# The root-side copy of the cache facts the host's nix daemon and hive-priv
# trust: 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 both into `dir`, which only root can read, and
# a nix.conf fragment at `confFile` that the host's nix.conf includes.
#
# What the daemon and hive-priv decide on is here or in the host's
# configuration, and nothing is read from a file hive-c0re (unprivileged)
# writes: the key and the token come from the store, the cache's address from
# `services.hyperhive.swarm.attic.{domain,cache}`. The fragment holds no secret
# (the key is public, the netrc stays in `dir`) and hive-c0re can read it: it
# takes the cache's address from there.
#
# A store that holds no facts yet, or cannot be reached, leaves what is in `dir`
# 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";
#   };
{ 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 and the netrc go.
  dir,
  # The cache's address as the daemon lists it in `trusted-substituters`.
  url,
  # Where the nix.conf fragment goes; its directory is root's and readable.
  confFile,
}:
''
  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}
  install -d -m 0700 "$dir"
  install -d -m 0755 "$(dirname -- "$conf")"

  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
  netrc="machine ${host} password $token"
  if secret_differs "$dir/netrc" "$netrc"; then
    atomic_write_secret 0600 "" "$dir/netrc" "$netrc"
  fi

  # Last, so a daemon that reads the fragment finds the netrc in place. The
  # address is the one hive-c0re may name as the substituter. The mtime moves
  # only with the content. Lix re-reads nix.conf for every connection, CppNix
  # only at start, so a daemon that started before this write is restarted.
  printf -v fragment '%s\n%s\n%s' \
    ${lib.escapeShellArg "extra-trusted-substituters = ${url}"} \
    "extra-trusted-public-keys = $key" \
    "netrc-file = $dir/netrc"
  if secret_differs "$conf" "$fragment"; then
    atomic_write_secret 0644 "" "$conf" "$fragment"
  fi
  refresh_unit nix-daemon.service "$conf"
''