#!/usr/bin/env bash
# @file ~/.local/bin/add-usergroup
# @brief Add a user and a group with the same name on either Linux or macOS
# @description
#     This script is utilized by other scripts to ensure that there is both a user and group
#     named by the two arguments that this executable accepts. It checks whether or not
#     there is already a user / group with the name present on the system before running
#     any code.

set -euo pipefail

### Check if the script is being run as root
if [[ $EUID -ne 0 ]]; then
  logg error "This script must be run as root"
  exit 1
fi

### Check if the correct number of arguments is provided
if [ "$#" -ne 2 ]; then
    logg error "Usage: $0 <username> <groupname>"
    exit 1
fi

### Assign arguments to variables
USERNAME="$1"
GROUPNAME="$2"

### Function to find the next available system ID on macOS
find_next_system_id_macos() {
    local id_type="$1"
    local id_tag="$2"
    local current_ids="$(dscl . -list /$id_type "$id_tag" | awk '{print $2}')"
    local min_id=20  # Start from 20 to avoid conflict with default system users/groups

    for id in $current_ids; do
        if [ "$id" -ge "$min_id" ] && [ "$id" -lt 500 ]; then
            min_id="$((id + 1))"
        fi
    done
    echo "$min_id"
}

### Detect the operating system
OS="$(uname)"

if [ "$OS" == "Darwin" ]; then
    ### macOS

    ### Create the group if it does not exist
    if ! dscl . -list /Groups | grep -q "^$GROUPNAME\$"; then
        logg info "Creating system group: $GROUPNAME"
        SYSTEM_GID="$(find_next_system_id_macos "Groups" "PrimaryGroupID")"
        logg info "Initializing $GROUPNAME group"
        sudo dscl . -create "/Groups/$GROUPNAME"
        logg info "Assigning $SYSTEM_GID PrimaryGroupID to group"
        sudo dscl . -create "/Groups/$GROUPNAME" PrimaryGroupID "$SYSTEM_GID"
    else
        logg info "Group $GROUPNAME already exists"
        SYSTEM_GID=$(dscl . -read "/Groups/$GROUPNAME" PrimaryGroupID | awk '{print $2}')
    fi

    ### Create the user if it does not exist
    if ! id -u "$USERNAME" > /dev/null 2>&1; then
        logg info "Creating system user: $USERNAME"
        SYSTEM_UID="$(find_next_system_id_macos "Users" "UniqueID")"
        logg info "Initializing $USERNAME user"
        sudo dscl . -create "/Users/$USERNAME"
        logg info "Assigning $USERNAME user attributes"
        sudo dscl . -create "/Users/$USERNAME" UserShell /bin/bash
        sudo dscl . -create "/Users/$USERNAME" RealName "$USERNAME"
        sudo dscl . -create "/Users/$USERNAME" UniqueID "$SYSTEM_UID"
        sudo dscl . -create "/Users/$USERNAME" PrimaryGroupID "$SYSTEM_GID"
        sudo dscl . -create "/Users/$USERNAME" NFSHomeDirectory /var/empty
        logg info "Finished assigning $USERNAME user attributes"
    else
        logg info "User $USERNAME already exists"
    fi

    ### Add the user to the group
    logg info "Adding user $USERNAME to group $GROUPNAME"
    sudo dscl . -append "/Groups/$GROUPNAME" GroupMembership "$USERNAME"

    logg info "System user $USERNAME added to system group $GROUPNAME successfully."

elif [ "$OS" == "Linux" ]; then
    ### Linux

    ### Create the group if it does not exist
    if ! getent group "$GROUPNAME" > /dev/null 2>&1; then
        logg info "Creating system group: $GROUPNAME"
        sudo groupadd -r "$GROUPNAME"
    else
        logg info "Group $GROUPNAME already exists"
    fi

    ### Create the user if it does not exist
    if ! id -u "$USERNAME" > /dev/null 2>&1; then
        logg info "Creating system user: $USERNAME"
        sudo useradd -r -g "$GROUPNAME" -s /bin/bash -M -N "$USERNAME"
    else
        logg info "User $USERNAME already exists"
    fi

    ### Add the user to the group (redundant on Linux since user is already added to the group during creation)
    sudo usermod -a -G "$GROUPNAME" "$USERNAME"

    logg info "System user $USERNAME added to system group $GROUPNAME successfully."

else
    logg info "Unsupported operating system: $OS"
    exit 1
fi