// Copyright (c) AlphaSierraPapa for the SharpDevelop Team (for details please see \doc\copyright.txt)
// This code is distributed under the GNU LGPL (for details please see \doc\license.txt)

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media.TextFormatting;

using ICSharpCode.AvalonEdit.Document;
using ICSharpCode.AvalonEdit.Rendering;
using ICSharpCode.AvalonEdit.Utils;

namespace ICSharpCode.AvalonEdit.Editing
{
	static class CaretNavigationCommandHandler
	{
		/// <summary>
		/// Creates a new <see cref="TextAreaInputHandler"/> for the text area.
		/// </summary>
		public static TextAreaInputHandler Create(TextArea textArea)
		{
			TextAreaInputHandler handler = new TextAreaInputHandler(textArea);
			handler.CommandBindings.AddRange(CommandBindings);
			handler.InputBindings.AddRange(InputBindings);
			return handler;
		}
		
		static readonly List<CommandBinding> CommandBindings = new List<CommandBinding>();
		static readonly List<InputBinding> InputBindings = new List<InputBinding>();
		
		static void AddBinding(ICommand command, ModifierKeys modifiers, Key key, ExecutedRoutedEventHandler handler)
		{
			CommandBindings.Add(new CommandBinding(command, handler));
			InputBindings.Add(TextAreaDefaultInputHandler.CreateFrozenKeyBinding(command, modifiers, key));
		}
		
		static CaretNavigationCommandHandler()
		{
			const ModifierKeys None = ModifierKeys.None;
			const ModifierKeys Ctrl = ModifierKeys.Control;
			const ModifierKeys Shift = ModifierKeys.Shift;
			
			AddBinding(EditingCommands.MoveLeftByCharacter, None, Key.Left, OnMoveCaret(CaretMovementType.CharLeft));
			AddBinding(EditingCommands.SelectLeftByCharacter, Shift, Key.Left, OnMoveCaretExtendSelection(CaretMovementType.CharLeft));
			AddBinding(EditingCommands.MoveRightByCharacter, None, Key.Right, OnMoveCaret(CaretMovementType.CharRight));
			AddBinding(EditingCommands.SelectRightByCharacter, Shift, Key.Right, OnMoveCaretExtendSelection(CaretMovementType.CharRight));
			
			AddBinding(EditingCommands.MoveLeftByWord, Ctrl, Key.Left, OnMoveCaret(CaretMovementType.WordLeft));
			AddBinding(EditingCommands.SelectLeftByWord, Ctrl | Shift, Key.Left, OnMoveCaretExtendSelection(CaretMovementType.WordLeft));
			AddBinding(EditingCommands.MoveRightByWord, Ctrl, Key.Right, OnMoveCaret(CaretMovementType.WordRight));
			AddBinding(EditingCommands.SelectRightByWord, Ctrl | Shift, Key.Right, OnMoveCaretExtendSelection(CaretMovementType.WordRight));
			
			AddBinding(EditingCommands.MoveUpByLine, None, Key.Up, OnMoveCaret(CaretMovementType.LineUp));
			AddBinding(EditingCommands.SelectUpByLine, Shift, Key.Up, OnMoveCaretExtendSelection(CaretMovementType.LineUp));
			AddBinding(EditingCommands.MoveDownByLine, None, Key.Down, OnMoveCaret(CaretMovementType.LineDown));
			AddBinding(EditingCommands.SelectDownByLine, Shift, Key.Down, OnMoveCaretExtendSelection(CaretMovementType.LineDown));
			
			AddBinding(EditingCommands.MoveDownByPage, None, Key.PageDown, OnMoveCaret(CaretMovementType.PageDown));
			AddBinding(EditingCommands.SelectDownByPage, Shift, Key.PageDown, OnMoveCaretExtendSelection(CaretMovementType.PageDown));
			AddBinding(EditingCommands.MoveUpByPage, None, Key.PageUp, OnMoveCaret(CaretMovementType.PageUp));
			AddBinding(EditingCommands.SelectUpByPage, Shift, Key.PageUp, OnMoveCaretExtendSelection(CaretMovementType.PageUp));
			
			AddBinding(EditingCommands.MoveToLineStart, None, Key.Home, OnMoveCaret(CaretMovementType.LineStart));
			AddBinding(EditingCommands.SelectToLineStart, Shift, Key.Home, OnMoveCaretExtendSelection(CaretMovementType.LineStart));
			AddBinding(EditingCommands.MoveToLineEnd, None, Key.End, OnMoveCaret(CaretMovementType.LineEnd));
			AddBinding(EditingCommands.SelectToLineEnd, Shift, Key.End, OnMoveCaretExtendSelection(CaretMovementType.LineEnd));
			
			AddBinding(EditingCommands.MoveToDocumentStart, Ctrl, Key.Home, OnMoveCaret(CaretMovementType.DocumentStart));
			AddBinding(EditingCommands.SelectToDocumentStart, Ctrl | Shift, Key.Home, OnMoveCaretExtendSelection(CaretMovementType.DocumentStart));
			AddBinding(EditingCommands.MoveToDocumentEnd, Ctrl, Key.End, OnMoveCaret(CaretMovementType.DocumentEnd));
			AddBinding(EditingCommands.SelectToDocumentEnd, Ctrl | Shift, Key.End, OnMoveCaretExtendSelection(CaretMovementType.DocumentEnd));
			
			CommandBindings.Add(new CommandBinding(ApplicationCommands.SelectAll, OnSelectAll));
		}
		
		static void OnSelectAll(object target, ExecutedRoutedEventArgs args)
		{
			TextArea textArea = GetTextArea(target);
			if (textArea != null && textArea.Document != null) {
				args.Handled = true;
				textArea.Caret.Offset = textArea.Document.TextLength;
				textArea.Selection = new SimpleSelection(0, textArea.Document.TextLength);
			}
		}
		
		static TextArea GetTextArea(object target)
		{
			return target as TextArea;
		}
		
		enum CaretMovementType
		{
			CharLeft,
			CharRight,
			WordLeft,
			WordRight,
			LineUp,
			LineDown,
			PageUp,
			PageDown,
			LineStart,
			LineEnd,
			DocumentStart,
			DocumentEnd
		}
		
		static ExecutedRoutedEventHandler OnMoveCaret(CaretMovementType direction)
		{
			return (target, args) => {
				TextArea textArea = GetTextArea(target);
				if (textArea != null && textArea.Document != null) {
					args.Handled = true;
					textArea.Selection = Selection.Empty;
					MoveCaret(textArea, direction);
					textArea.Caret.BringCaretToView();
				}
			};
		}
		
		static ExecutedRoutedEventHandler OnMoveCaretExtendSelection(CaretMovementType direction)
		{
			return (target, args) => {
				TextArea textArea = GetTextArea(target);
				if (textArea != null && textArea.Document != null) {
					args.Handled = true;
					int oldOffset = textArea.Caret.Offset;
					MoveCaret(textArea, direction);
					textArea.Selection = textArea.Selection.StartSelectionOrSetEndpoint(oldOffset, textArea.Caret.Offset);
					textArea.Caret.BringCaretToView();
				}
			};
		}
		
		#region Caret movement
		static void MoveCaret(TextArea textArea, CaretMovementType direction)
		{
			DocumentLine caretLine = textArea.Document.GetLineByNumber(textArea.Caret.Line);
			VisualLine visualLine = textArea.TextView.GetOrConstructVisualLine(caretLine);
			TextViewPosition caretPosition = textArea.Caret.Position;
			TextLine textLine = visualLine.GetTextLine(caretPosition.VisualColumn);
			switch (direction) {
				case CaretMovementType.CharLeft:
					MoveCaretLeft(textArea, caretPosition, visualLine, CaretPositioningMode.Normal);
					break;
				case CaretMovementType.CharRight:
					MoveCaretRight(textArea, caretPosition, visualLine, CaretPositioningMode.Normal);
					break;
				case CaretMovementType.WordLeft:
					MoveCaretLeft(textArea, caretPosition, visualLine, CaretPositioningMode.WordStart);
					break;
				case CaretMovementType.WordRight:
					MoveCaretRight(textArea, caretPosition, visualLine, CaretPositioningMode.WordStart);
					break;
				case CaretMovementType.LineUp:
				case CaretMovementType.LineDown:
				case CaretMovementType.PageUp:
				case CaretMovementType.PageDown:
					MoveCaretUpDown(textArea, direction, visualLine, textLine, caretPosition.VisualColumn);
					break;
				case CaretMovementType.DocumentStart:
					SetCaretPosition(textArea, 0, 0);
					break;
				case CaretMovementType.DocumentEnd:
					SetCaretPosition(textArea, -1, textArea.Document.TextLength);
					break;
				case CaretMovementType.LineStart:
					MoveCaretToStartOfLine(textArea, visualLine);
					break;
				case CaretMovementType.LineEnd:
					MoveCaretToEndOfLine(textArea, visualLine);
					break;
				default:
					throw new NotSupportedException(direction.ToString());
			}
		}
		#endregion
		
		#region Home/End
		static void MoveCaretToStartOfLine(TextArea textArea, VisualLine visualLine)
		{
			int newVC = visualLine.GetNextCaretPosition(-1, LogicalDirection.Forward, CaretPositioningMode.WordStart);
			if (newVC < 0)
				throw ThrowUtil.NoValidCaretPosition();
			// when the caret is already at the start of the text, jump to start before whitespace
			if (newVC == textArea.Caret.VisualColumn)
				newVC = 0;
			int offset = visualLine.FirstDocumentLine.Offset + visualLine.GetRelativeOffset(newVC);
			SetCaretPosition(textArea, newVC, offset);
		}
		
		static void MoveCaretToEndOfLine(TextArea textArea, VisualLine visualLine)
		{
			int newVC = visualLine.VisualLength;
			int offset = visualLine.FirstDocumentLine.Offset + visualLine.GetRelativeOffset(newVC);
			SetCaretPosition(textArea, newVC, offset);
		}
		#endregion
		
		#region By-character / By-word movement
		static void MoveCaretRight(TextArea textArea, TextViewPosition caretPosition, VisualLine visualLine, CaretPositioningMode mode)
		{
			int pos = visualLine.GetNextCaretPosition(caretPosition.VisualColumn, LogicalDirection.Forward, mode);
			if (pos >= 0) {
				SetCaretPosition(textArea, pos, visualLine.GetRelativeOffset(pos) + visualLine.FirstDocumentLine.Offset);
			} else {
				// move to start of next line
				DocumentLine nextDocumentLine = visualLine.LastDocumentLine.NextLine;
				if (nextDocumentLine != null) {
					VisualLine nextLine = textArea.TextView.GetOrConstructVisualLine(nextDocumentLine);
					pos = nextLine.GetNextCaretPosition(-1, LogicalDirection.Forward, mode);
					if (pos < 0)
						throw ThrowUtil.NoValidCaretPosition();
					SetCaretPosition(textArea, pos, nextLine.GetRelativeOffset(pos) + nextLine.FirstDocumentLine.Offset);
				} else {
					// at end of document
					Debug.Assert(visualLine.LastDocumentLine.Offset + visualLine.LastDocumentLine.TotalLength == textArea.Document.TextLength);
					SetCaretPosition(textArea, -1, textArea.Document.TextLength);
				}
			}
		}
		
		static void MoveCaretLeft(TextArea textArea, TextViewPosition caretPosition, VisualLine visualLine, CaretPositioningMode mode)
		{
			int pos = visualLine.GetNextCaretPosition(caretPosition.VisualColumn, LogicalDirection.Backward, mode);
			if (pos >= 0) {
				SetCaretPosition(textArea, pos, visualLine.GetRelativeOffset(pos) + visualLine.FirstDocumentLine.Offset);
			} else {
				// move to end of previous line
				DocumentLine previousDocumentLine = visualLine.FirstDocumentLine.PreviousLine;
				if (previousDocumentLine != null) {
					VisualLine previousLine = textArea.TextView.GetOrConstructVisualLine(previousDocumentLine);
					pos = previousLine.GetNextCaretPosition(previousLine.VisualLength + 1, LogicalDirection.Backward, mode);
					if (pos < 0)
						throw ThrowUtil.NoValidCaretPosition();
					SetCaretPosition(textArea, pos, previousLine.GetRelativeOffset(pos) + previousLine.FirstDocumentLine.Offset);
				} else {
					// at start of document
					Debug.Assert(visualLine.FirstDocumentLine.Offset == 0);
					SetCaretPosition(textArea, 0, 0);
				}
			}
		}
		#endregion

		#region Line+Page up/down
		static void MoveCaretUpDown(TextArea textArea, CaretMovementType direction, VisualLine visualLine, TextLine textLine, int caretVisualColumn)
		{
			// moving up/down happens using the desired visual X position
			double xPos = textArea.Caret.DesiredXPos;
			if (double.IsNaN(xPos))
				xPos = textLine.GetDistanceFromCharacterHit(new CharacterHit(caretVisualColumn, 0));
			// now find the TextLine+VisualLine where the caret will end up in
			VisualLine targetVisualLine = visualLine;
			TextLine targetLine;
			int textLineIndex = visualLine.TextLines.IndexOf(textLine);
			switch (direction) {
				case CaretMovementType.LineUp:
					{
						// Move up: move to the previous TextLine in the same visual line
						// or move to the last TextLine of the previous visual line
						int prevLineNumber = visualLine.FirstDocumentLine.LineNumber - 1;
						if (textLineIndex > 0) {
							targetLine = visualLine.TextLines[textLineIndex - 1];
						} else if (prevLineNumber >= 1) {
							DocumentLine prevLine = textArea.Document.GetLineByNumber(prevLineNumber);
							targetVisualLine = textArea.TextView.GetOrConstructVisualLine(prevLine);
							targetLine = targetVisualLine.TextLines[targetVisualLine.TextLines.Count - 1];
						} else {
							targetLine = null;
						}
						break;
					}
				case CaretMovementType.LineDown:
					{
						// Move down: move to the next TextLine in the same visual line
						// or move to the first TextLine of the next visual line
						int nextLineNumber = visualLine.LastDocumentLine.LineNumber + 1;
						if (textLineIndex < visualLine.TextLines.Count - 1) {
							targetLine = visualLine.TextLines[textLineIndex + 1];
						} else if (nextLineNumber <= textArea.Document.LineCount) {
							DocumentLine nextLine = textArea.Document.GetLineByNumber(nextLineNumber);
							targetVisualLine = textArea.TextView.GetOrConstructVisualLine(nextLine);
							targetLine = targetVisualLine.TextLines[0];
						} else {
							targetLine = null;
						}
						break;
					}
				case CaretMovementType.PageUp:
				case CaretMovementType.PageDown:
					{
						// Page up/down: find the target line using its visual position
						double yPos = visualLine.GetTextLineVisualYPosition(textLine, VisualYPosition.LineMiddle);
						if (direction == CaretMovementType.PageUp)
							yPos -= textArea.TextView.RenderSize.Height;
						else
							yPos += textArea.TextView.RenderSize.Height;
						DocumentLine newLine = textArea.TextView.GetDocumentLineByVisualTop(yPos);
						targetVisualLine = textArea.TextView.GetOrConstructVisualLine(newLine);
						targetLine = targetVisualLine.GetTextLineByVisualYPosition(yPos);
						break;
					}
				default:
					throw new NotSupportedException(direction.ToString());
			}
			if (targetLine != null) {
				CharacterHit ch = targetLine.GetCharacterHitFromDistance(xPos);
				SetCaretPosition(textArea, targetVisualLine, targetLine, ch, false);
				textArea.Caret.DesiredXPos = xPos;
			}
		}
		#endregion
		
		#region SetCaretPosition
		static void SetCaretPosition(TextArea textArea, VisualLine targetVisualLine, TextLine targetLine,
		                             CharacterHit ch, bool allowWrapToNextLine)
		{
			int newVisualColumn = ch.FirstCharacterIndex + ch.TrailingLength;
			int targetLineStartCol = targetVisualLine.GetTextLineVisualStartColumn(targetLine);
			if (!allowWrapToNextLine && newVisualColumn >= targetLineStartCol + targetLine.Length)
				newVisualColumn = targetLineStartCol + targetLine.Length - 1;
			int newOffset = targetVisualLine.GetRelativeOffset(newVisualColumn) + targetVisualLine.FirstDocumentLine.Offset;
			SetCaretPosition(textArea, newVisualColumn, newOffset);
		}
		
		static void SetCaretPosition(TextArea textArea, int newVisualColumn, int newOffset)
		{
			textArea.Caret.Position = new TextViewPosition(textArea.Document.GetLocation(newOffset), newVisualColumn);
			textArea.Caret.DesiredXPos = double.NaN;
		}
		#endregion
	}
}