// RichTextKit
// Copyright © 2019-2020 Topten Software. All Rights Reserved.
// 
// Licensed under the Apache License, Version 2.0 (the "License"); you may 
// not use this product except in compliance with the License. You may obtain 
// a copy of the License at
// 
// http://www.apache.org/licenses/LICENSE-2.0
// 
// Unless required by applicable law or agreed to in writing, software 
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT 
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the 
// License for the specific language governing permissions and limitations 
// under the License.
//
// Ported from: https://github.com/foliojs/linebreak

using System.Collections.Generic;
using Topten.RichTextKit.Utils;

namespace Topten.RichTextKit
{
	/// <summary>
	/// Implementation of the Unicode Line Break Algorithm
	/// </summary>
	internal class LineBreaker
	{
		/// <summary>
		/// Constructor
		/// </summary>
		static LineBreaker()
		{
		}

		/// <summary>
		/// Reset this line breaker
		/// </summary>
		/// <param name="str">The string to be broken</param>
		public void Reset( string str )
		{
			Reset( new Slice<int>( Utf32Utils.ToUtf32( str ) ) );
		}

		/// <summary>
		/// Reset this line breaker
		/// </summary>
		/// <param name="codePoints">The code points of the string to be broken</param>
		public void Reset( Slice<int> codePoints )
		{
			_codePoints = codePoints;
			_first = true;
			_pos = 0;
			_lastPos = 0;
			_LB8a = false;
			_LB21a = false;
			_LB30a = 0;
		}

		Slice<int> _codePoints;
		bool _first = true;
		int _pos;
		int _lastPos;
		LineBreakClass _curClass;
		LineBreakClass _nextClass;
		bool _LB8a = false;
		bool _LB21a = false;
		int _LB30a = 0;

		/// <summary>
		/// Enumerate all line breaks
		/// </summary>
		/// <returns>A collection of line break positions</returns>
		public List<LineBreak> GetBreaks( bool mandatoryOnly = false )
		{
			var list = new List<LineBreak>();
			if ( mandatoryOnly )
			{
				list.AddRange( FindMandatoryBreaks() );
			}
			else
			{
				while ( NextBreak( out var lb ) )
					list.Add( lb );
			}
			return list;
		}

		LineBreakClass mapClass( LineBreakClass c )
		{
			switch ( c )
			{
				case LineBreakClass.AI:
					return LineBreakClass.AL;

				case LineBreakClass.SA:
				case LineBreakClass.SG:
				case LineBreakClass.XX:
					return LineBreakClass.AL;

				case LineBreakClass.CJ:
					return LineBreakClass.NS;

				default:
					return c;
			}
		}

		LineBreakClass mapFirst( LineBreakClass c )
		{
			switch ( c )
			{
				case LineBreakClass.LF:
				case LineBreakClass.NL:
					return LineBreakClass.BK;

				case LineBreakClass.SP:
					return LineBreakClass.WJ;

				default:
					return c;
			}
		}

		// Get the next character class
		LineBreakClass nextCharClass()
		{
			return mapClass( UnicodeClasses.LineBreakClass( _codePoints[_pos++] ) );
		}

		bool? getSimpleBreak()
		{
			// handle classes not handled by the pair table
			switch ( _nextClass )
			{
				case LineBreakClass.SP:
					return false;

				case LineBreakClass.BK:
				case LineBreakClass.LF:
				case LineBreakClass.NL:
					_curClass = LineBreakClass.BK;
					return false;

				case LineBreakClass.CR:
					_curClass = LineBreakClass.CR;
					return false;
			}

			return null;
		}

		bool getPairTableBreak( LineBreakClass lastClass )
		{
			// if not handled already, use the pair table
			bool shouldBreak = false;
			switch ( LineBreakPairTable.table[(int)_curClass][(int)_nextClass] )
			{
				case LineBreakPairTable.DI_BRK: // Direct break
					shouldBreak = true;
					break;

				case LineBreakPairTable.IN_BRK: // possible indirect break
					shouldBreak = lastClass == LineBreakClass.SP;
					break;

				case LineBreakPairTable.CI_BRK:
					shouldBreak = lastClass == LineBreakClass.SP;
					if ( !shouldBreak )
					{
						shouldBreak = false;
						return shouldBreak;
					}
					break;

				case LineBreakPairTable.CP_BRK: // prohibited for combining marks
					if ( lastClass != LineBreakClass.SP )
					{
						return shouldBreak;
					}
					break;

				case LineBreakPairTable.PR_BRK:
					break;
			}

			if ( _LB8a )
			{
				shouldBreak = false;
			}

			// Rule LB21a
			if ( _LB21a && (_curClass == LineBreakClass.HY || _curClass == LineBreakClass.BA) )
			{
				shouldBreak = false;
				_LB21a = false;
			}
			else
			{
				_LB21a = (_curClass == LineBreakClass.HL);
			}

			// Rule LB30a
			if ( _curClass == LineBreakClass.RI )
			{
				_LB30a++;
				if ( _LB30a == 2 && (_nextClass == LineBreakClass.RI) )
				{
					shouldBreak = true;
					_LB30a = 0;
				}
			}
			else
			{
				_LB30a = 0;
			}

			_curClass = _nextClass;

			return shouldBreak;
		}


		public bool NextBreak( out LineBreak lineBreak )
		{
			// get the first char if we're at the beginning of the string
			if ( _first )
			{
				_first = false;
				var firstClass = nextCharClass();
				_curClass = mapFirst( firstClass );
				_nextClass = firstClass;
				_LB8a = (firstClass == LineBreakClass.ZWJ);
				_LB30a = 0;
			}

			while ( _pos < _codePoints.Length )
			{
				_lastPos = _pos;
				var lastClass = _nextClass;
				_nextClass = nextCharClass();

				// explicit newline
				if ( (_curClass == LineBreakClass.BK) || ((_curClass == LineBreakClass.CR) && (_nextClass != LineBreakClass.LF)) )
				{
					_curClass = mapFirst( mapClass( _nextClass ) );
					lineBreak = new LineBreak( findPriorNonWhitespace( _lastPos ), _lastPos, true );
					return true;
				}

				bool? shouldBreak = getSimpleBreak();

				if ( !shouldBreak.HasValue )
				{
					shouldBreak = getPairTableBreak( lastClass );
				}

				// Rule LB8a
				_LB8a = (_nextClass == LineBreakClass.ZWJ);

				if ( shouldBreak.Value )
				{
					lineBreak = new LineBreak( findPriorNonWhitespace( _lastPos ), _lastPos, false );
					return true;
				}
			}

			if ( _lastPos < _codePoints.Length )
			{
				_lastPos = _codePoints.Length;
				var required = (_curClass == LineBreakClass.BK) || ((_curClass == LineBreakClass.CR) && (_nextClass != LineBreakClass.LF));
				lineBreak = new LineBreak( findPriorNonWhitespace( _codePoints.Length ), _lastPos, required );
				return true;
			}
			else
			{
				lineBreak = new LineBreak( 0, 0, false );
				return false;
			}
		}
		public IEnumerable<LineBreak> FindMandatoryBreaks()
		{
			for ( int i = 0; i < _codePoints.Length; i++ )
			{
				var cls = UnicodeClasses.LineBreakClass( _codePoints[i] );
				switch ( cls )
				{
					case LineBreakClass.BK:
						yield return new LineBreak( i, i + 1, true );
						break;

					case LineBreakClass.CR:
						if ( i + 1 < _codePoints.Length && UnicodeClasses.LineBreakClass( _codePoints[i + 1] ) == LineBreakClass.LF )
						{
							yield return new LineBreak( i, i + 2, true );
						}
						else
						{
							yield return new LineBreak( i, i + 1, true );
						}
						break;

					case LineBreakClass.LF:
						yield return new LineBreak( i, i + 1, true );
						break;
				}
			}
		}

		int findPriorNonWhitespace( int from )
		{
			if ( from > 0 )
			{
				var cls = UnicodeClasses.LineBreakClass( _codePoints[from - 1] );
				if ( cls == LineBreakClass.BK || cls == LineBreakClass.LF || cls == LineBreakClass.CR )
					from--;
			}
			while ( from > 0 )
			{
				var cls = UnicodeClasses.LineBreakClass( _codePoints[from - 1] );
				if ( cls == LineBreakClass.SP )
					from--;
				else
					break;
			}
			return from;
		}
	}
}