#!/usr/bin/env bash
set -euo pipefail

top=$(dirname "$(realpath "$0")")
hostDir="$top/hosts/$HOSTNAME"
defaultConfigPath="$hostDir/default.nix"
privateConfigPath="$hostDir/private.nix"

case "${1:-}" in
  --default)
    configPath="$defaultConfigPath"
    shift
    ;;
  *)
    if [ -f "$privateConfigPath" ]; then
      configPath="$privateConfigPath"
    else
      configPath="$defaultConfigPath"
    fi
    ;;
esac

if [ ! -f "$configPath" ]; then
  echo "aborting: $configPath doesn't exist"
  exit 1
fi

nixpkgsPath=$(
  cd "$top" &&
  nix-instantiate --eval --raw \
    --argstr host "$HOSTNAME" \
    --expr '
      { host }:
      let
        toml = builtins.readFile ./hosts/${host}/metadata.toml;
        channel = (builtins.fromTOML toml).channel;
      in
      (import ./npins).${channel}.outPath
    '
)

(
  # The result symlink created in the current directory is registered as a root of the Nix
  # garbage collector, so it's important that we call nixos-rebuild from the host directory.
  # (nix-build has an --out-link option but that option cannot be set via nixos-rebuild).
  cd "$hostDir" &&

  # nixos-rebuild always reads Nixpkgs from the NIX_PATH,
  # so we need to set it explicitly to our pinned version
  exec nixos-rebuild "$@" -I nixpkgs="$nixpkgsPath" -I nixos-config="$configPath" -I top="$top"
)