//-----------------------------------------------------------------------
// -----------------------------------------------------------------------
// file="RegexInterpreter.IROptimize"
// Project: StgSharp
// AuthorGroup: Nitload
// Copyright (c) Nitload. 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.Linq;
using System.Runtime.InteropServices;
using System.Text;
using System.Threading.Tasks;

namespace StgSharp.RegularAnalysis.Text
{
    public partial class RegexAnalyzer
    {

        // this array is not thread safe so opt process must be done in single thread.
        private RegexIR[] _opt_buffer = new RegexIR[16];

        internal RegexInfo ScanAndOptimizeIR(
                           List<RegexIR> baseIR,
                           out List<RegexIR> optIR
        )
        {
            int index = 0;
            Span<RegexIR> origin_span = CollectionsMarshal.AsSpan(baseIR);
            List<RegexIR> optimizedIR = new(baseIR.Count);
            List<RegexIR> segment = [];
            RegexInfo info = new();
            do
            {
                OptimizeIR(origin_span, ref index, segment, info);
                optimizedIR.AddRange(segment);
                index++;
            } while (index < baseIR.Count);
            optIR = optimizedIR;
            return info;
        }

        private int ExpandCount(
                    string pattern,
                    int min,
                    int max,
                    bool is_greedy,
                    in Span<RegexIR> span
        )
        {
            // expand count operation to less cycles.

            const int fast_seq_length = 32;

            int fast_count = fast_seq_length / pattern.Length;
            fast_count = int.Min(fast_count, min);
            if (fast_count > 0)
            {
                string fast_pattern = string.Concat(Enumerable.Repeat(pattern, fast_count));

                int fast_min = min / fast_count;
                int consumed_count = fast_min * fast_count;
                int remain_min = min - consumed_count;
                int remain_max = max - consumed_count;
                remain_max = int.Max(-1, remain_max);    //for negative stands for infinitive
                if (remain_max == 0)
                {
                    // a{2}
                    RegexCountSeqIR fast = new(fast_min, fast_min, is_greedy, fast_pattern);
                    span[0] = fast;
                    return 1;
                } else
                {
                    // a{2,5}
                    RegexCountSeqIR fast = new(fast_min, fast_min, is_greedy, fast_pattern);
                    RegexCountSeqIR tail = new(remain_min, remain_max, is_greedy, pattern);
                    span[0] = fast;
                    span[1] = tail;
                    return 2;
                }
            } else if (fast_count == 0)
            {
                // least count is 0
                span[0] = new RegexCountSeqIR(0, max, is_greedy, pattern);
                return 1;
            } else
            {
                // least count is infinitive
                span[0] = new RegexCountSeqIR(-1, -1, is_greedy, pattern);
                return 1;
            }
        }

        private void OptimizeDot(
                     RegexCountSetIR root,
                     Span<RegexIR> ir,
                     ref int index,
                     List<RegexIR> optimizedIR,
                     RegexInfo info
        )
        {
            int next = index + 1;
            optimizedIR.Clear();
            if (next >= ir.Length)
            {
                optimizedIR.Add(root);
                return;
            }
            RegexIR nextIR = ir[next];
            if (nextIR is RegexMatchSeqIR match_seq)
            {
                // opt .*abc style
                RegexFindSeqIR find = new(match_seq.Pattern);
                optimizedIR.Add(find);
                info.MinLength += find.Pattern.Length;
                return;
            } else if (nextIR is RegexCountSeqIR count_seq)
            {
                // opt .* (abc)* or .*(abc){2,5} style
                string pattern = count_seq.Sequence;
                int min = count_seq.Min;
                int max = count_seq.Max;
                switch ((min, max))
                {
                    case (0, _):

                        break;
                    default:
                        RegexFindSeqIR find = new(pattern);

                        // RegexCountSeqIR 

                        break;
                }
            }
        }

        private void OptimizeIR(
                     Span<RegexIR> ir,
                     ref int index,
                     List<RegexIR> optimizedIR,
                     RegexInfo info
        )
        {
            optimizedIR.Clear();

            // TODO optimize here
            RegexIR root = ir[index];
            switch (root.Command)
            {
                case RegexIRCommand.Count_Set:
                    RegexCountSetIR count = (root as RegexCountSetIR)!;
                    if (count.CharSet == ".")
                    {
                        // opt for .+ / .* / .{}    pattern
                        OptimizeDot(count, ir, ref index, optimizedIR, info);
                    }
                    break;
                case RegexIRCommand.Match_Seq:
                    info.MinLength += (root as RegexMatchSeqIR)!.Pattern.Length;
                    optimizedIR.Add(root);
                    break;
                default:
                    optimizedIR.Add(root);
                    break;
            }
        }

        internal class RegexInfo
        {

            public int MinLength { get; set; }

            public int TryDepth { get; set; }

            public int GroupCount { get; set; }

        }

    }
}