//-----------------------------------------------------------------------
//-----------------------------------------------------------------------
//     file="ExpSourceReader.cs"
//     Project: StgSharp
//     AuthorGroup: Nitload Space
//     Copyright (c) Nitload Space. All rights reserved.
//     
//     Permission is hereby granted, free of charge, to any person 
//     obtaining a copy of this software and associated documentation 
//     files (the “Software”), to deal in the Software without restriction, 
//     including without limitation the rights to use, copy, modify, merge,
//     publish, distribute, sublicense, and/or sell copies of the Software, 
//     and to permit persons to whom the Software is furnished to do so, 
//     subject to the following conditions:
//     
//     The above copyright notice and 
//     this permission notice shall be included in all copies 
//     or substantial portions of the Software.
//     
//     THE SOFTWARE IS PROVIDED “AS IS”, 
//     WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, 
//     INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
//     FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. 
//     IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, 
//     DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, 
//     ARISING FROM, OUT OF OR IN CONNECTION WITH 
//     THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//     
//-----------------------------------------------------------------------
//-----------------------------------------------------------------------
using System;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.Text;
using System.Text.RegularExpressions;

namespace StgSharp.Script.Express
{
    public class ExpSourceReader
    {

        private static Regex 
            _commentSplitter = new Regex(
            @"(?<code>\S*)\s*--.*", RegexOptions.Compiled ),
            _multiLineCommentBegin = new Regex(
            @"(?<code>\S*)\s*\(\*.*", RegexOptions.Compiled ),
            _multiLineCommentEnd = new Regex(
            @".*\*\)\s*(?<code>\S*)", RegexOptions.Compiled );
        private bool _isReadingMultiLineComment;
        private IScriptSourceProvider _provider;

        public ExpSourceReader( IScriptSourceProvider provider )
        {
            _provider = provider;
        }

        public string ReadLine()
        {
            return _provider.ReadLine();
        }

        public string ReadNoCommentLine()
        {
            string line = string.Empty;
            while( TryReadNoCommentLine( ref line ) ) { }
            return line;
        }

        //Returns true when no usable string returns
        private bool TryReadNoCommentLine( ref string line )
        {
            int index;
            string str = _provider.ReadLine();
            if( string.IsNullOrEmpty( str ) ) {
                return true;
            }
            if( _isReadingMultiLineComment ) {
                index = str.LastIndexOf( @"*)" ) + 2; //calc by beginning of code
                if( index == 1 || index >= str.Length ) {
                    return true;
                }
                line = str.SliceAndTrim( index );
                _isReadingMultiLineComment = false;
                return string.IsNullOrEmpty(line);
            }
            index = str.IndexOf( @"--" );
            if( index != -1 ) {
                line = str.SliceAndTrim( 0, index );
                return string.IsNullOrEmpty(str);
            }
            index = str.IndexOf(@"(*");
            if (index > 0) {
                if (TrySliceMultiLineCommentInSingleLine(ref str, index))
                {
                    line = str;
                    return string.IsNullOrEmpty(str);
                }
                line = str.SliceAndTrim(0,index);
                _isReadingMultiLineComment = true;
                return string.IsNullOrEmpty(str);
            }
            line = str;
            return string.IsNullOrEmpty(str);
        }

        //returns true when a usable string returns
        private unsafe bool TrySliceMultiLineCommentInSingleLine(ref string source, int commentBegin)
        {
            string origin = source;
            int index = origin.IndexOf("*)",commentBegin);
            if (index == -1)
            {
                return false;
            }
            index += 2;
            int begin = commentBegin - 1;
            ReadOnlySpan<char> sourceSpan = origin.AsSpan();
            while (begin >= 0 && char.IsWhiteSpace(sourceSpan[begin])) 
            {
                begin--;
            }
            while (index < origin.Length && char.IsWhiteSpace(sourceSpan[index]))
            {
                index++;
            }
            if (begin == 0 && index == origin.Length - 1)
            {
                source = string.Empty;
                return true;
            }
            fixed (char* cPtr = sourceSpan)
            {
                int secLength = origin.Length - index;
                Span<char> o = new Span<char>(cPtr, origin.Length);
                Span<char> s = o.Slice(0, begin + 1 + secLength);
                Span<char> sec = o.Slice(index), dest = o.Slice(begin+1, secLength);
                sec.CopyTo(dest);
                source = new string(s);
            }
            return true;
        }
    }
}