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/*
 * Copyright 2012-2020 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
 *
 *      https://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 net.hasor.cobble.loader.jar;
import java.util.Objects;

/**
 * A {@link CharSequence} backed by a single shared {@link String}. Unlike a regular
 * {@link String}, {@link #subSequence(int, int)} operations will not copy the underlying
 * character array.
 *
 * @author Phillip Webb
 */
final class StringSequence implements CharSequence {
    private final String source;
    private final int    start;
    private final int    end;
    private       int    hash;

    StringSequence(String source) {
        this(source, 0, (source != null) ? source.length() : -1);
    }

    StringSequence(String source, int start, int end) {
        Objects.requireNonNull(source, "Source must not be null");
        if (start < 0) {
            throw new StringIndexOutOfBoundsException(start);
        }
        if (end > source.length()) {
            throw new StringIndexOutOfBoundsException(end);
        }
        this.source = source;
        this.start = start;
        this.end = end;
    }

    StringSequence subSequence(int start) {
        return subSequence(start, length());
    }

    @Override
    public StringSequence subSequence(int start, int end) {
        int subSequenceStart = this.start + start;
        int subSequenceEnd = this.start + end;
        if (subSequenceStart > this.end) {
            throw new StringIndexOutOfBoundsException(start);
        }
        if (subSequenceEnd > this.end) {
            throw new StringIndexOutOfBoundsException(end);
        }
        if (start == 0 && subSequenceEnd == this.end) {
            return this;
        }
        return new StringSequence(this.source, subSequenceStart, subSequenceEnd);
    }

    /**
     * Returns {@code true} if the sequence is empty. Public to be compatible with JDK 15.
     * @return {@code true} if {@link #length()} is {@code 0}, otherwise {@code false}
     */
    public boolean isEmpty() {
        return length() == 0;
    }

    @Override
    public int length() {
        return this.end - this.start;
    }

    @Override
    public char charAt(int index) {
        return this.source.charAt(this.start + index);
    }

    int indexOf(char ch) {
        return this.source.indexOf(ch, this.start) - this.start;
    }

    int indexOf(String str) {
        return this.source.indexOf(str, this.start) - this.start;
    }

    int indexOf(String str, int fromIndex) {
        return this.source.indexOf(str, this.start + fromIndex) - this.start;
    }

    boolean startsWith(String prefix) {
        return startsWith(prefix, 0);
    }

    boolean startsWith(String prefix, int offset) {
        int prefixLength = prefix.length();
        int length = length();
        if (length - prefixLength - offset < 0) {
            return false;
        }
        return this.source.startsWith(prefix, this.start + offset);
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (!(obj instanceof CharSequence)) {
            return false;
        }
        CharSequence other = (CharSequence) obj;
        int n = length();
        if (n != other.length()) {
            return false;
        }
        int i = 0;
        while (n-- != 0) {
            if (charAt(i) != other.charAt(i)) {
                return false;
            }
            i++;
        }
        return true;
    }

    @Override
    public int hashCode() {
        int hash = this.hash;
        if (hash == 0 && length() > 0) {
            for (int i = this.start; i < this.end; i++) {
                hash = 31 * hash + this.source.charAt(i);
            }
            this.hash = hash;
        }
        return hash;
    }

    @Override
    public String toString() {
        return this.source.substring(this.start, this.end);
    }
}