#!/bin/bash

# Usage: ./ping_sweep.sh <subnet-prefix>
# Example: ./ping_sweep.sh 192.168.1

if [ -z "$1" ]; then
    echo "Usage: $0 <subnet-prefix>"
    echo "Example: $0 192.168.1"
    exit 1
fi

SUBNET="$1"

echo "Scanning $SUBNET.1 to $SUBNET.254..."
echo "-------------------------------------"

TEMP_FILE=$(mktemp)

for host in {1..254}; do
    (
        IP="$SUBNET.$host"
        if ping -c 2 -W 1 "$IP" > /dev/null 2>&1; then
            # Try getent first, then fall back to host command for PTR lookup
            HOSTNAME=$(getent hosts "$IP" | awk '{print $2}')
            if [ -z "$HOSTNAME" ]; then
                HOSTNAME=$(host "$IP" 2>/dev/null | awk '/domain name pointer/ {print $NF}' | sed 's/\.$//')
            fi

            if [ -n "$HOSTNAME" ]; then
                echo "$IP (Hostname: $HOSTNAME)" >> "$TEMP_FILE"
            else
                echo "$IP (Hostname: Unknown)" >> "$TEMP_FILE"
            fi
        fi
    ) &
done

# Wait for all background tasks to finish
wait

# Output online hosts sorted naturally by IP
if [ -s "$TEMP_FILE" ]; then
    sort -V "$TEMP_FILE" | while read -r line; do
        echo "[+] $line"
    done
fi

# Calculate total hosts found
TOTAL_ONLINE=$(wc -l < "$TEMP_FILE" | tr -d ' ')

# Clean up temp file
rm -f "$TEMP_FILE"

echo "-------------------------------------"
echo "Scan complete. Total online hosts found: $TOTAL_ONLINE"