package de.gurkengewuerz.termbin.Utils;

import java.util.Arrays;

public class ImageUtils {

    static byte[] PNG_HEADER = hexStringToByteArray("89504e470d0a1a0a");
    /**
     * Check if the image is a PNG. The first eight bytes of a PNG file always
     * contain the following (decimal) values: 137 80 78 71 13 10 26 10 / Hex:
     * 89 50 4e 47 0d 0a 1a 0a
     */
    public static boolean isValidPNG(byte[] is) {
        try {
            byte[] b = Arrays.copyOfRange(is, 0, 8);
            if (Arrays.equals(b, PNG_HEADER)) {
                return true;
            }
        } catch (Exception e) {
            //Ignore
            return false;
        }
        return false;
    }

    /**
     * Check if the image is a JPEG. JPEG image files begin with FF D8 and end
     * with FF D9
     */
    public static boolean isValidJPEG(byte[] is) {
        try {
            // check first 2 bytes:
            byte[] b = Arrays.copyOfRange(is, 0, 2);
            if ((b[0]&0xff) != 0xff || (b[1]&0xff) != 0xd8) {
                return false;
            }
            // check last 2 bytes:
            b = Arrays.copyOfRange(is, is.length - 2, is.length);
            if ((b[0]&0xff) != 0xff || (b[1]&0xff) != 0xd9) {
                return false;
            }
        } catch (Exception e) {
            // Ignore
            return false;
        }
        return true;
    }

    /** Check if the image is a valid GIF. GIF files start with GIF and 87a or 89a.
     * http://www.onicos.com/staff/iz/formats/gif.html
     */
    public static boolean isValidGIF(byte[] is) {
        try {
            byte[] b = Arrays.copyOfRange(is, 0, 6);
            //check 1st 3 bytes
            if(b[0]!='G' || b[1]!='I' || b[2]!='F') {
                return false;
            }
            if(b[3]!='8' || !(b[4]=='7' || b[4]=='9') || b[5]!='a') {
                return false;
            }
        } catch(Exception e) {
            // Ignore
            return false;
        }
        return true;
    }

    public static byte[] hexStringToByteArray(String s) {
        int len = s.length();
        byte[] data = new byte[len / 2];
        for (int i = 0; i < len; i += 2) {
            data[i / 2] = (byte) ((Character.digit(s.charAt(i), 16) << 4)
                    + Character.digit(s.charAt(i+1), 16));
        }
        return data;
    }
}