package me.ag2s.epublib.util;

import java.io.CharArrayWriter;
import java.nio.charset.Charset;
import java.util.BitSet;
import java.util.Objects;

import kotlin.text.Charsets;

public class URLEncodeUtil {

    static BitSet dontNeedEncoding;
    static final int caseDiff = ('a' - 'A');

    static {
        dontNeedEncoding = new BitSet(256);
        int i;
        for (i = 'a'; i <= 'z'; i++) {
            dontNeedEncoding.set(i);
        }
        for (i = 'A'; i <= 'Z'; i++) {
            dontNeedEncoding.set(i);
        }
        for (i = '0'; i <= '9'; i++) {
            dontNeedEncoding.set(i);
        }
        String mark = "-_.!~*'()";
        for (i = 0; i < mark.length(); i++) {
            dontNeedEncoding.set(mark.charAt(i));
        }
        String reversed = ";/?:@&=+$,#";
        for (i = 0; i < reversed.length(); i++) {
            dontNeedEncoding.set(reversed.charAt(i));
        }
    }

    public static String encode(String s, Charset charset) {
        Objects.requireNonNull(charset, "charset");

        boolean needToChange = false;
        StringBuilder out = new StringBuilder(s.length());
        CharArrayWriter charArrayWriter = new CharArrayWriter();

        for (int i = 0; i < s.length(); ) {
            int c = s.charAt(i);
            //System.out.println("Examining character: " + c);
            if (dontNeedEncoding.get(c)) {
                //System.out.println("Storing: " + c);
                out.append((char) c);
                i++;
            } else {
                // convert to external encoding before hex conversion
                do {
                    charArrayWriter.write(c);
                    /*
                     * If this character represents the start of a Unicode
                     * surrogate pair, then pass in two characters. It's not
                     * clear what should be done if a byte reserved in the
                     * surrogate pairs range occurs outside of a legal
                     * surrogate pair. For now, just treat it as if it were
                     * any other character.
                     */
                    if (c >= 0xD800 && c <= 0xDBFF) {
                        /*
                          System.out.println(Integer.toHexString(c)
                          + " is high surrogate");
                        */
                        if ((i + 1) < s.length()) {
                            int d = (int) s.charAt(i + 1);
                            /*
                              System.out.println("\tExamining "
                              + Integer.toHexString(d));
                            */
                            if (d >= 0xDC00 && d <= 0xDFFF) {
                                /*
                                  System.out.println("\t"
                                  + Integer.toHexString(d)
                                  + " is low surrogate");
                                */
                                charArrayWriter.write(d);
                                i++;
                            }
                        }
                    }
                    i++;
                } while (i < s.length() && !dontNeedEncoding.get((c = (int) s.charAt(i))));

                charArrayWriter.flush();
                String str = new String(charArrayWriter.toCharArray());
                byte[] ba = str.getBytes(charset);
                for (int j = 0; j < ba.length; j++) {
                    out.append('%');
                    char ch = Character.forDigit((ba[j] >> 4) & 0xF, 16);
                    // converting to use uppercase letter as part of
                    // the hex value if ch is a letter.
                    if (Character.isLetter(ch)) {
                        ch -= caseDiff;
                    }
                    out.append(ch);
                    ch = Character.forDigit(ba[j] & 0xF, 16);
                    if (Character.isLetter(ch)) {
                        ch -= caseDiff;
                    }
                    out.append(ch);
                }
                charArrayWriter.reset();
                needToChange = true;
            }
        }

        return (needToChange ? out.toString() : s);
    }

    public static String encode(String s) {
        return encode(s, Charsets.UTF_8);
    }

}