using System;
using System.Globalization;
using System.IO;
using System.Text;
using XmlNames = Microsoft.Maui.Graphics.Text.XmlAttributedTextNames;
 
namespace Microsoft.Maui.Graphics.Text
{
	public class XmlAttributedTextWriter
	{
		public string Write(IAttributedText text)
		{
			using (var writer = new StringWriter())
			{
				Write(text, writer);
				return writer.ToString();
			}
		}
 
		public void Write(
			IAttributedText attributedText,
			TextWriter writer)
		{
			if (attributedText != null && !string.IsNullOrEmpty(attributedText.Text))
			{
				bool encode = attributedText.Text.IndexOf("]]", StringComparison.Ordinal) != -1;
 
				writer.Write($"<{XmlNames.AttributedText}>");
				if (encode)
				{
					writer.Write($"<{XmlNames.Content} {XmlNames.Encoded}=\"True\"><![CDATA[");
					byte[] bytes = Encoding.UTF8.GetBytes(attributedText.Text);
					writer.Write(Convert.ToBase64String(bytes));
					writer.Write($"]]></{XmlNames.Content}>");
				}
				else
				{
					writer.Write($"<{XmlNames.Content}><![CDATA[");
					writer.Write(attributedText.Text);
					writer.Write($"]]></{XmlNames.Content}>");
				}
 
				if (attributedText.Runs != null && attributedText.Runs.Count > 0)
				{
					foreach (var run in attributedText.Runs)
						WriteRun(run, writer);
				}
 
				writer.Write($"</{XmlNames.AttributedText}>");
			}
		}
 
		private void WriteRun(
			IAttributedTextRun run,
			TextWriter writer)
		{
			if (run.Attributes != null)
			{
				var attributes = run.Attributes;
 
				writer.Write($"<{XmlNames.Run}");
 
				writer.Write($" {XmlNames.Start}=\"");
				writer.Write(run.Start.ToString(CultureInfo.InvariantCulture));
				writer.Write("\"");
 
				writer.Write($" {XmlNames.Length}=\"");
				writer.Write(run.Length.ToString(CultureInfo.InvariantCulture));
				writer.Write("\"");
 
				foreach (var entry in run.Attributes)
					Write(attributes, entry.Key, null, writer);
 
				writer.Write(" />");
			}
		}
 
		private void Write(
			ITextAttributes currentAttributes,
			TextAttribute key,
			string defaultValue,
			TextWriter writer)
		{
			currentAttributes.TryGetValue(key, out var value);
 
			if (!string.Equals(value, defaultValue, StringComparison.Ordinal))
				WriteAttribute(writer, key.ToString(), value);
		}
 
		private void WriteAttribute(TextWriter writer, string attribute, string value)
		{
			if (value != null)
			{
				writer.Write(" ");
				writer.Write(attribute);
				writer.Write("=\"");
				writer.Write(value);
				writer.Write("\"");
			}
		}
	}
}