/*
 * 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 org.apache.commons.lang3;

import java.io.Serializable;
import java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * <p>
 * A contiguous range of characters, optionally negated.
 * </p>
 *
 * <p>
 * Instances are immutable.
 * </p>
 *
 * <p>
 * #ThreadSafe#
 * </p>
 * 
 * @since 1.0
 */
// TODO: This is no longer public and will be removed later as CharSet is moved
// to depend on Range.
final class CharRange implements Iterable<Character>, Serializable {

	/**
	 * Required for serialization support. Lang version 2.0.
	 *
	 * @see java.io.Serializable
	 */
	private static final long serialVersionUID = 8270183163158333422L;

	/** The first character, inclusive, in the range. */
	private final char start;
	/** The last character, inclusive, in the range. */
	private final char end;
	/** True if the range is everything except the characters specified. */
	private final boolean negated;

	/** Cached toString. */
	private transient String iToString;

	/** Empty array. */
	static final CharRange[] EMPTY_ARRAY = new CharRange[0];

	/**
	 * <p>
	 * Constructs a {@code CharRange} over a set of characters, optionally negating
	 * the range.
	 * </p>
	 *
	 * <p>
	 * A negated range includes everything except that defined by the start and end
	 * characters.
	 * </p>
	 *
	 * <p>
	 * If start and end are in the wrong order, they are reversed. Thus {@code a-e}
	 * is the same as {@code e-a}.
	 * </p>
	 *
	 * @param start   first character, inclusive, in this range
	 * @param end     last character, inclusive, in this range
	 * @param negated true to express everything except the range
	 */
	private CharRange(char start, char end, final boolean negated) {
		if (start > end) {
			final char temp = start;
			start = end;
			end = temp;
		}

		this.start = start;
		this.end = end;
		this.negated = negated;
	}

	/**
	 * <p>
	 * Constructs a {@code CharRange} over a single character.
	 * </p>
	 *
	 * @param ch only character in this range
	 * @return the new CharRange object
	 * @since 2.5
	 */
	public static CharRange is(final char ch) {
		return new CharRange(ch, ch, false);
	}

	/**
	 * <p>
	 * Constructs a negated {@code CharRange} over a single character.
	 * </p>
	 *
	 * <p>
	 * A negated range includes everything except that defined by the single
	 * character.
	 * </p>
	 *
	 * @param ch only character in this range
	 * @return the new CharRange object
	 * @since 2.5
	 */
	public static CharRange isNot(final char ch) {
		return new CharRange(ch, ch, true);
	}

	/**
	 * <p>
	 * Constructs a {@code CharRange} over a set of characters.
	 * </p>
	 *
	 * <p>
	 * If start and end are in the wrong order, they are reversed. Thus {@code a-e}
	 * is the same as {@code e-a}.
	 * </p>
	 *
	 * @param start first character, inclusive, in this range
	 * @param end   last character, inclusive, in this range
	 * @return the new CharRange object
	 * @since 2.5
	 */
	public static CharRange isIn(final char start, final char end) {
		return new CharRange(start, end, false);
	}

	/**
	 * <p>
	 * Constructs a negated {@code CharRange} over a set of characters.
	 * </p>
	 *
	 * <p>
	 * A negated range includes everything except that defined by the start and end
	 * characters.
	 * </p>
	 *
	 * <p>
	 * If start and end are in the wrong order, they are reversed. Thus {@code a-e}
	 * is the same as {@code e-a}.
	 * </p>
	 *
	 * @param start first character, inclusive, in this range
	 * @param end   last character, inclusive, in this range
	 * @return the new CharRange object
	 * @since 2.5
	 */
	public static CharRange isNotIn(final char start, final char end) {
		return new CharRange(start, end, true);
	}

	// Accessors
	// -----------------------------------------------------------------------
	/**
	 * <p>
	 * Gets the start character for this character range.
	 * </p>
	 *
	 * @return the start char (inclusive)
	 */
	public char getStart() {
		return this.start;
	}

	/**
	 * <p>
	 * Gets the end character for this character range.
	 * </p>
	 *
	 * @return the end char (inclusive)
	 */
	public char getEnd() {
		return this.end;
	}

	/**
	 * <p>
	 * Is this {@code CharRange} negated.
	 * </p>
	 *
	 * <p>
	 * A negated range includes everything except that defined by the start and end
	 * characters.
	 * </p>
	 *
	 * @return {@code true} if negated
	 */
	public boolean isNegated() {
		return negated;
	}

	// Contains
	// -----------------------------------------------------------------------
	/**
	 * <p>
	 * Is the character specified contained in this range.
	 * </p>
	 *
	 * @param ch the character to check
	 * @return {@code true} if this range contains the input character
	 */
	public boolean contains(final char ch) {
		return (ch >= start && ch <= end) != negated;
	}

	/**
	 * <p>
	 * Are all the characters of the passed in range contained in this range.
	 * </p>
	 *
	 * @param range the range to check against
	 * @return {@code true} if this range entirely contains the input range
	 * @throws IllegalArgumentException if {@code null} input
	 */
	public boolean contains(final CharRange range) {
		Validate.notNull(range, "range");
		if (negated) {
			if (range.negated) {
				return start >= range.start && end <= range.end;
			}
			return range.end < start || range.start > end;
		}
		if (range.negated) {
			return start == 0 && end == Character.MAX_VALUE;
		}
		return start <= range.start && end >= range.end;
	}

	// Basics
	// -----------------------------------------------------------------------
	/**
	 * <p>
	 * Compares two CharRange objects, returning true if they represent exactly the
	 * same range of characters defined in the same way.
	 * </p>
	 *
	 * @param obj the object to compare to
	 * @return true if equal
	 */
	@Override
	public boolean equals(final Object obj) {
		if (obj == this) {
			return true;
		}
		if (!(obj instanceof CharRange)) {
			return false;
		}
		final CharRange other = (CharRange) obj;
		return start == other.start && end == other.end && negated == other.negated;
	}

	/**
	 * <p>
	 * Gets a hashCode compatible with the equals method.
	 * </p>
	 *
	 * @return a suitable hashCode
	 */
	@Override
	public int hashCode() {
		return 83 + start + 7 * end + (negated ? 1 : 0);
	}

	/**
	 * <p>
	 * Gets a string representation of the character range.
	 * </p>
	 *
	 * @return string representation of this range
	 */
	@Override
	public String toString() {
		if (iToString == null) {
			final StringBuilder buf = new StringBuilder(4);
			if (isNegated()) {
				buf.append('^');
			}
			buf.append(start);
			if (start != end) {
				buf.append('-');
				buf.append(end);
			}
			iToString = buf.toString();
		}
		return iToString;
	}

	// Expansions
	// -----------------------------------------------------------------------
	/**
	 * <p>
	 * Returns an iterator which can be used to walk through the characters
	 * described by this range.
	 * </p>
	 *
	 * <p>
	 * #NotThreadSafe# the iterator is not thread-safe
	 * </p>
	 * 
	 * @return an iterator to the chars represented by this range
	 * @since 2.5
	 */
	@Override
	public Iterator<Character> iterator() {
		return new CharacterIterator(this);
	}

	/**
	 * Character {@link Iterator}.
	 * <p>
	 * #NotThreadSafe#
	 * </p>
	 */
	private static class CharacterIterator implements Iterator<Character> {
		/** The current character */
		private char current;

		private final CharRange range;
		private boolean hasNext;

		/**
		 * Constructs a new iterator for the character range.
		 *
		 * @param r The character range
		 */
		private CharacterIterator(final CharRange r) {
			range = r;
			hasNext = true;

			if (range.negated) {
				if (range.start == 0) {
					if (range.end == Character.MAX_VALUE) {
						// This range is an empty set
						hasNext = false;
					} else {
						current = (char) (range.end + 1);
					}
				} else {
					current = 0;
				}
			} else {
				current = range.start;
			}
		}

		/**
		 * Prepares the next character in the range.
		 */
		private void prepareNext() {
			if (range.negated) {
				if (current == Character.MAX_VALUE) {
					hasNext = false;
				} else if (current + 1 == range.start) {
					if (range.end == Character.MAX_VALUE) {
						hasNext = false;
					} else {
						current = (char) (range.end + 1);
					}
				} else {
					current = (char) (current + 1);
				}
			} else if (current < range.end) {
				current = (char) (current + 1);
			} else {
				hasNext = false;
			}
		}

		/**
		 * Has the iterator not reached the end character yet?
		 *
		 * @return {@code true} if the iterator has yet to reach the character date
		 */
		@Override
		public boolean hasNext() {
			return hasNext;
		}

		/**
		 * Returns the next character in the iteration
		 *
		 * @return {@code Character} for the next character
		 */
		@Override
		public Character next() {
			if (!hasNext) {
				throw new NoSuchElementException();
			}
			final char cur = current;
			prepareNext();
			return Character.valueOf(cur);
		}

		/**
		 * Always throws UnsupportedOperationException.
		 *
		 * @throws UnsupportedOperationException Always thrown.
		 * @see java.util.Iterator#remove()
		 */
		@Override
		public void remove() {
			throw new UnsupportedOperationException();
		}
	}
}