/*******************************************************************************
 * Copyright (c) 2017 Association for Decentralized Information Management in
 * Industry THTH ry.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 *     Semantum Oy - initial API and implementation
 *******************************************************************************/
package org.simantics.history.csv;

/**
 * @author Tuukka Lehtonen
 * @since 1.30.0, 1.28.1
 */
class URIs {

    public static String safeUnescape(String uri) {
        try {
            return unescape(uri);
        } catch (IllegalArgumentException e) {
            return uri;
        }
    }

    public static String unescape(String uri) {
        try {
            if (!needsUnescaping(uri))
                return uri;

            int len = uri.length();
            String unicode = uri;
            char result[] = new char[len];
            int in = 0;
            int out = 0;
            while (in < len) {
                char inCh = unicode.charAt(in++);
                if (inCh == '%' && in+1 < len) {
                    char d1 = unicode.charAt(in);
                    char d2 = unicode.charAt(in+1);
                    if (d1 > 127 || d2 > 127)
                        throw new IllegalArgumentException("Invalid hex digit escape sequence in " + uri + " at " + in);
                    result[out++] = (char) (hexDecode(d1) * 16 | hexDecode(d2));
                    in += 2;
                } else {
                    result[out++] = inCh;
                }
            }
            return new String(result, 0, out);
        } catch (IllegalArgumentException e) {
            throw new IllegalArgumentException("Problem while unescaping string: " + uri, e);
        } catch (IndexOutOfBoundsException ee) {
            throw new IllegalArgumentException("Incomplete hex digit escape sequence in " + uri);
        }
    }

    private static boolean needsUnescaping(String s) {
        int l = s.length();
        for (int i = -1; i < l;) {
            i = s.indexOf('%', i+1);
            if (i < 0)
                break;
            if (i+2 < l
                    && isHexDigit(s.charAt(i+1))
                    && isHexDigit(s.charAt(i+2)))
                return true;
        }
        return false;
    }

    private static int hexDecode(char c) {
        switch (c) {
            case 'a': case 'b': case 'c': case 'd': case 'e': case 'f':
                return ((c) & 255) - 'a' + 10;
            case 'A': case 'B': case 'C': case 'D': case 'E': case 'F':
                return c -  'A' + 10;
            case '0': case '1': case '2': case '3': case '4': case '5': case '6': case '7': case '8': case '9':
                return c -  '0';
            default:
                throw new IllegalArgumentException("Bad Hex escape character: " + ((c)&255) );
        }
    }

    private static boolean isHexDigit(char c) {
        return (c >= '0' && c <= '9') || (c >= 'A' && c <= 'F') || (c >= 'a' && c <= 'f');
    }

//    public static void main(String[] args) {
//        System.out.println(unescape("%"));
//        System.out.println(unescape("%.AI"));
//        System.out.println(unescape("%6B"));
//        System.out.println(unescape("%6g"));
//        System.out.println(unescape("%g5"));
//        System.out.println(unescape("%f5"));
//        System.out.println(unescape("%A1"));
//        System.out.println(unescape("%A"));
//        System.out.println(unescape("%A."));
//        System.out.println(unescape("%AI"));
//    }

}