/*
 * 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 com.google.common.annotations.GwtCompatible;
import com.google.common.annotations.VisibleForTesting;
import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Static utility methods pertaining to {@code String} or {@code CharSequence} instances.
 *
 * @author Kevin Bourrillion
 * @since 3.0
 */
@GwtCompatible
public final class Strings {
  private Strings() {}

  /**
   * Returns the given string if it is non-null; the empty string otherwise.
   *
   * @param string the string to test and possibly return
   * @return {@code string} itself if it is non-null; {@code ""} if it is null
   */
  public static String nullToEmpty(@Nullable String string) {
    return Platform.nullToEmpty(string);
  }

  /**
   * Returns the given string if it is nonempty; {@code null} otherwise.
   *
   * @param string the string to test and possibly return
   * @return {@code string} itself if it is nonempty; {@code null} if it is empty or null
   */
  public static @Nullable String emptyToNull(@Nullable String string) {
    return Platform.emptyToNull(string);
  }

  /**
   * Returns {@code true} if the given string is null or is the empty string.
   *
   * <p>Consider normalizing your string references with {@link #nullToEmpty}. If you do, you can
   * use {@link String#isEmpty()} instead of this method, and you won't need special null-safe forms
   * of methods like {@link String#toUpperCase} either. Or, if you'd like to normalize "in the other
   * direction," converting empty strings to {@code null}, you can use {@link #emptyToNull}.
   *
   * @param string a string reference to check
   * @return {@code true} if the string is null or is the empty string
   */
  public static boolean isNullOrEmpty(@Nullable String string) {
    return Platform.stringIsNullOrEmpty(string);
  }

  /**
   * Returns a string, of length at least {@code minLength}, consisting of {@code string} prepended
   * with as many copies of {@code padChar} as are necessary to reach that length. For example,
   *
   * <ul>
   *   <li>{@code padStart("7", 3, '0')} returns {@code "007"}
   *   <li>{@code padStart("2010", 3, '0')} returns {@code "2010"}
   * </ul>
   *
   * <p>See {@link java.util.Formatter} for a richer set of formatting capabilities.
   *
   * @param string the string which should appear at the end of the result
   * @param minLength the minimum length the resulting string must have. Can be zero or negative, in
   *     which case the input string is always returned.
   * @param padChar the character to insert at the beginning of the result until the minimum length
   *     is reached
   * @return the padded string
   */
  public static String padStart(String string, int minLength, char padChar) {
    checkNotNull(string); // eager for GWT.
    if (string.length() >= minLength) {
      return string;
    }
    StringBuilder sb = new StringBuilder(minLength);
    for (int i = string.length(); i < minLength; i++) {
      sb.append(padChar);
    }
    sb.append(string);
    return sb.toString();
  }

  /**
   * Returns a string, of length at least {@code minLength}, consisting of {@code string} appended
   * with as many copies of {@code padChar} as are necessary to reach that length. For example,
   *
   * <ul>
   *   <li>{@code padEnd("4.", 5, '0')} returns {@code "4.000"}
   *   <li>{@code padEnd("2010", 3, '!')} returns {@code "2010"}
   * </ul>
   *
   * <p>See {@link java.util.Formatter} for a richer set of formatting capabilities.
   *
   * @param string the string which should appear at the beginning of the result
   * @param minLength the minimum length the resulting string must have. Can be zero or negative, in
   *     which case the input string is always returned.
   * @param padChar the character to append to the end of the result until the minimum length is
   *     reached
   * @return the padded string
   */
  public static String padEnd(String string, int minLength, char padChar) {
    checkNotNull(string); // eager for GWT.
    if (string.length() >= minLength) {
      return string;
    }
    StringBuilder sb = new StringBuilder(minLength);
    sb.append(string);
    for (int i = string.length(); i < minLength; i++) {
      sb.append(padChar);
    }
    return sb.toString();
  }

  /**
   * Returns a string consisting of a specific number of concatenated copies of an input string. For
   * example, {@code repeat("hey", 3)} returns the string {@code "heyheyhey"}.
   *
   * @param string any non-null string
   * @param count the number of times to repeat it; a nonnegative integer
   * @return a string containing {@code string} repeated {@code count} times (the empty string if
   *     {@code count} is zero)
   * @throws IllegalArgumentException if {@code count} is negative
   */
  public static String repeat(String string, int count) {
    checkNotNull(string); // eager for GWT.

    if (count <= 1) {
      checkArgument(count >= 0, "invalid count: %s", count);
      return (count == 0) ? "" : string;
    }

    // IF YOU MODIFY THE CODE HERE, you must update StringsRepeatBenchmark
    final int len = string.length();
    final long longSize = (long) len * (long) count;
    final int size = (int) longSize;
    if (size != longSize) {
      throw new ArrayIndexOutOfBoundsException("Required array size too large: " + longSize);
    }

    final char[] array = new char[size];
    string.getChars(0, len, array, 0);
    int n;
    for (n = len; n < size - n; n <<= 1) {
      System.arraycopy(array, 0, array, n, n);
    }
    System.arraycopy(array, 0, array, n, size - n);
    return new String(array);
  }

  /**
   * Returns the longest string {@code prefix} such that {@code a.toString().startsWith(prefix) &&
   * b.toString().startsWith(prefix)}, taking care not to split surrogate pairs. If {@code a} and
   * {@code b} have no common prefix, returns the empty string.
   *
   * @since 11.0
   */
  public static String commonPrefix(CharSequence a, CharSequence b) {
    checkNotNull(a);
    checkNotNull(b);

    int maxPrefixLength = Math.min(a.length(), b.length());
    int p = 0;
    while (p < maxPrefixLength && a.charAt(p) == b.charAt(p)) {
      p++;
    }
    if (validSurrogatePairAt(a, p - 1) || validSurrogatePairAt(b, p - 1)) {
      p--;
    }
    return a.subSequence(0, p).toString();
  }

  /**
   * Returns the longest string {@code suffix} such that {@code a.toString().endsWith(suffix) &&
   * b.toString().endsWith(suffix)}, taking care not to split surrogate pairs. If {@code a} and
   * {@code b} have no common suffix, returns the empty string.
   *
   * @since 11.0
   */
  public static String commonSuffix(CharSequence a, CharSequence b) {
    checkNotNull(a);
    checkNotNull(b);

    int maxSuffixLength = Math.min(a.length(), b.length());
    int s = 0;
    while (s < maxSuffixLength && a.charAt(a.length() - s - 1) == b.charAt(b.length() - s - 1)) {
      s++;
    }
    if (validSurrogatePairAt(a, a.length() - s - 1)
        || validSurrogatePairAt(b, b.length() - s - 1)) {
      s--;
    }
    return a.subSequence(a.length() - s, a.length()).toString();
  }

  /**
   * Returns the given {@code template} string with each occurrence of {@code "%s"} replaced with
   * the corresponding argument value from {@code args}; or, if the placeholder and argument counts
   * do not match, returns a best-effort form of that string. Will not throw an exception under any
   * circumstances (as long as all arguments' {@code toString} methods successfully return).
   *
   * <p><b>Note:</b> For most string-formatting needs, use {@link String#format}, {@link
   * PrintWriter#format}, and related methods. These support the full range of {@linkplain
   * Formatter#syntax format specifiers}, and alert you to usage errors by throwing {@link
   * InvalidFormatException}.
   *
   * <p>In certain cases, such as outputting debugging information or constructing a message to be
   * used for another unchecked exception, an exception during string formatting would serve little
   * purpose except to supplant the real information you were trying to provide. These are the cases
   * this method is made for; it instead generates a best-effort string with all supplied argument
   * values present. This method is also useful in environments such as GWT where {@code
   * String.format} is not available. As an example, method implementations of the {@link
   * Preconditions} class use this formatter, for both of the reasons just discussed.
   *
   * <p><b>Warning:</b> Only the exact two-character placeholder sequence {@code "%s"} is
   * recognized.
   *
   * @param template a string containing zero or more {@code "%s"} placeholder sequences. {@code
   *     null} is treated as the four-character string {@code "null"}.
   * @param args the arguments to be substituted into the message template. The first argument
   *     specified is substituted for the first occurrence of {@code "%s"} in the template, and so
   *     forth. A {@code null} argument is converted to the four-character string {@code "null"};
   *     non-null values are converted to strings using {@link Object#toString()}.
   * @since 25.1
   */
  // TODO(diamondm) consider using Arrays.toString() for array parameters
  // TODO(diamondm) capture exceptions thrown from arguments' toString methods
  public static String lenientFormat(
      @Nullable String template, @Nullable Object @Nullable... args) {
    template = String.valueOf(template); // null -> "null"

    args = args == null ? new Object[] {"(Object[])null"} : args;

    // start substituting the arguments into the '%s' placeholders
    StringBuilder builder = new StringBuilder(template.length() + 16 * args.length);
    int templateStart = 0;
    int i = 0;
    while (i < args.length) {
      int placeholderStart = template.indexOf("%s", templateStart);
      if (placeholderStart == -1) {
        break;
      }
      builder.append(template, templateStart, placeholderStart);
      builder.append(args[i++]);
      templateStart = placeholderStart + 2;
    }
    builder.append(template, templateStart, template.length());

    // if we run out of placeholders, append the extra args in square braces
    if (i < args.length) {
      builder.append(" [");
      builder.append(args[i++]);
      while (i < args.length) {
        builder.append(", ");
        builder.append(args[i++]);
      }
      builder.append(']');
    }

    return builder.toString();
  }

  /**
   * True when a valid surrogate pair starts at the given {@code index} in the given {@code string}.
   * Out-of-range indexes return false.
   */
  @VisibleForTesting
  static boolean validSurrogatePairAt(CharSequence string, int index) {
    return index >= 0
        && index <= (string.length() - 2)
        && Character.isHighSurrogate(string.charAt(index))
        && Character.isLowSurrogate(string.charAt(index + 1));
  }
}