sources/Google.Solutions.Common/Text/StringExtensions.cs

//
// Copyright 2020 Google LLC
//
// 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.
//

using System;

namespace Google.Solutions.Common.Text
{
    public static class StringExtensions
    {
        /// <summary>
        /// Find the index of the first character that matches a predicate.
        /// </summary>
        /// <returns>Index, or -1 if not found</returns>
        public static int IndexOf(
            this string str,
            Predicate<char> predicate)
        {
            for (var i = 0; i < str.Length; i++)
            {
                if (predicate(str[i]))
                {
                    return i;
                }
            }

            return -1;
        }

        /// <summary>
        /// Find the index of the last character that matches a predicate.
        /// </summary>
        /// <returns>Index, or -1 if not found</returns>
        public static int LastIndexOf(
            this string str, 
            Predicate<char> predicate)
        {
            for (var i = str.Length - 1; i >= 0; i--)
            {
                if (predicate(str[i]))
                {
                    return i;
                }
            }

            return -1;
        }

        /// <summary>
        /// Truncate a string, adding an ellipsis if necessary.
        /// </summary>
        public static string Truncate(this string value, int maxChars)
        {
            return value.Length <= maxChars
                ? value
                : value.Substring(0, maxChars) + "...";
        }

        /// <summary>
        /// Convert an empty string to null.
        /// </summary>
        /// <returns>Input string, or null if it's empty</returns>
        public static string? NullIfEmpty(this string? s)
        {
            return string.IsNullOrEmpty(s) ? null : s;
        }

        /// <summary>
        /// Convert a whitespace string to null.
        /// </summary>
        /// <returns>Input string, or null if it's empty or whitespace</returns>
        public static string? NullIfEmptyOrWhitespace(this string? s)
        {
            return string.IsNullOrWhiteSpace(s) ? null : s;
        }
    }
}