/*
 * Copyright (c) 2014, 2021, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */

package jdk.internal.jimage;

import java.io.UTFDataFormatException;
import java.nio.ByteBuffer;
import java.nio.charset.StandardCharsets;
import java.util.Objects;

Implementation Note:
This class needs to maintain JDK 8 source compatibility.
It is used internally in the JDK to implement jimage/jrtfs access,
but also compiled and delivered as part of the jrtfs.jar to support access
to the jimage file provided by the shipped JDK by tools running on JDK 8./**
 * @implNote This class needs to maintain JDK 8 source compatibility.
 *
 * It is used internally in the JDK to implement jimage/jrtfs access,
 * but also compiled and delivered as part of the jrtfs.jar to support access
 * to the jimage file provided by the shipped JDK by tools running on JDK 8.
 */
public class ImageStringsReader implements ImageStrings {
    public static final int HASH_MULTIPLIER = 0x01000193;
    public static final int POSITIVE_MASK = 0x7FFFFFFF;

    private final BasicImageReader reader;

    ImageStringsReader(BasicImageReader reader) {
        this.reader = Objects.requireNonNull(reader);
    }

    @Override
    public String get(int offset) {
        return reader.getString(offset);
    }

    @Override
    public int match(int offset, String string, int stringOffset) {
        return reader.match(offset, string, stringOffset);
    }

    @Override
    public int add(final String string) {
        throw new InternalError("Can not add strings at runtime");
    }

    public static int hashCode(String s) {
        return hashCode(s, HASH_MULTIPLIER);
    }

    public static int hashCode(String s, int seed) {
        return unmaskedHashCode(s, seed) & POSITIVE_MASK;
    }

    public static int hashCode(String module, String name) {
        return hashCode(module, name, HASH_MULTIPLIER);
    }

    public static int hashCode(String module, String name, int seed) {
        seed = (seed * HASH_MULTIPLIER) ^ ('/');
        seed = unmaskedHashCode(module, seed);
        seed = (seed * HASH_MULTIPLIER) ^ ('/');
        seed = unmaskedHashCode(name, seed);
        return seed & POSITIVE_MASK;
    }

    public static int unmaskedHashCode(String s, int seed) {
        int slen = s.length();
        byte[] buffer = null;

        for (int i = 0; i < slen; i++) {
            int uch = s.charAt(i);

            if ((uch & ~0x7F) != 0) {
                if (buffer == null) {
                    buffer = new byte[8];
                }
                int mask = ~0x3F;
                int n = 0;

                do {
                    buffer[n++] = (byte)(0x80 | (uch & 0x3F));
                    uch >>= 6;
                    mask >>= 1;
                } while ((uch & mask) != 0);

                buffer[n] = (byte)((mask << 1) | uch);

                do {
                    seed = (seed * HASH_MULTIPLIER) ^ (buffer[n--] & 0xFF);
                } while (0 <= n);
            } else if (uch == 0) {
                seed = (seed * HASH_MULTIPLIER) ^ (0xC0);
                seed = (seed * HASH_MULTIPLIER) ^ (0x80);
            } else {
                seed = (seed * HASH_MULTIPLIER) ^ (uch);
            }
        }
        return seed;
    }

    static int charsFromMUTF8Length(byte[] bytes, int offset, int count) {
        int length = 0;

        for (int i = offset; i < offset + count; i++) {
            byte ch = bytes[i];

            if (ch == 0) {
                break;
            }

            if ((ch & 0xC0) != 0x80) {
                length++;
            }
        }

        return length;
    }

    static void charsFromMUTF8(char[] chars, byte[] bytes, int offset, int count) throws UTFDataFormatException {
        int j = 0;

        for (int i = offset; i < offset + count; i++) {
            byte ch = bytes[i];

            if (ch == 0) {
                break;
            }

            boolean is_unicode = (ch & 0x80) != 0;
            int uch = ch & 0x7F;

            if (is_unicode) {
                int mask = 0x40;

                while ((uch & mask) != 0) {
                    ch = bytes[++i];

                    if ((ch & 0xC0) != 0x80) {
                        throw new UTFDataFormatException("bad continuation 0x" + Integer.toHexString(ch));
                    }

                    uch = ((uch & ~mask) << 6) | (ch & 0x3F);
                    mask <<= 6 - 1;
                }

                if ((uch & 0xFFFF) != uch) {
                    throw new UTFDataFormatException("character out of range \\u" + Integer.toHexString(uch));
                }
            }

            chars[j++] = (char)uch;
        }
    }

    public static String stringFromMUTF8(byte[] bytes, int offset, int count) {
        int length = charsFromMUTF8Length(bytes, offset, count);
        char[] chars = new char[length];

        try {
            charsFromMUTF8(chars, bytes, offset, count);
        } catch (UTFDataFormatException ex) {
            throw new InternalError("Attempt to convert non modified UTF-8 byte sequence", ex);
        }

        return new String(chars);
    }

    public static String stringFromMUTF8(byte[] bytes) {
        return stringFromMUTF8(bytes, 0, bytes.length);
    }

    
Calculates the number of characters in the String present at the
specified offset. As an optimization, the length returned will
be positive if the characters are all ASCII, and negative otherwise.
/**
     * Calculates the number of characters in the String present at the
     * specified offset. As an optimization, the length returned will
     * be positive if the characters are all ASCII, and negative otherwise.
     */
    private static int charsFromByteBufferLength(ByteBuffer buffer, int offset) {
        int length = 0;

        int limit = buffer.limit();
        boolean asciiOnly = true;
        while (offset < limit) {
            byte ch = buffer.get(offset++);

            if (ch < 0) {
                asciiOnly = false;
            } else if (ch == 0) {
                return asciiOnly ? length : -length;
            }

            if ((ch & 0xC0) != 0x80) {
                length++;
            }
        }
        throw new InternalError("No terminating zero byte for modified UTF-8 byte sequence");
    }

    private static void charsFromByteBuffer(char[] chars, ByteBuffer buffer, int offset) {
        int j = 0;

        int limit = buffer.limit();
        while (offset < limit) {
            byte ch = buffer.get(offset++);

            if (ch == 0) {
                return;
            }

            boolean is_unicode = (ch & 0x80) != 0;
            int uch = ch & 0x7F;

            if (is_unicode) {
                int mask = 0x40;

                while ((uch & mask) != 0) {
                    ch = buffer.get(offset++);

                    if ((ch & 0xC0) != 0x80) {
                        throw new InternalError("Bad continuation in " +
                            "modified UTF-8 byte sequence: " + ch);
                    }

                    uch = ((uch & ~mask) << 6) | (ch & 0x3F);
                    mask <<= 6 - 1;
                }
            }

            if ((uch & 0xFFFF) != uch) {
                throw new InternalError("UTF-32 char in modified UTF-8 " +
                    "byte sequence: " + uch);
            }

            chars[j++] = (char)uch;
        }

        throw new InternalError("No terminating zero byte for modified UTF-8 byte sequence");
    }

    public static String stringFromByteBuffer(ByteBuffer buffer) {
        return stringFromByteBuffer(buffer, 0);
    }

    /* package-private */
    static String stringFromByteBuffer(ByteBuffer buffer, int offset) {
        int length = charsFromByteBufferLength(buffer, offset);
        if (length > 0) {
            byte[] asciiBytes = new byte[length];
            // Ideally we could use buffer.get(offset, asciiBytes, 0, length)
            // here, but that was introduced in JDK 13
            for (int i = 0; i < length; i++) {
                asciiBytes[i] = buffer.get(offset++);
            }
            return new String(asciiBytes, StandardCharsets.US_ASCII);
        }
        char[] chars = new char[-length];
        charsFromByteBuffer(chars, buffer, offset);
        return new String(chars);
    }

    /* package-private */
    static int stringFromByteBufferMatches(ByteBuffer buffer, int offset, String string, int stringOffset) {
        // ASCII fast-path
        int limit = buffer.limit();
        int current = offset;
        int slen = string.length();
        while (current < limit) {
            byte ch = buffer.get(current);
            if (ch <= 0) {
                if (ch == 0) {
                    // Match
                    return current - offset;
                }
                // non-ASCII byte, run slow-path from current offset
                break;
            }
            if (slen <= stringOffset || string.charAt(stringOffset) != (char)ch) {
                // No match
                return -1;
            }
            stringOffset++;
            current++;
        }
        // invariant: remainder of the string starting at current is non-ASCII,
        // so return value from charsFromByteBufferLength will be negative
        int length = -charsFromByteBufferLength(buffer, current);
        char[] chars = new char[length];
        charsFromByteBuffer(chars, buffer, current);
        for (int i = 0; i < length; i++) {
            if (string.charAt(stringOffset++) != chars[i]) {
                return -1;
            }
        }
        return length;
    }

    static int mutf8FromStringLength(String s) {
        int length = 0;
        int slen = s.length();

        for (int i = 0; i < slen; i++) {
            char ch = s.charAt(i);
            int uch = ch & 0xFFFF;

            if ((uch & ~0x7F) != 0) {
                int mask = ~0x3F;
                int n = 0;

                do {
                    n++;
                    uch >>= 6;
                    mask >>= 1;
                } while ((uch & mask) != 0);

                length += n + 1;
            } else if (uch == 0) {
                length += 2;
            } else {
                length++;
            }
        }

        return length;
    }

    static void mutf8FromString(byte[] bytes, int offset, String s) {
        int j = offset;
        byte[] buffer = null;
        int slen = s.length();

        for (int i = 0; i < slen; i++) {
            char ch = s.charAt(i);
            int uch = ch & 0xFFFF;

            if ((uch & ~0x7F) != 0) {
                if (buffer == null) {
                    buffer = new byte[8];
                }
                int mask = ~0x3F;
                int n = 0;

                do {
                    buffer[n++] = (byte)(0x80 | (uch & 0x3F));
                    uch >>= 6;
                    mask >>= 1;
                } while ((uch & mask) != 0);

                buffer[n] = (byte)((mask << 1) | uch);

                do {
                    bytes[j++] = buffer[n--];
                } while (0 <= n);
            } else if (uch == 0) {
                bytes[j++] = (byte)0xC0;
                bytes[j++] = (byte)0x80;
            } else {
                bytes[j++] = (byte)uch;
            }
        }
    }

    public static byte[] mutf8FromString(String string) {
        int length = mutf8FromStringLength(string);
        byte[] bytes = new byte[length];
        mutf8FromString(bytes, 0, string);

        return bytes;
    }
}