SubtitleEdit/libse/StringExtensions.cs

using System;
using System.Text;

namespace Nikse.SubtitleEdit.Core
{
    public static class StringExtensions
    {
        public static bool LineStartsWithHtmlTag(this string text, bool threeLengthTag, bool includeFont = false)
        {
            if (text == null || (!threeLengthTag && !includeFont))
                return false;
            return StartsWithHtmlTag(text, threeLengthTag, includeFont);
        }

        public static bool LineEndsWithHtmlTag(this string text, bool threeLengthTag, bool includeFont = false)
        {
            if (text == null)
                return false;

            var len = text.Length;
            if (len < 6 || text[len - 1] != '>')
                return false;

            // </font> </i>
            if (threeLengthTag && len > 3 && text[len - 4] == '<' && text[len - 3] == '/')
                return true;
            if (includeFont && len > 8 && text[len - 7] == '<' && text[len - 6] == '/')
                return true;
            return false;
        }

        public static bool LineBreakStartsWithHtmlTag(this string text, bool threeLengthTag, bool includeFont = false)
        {
            if (text == null || (!threeLengthTag && !includeFont))
                return false;
            var newLineIdx = text.IndexOf(Environment.NewLine, StringComparison.Ordinal);
            if (newLineIdx < 0 || text.Length < newLineIdx + 5)
                return false;
            text = text.Substring(newLineIdx + 2);
            return StartsWithHtmlTag(text, threeLengthTag, includeFont);
        }

        private static bool StartsWithHtmlTag(string text, bool threeLengthTag, bool includeFont)
        {
            if (threeLengthTag && text.Length >= 3 && text[0] == '<' && text[2] == '>' && (text[1] == 'i' || text[1] == 'I' || text[1] == 'u' || text[1] == 'U' || text[1] == 'b' || text[1] == 'B'))
                return true;
            if (includeFont && text.Length > 5 && text.StartsWith("<font", StringComparison.OrdinalIgnoreCase))
                return text.IndexOf('>', 5) >= 5; // <font> or <font color="#000000">
            return false;
        }

        public static bool StartsWith(this string s, char c)
        {
            return s.Length > 0 && s[0] == c;
        }

        public static bool StartsWith(this StringBuilder sb, char c)
        {
            return sb.Length > 0 && sb[0] == c;
        }

        public static bool EndsWith(this string s, char c)
        {
            return s.Length > 0 && s[s.Length - 1] == c;
        }

        public static bool EndsWith(this StringBuilder sb, char c)
        {
            return sb.Length > 0 && sb[sb.Length - 1] == c;
        }

        public static bool Contains(this string source, char value)
        {
            return source.IndexOf(value) >= 0;
        }

        public static bool Contains(this string source, char[] value)
        {
            return source.IndexOfAny(value) >= 0;
        }

        public static bool Contains(this string source, string value, StringComparison comparisonType)
        {
            return source.IndexOf(value, comparisonType) >= 0;
        }

        public static string[] SplitToLines(this string source)
        {
            return source.Replace("\r\n", "\n").Replace('\r', '\n').Split('\n');
        }

        // http://www.codeproject.com/Articles/43726/Optimizing-string-operations-in-C
        public static int FastIndexOf(this string source, string pattern)
        {
            if (pattern == null) throw new ArgumentNullException();
            if (pattern.Length == 0) return 0;
            if (pattern.Length == 1) return source.IndexOf(pattern[0]);
            int limit = source.Length - pattern.Length + 1;
            if (limit < 1) return -1;
            // Store the first 2 characters of "pattern"
            char c0 = pattern[0];
            char c1 = pattern[1];
            // Find the first occurrence of the first character
            int first = source.IndexOf(c0, 0, limit);
            while (first != -1)
            {
                // Check if the following character is the same like
                // the 2nd character of "pattern"
                if (source[first + 1] != c1)
                {
                    first = source.IndexOf(c0, ++first, limit - first);
                    continue;
                }
                // Check the rest of "pattern" (starting with the 3rd character)
                bool found = true;
                for (var j = 2; j < pattern.Length; j++)
                    if (source[first + j] != pattern[j])
                    {
                        found = false;
                        break;
                    }
                // If the whole word was found, return its index, otherwise try again
                if (found) return first;
                first = source.IndexOf(c0, ++first, limit - first);
            }
            return -1;
        }

        public static int IndexOfAny(this string s, string[] words, StringComparison comparionType)
        {
            if (words == null || string.IsNullOrEmpty(s))
                return -1;
            for (int i = 0; i < words.Length; i++)
            {
                var idx = s.IndexOf(words[i], comparionType);
                if (idx >= 0)
                    return idx;
            }
            return -1;
        }

        public static string FixExtraSpaces(this string s)
        {
            if (string.IsNullOrEmpty(s))
                return s;

            while (s.Contains("  "))
                s = s.Replace("  ", " ");
            s = s.Replace(" " + Environment.NewLine, Environment.NewLine);
            return s.Replace(Environment.NewLine + " ", Environment.NewLine);
        }

        public static bool ContainsLetter(this string s)
        {
            if (string.IsNullOrWhiteSpace(s))
                return false;

            foreach (var c in s)
            {
                if (char.IsLetter(c))
                    return true;
            }
            return false;
        }
    }
}