apewer-dotnet/Apewer/TextUtility.cs

using Apewer.Internals;
using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Text.RegularExpressions;

namespace Apewer
{

    /// <summary>文本实用工具。</summary>
    public class TextUtility
    {

        const string BlankChars = " 　\n\r\t\f\b\a"; // 在 IsBlank 和 Trim 中视为空白的字符。
        const string LineFeed = "\r\n"; // 换行符，由 ASCII 13 和 ASCII 10 组成。
        const string SpaceDbc = " ";
        const string SpaceSbc = "　";
        const string LucidChars = "3456789acefhknpstwxyz";
        const string KeyChars = "0123456789abcdefghijklmnopqrstuvwxyz";
        const string HexChars = "0123456789abcdef";
        const string NumericChars = "0123456789";
        const string LowerChars = "abcdefghijklmnopqrstuvwxyz";
        const string UpperChars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        const string LetterChars = LowerChars + UpperChars;

        /// <summary>UTF-8 BOM。</summary>
        public static byte[] Bom { get => new byte[] { 0xEF, 0xBB, 0xBF }; }

        /// <summary>CRLF。</summary>
        public const string CRLF = "\r\n";

        /// <summary>LF。</summary>
        public const string LF = "\n";

        /// <summary>空文本。</summary>
        public const string Empty = "";

        /// <summary>字符串为空。</summary>
        public static bool IsEmpty(string text) => text == null || text == Empty;

        /// <summary>字符串不为空。</summary>
        public static bool NotEmpty(string text) => text != null && text != Empty;

        /// <summary>字符串为空，或只含有空白字符。</summary>
        public static bool IsBlank(string text)
        {
            if (IsEmpty(text)) return true;
            var length = text.Length;
            var bcs = BlankChars.ToCharArray();
            var bcl = bcs.Length;
            bool b;
            char c;
            for (var i = 0; i < length; i++)
            {
                c = text[i];
                b = false;
                for (var j = 0; j < bcl; j++)
                {
                    if (c == bcs[j])
                    {
                        b = true;
                        break;
                    }
                }
                if (!b) return false;
            }
            return true;
        }

        /// <summary>字符串不为空，切含有非空白字符。</summary>
        public static bool NotBlank(string text) => !IsBlank(text);

        private static string PrivateJoin(string separator, IEnumerable cells)
        {
            if (cells == null) return Empty;
            var sb = new StringBuilder();
            var first = true;
            var hasSeparator = !string.IsNullOrEmpty(separator);
            foreach (var cell in cells)
            {
                if (cell == null) continue;
                var text = (cell is string) ? (cell as string) : cell.ToString();
                if (string.IsNullOrEmpty(text)) continue;

                if (!first && hasSeparator) sb.Append(separator);
                first = false;
                sb.Append(text);
            }
            var result = sb.ToString();
            return result;
        }

        /// <summary>合并为字符串。</summary>
        public static string Merge(params object[] cells) => PrivateJoin(null, cells);

        /// <summary>合并为字符串。</summary>
        public static string Merge(IEnumerable cells) => PrivateJoin(null, cells);

        /// <summary>合并为字符串。</summary>
        public static string Join(string separator, params object[] cells) => PrivateJoin(separator, cells);

        /// <summary>合并为字符串。</summary>
        public static string Join(string separator, IEnumerable cells) => PrivateJoin(separator, cells);

        /// <summary>重复指定字符，直到达到指定长度。</summary>
        /// <param name="cell">要重复的字符。</param>
        /// <param name="count">重复的次数。</param>
        public static string Duplicate(char cell, int count)
        {
            if (count < 1) return Empty;
            var chars = new char[count];
            for (var i = 0; i < count; i++) chars[i] = cell;
            return new string(chars);
        }

        /// <summary>重复指定字符串，直到达到指定长度。</summary>
        /// <param name="cell">要重复的字符串。</param>
        /// <param name="count">重复的次数。</param>
        public static string Duplicate(string cell, int count)
        {
            if (IsEmpty(cell) || count < 1) return Empty;
            var length = cell.Length;
            var total = length * count;
            var output = new char[total];
            var input = cell.ToCharArray();
            for (var i = 0; i < count; i++)
            {
                Array.Copy(input, 0, output, length * i, length);
            }
            return new string(output);
        }

        /// <summary>获取指定长的的空格。</summary>
        public static string Space(int length) => Duplicate(' ', length);

        /// <summary>将文本以转换为字节数组。默认 Encoding 为 UTF-8。</summary>
        public static byte[] Bytes(string text, Encoding encoding = null)
        {
            if (text == null || text == Empty) return BytesUtility.Empty;
            try { return (encoding ?? Encoding.UTF8).GetBytes(text); }
            catch { return BytesUtility.Empty; }
        }

        /// <summary>将字节数组转换为文本。默认 Encoding 为 UTF-8。</summary>
        public static string FromBytes(byte[] bytes, Encoding encoding = null)
        {
            if (bytes == null || bytes.LongLength < 1L) return Empty;
            try { return (encoding ?? Encoding.UTF8).GetString(bytes); }
            catch { return Empty; }
        }

        /// <summary>将明文文本以 UTF-8 转换为 Base64 文本。</summary>
        public static string ToBase64(string plain)
        {
            if (plain == null || plain == Empty) return Empty;
            return BytesUtility.ToBase64(Bytes(plain));
        }

        /// <summary>将 Base64 文本以 UTF-8 转换为明文文本。</summary>
        public static string FromBase64(string cipher)
        {
            if (cipher == null || cipher == Empty) return Empty;
            return FromBytes(BytesUtility.FromBase64(cipher));
        }

        /// <summary>从字符串中删除子字符串。</summary>
        /// <param name="text">要查询的字符串。</param>
        /// <param name="sub">子字符串。</param>
        /// <param name="ignoreCase">是否忽略大小写。</param>
        /// <returns>删除子字符串后的父字符串。</returns>
        private static string Exlude(string text, string sub, bool ignoreCase = false)
        {
            if (string.IsNullOrEmpty(text)) return "";
            if (string.IsNullOrEmpty(sub)) return text;
            try
            {
                string vp = text;
                string vs = sub;
                string vr = "";
                int vl;
                int vi;
                if (ignoreCase)
                {
                    vp = TextHelper.LCase(vp);
                    vs = TextHelper.LCase(vs);
                }
                vl = vs.Length;
                vi = 1;
                while (vi <= (vp.Length - vl + 1))
                {
                    if (TextHelper.Middle(vp, vi, vl) == vs)
                    {
                        vi = vi + vl;
                    }
                    else
                    {
                        vr = vr + TextHelper.Middle(text, vi, 1);
                        vi = vi + 1;
                    }

                }
                return vr;
            }
            catch { return text; }
        }

        /// <summary>替换字符串中的子字符串。</summary>
        /// <param name="text">要查询的字符串。</param>
        /// <param name="new">新子字符串，保留大小写。</param>
        /// <param name="old">原子字符串。</param>
        /// <param name="ignoreCase">查找时是否忽略父字符串和原子字符串大小写。</param>
        /// <returns>替换后的父字符串。</returns>
        private static string Replace(string text, string old, string @new, bool ignoreCase = false)
        {
            if (string.IsNullOrEmpty(text)) return "";
            if (string.IsNullOrEmpty(old)) return text;
            if (string.IsNullOrEmpty(@new)) return Exlude(text, old, ignoreCase);
            if (TextHelper.Len(text) < TextHelper.Len(old)) return text;
            if (ignoreCase)
            {
                try
                {
                    string p = TextHelper.LCase(text);
                    string o = TextHelper.LCase(old);
                    int vil = TextHelper.Len(old);
                    int viv = 1;
                    int vend = TextHelper.Len(text) - vil + 1;
                    string vcell;
                    string vresult = "";
                    while (viv <= vend)
                    {
                        vcell = TextHelper.Middle(p, viv, vil);
                        if (vcell == o)
                        {
                            vresult = vresult + @new;
                            viv = viv + vil;
                        }
                        else
                        {
                            vresult = vresult + TextHelper.Middle(text, viv, 1);
                            viv = viv + 1;
                        }
                    }
                    return vresult;
                }
                catch { return text; }
            }
            else
            {
                try
                {
                    string vresult = text.Replace(old, @new);
                    return vresult;
                }
                catch { return ""; }
            }
        }

        /// <summary>修复文本前缀。</summary>
        /// <param name="text">原文本。</param>
        /// <param name="include">TRUE：追加指定缀；FALSE：去除指定缀。</param>
        /// <param name="head">前缀文本。</param>
        public static string AssureStarts(string text, string head, bool include = true)
        {
            if (string.IsNullOrEmpty(text)) return Empty;
            if (string.IsNullOrEmpty(head)) return text;

            if (include)
            {
                return text.StartsWith(head) ? text : (head + text);
            }
            else
            {
                var headLength = head.Length;
                if (!text.StartsWith(head)) return text;
                var result = text;
                while (true)
                {
                    result = result.Substring(headLength);
                    if (!result.StartsWith(head)) return result;
                }
            }
        }

        /// <summary>修复文本后缀。</summary>
        /// <param name="text">原文本。</param>
        /// <param name="include">TRUE：追加指定后缀；FALSE：去除指定后缀。</param>
        /// <param name="foot">后缀文本。</param>
        public static string AssureEnds(string text, string foot, bool include = true)
        {
            if (string.IsNullOrEmpty(text)) return Empty;
            if (string.IsNullOrEmpty(foot)) return text;

            if (include == true)
            {
                return text.EndsWith(foot) ? text : (text + foot);
            }
            else
            {
                var footLength = foot.Length;
                if (!text.EndsWith(foot)) return text;
                var result = text;
                while (true)
                {
                    result = result.Substring(0, result.Length - footLength);
                    if (!result.EndsWith(foot)) return result;
                }
            }
        }

        /// <summary>用单字符作为分隔符拆分文本。</summary>
        public static string[] Split(string text, char separator)
        {
            if (text == null) return new string[0];
            if (text.Length < 1) return new string[] { "" };
            if ((object)separator == null) return new string[] { text };

            return text.Split(separator);
        }

        /// <summary>用字符串作为分隔符拆分文本。</summary>
        public static string[] Split(string text, string separator)
        {
            if (text == null) return new string[0];
            if (text.Length < 1) return new string[] { "" };
            if (string.IsNullOrEmpty(separator)) return new string[] { text };
            if (separator.Length > text.Length) return new string[] { text };

            var list = new List<string>();
            var position = 0;
            var total = text.Length;
            var length = separator.Length;
            var cell = new StringBuilder();
            while (position < total)
            {
                var read = null as string;
                if (position + length < total) read = text.Substring(position, length);
                else read = text.Substring(position);

                if (read == separator)
                {
                    if (cell.Length > 0)
                    {
                        list.Add(cell.ToString());
                        // cell.Clear();
                        cell = new StringBuilder();
                    }
                    else
                    {
                        list.Add("");
                    }
                    position += length;
                }
                else
                {
                    cell.Append((char)text[position]);
                    position += 1;
                }

                if (position >= total)
                {
                    list.Add(cell.ToString());
                }
            }

            var array = list.ToArray();
            return array;
        }

        /// <summary>用多个分隔符拆分文本。</summary>
        public static string[] Split(string text, params char[] separators)
        {
            if (text == null) return new string[0];
            if (text.Length < 1) return new string[] { "" };
            if (separators == null || separators.Length < 1) return new string[] { text };
            if (separators.Length == 1) return Split(text, separators[0]);

            var list = new List<string>();
            var separatorsText = new string(separators);
            var sb = new StringBuilder();
            foreach (var c in text)
            {
                if (separatorsText.IndexOf(c) >= 0)
                {
                    list.Add(sb.ToString());
                    //sb.Clear();
                    sb = new StringBuilder();
                    continue;
                }
                sb.Append(c);
            }
            list.Add(sb.ToString());
#if !NET20
            sb.Clear();
#endif

            return list.ToArray();
        }

        /// <summary>移除字符串前后的空字符。</summary>
        /// <param name="text">原始字符串。</param>
        /// <param name="trimBlank">移除空格、全角空格、换行符、回车符、制表符和换页符。</param>
        public static string Trim(string text, bool trimBlank = false)
        {
            if (text == null || text == Empty) return Empty;
            if (!trimBlank) return Trim(text, ' ');
            return Trim(text, BlankChars.ToCharArray());
        }

        /// <summary>移除字符串前后的指定字符。</summary>
        /// <param name="text">原始字符串。</param>
        /// <param name="chars">要移除的字符。</param>
        public static string Trim(string text, params char[] chars)
        {
            if (text == null || text == Empty) return Empty;
            if (chars == null || chars.Length < 1) return text;

            var length = text.Length;
            var charsLength = chars.Length;

            var starts = 0;
            var offset = 0;
            while (true)
            {
                if (offset >= length) break;
                var c = text[offset];
                var trim = false;
                for (var i = 0; i < charsLength; i++)
                {
                    if (c == chars[i])
                    {
                        starts += 1;
                        offset += 1;
                        trim = true;
                        break;
                    }
                }
                if (trim) continue; else break;
            }

            var ends = 0;
            if (starts < length)
            {
                offset = length - 1;
                while (true)
                {
                    if (offset <= starts) break;
                    var c = text[offset];
                    var trim = false;
                    for (var i = 0; i < charsLength; i++)
                    {
                        if (c == chars[i])
                        {
                            ends += 1;
                            offset -= 1;
                            trim = true;
                            break;
                        }
                    }
                    if (trim) continue; else break;
                }
            }

            if (starts == 0 && ends == 0) return text;
            return text.Substring(starts, length - starts - ends);
        }

        /// <summary>剪取文本内容，若指定头部为空则从原文本首部起，若指定尾部为空则至原文本末尾。</summary>
        /// <returns>剪取后的内容，不包含 head 和 foot。</returns>
        public static string Cut(string text, string head = null, string foot = null)
        {
            if (IsEmpty(text)) return Empty;

            int start, length;
            if (IsEmpty(head))
            {
                // none
                if (IsEmpty(foot)) return Empty;

                // foot
                length = text.IndexOf(foot);
                if (length < 1) return text;
                return text.Substring(0, length);
            }
            else
            {
                if (IsEmpty(foot))
                {
                    // head
                    start = text.IndexOf(head);
                    if (start < 0) return text;
                    start += head.Length;
                    return text.Substring(start);
                }

                // both
                start = text.IndexOf(head);
                if (start < 0) start = 0;
                else start += head.Length;
                var temp = start == 0 ? text : text.Substring(start);
                length = temp.IndexOf(foot);
                if (length < 0) return temp;
                if (length == 0) return Empty;
                return temp.Substring(0, length);
            }
        }

        /// <summary>比较两个字符串的相似度。返回值大于 0，小于等于 1。</summary>
        /// <param name="arg1"></param>
        /// <param name="arg2"></param>
        /// <returns></returns>
        public static double Similarity(string arg1, string arg2) => Levenshtein.Compute(arg1, arg2).Rate;

        /// <summary>生成新的 GUID，默认为小写，且不包含连字符，长度为 32 位。</summary>
        public static string Guid(bool hyphenation = false, bool lower = true)
        {
            var guid = System.Guid.NewGuid();
            if (!hyphenation && lower) return guid.ToString("n");

            var text = System.Guid.NewGuid().ToString();
            if (lower) text = text.ToLower();
            else text = text.ToUpper();
            if (!hyphenation) text = text.Replace("-", "");
            return text;
        }

        /// <summary>生成新主键。</summary>
        public static string Key() => System.Guid.NewGuid().ToString().ToLower().Replace("-", "");

        /// <summary>生成随机字符串，出现的字符由字符池指定，默认池包含数字和字母。</summary>
        /// <param name="length">随机字符串的长度。</param>
        /// <param name="pool">字符池，字符池中每个字符在随机字符串中出现的概率约等。</param>
        public static string Random(int length, string pool = "0123456789abcdefghijklmnopqrstuvwxyz")
        {
            if (length < 1) return Empty;
            if (IsEmpty(pool)) return Duplicate(SpaceDbc, length);
            var array = new char[length];
            var max = pool.Length - 1;
            for (var i = 0; i < length; i++) array[i] = pool[NumberUtility.Random(0, max)];
            return new string(array);
        }

        /// <summary>对字符串列表去重。指定 valid 参数时将去除无效字符串。</summary>
        public static List<string> Distinct(IEnumerable<string> strings, bool valid = false)
        {
            if (strings == null) return new List<string>();

            const string space = " ";

            var count = strings.Count();
            var array = new string[count];
            var added = 0;
            var hasNull = false;
            var hasEmpty = false;
            var hasSpace = false;
            foreach (var s in strings)
            {
                if (s == null)
                {
                    if (valid) continue;
                    if (hasNull) continue;
                    hasNull = true;
                    array[added] = s;
                    added += 1;
                    continue;
                }
                if (s == Empty)
                {
                    if (valid) continue;
                    if (hasEmpty) continue;
                    hasEmpty = true;
                    array[added] = s;
                    added += 1;
                    continue;
                }
                if (s == space)
                {
                    if (valid) continue;
                    if (hasSpace) continue;
                    hasSpace = true;
                    array[added] = s;
                    added += 1;
                    continue;
                }

                var exist = false;
                for (var i = 0; i < added; i++)
                {
                    if (array[i] == s)
                    {
                        exist = true;
                        break;
                    }
                }
                if (exist) continue;

                array[added] = s;
                added += 1;
            }

            if (added < 1) return new List<string>();
            var list = new List<string>(added);
            for (var i = 0; i < added; i++) list.Add(array[i]);
            return list;
        }

        /// <summary>约束字符串中的字符，只包含指定的字符。</summary>
        public static string Restrict(string text, char[] chars)
        {
            if (IsEmpty(text)) return Empty;
            if (chars == null || chars.Length < 1) return Empty;

            var total = text.Length;
            var count = chars.Length;
            var array = new char[total];
            var added = 0;
            for (var i = 0; i < total; i++)
            {
                var c = text[i];
                for (var j = 0; j < count; j++)
                {
                    if (c == chars[j])
                    {
                        array[added] = c;
                        added += 1;
                        break;
                    }
                }
            }
            if (added < 1) return Empty;
            return new string(array, 0, added);
        }

        /// <summary>约束字符串中的字符，只包含指定的字符。</summary>
        public static string Restrict(string text, string chars) => IsEmpty(text) || IsEmpty(chars) ? Empty : Restrict(text, chars.ToCharArray());

        /// <summary>约束字符串中的字符，只包含字母。</summary>
        public static string RestrictLetters(string text) => Restrict(text, LetterChars.ToCharArray());

        /// <summary>约束字符串中的字符，只包含数字。</summary>
        public static string RestrictNumeric(string text) => Restrict(text, NumericChars.ToCharArray());

        /// <summary>返回此字符串的安全键副本，只保留数据记录主键中可能出现的字符，默认限制长度为 255 字符。</summary>
        public static string SafeKey(string text, int maxLength = 255)
        {
            if (string.IsNullOrEmpty(text)) return Empty;
            var input = text;

            var max = maxLength;
            if (max < 1 || max > input.Length) max = input.Length;

            // 允许用于主键值的字符。
            const string KeyCollection = "-_0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";

            var sb = new StringBuilder();
            var total = input.Length;
            var length = 0;
            for (var i = 0; i < total; i++)
            {
                var c = input[i];
                if (KeyCollection.IndexOf(c) < 0) continue;
                sb.Append(c);
                length += 1;
                if (length >= max) break;
            }
            var result = sb.ToString();
            if (result.Length > max) result = result.Substring(0, max);
            return result;
        }

        /// <summary>追加字符串。</summary>
        public static StringBuilder Append(StringBuilder builder, params object[] cells)
        {
            if (builder != null) builder.Append(Join(null, cells));
            return builder;
        }

        /// <summary>对 URL 编码。</summary>
        public static string EncodeUrl(string plain)
        {
            return UrlEncoding.Encode(plain);
        }

        /// <summary>对 URL 解码。</summary>
        public static string DecodeUrl(string escaped)
        {
            return UrlEncoding.Decode(escaped);
        }

        /// <summary>返回此字符串转换为小写形式的副本。</summary>
        public static string Lower(string text)
        {
            if (text == null) return null;
            else if (text.Length < 1) return Empty;
            else return text.ToLower();
        }

        /// <summary>返回此字符串转换为大写形式的副本。</summary>
        public static string Upper(string text)
        {
            if (text == null) return null;
            else if (text.Length < 1) return Empty;
            else return text.ToUpper();
        }

        /// <summary>检查中国手机号码，包含 13x、14x、15x、16x、17x、18x 和 19x 号段。</summary>
        public static bool IsPhone(string phone)
        {
            if (string.IsNullOrEmpty(phone)) return false;
            var regex = new Regex(@"^(13|14|15|16|17|18|19)\d{9}$", RegexOptions.None);
            var match = regex.Match(phone);
            return match.Success;
        }

        /// <summary>渲染 Markdown 文本为 HTML 文本。</summary>
        public static string RenderMarkdown(string markdown) => MarkdownSharp.Demo.ToHtml(markdown);

        /// <summary>合并用于启动进程的参数。</summary>
        public static string MergeProcessArgument(params object[] args)
        {
            // var special = " \"\n\r\b\t\f";

            var list = new List<string>();
            if (args != null)
            {
                foreach (var i in args)
                {
                    var arg = null as string;
                    if (i != null)
                    {
                        if (i is string) arg = i as string;
                        else arg = i.ToString();
                    }

                    if (string.IsNullOrEmpty(arg))
                    {
                        list.Add("\"\"");
                        continue;
                    }
                    if (arg.Contains(" ") || arg.Contains("\""))
                    {
                        list.Add(Merge("\"", arg.Replace("\"", "\\\""), "\""));
                        continue;
                    }
                    list.Add(arg);
                }
            }
            var result = Join(" ", list.ToArray());
            return result;
        }

        /// <summary>合并用于启动进程的参数。</summary>
        private static string MergeProcessArgument_2(params object[] args)
        {
            if (args == null) return "";
            if (args.Length < 1) return "";

            var sb = new StringBuilder();
            for (var i = 0; i < args.Length; i++)
            {
                if (i > 0) sb.Append(" ");

                var arg = null as string;
                if (args[i] != null)
                {
                    if (args[i] is string) arg = args[i] as string;
                    else arg = args[i].ToString();
                }

                if (arg.IsEmpty())
                {
                    sb.Append("\"\"");
                    continue;
                }

                // var special = " \"\n\r\b\t\f";
                var special = " \"";
                if (arg.IndexOfAny(special.ToCharArray()) < 0)
                {
                    sb.Append(arg);
                }
                else
                {
                    sb.Append("\"");
                    if (arg.NotEmpty())
                    {
                        foreach (var c in arg)
                        {
                            switch (c)
                            {
                                case '"':
                                    sb.Append("\\\"");
                                    break;
                                // case '\n':
                                //     sb.Append("\\n");
                                //     break;
                                // case '\r':
                                //     sb.Append("\\r");
                                //     break;
                                // case '\b':
                                //     sb.Append("\\b");
                                //     break;
                                // case '\t':
                                //     sb.Append("\\t");
                                //     break;
                                default:
                                    sb.Append(c);
                                    break;
                            }
                        }
                    }
                    sb.Append("\"");
                }
            }

            var result = sb.ToString();
            return result;
        }

        /// <summary>字符串仅使用英文。可指定空字符串的返回值。</summary>
        public static bool IsEnglish(string text, bool ifEmpty = true)
        {
            if (string.IsNullOrEmpty(text)) return ifEmpty;
            var trim = text.Trim();
            if (string.IsNullOrEmpty(trim)) return ifEmpty;
            return Regex.IsMatch(trim, "(^[0-9a-zA-Z_ -;:,~!@#%&=<>~\\(\\)\\.\\$\\^\\`\\'\\\"\\&\\{\\}\\[\\]\\|\\*\\+\\?]{0,80}$)");
        }

        /// <summary>转换文本为驼峰形式。</summary>
        public static string Camel(string text)
        {
            if (string.IsNullOrEmpty(text) || !char.IsUpper(text[0])) return text;

            var chars = text.ToCharArray();
            for (int i = 0; i < chars.Length; i++)
            {
                if (i == 1 && !char.IsUpper(chars[i]))
                {
                    break;
                }

                bool hasNext = (i + 1) < chars.Length;
                if (i > 0 && hasNext)
                {
                    // if the next character is a space, which is not considered uppercase 
                    // (otherwise we wouldn't be here...)
                    // we want to ensure that the following:
                    // 'FOO bar' is rewritten as 'foo bar', and not as 'foO bar'
                    // The code was written in such a way that the first word in uppercase
                    // ends when if finds an uppercase letter followed by a lowercase letter.
                    // now a ' ' (space, (char)32) is considered not upper
                    // but in that case we still want our current character to become lowercase
                    var nextChar = chars[i + 1];
                    if (!char.IsUpper(nextChar))
                    {
                        if (char.IsSeparator(nextChar)) chars[i] = char.ToLowerInvariant(chars[i]);
                        break;
                    }
                }

                chars[i] = char.ToLowerInvariant(chars[i]);
            }

            return new string(chars);
        }

        /// <summary>移除参数 chars 中的每一个字符。</summary>
        public static string RemoveChars(string text, string chars)
        {
            if (IsEmpty(text)) return Empty;
            if (IsEmpty(chars)) return text;
            return RemoveChar(text, chars.ToCharArray());
        }

        /// <summary>移除指定的一个或多个字符。</summary>
        public static string RemoveChar(string text, params char[] chars)
        {
            if (IsEmpty(text)) return Empty;
            if (chars == null || chars.Length < 1) return text;

            var length = text.Length;
            var array = new char[length];
            var count = chars.Length;

            var added = 0;
            for (var i = 0; i < length; i++)
            {
                var c = text[i];
                var removed = false;
                for (var j = 0; j < count; j++)
                {
                    if (c == chars[j])
                    {
                        removed = true;
                        break;
                    }
                }
                if (removed) continue;
                array[added] = c;
                added += 1;
            }
            if (added < 1) return Empty;
            return new string(array, 0, added);
        }

        /// <summary>防注入，去除常见的功能符号。可限定字符串长度。</summary>
        public static string AntiInject(string text, int length = -1, string chars = "\"'`\b\f\n\r\t\\/:*?<>|@")
        {
            if (IsEmpty(text) || length == 0) return Empty;

            var t = Trim(text);
            t = RemoveChars(t, chars);
            if (length > 0 && t.Length > length) t = t.Substring(0, length);
            return t;
        }

        /// <summary>获取指定长度的字符串片段，可指定 trim 参数对片段再次修剪。</summary>
        public static string Left(string text, int maxLength, bool trim = false, bool trimBlank = false)
        {
            if (IsEmpty(text)) return Empty;
            if (maxLength > 0 && text.Length > maxLength)
            {
                var left = text.Substring(0, maxLength);
                return trim ? Trim(left, trimBlank) : left;
            }
            else return trim ? Trim(text, trimBlank) : text;
        }

        /// <summary>获取指定长度的字符串片段，可指定 trim 参数对片段再次修剪。</summary>
        public static string Right(string text, int maxLength, bool trim = false, bool trimBlank = false)
        {
            if (IsEmpty(text)) return Empty;
            if (maxLength > 0 && text.Length > maxLength)
            {
                var left = text.Substring(text.Length - maxLength);
                return trim ? Trim(left, trimBlank) : left;
            }
            else return trim ? Trim(text, trimBlank) : text;
        }

        /// <summary>获取字符串片段，起始位置从 0 开始，可指定 trim 参数对片段再次修剪。</summary>
        /// <exception cref="ArgumentOutOfRangeException"></exception>
        public static string Middle(string text, int startIndex, int maxLength = -1, bool trim = false, bool trimBlank = false)
        {
            if (IsEmpty(text) || maxLength == 0) return Empty;
            var total = text.Length;
            var start = startIndex;
            var length = maxLength;
            if (start < 0)
            {
                length = length + start;
                start = 0;
            }
            if (maxLength < 0) length = total;
            if (start + length > total) length = total - start;
            if (start == 0 && length == total) return trim ? Trim(text, trimBlank) : text;

            var middle = text.Substring(start, length);
            return trim ? Trim(middle, trimBlank) : middle;
        }

        #region encoding

        /// <summary>检查字节数组包含 UTF-8 BOM 头。</summary>
        public static bool ContainsBOM(byte[] bytes)
        {
            if (bytes == null) return false;
            if (bytes.LongLength < 3L) return false;
            return bytes[0L] == 0xEF && bytes[1L] == 0xBB && bytes[2L] == 0xBF;
        }

        /// <summary>检查字节数组是 UTF-8 文本。可指定检查的最大字节长度。</summary>
        /// <param name="bytes">要检查的字节数组。</param>
        /// <param name="offset">已检查的偏移量。</param>
        /// <param name="checkLength">检查的最大字节长度。</param>
        public static bool IsUTF8(byte[] bytes, Class<int> offset, int checkLength = 1048576)
        {
            return IsUTF8(bytes, offset, checkLength);
        }

        /// <summary>检查字节数组是 UTF-8 文本，默认最多检测 1MB 数据。</summary>
        /// <param name="bytes">要检查的字节数组。</param>
        /// <param name="checkLength">检查的最大字节长度，指定为 0 将不限制检查长度。</param>
        /// <param name="offset">已检查的偏移量，用于调试。</param>
        public static bool IsUTF8(byte[] bytes, int checkLength = 1048576, Class<int> offset = null)
        {
            // UTF8在Unicode的基础上制定了这样一套规则：
            // 1.对于单字节字符，比特位的最高位为0；
            // 2.对于多字节字符，第一个字节的比特位中，最高位有n个1，剩下的n - 1个字节的比特位中，最高位都是10。
            // 好了，我知道你一定看不懂，那就先来看看下面例子后，再去看上面定义吧。
            // 比如一个字符（“A”），它在UTF8中的编码为（用二进制表示）：01000001。由于比特位的最高位是0，表示它是单字节，它只需要1个字节就可以表示。
            // 再比如一个字符（“判”），它在UTF8中的编码为（用二进制表示）：11100101 10001000 10100100。由于在第一个字节中，比特位最高位有3个1，说明这个字符总共需要3个字节来表示，且后3 - 1 = 2位字节中，比特位的最高位为10。

            if (bytes == null) return false;
            var length = bytes.LongLength;

            // 检查 BOM 头。
            if (ContainsBOM(bytes)) return true;

            var hasOffset = offset != null;

            var append = 0;
            if (hasOffset) offset.Value = 0;
            for (int i = 0; i < length; i++)
            {
                if (checkLength > 0 && i >= checkLength) break;

                var b = bytes[i];
                if (hasOffset) offset.Value = i;

                // 追加字节最高位为 0。
                if (append > 0)
                {
                    if (b >> 6 != 2) return false;
                    append -= 1;
                    continue;
                }

                // ASCII 字符。
                if (b < 128) continue;

                // 2 字节 UTF-8。
                if (b >= 0xC0 && b <= 0xDF)
                {
                    append = 1;
                    continue;
                }

                // 3 字节 UTF-8 字符。
                if (b >= 0xE0 && b <= 0xEF)
                {
                    append = 2;
                    continue;
                }

                // 4 字节 UTF-8 字符。
                if (b >= 0xF0 && b <= 0xF7)
                {
                    append = 3;
                    continue;
                }

                // 5 字节 UTF-8 字符。
                if (b >= 0xF8 && b <= 0xFB)
                {
                    append = 4;
                    continue;
                }

                // 6 字节 UTF-8 字符。
                if (b >= 0xFC && b <= 0xFD)
                {
                    append = 5;
                    continue;
                }

                // 未知字节，非 UTF-8 定义。
                return false;
            }

            return true;
        }

        #endregion

    }

}