using System;
using System.Text;
using System.Collections.Generic;

public static class ClipboardFusionHelper
{
    private static readonly string[] ExceptionsArray = 
    { 	
        //articles
        "a",
        "an",
        "the",
        
        //prepositions (incomplete)
        "on",
        "in",
        "at",
        "for",
        "ago",
        "to",
        "from",
        "by",
        "of",
        "with",
        
        //coordinating conjunctions			
        "and",
        "but",
        "or",
        "nor",
        "for",
        "yet",
        "so"
    };
		
    private static readonly HashSet<string> Exceptions = new HashSet<string>(ExceptionsArray);

    public static string ProcessText(string text)
    {   
        //get the highlighted text
        text = BFS.Clipboard.CopyText();
        
        //convert the text to lower case
        string lower = text.ToLowerInvariant();
        
        //if the copied text is lower case, convert it to title case
        if(lower.Equals(text, StringComparison.Ordinal))
        {
            BFS.Clipboard.PasteText(ToTitleCaseSmart(text));
            return null;
        }
        
        //convert to text to title case
        string title = ToTitleCaseSmart(text);
        
        //if the copied text is title case, convert it to upper case
        if(title.Equals(text, StringComparison.Ordinal))
        {
            BFS.Clipboard.PasteText(text.ToUpperInvariant());
            return null;
        }
               
        //otherwise, paste the lower case text
        BFS.Clipboard.PasteText(lower);
        return null;
    }
        
	private static string ToTitleCaseSmart(string text)
	{
        Queue<string> words = new Queue<string>(System.Threading.Thread.CurrentThread.CurrentCulture.TextInfo.ToTitleCase(text.ToLowerInvariant()).Split(new char[] { ' ' }));

        //Always leave the first word capitalized, regardless of what it is
        StringBuilder builder = new StringBuilder(words.Dequeue());
        
        while(words.Count > 0)
        {
            string word = words.Dequeue();
            string lower = word.ToLower();
            builder.Append(" ");
            if(Exceptions.Contains(lower))
                builder.Append(lower);
            else
                builder.Append(word);
        }

	    return builder.ToString();
	}
}