using System;
using System.Linq;
using System.Text.RegularExpressions;

namespace AMWD.Common.AspNetCore.Utilities
{
	/// <summary>
	/// Provides helpers for webpages.
	/// </summary>
	public static class HtmlHelper
	{
		/// <summary>
		/// Checks whether a color is considered as dark.
		/// </summary>
		/// <param name="color">The color (hex or rgb - as defined in CSS)</param>
		/// <returns><c>true</c> when the color is dark otherwise <c>false</c>.</returns>
		public static bool IsDarkColor(string color)
		{
			if (string.IsNullOrWhiteSpace(color))
				return false;

			int r, g, b;

			var rgbMatch = Regex.Match(color, @"^rgba?\(([0-9]+), ?([0-9]+), ?([0-9]+)");
			var hexMatchFull = Regex.Match(color, @"^#?([0-9a-fA-F]{2})([0-9a-fA-F]{2})([0-9a-fA-F]{2})$");
			var hexMatchLite = Regex.Match(color, @"^#?([0-9a-fA-F]{1})([0-9a-fA-F]{1})([0-9a-fA-F]{1})$");

			if (rgbMatch.Success)
			{
				r = Convert.ToInt32(rgbMatch.Groups[1].Value);
				g = Convert.ToInt32(rgbMatch.Groups[2].Value);
				b = Convert.ToInt32(rgbMatch.Groups[3].Value);
			}
			else if (hexMatchFull.Success)
			{
				r = Convert.ToInt32(hexMatchFull.Groups[1].Value, 16);
				g = Convert.ToInt32(hexMatchFull.Groups[2].Value, 16);
				b = Convert.ToInt32(hexMatchFull.Groups[3].Value, 16);
			}
			else if (hexMatchLite.Success)
			{
				r = Convert.ToInt32(new string(hexMatchLite.Groups[1].Value.First(), 2), 16);
				g = Convert.ToInt32(new string(hexMatchLite.Groups[2].Value.First(), 2), 16);
				b = Convert.ToInt32(new string(hexMatchLite.Groups[3].Value.First(), 2), 16);
			}
			else
			{
				return false;
			}

			double luminance = (r * 0.299 + g * 0.587 + b * 0.114) / 255;
			return luminance <= 0.5;
		}
	}
}