/*
 * Copyright (C) 2010 The Guava 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 com.google.common.base;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkNotNull;

import javax.annotation.CheckReturnValue;

import com.google.common.annotations.Beta;
import com.google.common.annotations.GwtCompatible;

/**
 * Static methods pertaining to ASCII characters (those in the range of values
 * {@code 0x00} through {@code 0x7F}), and to strings containing such
 * characters.
 *
 * <p>
 * ASCII utilities also exist in other classes of this package:
 * <ul>
 * <!-- TODO(kevinb): how can we make this not produce a warning when building
 * gwt javadoc? -->
 * <li>{@link Charsets#US_ASCII} specifies the {@code Charset} of ASCII
 * characters.
 * <li>{@link CharMatcher#ASCII} matches ASCII characters and provides text
 * processing methods which operate only on the ASCII characters of a string.
 * </ul>
 *
 * @author Craig Berry
 * @author Gregory Kick
 * @since 7.0
 */
@GwtCompatible
public final class Ascii {

	private Ascii() {
	}

	/* The ASCII control characters, per RFC 20. */
	/**
	 * Null ('\0'): The all-zeros character which may serve to accomplish time fill
	 * and media fill. Normally used as a C string terminator.
	 * <p>
	 * Although RFC 20 names this as "Null", note that it is distinct from the C/C++
	 * "NULL" pointer.
	 *
	 * @since 8.0
	 */
	public static final byte NUL = 0;

	/**
	 * Start of Heading: A communication control character used at the beginning of
	 * a sequence of characters which constitute a machine-sensible address or
	 * routing information. Such a sequence is referred to as the "heading." An STX
	 * character has the effect of terminating a heading.
	 *
	 * @since 8.0
	 */
	public static final byte SOH = 1;

	/**
	 * Start of Text: A communication control character which precedes a sequence of
	 * characters that is to be treated as an entity and entirely transmitted
	 * through to the ultimate destination. Such a sequence is referred to as
	 * "text." STX may be used to terminate a sequence of characters started by SOH.
	 *
	 * @since 8.0
	 */
	public static final byte STX = 2;

	/**
	 * End of Text: A communication control character used to terminate a sequence
	 * of characters started with STX and transmitted as an entity.
	 *
	 * @since 8.0
	 */
	public static final byte ETX = 3;

	/**
	 * End of Transmission: A communication control character used to indicate the
	 * conclusion of a transmission, which may have contained one or more texts and
	 * any associated headings.
	 *
	 * @since 8.0
	 */
	public static final byte EOT = 4;

	/**
	 * Enquiry: A communication control character used in data communication systems
	 * as a request for a response from a remote station. It may be used as a "Who
	 * Are You" (WRU) to obtain identification, or may be used to obtain station
	 * status, or both.
	 *
	 * @since 8.0
	 */
	public static final byte ENQ = 5;

	/**
	 * Acknowledge: A communication control character transmitted by a receiver as
	 * an affirmative response to a sender.
	 *
	 * @since 8.0
	 */
	public static final byte ACK = 6;

	/**
	 * Bell ('\a'): A character for use when there is a need to call for human
	 * attention. It may control alarm or attention devices.
	 *
	 * @since 8.0
	 */
	public static final byte BEL = 7;

	/**
	 * Backspace ('\b'): A format effector which controls the movement of the
	 * printing position one printing space backward on the same printing line.
	 * (Applicable also to display devices.)
	 *
	 * @since 8.0
	 */
	public static final byte BS = 8;

	/**
	 * Horizontal Tabulation ('\t'): A format effector which controls the movement
	 * of the printing position to the next in a series of predetermined positions
	 * along the printing line. (Applicable also to display devices and the skip
	 * function on punched cards.)
	 *
	 * @since 8.0
	 */
	public static final byte HT = 9;

	/**
	 * Line Feed ('\n'): A format effector which controls the movement of the
	 * printing position to the next printing line. (Applicable also to display
	 * devices.) Where appropriate, this character may have the meaning "New Line"
	 * (NL), a format effector which controls the movement of the printing point to
	 * the first printing position on the next printing line. Use of this convention
	 * requires agreement between sender and recipient of data.
	 *
	 * @since 8.0
	 */
	public static final byte LF = 10;

	/**
	 * Alternate name for {@link #LF}. ({@code LF} is preferred.)
	 *
	 * @since 8.0
	 */
	public static final byte NL = 10;

	/**
	 * Vertical Tabulation ('\v'): A format effector which controls the movement of
	 * the printing position to the next in a series of predetermined printing
	 * lines. (Applicable also to display devices.)
	 *
	 * @since 8.0
	 */
	public static final byte VT = 11;

	/**
	 * Form Feed ('\f'): A format effector which controls the movement of the
	 * printing position to the first pre-determined printing line on the next form
	 * or page. (Applicable also to display devices.)
	 *
	 * @since 8.0
	 */
	public static final byte FF = 12;

	/**
	 * Carriage Return ('\r'): A format effector which controls the movement of the
	 * printing position to the first printing position on the same printing line.
	 * (Applicable also to display devices.)
	 *
	 * @since 8.0
	 */
	public static final byte CR = 13;

	/**
	 * Shift Out: A control character indicating that the code combinations which
	 * follow shall be interpreted as outside of the character set of the standard
	 * code table until a Shift In character is reached.
	 *
	 * @since 8.0
	 */
	public static final byte SO = 14;

	/**
	 * Shift In: A control character indicating that the code combinations which
	 * follow shall be interpreted according to the standard code table.
	 *
	 * @since 8.0
	 */
	public static final byte SI = 15;

	/**
	 * Data Link Escape: A communication control character which will change the
	 * meaning of a limited number of contiguously following characters. It is used
	 * exclusively to provide supplementary controls in data communication networks.
	 *
	 * @since 8.0
	 */
	public static final byte DLE = 16;

	/**
	 * Device Control 1. Characters for the control of ancillary devices associated
	 * with data processing or telecommunication systems, more especially switching
	 * devices "on" or "off." (If a single "stop" control is required to interrupt
	 * or turn off ancillary devices, DC4 is the preferred assignment.)
	 *
	 * @since 8.0
	 */
	public static final byte DC1 = 17; // aka XON

	/**
	 * Transmission On: Although originally defined as DC1, this ASCII control
	 * character is now better known as the XON code used for software flow control
	 * in serial communications. The main use is restarting the transmission after
	 * the communication has been stopped by the XOFF control code.
	 *
	 * @since 8.0
	 */
	public static final byte XON = 17; // aka DC1

	/**
	 * Device Control 2. Characters for the control of ancillary devices associated
	 * with data processing or telecommunication systems, more especially switching
	 * devices "on" or "off." (If a single "stop" control is required to interrupt
	 * or turn off ancillary devices, DC4 is the preferred assignment.)
	 *
	 * @since 8.0
	 */
	public static final byte DC2 = 18;

	/**
	 * Device Control 3. Characters for the control of ancillary devices associated
	 * with data processing or telecommunication systems, more especially switching
	 * devices "on" or "off." (If a single "stop" control is required to interrupt
	 * or turn off ancillary devices, DC4 is the preferred assignment.)
	 *
	 * @since 8.0
	 */
	public static final byte DC3 = 19; // aka XOFF

	/**
	 * Transmission off. See {@link #XON} for explanation.
	 *
	 * @since 8.0
	 */
	public static final byte XOFF = 19; // aka DC3

	/**
	 * Device Control 4. Characters for the control of ancillary devices associated
	 * with data processing or telecommunication systems, more especially switching
	 * devices "on" or "off." (If a single "stop" control is required to interrupt
	 * or turn off ancillary devices, DC4 is the preferred assignment.)
	 *
	 * @since 8.0
	 */
	public static final byte DC4 = 20;

	/**
	 * Negative Acknowledge: A communication control character transmitted by a
	 * receiver as a negative response to the sender.
	 *
	 * @since 8.0
	 */
	public static final byte NAK = 21;

	/**
	 * Synchronous Idle: A communication control character used by a synchronous
	 * transmission system in the absence of any other character to provide a signal
	 * from which synchronism may be achieved or retained.
	 *
	 * @since 8.0
	 */
	public static final byte SYN = 22;

	/**
	 * End of Transmission Block: A communication control character used to indicate
	 * the end of a block of data for communication purposes. ETB is used for
	 * blocking data where the block structure is not necessarily related to the
	 * processing format.
	 *
	 * @since 8.0
	 */
	public static final byte ETB = 23;

	/**
	 * Cancel: A control character used to indicate that the data with which it is
	 * sent is in error or is to be disregarded.
	 *
	 * @since 8.0
	 */
	public static final byte CAN = 24;

	/**
	 * End of Medium: A control character associated with the sent data which may be
	 * used to identify the physical end of the medium, or the end of the used, or
	 * wanted, portion of information recorded on a medium. (The position of this
	 * character does not necessarily correspond to the physical end of the medium.)
	 *
	 * @since 8.0
	 */
	public static final byte EM = 25;

	/**
	 * Substitute: A character that may be substituted for a character which is
	 * determined to be invalid or in error.
	 *
	 * @since 8.0
	 */
	public static final byte SUB = 26;

	/**
	 * Escape: A control character intended to provide code extension (supplementary
	 * characters) in general information interchange. The Escape character itself
	 * is a prefix affecting the interpretation of a limited number of contiguously
	 * following characters.
	 *
	 * @since 8.0
	 */
	public static final byte ESC = 27;

	/**
	 * File Separator: These four information separators may be used within data in
	 * optional fashion, except that their hierarchical relationship shall be: FS is
	 * the most inclusive, then GS, then RS, and US is least inclusive. (The content
	 * and length of a File, Group, Record, or Unit are not specified.)
	 *
	 * @since 8.0
	 */
	public static final byte FS = 28;

	/**
	 * Group Separator: These four information separators may be used within data in
	 * optional fashion, except that their hierarchical relationship shall be: FS is
	 * the most inclusive, then GS, then RS, and US is least inclusive. (The content
	 * and length of a File, Group, Record, or Unit are not specified.)
	 *
	 * @since 8.0
	 */
	public static final byte GS = 29;

	/**
	 * Record Separator: These four information separators may be used within data
	 * in optional fashion, except that their hierarchical relationship shall be: FS
	 * is the most inclusive, then GS, then RS, and US is least inclusive. (The
	 * content and length of a File, Group, Record, or Unit are not specified.)
	 *
	 * @since 8.0
	 */
	public static final byte RS = 30;

	/**
	 * Unit Separator: These four information separators may be used within data in
	 * optional fashion, except that their hierarchical relationship shall be: FS is
	 * the most inclusive, then GS, then RS, and US is least inclusive. (The content
	 * and length of a File, Group, Record, or Unit are not specified.)
	 *
	 * @since 8.0
	 */
	public static final byte US = 31;

	/**
	 * Space: A normally non-printing graphic character used to separate words. It
	 * is also a format effector which controls the movement of the printing
	 * position, one printing position forward. (Applicable also to display
	 * devices.)
	 *
	 * @since 8.0
	 */
	public static final byte SP = 32;

	/**
	 * Alternate name for {@link #SP}.
	 *
	 * @since 8.0
	 */
	public static final byte SPACE = 32;

	/**
	 * Delete: This character is used primarily to "erase" or "obliterate" erroneous
	 * or unwanted characters in perforated tape.
	 *
	 * @since 8.0
	 */
	public static final byte DEL = 127;

	/**
	 * The minimum value of an ASCII character.
	 *
	 * @since 9.0 (was type {@code int} before 12.0)
	 */
	public static final char MIN = 0;

	/**
	 * The maximum value of an ASCII character.
	 *
	 * @since 9.0 (was type {@code int} before 12.0)
	 */
	public static final char MAX = 127;

	/**
	 * Returns a copy of the input string in which all
	 * {@linkplain #isUpperCase(char) uppercase ASCII characters} have been
	 * converted to lowercase. All other characters are copied without modification.
	 */
	public static String toLowerCase(String string) {
		int length = string.length();
		for (int i = 0; i < length; i++) {
			if (isUpperCase(string.charAt(i))) {
				char[] chars = string.toCharArray();
				for (; i < length; i++) {
					char c = chars[i];
					if (isUpperCase(c)) {
						chars[i] = (char) (c ^ 0x20);
					}
				}
				return String.valueOf(chars);
			}
		}
		return string;
	}

	/**
	 * Returns a copy of the input character sequence in which all
	 * {@linkplain #isUpperCase(char) uppercase ASCII characters} have been
	 * converted to lowercase. All other characters are copied without modification.
	 *
	 * @since 14.0
	 */
	public static String toLowerCase(CharSequence chars) {
		if (chars instanceof String) {
			return toLowerCase((String) chars);
		}
		int length = chars.length();
		StringBuilder builder = new StringBuilder(length);
		for (int i = 0; i < length; i++) {
			builder.append(toLowerCase(chars.charAt(i)));
		}
		return builder.toString();
	}

	/**
	 * If the argument is an {@linkplain #isUpperCase(char) uppercase ASCII
	 * character} returns the lowercase equivalent. Otherwise returns the argument.
	 */
	public static char toLowerCase(char c) {
		return isUpperCase(c) ? (char) (c ^ 0x20) : c;
	}

	/**
	 * Returns a copy of the input string in which all
	 * {@linkplain #isLowerCase(char) lowercase ASCII characters} have been
	 * converted to uppercase. All other characters are copied without modification.
	 */
	public static String toUpperCase(String string) {
		int length = string.length();
		for (int i = 0; i < length; i++) {
			if (isLowerCase(string.charAt(i))) {
				char[] chars = string.toCharArray();
				for (; i < length; i++) {
					char c = chars[i];
					if (isLowerCase(c)) {
						chars[i] = (char) (c & 0x5f);
					}
				}
				return String.valueOf(chars);
			}
		}
		return string;
	}

	/**
	 * Returns a copy of the input character sequence in which all
	 * {@linkplain #isLowerCase(char) lowercase ASCII characters} have been
	 * converted to uppercase. All other characters are copied without modification.
	 *
	 * @since 14.0
	 */
	public static String toUpperCase(CharSequence chars) {
		if (chars instanceof String) {
			return toUpperCase((String) chars);
		}
		int length = chars.length();
		StringBuilder builder = new StringBuilder(length);
		for (int i = 0; i < length; i++) {
			builder.append(toUpperCase(chars.charAt(i)));
		}
		return builder.toString();
	}

	/**
	 * If the argument is a {@linkplain #isLowerCase(char) lowercase ASCII
	 * character} returns the uppercase equivalent. Otherwise returns the argument.
	 */
	public static char toUpperCase(char c) {
		return isLowerCase(c) ? (char) (c & 0x5f) : c;
	}

	/**
	 * Indicates whether {@code c} is one of the twenty-six lowercase ASCII
	 * alphabetic characters between {@code 'a'} and {@code 'z'} inclusive. All
	 * others (including non-ASCII characters) return {@code false}.
	 */
	public static boolean isLowerCase(char c) {
		// Note: This was benchmarked against the alternate expression "(char)(c - 'a')
		// < 26" (Nov '13)
		// and found to perform at least as well, or better.
		return (c >= 'a') && (c <= 'z');
	}

	/**
	 * Indicates whether {@code c} is one of the twenty-six uppercase ASCII
	 * alphabetic characters between {@code 'A'} and {@code 'Z'} inclusive. All
	 * others (including non-ASCII characters) return {@code false}.
	 */
	public static boolean isUpperCase(char c) {
		return (c >= 'A') && (c <= 'Z');
	}

	/**
	 * Truncates the given character sequence to the given maximum length. If the
	 * length of the sequence is greater than {@code maxLength}, the returned string
	 * will be exactly {@code maxLength} chars in length and will end with the given
	 * {@code truncationIndicator}. Otherwise, the sequence will be returned as a
	 * string with no changes to the content.
	 *
	 * <p>
	 * Examples:
	 *
	 * <pre>
	 *    {@code
	 *   Ascii.truncate("foobar", 7, "..."); // returns "foobar"
	 *   Ascii.truncate("foobar", 5, "..."); // returns "fo..." }
	 * </pre>
	 *
	 * <p>
	 * <b>Note:</b> This method <i>may</i> work with certain non-ASCII text but is
	 * not safe for use with arbitrary Unicode text. It is mostly intended for use
	 * with text that is known to be safe for use with it (such as all-ASCII text)
	 * and for simple debugging text. When using this method, consider the
	 * following:
	 *
	 * <ul>
	 * <li>it may split surrogate pairs</li>
	 * <li>it may split characters and combining characters</li>
	 * <li>it does not consider word boundaries</li>
	 * <li>if truncating for display to users, there are other considerations that
	 * must be taken into account</li>
	 * <li>the appropriate truncation indicator may be locale-dependent</li>
	 * <li>it is safe to use non-ASCII characters in the truncation indicator</li>
	 * </ul>
	 *
	 *
	 * @throws IllegalArgumentException if {@code maxLength} is less than the length
	 *                                  of {@code truncationIndicator}
	 * @since 16.0
	 */
	@Beta
	@CheckReturnValue
	public static String truncate(CharSequence seq, int maxLength, String truncationIndicator) {
		checkNotNull(seq);

		// length to truncate the sequence to, not including the truncation indicator
		int truncationLength = maxLength - truncationIndicator.length();

		// in this worst case, this allows a maxLength equal to the length of the
		// truncationIndicator,
		// meaning that a string will be truncated to just the truncation indicator
		// itself
		checkArgument(truncationLength >= 0, "maxLength (%s) must be >= length of the truncation indicator (%s)",
				maxLength, truncationIndicator.length());

		if (seq.length() <= maxLength) {
			String string = seq.toString();
			if (string.length() <= maxLength) {
				return string;
			}
			// if the length of the toString() result was > maxLength for some reason,
			// truncate that
			seq = string;
		}

		return new StringBuilder(maxLength).append(seq, 0, truncationLength).append(truncationIndicator).toString();
	}

	/**
	 * Indicates whether the contents of the given character sequences {@code s1}
	 * and {@code s2} are equal, ignoring the case of any ASCII alphabetic
	 * characters between {@code 'a'} and {@code 'z'} or {@code 'A'} and {@code 'Z'}
	 * inclusive.
	 *
	 * <p>
	 * This method is significantly faster than {@link String#equalsIgnoreCase} and
	 * should be used in preference if at least one of the parameters is known to
	 * contain only ASCII characters.
	 *
	 * <p>
	 * Note however that this method does not always behave identically to
	 * expressions such as:
	 * <ul>
	 * <li>{@code string.toUpperCase().equals("UPPER CASE ASCII")}
	 * <li>{@code string.toLowerCase().equals("lower case ascii")}
	 * </ul>
	 * <p>
	 * due to case-folding of some non-ASCII characters (which does not occur in
	 * {@link String#equalsIgnoreCase}). However in almost all cases that ASCII
	 * strings are used, the author probably wanted the behavior provided by this
	 * method rather than the subtle and sometimes surprising behavior of
	 * {@code toUpperCase()} and {@code toLowerCase()}.
	 *
	 * @since 16.0
	 */
	@Beta
	public static boolean equalsIgnoreCase(CharSequence s1, CharSequence s2) {
		// Calling length() is the null pointer check (so do it before we can exit
		// early).
		int length = s1.length();
		if (s1 == s2) {
			return true;
		}
		if (length != s2.length()) {
			return false;
		}
		for (int i = 0; i < length; i++) {
			char c1 = s1.charAt(i);
			char c2 = s2.charAt(i);
			if (c1 == c2) {
				continue;
			}
			int alphaIndex = getAlphaIndex(c1);
			// This was also benchmarked using '&' to avoid branching (but always evaluate
			// the rhs),
			// however this showed no obvious improvement.
			if (alphaIndex < 26 && alphaIndex == getAlphaIndex(c2)) {
				continue;
			}
			return false;
		}
		return true;
	}

	/**
	 * Returns the non-negative index value of the alpha character {@code c},
	 * regardless of case. Ie, 'a'/'A' returns 0 and 'z'/'Z' returns 25. Non-alpha
	 * characters return a value of 26 or greater.
	 */
	private static int getAlphaIndex(char c) {
		// Fold upper-case ASCII to lower-case and make zero-indexed and unsigned (by
		// casting to char).
		return (char) ((c | 0x20) - 'a');
	}
}
