# takes lines without duplicates from one file and outputs them in another
# Useful for filters, hosts, etc.
import os

seen = set()
filename = './hosts.txt'            # f
filename_out = './hosts_new.txt'    # fout

try:
    with open(filename, 'r+') as f, open('./hosts_new.txt', 'w') as fout:
        lines = f.readlines()
        if not lines:
            print("The file is empty.")
            exit(0)
        print(f"Read {len(lines)} lines from the file.")
        f.seek(0)
        f.truncate()
        for line in lines:
            line_lower = line.lower().strip()  # convert line, strip whitespace - is it necessary?
            if line_lower not in seen:
                fout.write(line)
                seen.add(line_lower)
        print(f"Wrote {len(seen)} unique lines to fout.")
except FileNotFoundError:
    print(f"File not found: {filename}")
except PermissionError:
    print(f"Permission denied. Please run the script as administrator/root.")
except Exception as e:
    print(f"An error occurred: {e}")