I did a program that can parse your strings in a debugable, developer-friendly way. It is not a small code like those regexes, but it has a positive side: you can debug it, and fine tune it as you need.
The implementation is a descent recursive parser, but if you need some kind of contextual data, you can place it all inside the ParseContext class.
It is quite long, but I consider it as being better than a a regex based solution.
To test it, create a console application, and replace all the code inside Program.cs with the following code:
using System.Collections.Generic;
namespace q7922337
{
static class Program
{
static void Main(string[] args)
{
var result1 = Match.ParseList<TagsGroup>("[code]This is a successful match.[/code]");
var result2 = Match.ParseList<TagsGroup>("[code]This is an [ unsuccessful match.[/code]");
var result3 = Match.ParseList<TagsGroup>("[code]This is also an [unsuccessful] match.[/code]");
var result4 = Match.ParseList<TagsGroup>(@"
[code]
some code
[b]some text [url=http://www.google.com]some link[/url][/b]
[/code]");
}
class ParseContext
{
public string Source { get; set; }
public int Position { get; set; }
}
abstract class Match
{
public override string ToString()
{
return this.Text;
}
public string Source { get; set; }
public int Start { get; set; }
public int Length { get; set; }
public string Text { get { return this.Source.Substring(this.Start, this.Length); } }
protected abstract bool ParseInternal(ParseContext context);
public bool Parse(ParseContext context)
{
var result = this.ParseInternal(context);
this.Length = context.Position - this.Start;
return result;
}
public bool MarkBeginAndParse(ParseContext context)
{
this.Start = context.Position;
var result = this.ParseInternal(context);
this.Length = context.Position - this.Start;
return result;
}
public static List<T> ParseList<T>(string source)
where T : Match, new()
{
var context = new ParseContext
{
Position = 0,
Source = source
};
var result = new List<T>();
while (true)
{
var item = new T { Source = source, Start = context.Position };
if (!item.Parse(context))
break;
result.Add(item);
}
return result;
}
public static T ParseSingle<T>(string source)
where T : Match, new()
{
var context = new ParseContext
{
Position = 0,
Source = source
};
var result = new T { Source = source, Start = context.Position };
if (result.Parse(context))
return result;
return null;
}
protected List<T> ReadList<T>(ParseContext context)
where T : Match, new()
{
var result = new List<T>();
while (true)
{
var item = new T { Source = this.Source, Start = context.Position };
if (!item.Parse(context))
break;
result.Add(item);
}
return result;
}
protected T ReadSingle<T>(ParseContext context)
where T : Match, new()
{
var result = new T { Source = this.Source, Start = context.Position };
if (result.Parse(context))
return result;
return null;
}
protected int ReadSpaces(ParseContext context)
{
int startPos = context.Position;
int cnt = 0;
while (true)
{
if (startPos + cnt >= context.Source.Length)
break;
if (!char.IsWhiteSpace(context.Source[context.Position + cnt]))
break;
cnt++;
}
context.Position = startPos + cnt;
return cnt;
}
protected bool ReadChar(ParseContext context, char p)
{
int startPos = context.Position;
if (startPos >= context.Source.Length)
return false;
if (context.Source[startPos] == p)
{
context.Position = startPos + 1;
return true;
}
return false;
}
}
class Tag : Match
{
protected override bool ParseInternal(ParseContext context)
{
int startPos = context.Position;
if (!this.ReadChar(context, '['))
return false;
this.ReadSpaces(context);
if (this.ReadChar(context, '/'))
this.IsEndTag = true;
this.ReadSpaces(context);
var validName = this.ReadValidName(context);
if (validName != null)
this.Name = validName;
this.ReadSpaces(context);
if (this.ReadChar(context, ']'))
return true;
context.Position = startPos;
return false;
}
protected string ReadValidName(ParseContext context)
{
int startPos = context.Position;
int endPos = startPos;
while (char.IsLetter(context.Source[endPos]))
endPos++;
if (endPos == startPos) return null;
context.Position = endPos;
return context.Source.Substring(startPos, endPos - startPos);
}
public bool IsEndTag { get; set; }
public string Name { get; set; }
}
class TagsGroup : Match
{
public TagsGroup()
{
}
protected TagsGroup(Tag openTag)
{
this.Start = openTag.Start;
this.Source = openTag.Source;
this.OpenTag = openTag;
}
protected override bool ParseInternal(ParseContext context)
{
var startPos = context.Position;
if (this.OpenTag == null)
{
this.ReadSpaces(context);
this.OpenTag = this.ReadSingle<Tag>(context);
}
if (this.OpenTag != null)
{
int textStart = context.Position;
int textLength = 0;
while (true)
{
Tag tag = new Tag { Source = this.Source, Start = context.Position };
while (!tag.MarkBeginAndParse(context))
{
if (context.Position >= context.Source.Length)
{
context.Position = startPos;
return false;
}
context.Position++;
textLength++;
}
if (!tag.IsEndTag)
{
var tagGrpStart = context.Position;
var tagGrup = new TagsGroup(tag);
if (tagGrup.Parse(context))
{
if (textLength > 0)
{
if (this.Contents == null) this.Contents = new List<Match>();
this.Contents.Add(new Text { Source = this.Source, Start = textStart, Length = textLength });
textStart = context.Position;
textLength = 0;
}
this.Contents.Add(tagGrup);
}
else
{
textLength += tag.Length;
}
}
else
{
if (tag.Name == this.OpenTag.Name)
{
if (textLength > 0)
{
if (this.Contents == null) this.Contents = new List<Match>();
this.Contents.Add(new Text { Source = this.Source, Start = textStart, Length = textLength });
textStart = context.Position;
textLength = 0;
}
this.CloseTag = tag;
return true;
}
else
{
textLength += tag.Length;
}
}
}
}
context.Position = startPos;
return false;
}
public Tag OpenTag { get; set; }
public Tag CloseTag { get; set; }
public List<Match> Contents { get; set; }
}
class Text : Match
{
protected override bool ParseInternal(ParseContext context)
{
return true;
}
}
}
}
If you use this code, and someday find that you need optimizations because the parser has become ambiguous, then try using a dictionary in the ParseContext, take a look here for more info: http://en.wikipedia.org/wiki/Top-down_parsing in the topic Time and space complexity of top-down parsing. I find it very interesting.
