#!/bin/sh

ETC_HOSTS="/etc/hosts"
DHCP_HOSTS="/tmp/dhcp.hosts"
MERGED_HOSTS="/tmp/merged.hosts"

# Ensure both input files exist
[ -f "$ETC_HOSTS" ] || { echo "Error: $ETC_HOSTS not found!"; exit 1; }
[ -f "$DHCP_HOSTS" ] || { echo "Error: $DHCP_HOSTS not found!"; exit 1; }

# Create a clean merged hosts file
echo "# Merged hosts file - Static + DHCP" > "$MERGED_HOSTS"

# Use associative arrays (requires BusyBox-compatible shell)
awk '
BEGIN {
    # Declare maps to track used IPs and hostnames
    FS=" ";
}

# Process /etc/hosts first
NR == FNR {
    if ($1 ~ /^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$/) {
        ip_map[$1] = 1;  # Track IPs
        for (i = 2; i <= NF; i++) {
            if (!host_map[$i]) {
                host_map[$i] = $1;  # Track hostnames
            } else {
                print "Conflict: hostname \"" $i "\" already exists in /etc/hosts (keeping existing entry)" > "/dev/stderr";
            }
        }
    }
    print > "'$MERGED_HOSTS'";
    next;
}

# Process dhcp.hosts
{
    if ($1 in ip_map) {
        print "Conflict: IP " $1 " already exists in /etc/hosts (ignoring DHCP entry)" > "/dev/stderr";
        next;
    }

    for (i = 2; i <= NF; i++) {
        if ($i in host_map) {
            print "Conflict: hostname \"" $i "\" already exists in /etc/hosts (ignoring DHCP entry)" > "/dev/stderr";
            next;
        }
    }

    print >> "'$MERGED_HOSTS'";
}
' "$ETC_HOSTS" "$DHCP_HOSTS"

echo "Merged hosts file created at $MERGED_HOSTS"