/**
 *
 * Copyright © 2014-2024 Florian Schmaus
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.jxmpp.stringprep.simple;

import java.util.Arrays;
import java.util.Locale;

import org.jxmpp.JxmppContext;
import org.jxmpp.XmppAddressParttype;
import org.jxmpp.stringprep.XmppStringprep;
import org.jxmpp.stringprep.XmppStringprepException;
import org.jxmpp.util.ArraysUtil;

public final class SimpleXmppStringprep implements XmppStringprep {

        private static SimpleXmppStringprep instance;

        public static final String NAME = "simple";

        /**
         * Setup Simple XMPP Stringprep as implementation to use.
         */
        public static void setup() {
                JxmppContext.setDefaultXmppStringprep(getInstance());
        }

        /**
         * Get the Simple XMPP Stringprep singleton.
         *
         * @return the simple XMPP Stringprep singleton.
         */
        public static SimpleXmppStringprep getInstance() {
                if (instance == null) {
                        instance = new SimpleXmppStringprep();
                }
                return instance;
        }

        private SimpleXmppStringprep() {
        }

        /**
         * From <a href="https://tools.ietf.org/html/rfc7622#section-3.3.1">RFC 7622 §
         * 3.3.1</a>.
         */
        // @formatter:off
        private static final char[] LOCALPART_FURTHER_EXCLUDED_CHARACTERS = new char[] {
                '"',   // U+0022 (QUOTATION MARK) , i.e., "
                '&',   // U+0026 (AMPERSAND), i.e., &
                '\'',  // U+0027 (APOSTROPHE), i.e., '
                '/',   // U+002F (SOLIDUS), i.e., /
                ':',   // U+003A (COLON), i.e., :
                '<',   // U+003C (LESS-THAN SIGN), i.e., <
                '>',   // U+003E (GREATER-THAN SIGN), i.e., >
                '@',   // U+0040 (COMMERCIAL AT), i.e., @
        };
        // @formatter:on

        // @formatter:off
        private static final char[] USERNAME_CASE_MAPPED_EXCLUDED_CHARACTERS = new char[] {
                ' ',   // U+0020 (SPACE) - forbidden by PRECIS IdentifierClass.
        };
        // @formatter:on

        private static final char[] LOCALPART_EXCLUDED_CHARACTERS;

        static {
                // Ensure that the char array is sorted as we use Arrays.binarySearch() on it.
                Arrays.sort(LOCALPART_FURTHER_EXCLUDED_CHARACTERS);

                // Combine LOCALPART_FURTHER_EXCLUDED_CHARACTERS and USERNAME_CASE_MAPPED_EXCLUDED_CHARACTERS into
                // LOCALPART_EXCLUDED_CHARACTERS.
                LOCALPART_EXCLUDED_CHARACTERS = ArraysUtil.concatenate(
                                LOCALPART_FURTHER_EXCLUDED_CHARACTERS,
                                USERNAME_CASE_MAPPED_EXCLUDED_CHARACTERS);
                Arrays.sort(LOCALPART_EXCLUDED_CHARACTERS);
        }

        @Override
        public String localprep(String string) throws XmppStringprepException {
                string = simpleStringprep(string);

                ensurePartDoesNotContain(XmppAddressParttype.localpart, string, LOCALPART_EXCLUDED_CHARACTERS);
                ensureValid(XmppAddressParttype.localpart, string);

                return string;
        }

        private static void ensurePartDoesNotContain(XmppAddressParttype parttype, String input, char[] excludedChars)
                        throws XmppStringprepException {
                assert isSorted(excludedChars);

                for (int i = 0; i < input.length(); i++) {
                        char c = input.charAt(i);
                        int forbiddenCharPos = Arrays.binarySearch(excludedChars, c);
                        if (forbiddenCharPos >= 0) {
                                throw new XmppStringprepException(input, parttype.getCapitalizedName() + " must not contain '"
                                                + excludedChars[forbiddenCharPos] + "'");
                        }
                }
        }

        /**
         * Ensure that the input string does not contain any of the further excluded characters of XMPP localparts.
         *
         * @param localpart the input string.
         * @throws XmppStringprepException if one of the further excluded characters is found.
         * @see <a href="https://tools.ietf.org/html/rfc7622#section-3.3.1">RFC 7622 § 3.3.1</a>
         */
        public static void ensureLocalpartDoesNotIncludeFurtherExcludedCharacters(String localpart)
                        throws XmppStringprepException {
                ensurePartDoesNotContain(XmppAddressParttype.localpart, localpart, LOCALPART_FURTHER_EXCLUDED_CHARACTERS);
        }

        @Override
        public String domainprep(String string) throws XmppStringprepException {
                string = simpleStringprep(string);
                ensureValid(XmppAddressParttype.localpart, string);
                return string;
        }

        @Override
        public String resourceprep(String string) throws XmppStringprepException {
                // rfc6122-bis specifies that resourceprep uses saslprep-bis OpaqueString Profile which says that
                // "Uppercase and titlecase characters MUST NOT be mapped to their lowercase equivalents."

                // TODO apply Unicode Normalization Form C (NFC) with help of java.text.Normalize
                // but unfortunately this is API is only available on Android API 9 or higher and Smack is currently API 8

                ensureValid(XmppAddressParttype.resourcepart, string);

                return string;
        }

        private static String simpleStringprep(String string) {
                String res = string.toLowerCase(Locale.US);
                return res;
        }

        private static boolean isSorted(char[] chars) {
                for (int i = 1; i < chars.length; i++) {
                        if (chars[i-1] > chars[i]) {
                                return false;
                        }
                }
                return true;
        }

        private static void ensureValid(XmppAddressParttype parttype, String input) throws XmppStringprepException {
                for (int i = 0; i < input.length(); i++) {
                        char c = input.charAt(i);

                        boolean disallowedAsciiChar = isDisallowedAsciiChar(c);
                        if (disallowedAsciiChar)
                                throw new XmppStringprepException(input,
                                                parttype.getCapitalizedName() + " does contain disallowed ASCII character at pos " + i);
                }
        }

        /**
         * XML 1.0 disallows certain characters. Below 0x20 (SPACE) only 0x09 (\t), 0x0A (\n), and 0x0D (\r) are allowed. See XML 1.0 § 2.2 which has the following production rule:
         *  Char       ::=       #x9 | #xA | #xD | [#x20-#xD7FF] | [#xE000-#xFFFD] | [#x10000-#x10FFFF]
     *
         * @param c the character is check.
         * @return true if the character is disallowed by XML.
         */
        private static boolean isDisallowedAsciiChar(char c) {
                if (c >= 0x20) return false;

                switch (c) {
                case 0x09:
                case 0x0A:
                case 0X0D:
                        return false;
                default:
                        return true;
                }
        }
}