AndroidIDE/common/src/main/java/com/itsaky/androidide/utils/CharSequenceReader.java

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 com.itsaky.androidide.utils;

import androidx.annotation.NonNull;

import java.io.Reader;
import java.io.Serializable;
import java.util.Objects;

/**
 * {@link Reader} implementation that can read from String, StringBuffer, StringBuilder or
 * CharBuffer.
 *
 * <p><strong>Note:</strong> Supports {@link #mark(int)} and {@link #reset()}.
 *
 * @since 1.4
 */
public class CharSequenceReader extends Reader implements Serializable {

  private static final long serialVersionUID = 3724187752191401220L;
  private final CharSequence charSequence;
  /**
   * The start index in the character sequence, inclusive.
   *
   * <p>When de-serializing a CharSequenceReader that was serialized before this fields was added,
   * this field will be initialized to 0, which gives the same behavior as before: start reading
   * from the start.
   *
   * @see #start()
   * @since 2.7
   */
  private final int start;
  /**
   * The end index in the character sequence, exclusive.
   *
   * <p>When de-serializing a CharSequenceReader that was serialized before this fields was added,
   * this field will be initialized to {@code null}, which gives the same behavior as before: stop
   * reading at the CharSequence's length. If this field was an int instead, it would be initialized
   * to 0 when the CharSequenceReader is de-serialized, causing it to not return any characters at
   * all.
   *
   * @see #end()
   * @since 2.7
   */
  private final Integer end;

  private int idx;
  private int mark;

  /**
   * Constructs a new instance with the specified character sequence.
   *
   * @param charSequence The character sequence, may be {@code null}
   */
  public CharSequenceReader(final CharSequence charSequence) {
    this(charSequence, 0);
  }

  /**
   * Constructs a new instance with a portion of the specified character sequence.
   *
   * <p>The start index is not strictly enforced to be within the bounds of the character sequence.
   * This allows the character sequence to grow or shrink in size without risking any {@link
   * IndexOutOfBoundsException} to be thrown. Instead, if the character sequence grows smaller than
   * the start index, this instance will act as if all characters have been read.
   *
   * @param charSequence The character sequence, may be {@code null}
   * @param start The start index in the character sequence, inclusive
   * @throws IllegalArgumentException if the start index is negative
   * @since 2.7
   */
  public CharSequenceReader(final CharSequence charSequence, final int start) {
    this(charSequence, start, Integer.MAX_VALUE);
  }

  /**
   * Constructs a new instance with a portion of the specified character sequence.
   *
   * <p>The start and end indexes are not strictly enforced to be within the bounds of the character
   * sequence. This allows the character sequence to grow or shrink in size without risking any
   * {@link IndexOutOfBoundsException} to be thrown. Instead, if the character sequence grows
   * smaller than the start index, this instance will act as if all characters have been read; if
   * the character sequence grows smaller than the end, this instance will use the actual character
   * sequence length.
   *
   * @param charSequence The character sequence, may be {@code null}
   * @param start The start index in the character sequence, inclusive
   * @param end The end index in the character sequence, exclusive
   * @throws IllegalArgumentException if the start index is negative, or if the end index is smaller
   *     than the start index
   * @since 2.7
   */
  public CharSequenceReader(final CharSequence charSequence, final int start, final int end) {
    if (start < 0) {
      throw new IllegalArgumentException("Start index is less than zero: " + start);
    }
    if (end < start) {
      throw new IllegalArgumentException("End index is less than start " + start + ": " + end);
    }
    // Don't check the start and end indexes against the CharSequence,
    // to let it grow and shrink without breaking existing behavior.

    this.charSequence = charSequence != null ? charSequence : "";
    this.start = start;
    this.end = end;

    this.idx = start;
    this.mark = start;
  }

  /**
   * Return a String representation of the underlying character sequence.
   *
   * @return The contents of the character sequence
   */
  @NonNull
  @Override
  public String toString() {
    final CharSequence subSequence = charSequence.subSequence(start(), end());
    return subSequence.toString();
  }
  /** Close resets the file back to the start and removes any marked position. */

  @Override
  public void close() {
    idx = start;
    mark = start;
  }

  /**
   * Returns the index in the character sequence to start reading from, taking into account its
   * length.
   *
   * @return The start index in the character sequence (inclusive).
   */
  private int start() {
    return Math.min(charSequence.length(), start);
  }
  /**
   * Returns the index in the character sequence to end reading at, taking into account its length.
   *
   * @return The end index in the character sequence (exclusive).
   */

  private int end() {
    /*
     * end == null for de-serialized instances that were serialized before start and end were added.
     * Use Integer.MAX_VALUE to get the same behavior as before - use the entire CharSequence.
     */
    return Math.min(charSequence.length(), end == null ? Integer.MAX_VALUE : end);
  }

  /**
   * Mark the current position.
   *
   * @param readAheadLimit ignored
   */
  @Override
  public void mark(final int readAheadLimit) {
    mark = idx;
  }

  /**
   * Mark is supported (returns true).
   *
   * @return {@code true}
   */
  @Override
  public boolean markSupported() {
    return true;
  }

  /**
   * Read a single character.
   *
   * @return the next character from the character sequence or -1 if the end has been reached.
   */
  @Override
  public int read() {
    if (idx >= end()) {
      return -1;
    }
    return charSequence.charAt(idx++);
  }

  /**
   * Read the specified number of characters into the array.
   *
   * @param array The array to store the characters in
   * @param offset The starting position in the array to store
   * @param length The maximum number of characters to read
   * @return The number of characters read or -1 if there are no more
   */
  @Override
  public int read(final char[] array, final int offset, final int length) {
    if (idx >= end()) {
      return -1;
    }
    Objects.requireNonNull(array, "array");
    if (length < 0 || offset < 0 || offset + length > array.length) {
      throw new IndexOutOfBoundsException(
          "Array Size=" + array.length + ", offset=" + offset + ", length=" + length);
    }

    if (charSequence instanceof String) {
      final int count = Math.min(length, end() - idx);
      ((String) charSequence).getChars(idx, idx + count, array, offset);
      idx += count;
      return count;
    }
    if (charSequence instanceof StringBuilder) {
      final int count = Math.min(length, end() - idx);
      ((StringBuilder) charSequence).getChars(idx, idx + count, array, offset);
      idx += count;
      return count;
    }
    if (charSequence instanceof StringBuffer) {
      final int count = Math.min(length, end() - idx);
      ((StringBuffer) charSequence).getChars(idx, idx + count, array, offset);
      idx += count;
      return count;
    }

    int count = 0;
    for (int i = 0; i < length; i++) {
      final int c = read();
      if (c == -1) {
        return count;
      }
      array[offset + i] = (char) c;
      count++;
    }
    return count;
  }

  /**
   * Tells whether this stream is ready to be read.
   *
   * @return {@code true} if more characters from the character sequence are available, or {@code
   *     false} otherwise.
   */
  @Override
  public boolean ready() {
    return idx < end();
  }

  /**
   * Reset the reader to the last marked position (or the beginning if mark has not been called).
   */
  @Override
  public void reset() {
    idx = mark;
  }

  /**
   * Skip the specified number of characters.
   *
   * @param n The number of characters to skip
   * @return The actual number of characters skipped
   */
  @Override
  public long skip(final long n) {
    if (n < 0) {
      throw new IllegalArgumentException("Number of characters to skip is less than zero: " + n);
    }
    if (idx >= end()) {
      return 0;
    }
    final int dest = (int) Math.min(end(), idx + n);
    final int count = dest - idx;
    idx = dest;
    return count;
  }
}