using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Volian.Base.Library
{
	// Part of fix for B2019-032 - will clean up the passed in file name.
	public static class ValidFileName
	{
		/// <summary>
		/// Replaces characters in orgTxt that are not allowed in file names with the specified replacement character.
		/// </summary>
		/// <remarks>
		/// Note that Forward Slash, Back Slash and Pipe (vertical bar) are replaced with a dash '-'.
		/// The Double quote is replaced with a single quote.
		/// Everything else is replaced with a '_' unless a different replace char is passed in.
		/// A null (zero) replacement character will cause the invalid characters to be removed.
		/// The list of invalid characters include Double Quote, Less Than, Greater Than, Pipe, Question Mark, Back and Forward Slashes, Colin.
		/// Also invalid are characters less than Ascii 32 (space) and greater than Ascii 126 (tilde)
		/// </remarks>
		/// <param name="orgTxt">Text to make into a valid filename. The same string is returned if it is valid already.</param>
		/// <param name="replacementChar">Replacement character ('_' is the default), or null to simply remove bad characters.</param>
		/// <param name="additionalInvalidChars">Character array of additional character to replace.</param>
		/// <returns>A string that can be used as a filename. If the output string would otherwise be empty, returns "_".</returns>
		public static string FixFileName(string orgTxt, char? replacementChar = '_', char[] additionalInvalidChars = null)
		{
			StringBuilder sb = new StringBuilder(orgTxt.Length);
			bool changed = false;
			//var invalidChars = System.IO.Path.GetInvalidFileNameChars();
			char[] invalidChars = { '"', '<', '>', '|', '?', '\\', '/', ':' };
			if (additionalInvalidChars != null) invalidChars = invalidChars.Union(additionalInvalidChars).ToArray();
			for (int i = 0; i < orgTxt.Length; i++)
			{
				char c = orgTxt[i];
				if (invalidChars.Contains(c) || !(c >= ' ' && c <= '~'))
				{
					changed = true;
					var repl = replacementChar ?? '\0';
					if (repl != '\0')
					{
						if (c == '\\' || c == '/' || c == '|')
							sb.Append('-'); // replace forward slash, back slash, and vertical line (pipe) with a dash
						else if (c == '"')
							sb.Append('\''); // replace a double quote with a single quote
						else
							sb.Append(repl); // replace with '_' or passed in replacement character
					}
				}
				else
					sb.Append(c); // the character is OK just add it to the return string
			}
			if (sb.Length == 0)
				return "_"; // return a '_' if return string is empty.
			return changed ? sb.ToString() : orgTxt; // if we replaced a character return the corrected file name, else return the original file name
		}
	}
}