package ui;

import model.asn1.exceptions.ParseException;

import java.math.BigInteger;
import java.nio.charset.StandardCharsets;
import java.util.Base64;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Useful small methods for the whole program.
 */
public final class Utils {
    /**
     * EFFECTS: Convert the input primitive byte array into the boxed Byte array.
     */
    public static Byte[] byteToByte(byte[] array) {
        Byte[] arr = new Byte[array.length];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = array[i];
        }
        return arr;
    }

    /**
     * EFFECTS: Convert the input boxed Byte array into primitive byte array.
     */
    public static byte[] byteToByte(Byte[] array) {
        byte[] arr = new byte[array.length];
        for (int i = 0; i < arr.length; i++) {
            arr[i] = array[i];
        }
        return arr;
    }

    /**
     * EFFECTS: Pack the big-endian bytes into a 32bit integer.
     * Throws {@link model.asn1.exceptions.ParseException} if the value is too large.
     */
    public static int bytesToInt(Byte[] array) throws ParseException {
        try {
            return new BigInteger(byteToByte(array)).intValueExact();
        } catch (ArithmeticException ignored) {
            throw new ParseException("Value is too large.");
        }
    }

    /**
     * EFFECTS: Unpack the multibyte 64bit integer to its shortest array of byte format. Remove leading empty byte
     * if that number is not zero.
     */
    public static Byte[] valToByte(long val) {
        byte[] v = BigInteger.valueOf(val).toByteArray();
        if (val != 0 && v[0] == 0) {
            if (v.length == 1) {
                return new Byte[0];
            }
            byte[] arr = new byte[v.length - 1];
            System.arraycopy(v, 1, arr, 0, arr.length);
            return byteToByte(arr);
        }
        return byteToByte(v);
    }

    /**
     * EFFECTS: Decode the input PEM file, with optional check on tags. \n must present after each line, optional after
     * the last.
     * Throws {@link ParseException} if the desiredTag is specified but the input does not have the specific tag, or
     * if the input does not have any tags at all (not a PEM).
     */
    public static Byte[] parsePEM(Byte[] input, String desiredTag) throws ParseException {
        final String str = new String(byteToByte(input), StandardCharsets.UTF_8);
        Pattern pattern =
                Pattern.compile("^-----BEGIN " + desiredTag
                                + "-----$\n^(.*)$\n^-----END " + desiredTag + "-----$\n*",
                        Pattern.DOTALL | Pattern.MULTILINE);
        final Matcher matcher = pattern.matcher(str);
        if (!matcher.matches()) {
            throw new ParseException("Not a valid PEM");
        }
        final String b64 = matcher.group(1).replace("\n", "");
        try {
            return byteToByte(Base64.getDecoder().decode(b64));
        } catch (IllegalArgumentException e) {
            throw new ParseException(e.getMessage());
        }
    }

    /**
     * EFFECTS: Base64 encode the input bytes and convert them into PEM format.
     * REQUIRES: desiredTag must be upper case and not empty.
     */
    public static String toPEM(Byte[] input, String tag) {
        return "-----BEGIN " + tag + "-----\n"
                + Base64.getEncoder().encodeToString(byteToByte(input))
                + "\n-----END "
                + tag
                + "-----";
    }
}