# The root-side copy of the cache facts the host's nix daemon and hive-priv
# use: the key a downloaded closure must be signed by and the netrc the pull
# token goes out in. 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`
#   followed by the entries of the host's own netrc (`hostNetrc`) for other
#   machines. `netrc-file` is one path, so a fragment that names this file must
#   carry what the host already keeps there;
# - a nix.conf fragment at `confFile` that the host's nix.conf includes, with
#   `extra-substituters` (the cache's address), `extra-trusted-public-keys` and
#   `netrc-file` (that merged netrc), so the daemon
#   substitutes from the cache and its other substituters. 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` 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` and `systemd` on its `path` and the `BAO_*`
# client environment 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";
#   };
{ 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,
}:
''
  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}
  install -d -m 0700 "$dir"
  install -d -m 0755 "$(dirname -- "$conf")" "$(dirname -- "$netrc_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

  # Last, so a daemon that reads the fragment finds the netrc 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' \
    ${lib.escapeShellArg "extra-substituters = ${url}"} \
    "extra-trusted-public-keys = $key" \
    "netrc-file = $netrc_file"
  if secret_differs "$conf" "$fragment"; then
    atomic_write_secret 0644 "" "$conf" "$fragment"
  fi
  refresh_unit nix-daemon.service "$conf"
''