using System.Text;

namespace CompilerDesignIFlr1
{
    internal class LR1Closure
    {
        internal static int GlobalIndex = 0;
        internal int Index = 0;
        internal LR1Creator LR1Creator;
        internal HashSet<LR1Unit> Units { get; set; } = [];
        internal Dictionary<string, int> Next { get; set; } = [];

        internal LR1Closure(LR1Creator lr1Creator)
        {
            LR1Creator = lr1Creator;
            Index = GlobalIndex++;
        }

        internal LR1Closure(LR1Creator lr1Creator, List<LR1Unit> units)
        {
            Units.UnionWith(units);
            Index = GlobalIndex++;
            LR1Creator = lr1Creator;
            AddMissingUnits();
            CalculateProspects();
        }

        internal void CalculateProspects()
        {

            bool haveChange = true;
            while (haveChange)
            {
                haveChange = false;
                foreach (var unit in Units)
                {
                    var left = unit.Name;
                    var units = UnitsHaveDotBefore(left);
                    HashSet<string> prospect = units
                        .Select(x => GetProspectsOf(x))
                        .Aggregate(
                            unit.Prospect,
                            (set, x) =>
                            {
                                set.UnionWith(x);
                                return set;
                            }
                        );
                    if (!prospect.IsSubsetOf(unit.Prospect))
                        haveChange = true;
                    unit.Prospect.UnionWith(prospect);
                }
            }
        }

        internal List<LR1Unit> UnitsHaveDotBefore(string name)
        {
            List<LR1Unit> res = [];
            foreach (LR1Unit unit in Units)
            {
                if (unit.Next() == name)
                    res.Add(unit);
            }
            return res;
        }
        // 对于文法 X => yz... 
        // 该方法返回 A => .XB 中的B 以及B可能为空时其后的元素
        internal List<string> GetProspectsOf(LR1Unit unit)
        {
            if (unit.Name == LR1Creator.StartSymbol)
                return ["End"];
            //if(unit.Prospect.Count != 0)
            //{
            //    throw new Exception("有环？？？");
            //}

            List<string> ans = unit.PointPosition + 1 == unit.Grammar.Count ? [.. unit.Prospect] : [];
            for (int i = unit.PointPosition + 1; i < unit.Grammar.Count; i++)
            {
                var units = LR1Creator.GetUnits(unit.Grammar[i]);
                ans.AddRange(LR1Creator.FirstGroup[unit.Grammar[i]]);
                if (units.All(x => !x.Nullable()))
                    break;
                else if (i == unit.Grammar.Count - 1)
                    ans.AddRange(unit.Prospect);
            }
            return ans;
        }
        internal void AddMissingUnits()
        {
            bool haveNew = true;
            while (haveNew)
            {
                HashSet<LR1Unit> addingUnits = [];
                haveNew = false;
                foreach (LR1Unit unit in Units)
                {
                    string? next = unit.Next();
                    if (next is null)
                        continue;
                    if (LR1Creator.GrammarUnit.TryGetValue(next, out var value))
                    {
                        var set = new HashSet<LR1Unit>(value.Select(x => x.Clone()));
                        if (set.IsSubsetOf(Units))
                            continue;
                        haveNew = true;
                        addingUnits.UnionWith(set);
                    }
                }
                Units.UnionWith(addingUnits);
            }
        }
        internal List<LR1Closure> NextClosures()
        {
            List<LR1Closure> ans = [];
            Dictionary<string, List<LR1Unit>> nextSteps = [];
            foreach(LR1Unit unit in Units)
            {
                string? next = unit.Next();
                if (next is null)
                    continue;
                if (nextSteps.TryGetValue(next, out var units))
                    units.Add(unit);
                else
                    nextSteps.Add(next, [unit]);
            }
            foreach(var (next,value) in nextSteps)
            {
                var closure = new LR1Closure(LR1Creator, value.Select(x => x.ToNext()).ToList());
                var existClosure = LR1Creator.Closures.Values.Where(x => x.Equals(closure)).FirstOrDefault();
                if(existClosure is not null)
                {
                    LR1Closure.GlobalIndex--;
                    Next.Add(next,existClosure.Index);
                    continue;
                }
                ans.Add(closure);
                Next.Add(next, closure.Index);
            }
            return ans;
        }

        internal List<LR1Unit> GetReduceUnits()
            => Units.Where(x => x.ReadyToReduce()).ToList();

        public override bool Equals(object? obj)
        {
            if (obj is not LR1Closure closure || obj is null)
                return false;

            return closure.Units.Count == Units.Count && closure.Units.Select(x => Units.Where(y => y.Equals(x)).Any()).All(x=> x);
        }

        public override int GetHashCode()
        {
            int hash = 0;
            foreach (var unit in Units.OrderBy(e => e.GetHashCode()))
            {
                hash ^= unit.GetHashCode();
            }
            return hash;
        }

        public override string ToString()
        {
            StringBuilder sb = new();
            sb.Append($"闭包{Index}:\n");
            foreach (var unit in Units)
            {
                sb.Append(unit + "\n");
            }
            return sb.ToString();
        }
    }
}