#
#   script = import ./lib/attic-root-facts.nix { inherit lib; } {
#     hive = "alpha"; host = "attic.example.org"; dir = "/run/hyperhive-priv/attic";
#     url = "https://attic.example.org/swarm"; confFile = "/run/hyperhive-nix/cache.conf";
#     netrcFile = "/run/hyperhive-nix/netrc"; hostNetrc = "/etc/nix/netrc";
#     caBundleFile = "/run/hyperhive-nix/ca-bundle.crt"; baseBundle = "/etc/ssl/certs/ca-certificates.crt";
#     swarmCa = "/var/lib/hive-tls/swarm-services-root.pem";
#   };
{ lib }:
{
  # The hive's name in the store: facts are read from
  # `secret/swarm/hives/<hive>/attic/`.
  hive,
  # The cache server's host name, which the netrc line names.
  host,
  # Where the key goes.
  dir,
  # The cache's address as the daemon lists it in `extra-substituters`.
  url,
  # Where the nix.conf fragment goes; its directory is root's and readable.
  confFile,
  # Where the merged netrc goes, and the netrc the host uses without this
  # module, which is merged in and never written.
  netrcFile,
  hostNetrc,
  # Where the CA bundle goes.
  caBundleFile,
  # The CA bundle nix uses without this module, copied in and never written:
  # `ssl-cert-file` is one path, so a fragment that names the new bundle must
  # carry the host's CAs.
  baseBundle,
  # The swarm's root certificate. The file may be absent: the bundle then holds
  # the host's CAs alone until a later run finds it.
  swarmCa,
}:
''
  set -euo pipefail
  ${import ./store-seeded-secret.nix { }}
  ${import ./atomic-write-secret.nix { }}
  ${import ./refresh-consumer.nix { }}

  dir=${lib.escapeShellArg dir}
  conf=${lib.escapeShellArg confFile}
  netrc_file=${lib.escapeShellArg netrcFile}
  host_netrc=${lib.escapeShellArg hostNetrc}
  ca_bundle_file=${lib.escapeShellArg caBundleFile}
  base_bundle=${lib.escapeShellArg baseBundle}
  swarm_ca=${lib.escapeShellArg swarmCa}
  install -d -m 0700 "$dir"
  install -d -m 0755 "$(dirname -- "$conf")" "$(dirname -- "$netrc_file")" "$(dirname -- "$ca_bundle_file")"

  store_init
  store_login
  if [ "$STORE_UP" != 1 ]; then
    echo "could not read the cache facts; $dir stays as it is." >&2
    exit 1
  fi

  # <leaf> <variable>. Sets the variable to the leaf's value. A leaf the store
  # does not hold sets `missing`; any other failure ends the run.
  missing=0
  fetch() {
    local value
    if value="$(store_bao kv get -field=value ${lib.escapeShellArg "secret/swarm/hives/${hive}/attic"}/"$1" 2>"$STORE_ERR")"; then
      printf -v "$2" '%s' "$value"
    elif grep -qi 'no value found' "$STORE_ERR"; then
      missing=1
    else
      cat "$STORE_ERR" >&2
      echo "could not read the cache fact $1; $dir stays as it is." >&2
      exit 1
    fi
  }

  key=""
  token=""
  fetch public-key key
  fetch pull-token token
  if [ "$missing" = 1 ]; then
    echo "the swarm has not given this hive its cache facts yet; $dir stays as it is."
    exit 0
  fi

  # One token each: both land in a file nix and hive-priv parse by whitespace.
  if [[ ! "$key" =~ ^[^[:space:]:]+:[^[:space:]]+$ ]] || [[ ! "$token" =~ ^[^[:space:]]+$ ]]; then
    echo "the stored cache facts are not a <name>:<key> and a single token; $dir stays as it is." >&2
    exit 1
  fi

  # Written only when the value changed, so the files keep their mtime between
  # runs. The owner is the running user, root, and the mode is 0600.
  if secret_differs "$dir/public-key" "$key"; then
    atomic_write_secret 0600 "" "$dir/public-key" "$key"
  fi

  # The host's netrc without its lines for this cache's host: an entry runs from
  # a `machine` or `default` line to the next one. A missing file is no entries.
  # Our entry goes first, which is the one curl takes when an entry the filter
  # does not recognise names the cache's host too.
  other_netrc_entries() {
    local line skip=0 tok kept=""
    [ -f "$host_netrc" ] || return 0
    while IFS= read -r line || [ -n "$line" ]; do
      read -ra tok <<<"$line"
      case "''${tok[0]-}" in
        machine) if [ "''${tok[1]-}" = ${lib.escapeShellArg host} ]; then skip=1; else skip=0; fi ;;
        default) skip=0 ;;
      esac
      [ "$skip" = 1 ] || kept+="$line"$'\n'
    done <"$host_netrc"
    printf '%s' "$kept"
  }
  netrc="machine ${host} password $token"
  others="$(other_netrc_entries)"
  if [ -n "$others" ]; then netrc="$netrc"$'\n'"$others"; fi
  # The mode too: an earlier deploy left this path 0640 for a group.
  if secret_differs "$netrc_file" "$netrc" || [ "$(stat -c %a "$netrc_file")" != 600 ]; then
    atomic_write_secret 0600 "" "$netrc_file" "$netrc"
  fi

  # The host's CAs, then the swarm's root. Nix reads the file for each
  # download, so a root that lands after the fragment reaches the next one
  # without a restart. A file without a certificate is not appended: the bundle
  # serves every https fetch of every nix client.
  if [ ! -r "$base_bundle" ]; then
    echo "cannot read the host's CA bundle $base_bundle; $ca_bundle_file stays as it is." >&2
    exit 1
  fi
  bundle="$(< "$base_bundle")"
  if [ -s "$swarm_ca" ] && grep -q -- '-----BEGIN CERTIFICATE-----' "$swarm_ca"; then
    bundle+=$'\n'"$(< "$swarm_ca")"
  else
    echo "the swarm's root $swarm_ca is not on this host yet; $ca_bundle_file holds the host's CAs only."
  fi
  if secret_differs "$ca_bundle_file" "$bundle" || [ "$(stat -c %a "$ca_bundle_file")" != 644 ]; then
    atomic_write_secret 0644 "" "$ca_bundle_file" "$bundle"
  fi

  # Last, so a daemon that reads the fragment finds the netrc and the bundle in
  # place. The mtime moves only with the content. Lix re-reads nix.conf for
  # every connection, CppNix only at start, so a CppNix daemon that started
  # before this write is restarted.
  printf -v fragment '%s\n%s\n%s\n%s' \
    ${lib.escapeShellArg "extra-substituters = ${url}"} \
    "extra-trusted-public-keys = $key" \
    "netrc-file = $netrc_file" \
    "ssl-cert-file = $ca_bundle_file"
  if secret_differs "$conf" "$fragment"; then
    atomic_write_secret 0644 "" "$conf" "$fragment"
  fi
  refresh_unit nix-daemon.service "$conf"
''