package com.github.hunter0x7c7.sync.utils;

import java.io.BufferedInputStream;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileInputStream;
import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

public class Base64Decoder extends FilterInputStream {

    private static final char[] chars = {'A', 'B', 'C', 'D', 'E', 'F', 'G',
            'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T',
            'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g',
            'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't',
            'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6',
            '7', '8', '9', '+', '/'};

    // A mapping between char values and six-bit integers
    private static final int[] ints = new int[128];

    static {
        for (int i = 0; i < 64; i++) {
            ints[chars[i]] = i;
        }
    }

    private int charCount;
    private int carryOver;

    /***
     * Constructs a new Base64 decoder that reads input from the given
     * InputStream.
     *
     * @param in
     *            the input stream
     */
    public Base64Decoder(InputStream in) {
        super(in);
    }

    /***
     * Returns the next decoded character from the stream, or -1 if end of
     * stream was reached.
     *
     * @return the decoded character, or -1 if the end of the input stream is
     *         reached
     * @exception IOException
     *                if an I/O error occurs
     */
    public int read() throws IOException {
        // Read the next non-whitespace character
        int x;
        do {
            x = in.read();
            if (x == -1) {
                return -1;
            }
        } while (Character.isWhitespace((char) x));
        charCount++;

        // The '=' sign is just padding
        if (x == '=') {
            return -1; // effective end of stream
        }

        // Convert from raw form to 6-bit form
        x = ints[x];

        // Calculate which character we're decoding now
        int mode = (charCount - 1) % 4;

        // First char save all six bits, go for another
        if (mode == 0) {
            carryOver = x & 63;
            return read();
        }
        // Second char use previous six bits and first two new bits,
        // save last four bits
        else if (mode == 1) {
            int decoded = ((carryOver << 2) + (x >> 4)) & 255;
            carryOver = x & 15;
            return decoded;
        }
        // Third char use previous four bits and first four new bits,
        // save last two bits
        else if (mode == 2) {
            int decoded = ((carryOver << 4) + (x >> 2)) & 255;
            carryOver = x & 3;
            return decoded;
        }
        // Fourth char use previous two bits and all six new bits
        else if (mode == 3) {
            return ((carryOver << 6) + x) & 255;
        }
        return -1; // can't actually reach this line
    }

    /***
     * Reads decoded data into an array of bytes and returns the actual number
     * of bytes read, or -1 if end of stream was reached.
     *
     * @param buf
     *            the buffer into which the data is read
     * @param off
     *            the start offset of the data
     * @param len
     *            the maximum number of bytes to read
     * @return the actual number of bytes read, or -1 if the end of the input
     *         stream is reached
     * @exception IOException
     *                if an I/O error occurs
     */
    public int read(byte[] buf, int off, int len) throws IOException {
        if (buf.length < (len + off - 1)) {
            throw new IOException("The input buffer is too small: " + len
                    + " bytes requested starting at offset " + off
                    + " while the buffer " + " is only " + buf.length
                    + " bytes long.");
        }

        // This could of course be optimized
        int i;
        for (i = 0; i < len; i++) {
            int x = read();
            if (x == -1 && i == 0) { // an immediate -1 returns -1
                return -1;
            } else if (x == -1) { // a later -1 returns the chars read so far
                break;
            }
            buf[off + i] = (byte) x;
        }
        return i;
    }

    /***
     * Returns the decoded form of the given encoded string, as a String. Note
     * that not all binary data can be represented as a String, so this method
     * should only be used for encoded String data. Use decodeToBytes()
     * otherwise.
     *
     * @param encoded
     *            the string to decode
     * @return the decoded form of the encoded string
     */
    public static String decode(String encoded) {
        return new String(decodeToBytes(encoded));
    }

    /***
     * Returns the decoded form of the given encoded string, as bytes.
     *
     * @param encoded the string to decode
     * @return the decoded form of the encoded string
     */
    public static byte[] decodeToBytes(String encoded) {
        byte[] bytes = null;
        try {
            bytes = encoded.getBytes("UTF-8");
        } catch (Exception e) {
            e.printStackTrace();
        }
        if (bytes != null) {
            Base64Decoder in = new Base64Decoder(new ByteArrayInputStream(bytes));
            ByteArrayOutputStream out = new ByteArrayOutputStream((int) (bytes.length * 0.67));

            try {
                byte[] buf = new byte[4 * 1024]; // 4K buffer
                int bytesRead;
                while ((bytesRead = in.read(buf)) != -1) {
                    out.write(buf, 0, bytesRead);
                }
                out.close();

                return out.toByteArray();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
        return null;
    }

    public static void main(String[] args) throws Exception {
        if (args.length != 1) {
            System.err.println("Usage: java Base64Decoder fileToDecode");
            return;
        }

        Base64Decoder decoder = null;
        try {
            decoder = new Base64Decoder(new BufferedInputStream(new FileInputStream(args[0])));
            byte[] buf = new byte[4 * 1024]; // 4K buffer
            int bytesRead;
            while ((bytesRead = decoder.read(buf)) != -1) {
                System.out.write(buf, 0, bytesRead);
            }
        } finally {
            if (decoder != null)
                decoder.close();
        }
    }
}