#!/bin/bash
# Shared helpers for raspberrypi scripts. Sourced, not executed directly:
#   SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
#   source "${SCRIPT_DIR}/lib/common.sh"

require_root() {
    if [ "$(id -u)" -ne 0 ]; then
        echo "Must run as root." >&2
        exit 1
    fi
}

# backup_file <path>
# Copies an existing file to <path>.bak.<epoch>. No-op if it doesn't exist.
backup_file() {
    local path="$1"
    if [ -f "$path" ]; then
        cp "$path" "${path}.bak.$(date +%s)"
        echo "Backed up ${path}"
    fi
}

# write_if_changed <path> <content>
# Writes content to path only if it differs from what's already there,
# backing up the previous version first. Prints what happened.
write_if_changed() {
    local path="$1" content="$2"
    if [ -f "$path" ] && [ "$(cat "$path")" = "$content" ]; then
        echo "Already up to date: $path"
        return 0
    fi
    backup_file "$path"
    printf '%s\n' "$content" > "$path"
    echo "Wrote $path"
}