using AppKit;
using Foundation;

namespace Cauldron.Macos.SourceWriter;

[Register("LanguageFormatter")]
public class LanguageFormatter : NSObject
{
	#region Private Variables

	/// <summary>The current language syntax highlighting descriptor.</summary>
	private LanguageDescriptor _language = new();

	#endregion

	#region Computed Properties

	/// <summary>
	/// Gets or sets the text view that this language formatter will be performing syntax
	/// highlighting on.
	/// </summary>
	/// <value>The <c>NSTextView</c> to syntax highlight.</value>
	public NSTextView TextEditor { get; set; }

	/// <summary>Gets or sets the newline character used to define a given line of text.</summary>
	/// <value>The newline character.</value>
	public char Newline { get; set; } = '\n';

	/// <summary>
	/// Gets or sets the Unitext line separator used to define a given line of text.
	/// </summary>
	/// <value>The line separator.</value>
	public char LineSeparator { get; set; } = '\u2028';

	/// <summary>
	/// Gets or sets the Unitext paragraph separator used to define a given paragraph of text.
	/// </summary>
	/// <value>The paragraph separator.</value>
	public char ParagraphSeparator { get; set; } = '\u2029';

	/// <summary>
	/// Gets or sets the descriptor used to define the syntax highlighting rules for a given
	/// language.
	/// </summary>
	/// <value>The <see cref="LanguageDescriptor"/> to syntax highlight.</value>
	public LanguageDescriptor Language
	{
		get { return _language; }
		set
		{
			_language = value;
			_language.Define();
			Reformat();
		}
	}

	#endregion

	#region Constructor

	/// <summary>
	/// Initializes a new instance of the <see cref="LanguageFormatter"/> class.
	/// </summary>
	/// <param name="textEditor">
	/// The <c>NSTextView</c> that this language formatter will syntax highlight.
	/// </param>
	/// <param name="language">The <see cref="LanguageDescriptor"/> defining the 
	/// language syntax highlighting rules.</param>
	public LanguageFormatter(NSTextView textEditor, LanguageDescriptor language)
	{
		this.TextEditor = textEditor;
		this.Language = language;
	}

	#endregion

	#region Public Methods

	/// <summary>
	/// Forces all of the text in the attached <c>NSTextView</c> (the <c>TextEditor</c> property) to
	/// have its syntax rehighlighted by re-running the formatter.
	/// </summary>
	public virtual void Reformat()
	{
		// Reformat all text in the view control
		NSRange range = new(0, TextEditor.Value.Length);
		TextEditor.LayoutManager.RemoveTemporaryAttribute(NSStringAttributeKey.ForegroundColor, range);
		HighlightSyntaxRegion(TextEditor.Value, range);
		TextEditor.SetNeedsDisplay(TextEditor.Frame, false);
	}

	/// <summary>Determines whether the passed in character is a language separator.</summary>
	/// <returns>
	/// <c>true</c> if the character is a language separator; otherwise, <c>false</c>.
	/// </returns>
	/// <param name="c">The character being tested.</param>
	public virtual bool IsLanguageSeparator(char c)
	{
		// Found separator?
		for (var n = 0; n < Language.LanguageSeparators.Length; ++n)
		{
			if (Language.LanguageSeparators[n] == c)
				return true;
		}

		// Not found
		return false;
	}

	/// <summary>
	/// Finds the word boundries as defined by the <c>LanguageSeparators</c> in the
	/// <see cref="AppKit.TextKit.Formatter.LanguageDescriptor"/> that is currently
	/// being syntax highlighted.
	/// </summary>
	/// <returns>An <c>NSRange</c> containing the starting and ending character locations
	/// of the current word.</returns>
	/// <param name="text">The string to be searched.</param>
	/// <param name="position">
	/// The <c>NSRange</c> specifying the starting location of a possible word.
	/// </param>
	public virtual NSRange FindWordBoundries(string text, NSRange position)
	{
		NSRange results = new(position.Location, 0);
		bool found = false;

		// Find starting "word" boundry
		while (results.Location > 0 && !found)
		{
			var c = text[(int)results.Location - 1];
			found = char.IsWhiteSpace(c) || IsLanguageSeparator(c);
			if (!found) results.Location -= 1;
		};

		// Find ending "word" boundry
		found = false;
		while ((int)(results.Location + results.Length) < text.Length && !found)
		{
			var c = text[(int)(results.Location + results.Length)];
			found = char.IsWhiteSpace(c) || IsLanguageSeparator(c);
			if (!found) results.Length += 1;
		};

		return results;
	}

	/// <summary>
	/// Finds the line boundries as defined by the <c>NewLine</c>, <c>LineSeparator</c>
	/// and <c>ParagraphSeparator</c> characters.
	/// </summary>
	/// <returns>An <c>NSRange</c> containing the starting and ending character locations
	/// of the current line of text.</returns>
	/// <param name="text">The string to be searched.</param>
	/// <param name="position">The <c>NSRange</c> specifying the starting location of a possible 
	/// line of text.</param>
	public virtual NSRange FindLineBoundries(string text, NSRange position)
	{
		NSRange results = position;
		bool found = false;

		// Find starting line boundry
		while (results.Location > 0 && !found)
		{
			var c = text[(int)results.Location - 1];
			found = (c == Newline || c == LineSeparator || c == ParagraphSeparator);
			if (!found) results.Location -= 1;
		};

		// Find ending line boundry
		found = false;
		while ((int)(results.Location + results.Length) < text.Length && !found)
		{
			var c = text[(int)(results.Location + results.Length)];
			found = (c == Newline || c == LineSeparator || c == ParagraphSeparator);
			if (!found) results.Length += 1;
		};

		return results;
	}

	/// <summary>
	/// Finds the start of line for the given location in the text as defined by the <c>NewLine</c>,
	/// <c>LineSeparator</c> and <c>ParagraphSeparator</c> characters.
	/// </summary>
	/// <returns>
	/// A <c>NSRange</c> containing the start of the line to the current cursor position.
	/// </returns>
	/// <param name="text">The text to find the start of the line in.</param>
	/// <param name="position">
	/// The current location of the cursor in the text and possible selection.
	/// </param>
	public virtual NSRange FindStartOfLine(string text, NSRange position)
	{
		NSRange results = new(position.Location, position.Length);
		bool found = false;

		// Find starting line boundry
		while (results.Location > 0 && !found)
		{
			var c = text[(int)results.Location - 1];
			found = (c == Newline || c == LineSeparator || c == ParagraphSeparator);
			if (!found) results.Location -= 1;
		};

		// Calculate length
		results.Length = position.Location - results.Location;

		return results;
	}

	/// <summary>
	/// Finds the start of end for the given location in the text as defined by the <c>NewLine</c>,
	/// <c>LineSeparator</c> and <c>ParagraphSeparator</c> characters.
	/// </summary>
	/// <returns>
	/// A <c>NSRange</c> containing the end of the line from the current cursor position.
	/// </returns>
	/// <param name="text">The text to find the end of the line in.</param>
	/// <param name="position">
	/// The current location of the cursor in the text and possible selection.
	/// </param>
	public virtual NSRange FindEndOfLine(string text, NSRange position)
	{
		NSRange results = position;

		// Find ending line boundry
		bool found = false;
		while ((int)(results.Location + results.Length) < text.Length && !found)
		{
			char c = text[(int)(results.Location + results.Length)];
			found = (c == Newline || c == LineSeparator || c == ParagraphSeparator);
			if (!found) results.Length += 1;
		};

		return results;
	}

	/// <summary>Tests to see if the preceeding character is whitespace or terminator.</summary>
	/// <returns>
	/// <c>true</c>, if character is whitespace or terminator, <c>false</c> otherwise.
	/// </returns>
	/// <param name="text">The text to test.</param>
	/// <param name="position">The current cursor position inside the text.</param>
	/// <remarks>Returns <c>true</c> if at start of line.</remarks>
	public virtual bool PreceedingCharacterIsWhitespaceOrTerminator(string text, NSRange position)
	{
		// At start of line?
		if (position.Location == 0)
		{
			// Yes, always true
			return true;
		}

		// Found?
		char c = text[(int)(position.Location - 1)];
		bool found = c == ' ' | c == Newline || c == LineSeparator || c == ParagraphSeparator;

		// Return result
		return found;
	}

	/// <summary>Tests to see if the trailing character is whitespace or terminator.</summary>
	/// <returns>
	/// <c>true</c>, if character is whitespace or terminator, <c>false</c> otherwise.
	/// </returns>
	/// <param name="text">The text to test.</param>
	/// <param name="position">The current cursor position inside the text.</param>
	/// <remarks>Returns <c>true</c> if at end of line.</remarks>
	public virtual bool TrailingCharacterIsWhitespaceOrTerminator(string text, NSRange position)
	{
		// At end of line?
		if (position.Location >= text.Length - 1)
		{
			// Yes, always true
			return true;
		}

		// Found?
		char c = text[(int)(position.Location + 1)];
		bool found = c == ' ' | c == Newline || c == LineSeparator || c == ParagraphSeparator;

		// Return result
		return found;
	}

	/// <summary>
	/// Uses the current <c>Language</c> (<see cref="LanguageDescriptor"/>) to syntax highlight the
	/// given word in the attached <c>TextEditor</c> (<c>NSTextView</c>) at the given character
	/// locations.
	/// </summary>
	/// <param name="word">The possible keyword to highlight.</param>
	/// <param name="range">An <c>NSRange</c> specifying the starting and ending character locations
	/// for the word to highlight.</param>
	/// <remarks>
	/// TODO: The Text Kit <c>SetTemporaryAttributes</c> routines are handiling the format of
	/// character strings such as HTML or XML tag incorrectly.
	/// </remarks>
	public virtual void HighlightSyntax(string word, NSRange range)
	{
		try
		{
			// Found a keyword?
			if (Language.Keywords.TryGetValue(word, out KeywordDescriptor info))
			{
				// Yes, adjust attributes
				TextEditor.LayoutManager.SetTemporaryAttributes(
					new NSDictionary(NSStringAttributeKey.ForegroundColor, info.Color), range);
			}
			else
			{
				TextEditor.LayoutManager.RemoveTemporaryAttribute(
					NSStringAttributeKey.ForegroundColor, range);
			}
		}
		catch
		{
			// Ignore any exceptions at this point
		}
	}

	/// <summary>
	/// Based on the current <c>Language</c> (<see cref="AppKit.TextKit.Formatter.LanguageDescriptor"/>),
	/// highlight the syntax of the given character region.
	/// </summary>
	/// <param name="text">The string value to be syntax highlighted.</param>
	/// <param name="position">The starting location of the text to be highlighted.</param>
	public virtual void HighlightSyntaxRegion(string text, NSRange position)
	{
		NSRange range = FindLineBoundries(text, position);
		string word = "";
		nint location = range.Location;
		char l = ' ';
		NSRange segment = new(range.Location, 0);
		bool handled = false;
		FormatDescriptor inFormat = null;

		// Initialize
		Language.ClearFormats();

		// Process all characters in range
		for (int n = 0; n < range.Length; ++n)
		{
			// Get next character
			char c = text[(int)(range.Location + n)];
			//Console.Write ("[{0}]={1}", n, c);

			// Excape character?
			if (c == Language.EscapeCharacter || l == Language.EscapeCharacter)
			{
				// Was the last chanacter an escape?
				if (l == Language.EscapeCharacter)
				{
					// Handling outlying format exception
					c = ' ';
				}
				handled = true;

				// Are we inside a format?
				if (inFormat != null)
				{
					// Yes, increase segment count
					++segment.Length;
				}
			}
			else
			{
				// Are we inside of a formatter?
				if (inFormat == null)
				{
					// No, see if this character is recognized by a formatter
					foreach (FormatDescriptor format in Language.Formats)
					{
						if (format.MatchesCharacter(c))
						{
							if (format.Triggered)
							{
								Language.ClearFormats();
								inFormat = format;
								inFormat.Active = true;
								segment = new NSRange((range.Location + n) - (inFormat.StartsWith.Length - 1), inFormat.StartsWith.Length);
								//Console.WriteLine ("Found Format [{0}] = {1}", inFormat.StartsWith, segment);
							}
							handled = true;
						}
					}
				}
				else
				{
					// Prefix or enclosure?
					if (inFormat.Type == FormatDescriptorType.Prefix)
					{
						// At end of line?
						if (c == Newline || c == LineSeparator || c == ParagraphSeparator)
						{
							++segment.Length;
							TextEditor.LayoutManager.SetTemporaryAttributes(new NSDictionary(NSStringAttributeKey.ForegroundColor, inFormat.Color), segment);
							//Console.WriteLine ("Complete Prefix [{0}] = {1}", inFormat.StartsWith, segment);
							location = range.Location + n + 1;
							word = "";
							inFormat = null;
							Language.ClearFormats();
						}
						else
						{
							++segment.Length;
						}
						handled = true;
					}
					else
					{
						if (inFormat.MatchesCharacter(c))
						{
							if (inFormat.Triggered)
							{
								++segment.Length;
								TextEditor.LayoutManager.SetTemporaryAttributes(new NSDictionary(NSStringAttributeKey.ForegroundColor, inFormat.Color), segment);
								//Console.WriteLine ("Complete Enclosure [{0}] = {1}", inFormat.EndsWith, segment);
								inFormat = null;
								Language.ClearFormats();
							}
						}
						++segment.Length;
						handled = true;
					}
				}
			}

			// Has this character already been handled?
			if (!handled)
			{
				// No, handle normal characters
				bool found = char.IsWhiteSpace(c) || IsLanguageSeparator(c);
				if (found)
				{
					segment = new NSRange(location, word.Length);
					if (segment.Length > 0)
					{
						HighlightSyntax(word, segment);
					}
					location = range.Location + n + 1;
					word = "";
				}
				else
				{
					word += c;
				}

				// Clear any fully unmatched formats
				if (inFormat == null)
				{
					Language.ClearFormats();
				}
			}

			// Save last character
			l = c;
			handled = false;
		}

		// Finalize
		if (inFormat != null)
		{
			if (inFormat.Type == FormatDescriptorType.Prefix)
			{
				TextEditor.LayoutManager.SetTemporaryAttributes(new NSDictionary(NSStringAttributeKey.ForegroundColor, inFormat.Color), segment);
				//Console.WriteLine ("Finalize Prefix [{0}] = {1}", inFormat.StartsWith, segment);
			}

			Language.ClearFormats();
		}
		else if (word != "")
		{
			segment = new NSRange(location, word.Length);
			if (segment.Length > 0)
			{
				HighlightSyntax(word, segment);
			}
		}
		//Console.WriteLine (";");
	}

	#endregion
}