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/*
 * Copyright 2012-2015 the original author or authors.
 *
 * 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 io.joshworks.snappy.loader.util;

import java.nio.charset.Charset;

/**
 * Simple wrapper around a byte array that represents an ASCII. Used for performance
 * reasons to save constructing Strings for ZIP data.
 *
 * @author Phillip Webb
 */
public final class AsciiBytes {

    private static final Charset UTF_8 = Charset.forName("UTF-8");

    private static final int INITIAL_HASH = 7;

    private static final int MULTIPLIER = 31;

    private final byte[] bytes;

    private final int offset;

    private final int length;

    private String string;

    /**
     * Create a new {@link AsciiBytes} from the specified String.
     *
     * @param string the source string
     */
    public AsciiBytes(String string) {
        this(string.getBytes(UTF_8));
        this.string = string;
    }

    /**
     * Create a new {@link AsciiBytes} from the specified bytes. NOTE: underlying bytes
     * are not expected to change.
     *
     * @param bytes the source bytes
     */
    public AsciiBytes(byte[] bytes) {
        this(bytes, 0, bytes.length);
    }

    /**
     * Create a new {@link AsciiBytes} from the specified bytes. NOTE: underlying bytes
     * are not expected to change.
     *
     * @param bytes  the source bytes
     * @param offset the offset
     * @param length the length
     */
    public AsciiBytes(byte[] bytes, int offset, int length) {
        if (offset < 0 || length < 0 || (offset + length) > bytes.length) {
            throw new IndexOutOfBoundsException();
        }
        this.bytes = bytes;
        this.offset = offset;
        this.length = length;
    }

    public int length() {
        return this.length;
    }

    public boolean startsWith(AsciiBytes prefix) {
        if (this == prefix) {
            return true;
        }
        if (prefix.length > this.length) {
            return false;
        }
        for (int i = 0; i < prefix.length; i++) {
            if (this.bytes[i + this.offset] != prefix.bytes[i + prefix.offset]) {
                return false;
            }
        }
        return true;
    }

    public boolean endsWith(AsciiBytes postfix) {
        if (this == postfix) {
            return true;
        }
        if (postfix.length > this.length) {
            return false;
        }
        for (int i = 0; i < postfix.length; i++) {
            if (this.bytes[this.offset + (this.length - 1)
                    - i] != postfix.bytes[postfix.offset + (postfix.length - 1) - i]) {
                return false;
            }
        }
        return true;
    }

    public AsciiBytes substring(int beginIndex) {
        return substring(beginIndex, this.length);
    }

    public AsciiBytes substring(int beginIndex, int endIndex) {
        int length = endIndex - beginIndex;
        if (this.offset + length > this.length) {
            throw new IndexOutOfBoundsException();
        }
        return new AsciiBytes(this.bytes, this.offset + beginIndex, length);
    }

    public AsciiBytes append(String string) {
        if (string == null || string.length() == 0) {
            return this;
        }
        return append(string.getBytes(UTF_8));
    }

    public AsciiBytes append(AsciiBytes asciiBytes) {
        if (asciiBytes == null || asciiBytes.length() == 0) {
            return this;
        }
        return append(asciiBytes.bytes);
    }

    public AsciiBytes append(byte[] bytes) {
        if (bytes == null || bytes.length == 0) {
            return this;
        }
        byte[] combined = new byte[this.length + bytes.length];
        System.arraycopy(this.bytes, this.offset, combined, 0, this.length);
        System.arraycopy(bytes, 0, combined, this.length, bytes.length);
        return new AsciiBytes(combined);
    }

    @Override
    public String toString() {
        if (this.string == null) {
            this.string = new String(this.bytes, this.offset, this.length, UTF_8);
        }
        return this.string;
    }

    @Override
    public int hashCode() {
        int hash = INITIAL_HASH;
        for (int i = 0; i < this.length; i++) {
            hash = MULTIPLIER * hash + this.bytes[this.offset + i];
        }
        return hash;

    }

    @Override
    public boolean equals(Object obj) {
        if (obj == null) {
            return false;
        }
        if (this == obj) {
            return true;
        }
        if (obj.getClass().equals(AsciiBytes.class)) {
            AsciiBytes other = (AsciiBytes) obj;
            if (this.length == other.length) {
                for (int i = 0; i < this.length; i++) {
                    if (this.bytes[this.offset + i] != other.bytes[other.offset + i]) {
                        return false;
                    }
                }
                return true;
            }
        }
        return false;
    }

}