# heavily inspired from https://github.com/oddlama/nix-config/blob/d42cbde676001a7ad8a3cace156e050933a4dcc3/pkgs/deploy.nix
{ name, bc, nix-output-monitor, writeShellApplication, ... }:
writeShellApplication {
  runtimeInputs = [ bc nix-output-monitor ];
  inherit name;
  text = ''
    set -euo pipefail
    shopt -s lastpipe # allow cmd | readarray

    function die() {
        echo "error: $*" >&2
        exit 1
    }
    function show_help() {
        echo 'Usage: deploy [OPTIONS] <host,...> [ACTION]'
        echo "Builds, pushes and activates nixosConfigurations on target systems."
        echo ""
        echo 'ACTION:'
        echo '  switch          [default] Switch immediately to the new configuration and make it the boot default'
        echo '  boot            Make the configuration the new boot default'
        echo "  test            Activate the configuration but don't make it the boot default"
        echo "  dry-activate    Don't activate, just show what would be done"
        echo ""
        echo 'OPTIONS: [passed to nix build]'
    }

    function time_start() {
        T_START=$(date +%s.%N)
    }

    function time_next() {
        T_END=$(date +%s.%N)
        T_LAST=$(${bc}/bin/bc <<< "scale=1; ($T_END - $T_START)/1")
        T_START="$T_END"
    }

    USER_FLAKE_DIR=$(git rev-parse --show-toplevel 2> /dev/null || pwd) ||
        die "Could not determine current working directory. Something went very wrong."
    [[ -e "$USER_FLAKE_DIR/flake.nix" ]] ||
        die "Could not determine location of your project's flake.nix. Please run this at or below your main directory containing the flake.nix."
    cd "$USER_FLAKE_DIR"

    [[ $# -gt 0 ]] || {
        show_help
        exit 1
    }

    OPTIONS=()
    POSITIONAL_ARGS=()
    while [[ $# -gt 0 ]]; do
        case "$1" in
        "help" | "--help" | "-help" | "-h")
            show_help
            exit 1
            ;;

        -*) OPTIONS+=("$1") ;;
        *) POSITIONAL_ARGS+=("$1") ;;
        esac
        shift
    done

    [[ ''${#POSITIONAL_ARGS[@]} -ge 1 ]] ||
        die "Missing argument: <hosts...>"
    [[ ''${#POSITIONAL_ARGS[@]} -le 2 ]] ||
        die "Too many arguments given."

    tr , '\n' <<< "''${POSITIONAL_ARGS[0]}" | sort -u | readarray -t HOSTS
    ACTION="''${POSITIONAL_ARGS[1]-switch}"

    # Expand flake paths for hosts definitions
    declare -A TOPLEVEL_FLAKE_PATHS
    for host in "''${HOSTS[@]}"; do
        TOPLEVEL_FLAKE_PATHS["$host"]=".#nixosConfigurations.$host.config.system.build.toplevel"
    done

    time_start

    # Get outputs of all derivations (should be cached)
    declare -A TOPLEVEL_STORE_PATHS
    for host in "''${HOSTS[@]}"; do
        toplevel="''${TOPLEVEL_FLAKE_PATHS["$host"]}"
        # Make sudo call to get prompt out of the way
        sudo echo "    Building 📦 $host"
        nix build --no-link "''${OPTIONS[@]}" --show-trace --log-format internal-json -v "$toplevel" |& ${nix-output-monitor}/bin/nom --json ||
            die "Failed to get derivation path for $host from ''${TOPLEVEL_FLAKE_PATHS["$host"]}"
        TOPLEVEL_STORE_PATHS["$host"]=$(nix build --no-link --print-out-paths "''${OPTIONS[@]}" "$toplevel")
        time_next
        echo "       Built ✅ $host ''${TOPLEVEL_STORE_PATHS["$host"]} in ''${T_LAST}s"
    done

    current_host=$(hostname)

    for host in "''${HOSTS[@]}"; do
        store_path="''${TOPLEVEL_STORE_PATHS["$host"]}"

        if [ "$host" = "$current_host" ]; then
            echo -e "\033[1;36m    Running locally for $host... \033[m"
            ssh_prefix="sudo"
        else
            echo -e "\033[1;36m     Copying \033[m➡️  \033[34m$host\033[m"
            nix copy --to "ssh://$host" "$store_path"
            time_next
            echo -e "\033[1;32m      Copied \033[m✅  \033[34m$host\033[m \033[90min ''${T_LAST}s\033[m"
            ssh_prefix="ssh $host --"
        fi

        echo -e "\033[1;36m    Applying \033[m⚙️  \033[34m$host\033[m"
        prev_system=$($ssh_prefix readlink -e /nix/var/nix/profiles/system)
        $ssh_prefix /run/current-system/sw/bin/nix-env --profile /nix/var/nix/profiles/system --set "$store_path" ||
            die "Failed to set system profile"
        $ssh_prefix "$store_path"/bin/switch-to-configuration "$ACTION" ||
            echo "Error while activating new system" >&2

        if [[ -n $prev_system ]]; then
            $ssh_prefix nvd --color always diff "$prev_system" "$store_path" || true
        fi

        time_next
        echo -e "\033[1;32m     Applied \033[m✅  \033[34m$host\033[m \033[90min ''${T_LAST}s\033[m"
    done
  '';
}