using System;
using System.Collections;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Text;
using System.Threading.Tasks;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Threading;

namespace libsex
{
    [Serializable]
    public class SExpression : IList<object>
    {
        private readonly List<object> inter = new List<object>();

        public SExpression()
        {

        }

        public static SExpression Concat(params SExpression[] sexs)
        {
            var sex = new SExpression();
            sex.inter.AddRange(sexs);
            return sex;
        }

        public object Car()
            => inter.Count < 1 ? null : inter[0];
        public SExpression Cdr()
        {
            if (inter.Count < 2) return new SExpression();
            else return new SExpression(inter.Skip(1));
        }

        public SExpression IPWhere(Func<object,bool> predicate)
        {
            var add = inter.Where(predicate).ToArray();
            inter.Clear();
            inter.AddRange(add);
            return this;
        }

        public SExpression IPSelect(Func<object,object> transform)
        {
            var add = inter.Select(transform).ToArray();
            inter.Clear();
            inter.AddRange(add);
            return this;
        }

        public SExpression Take(Func<object, bool> transform)
        {
            SExpression sexpr = new SExpression();
            foreach (var obj in inter.ToArray())
            {
                if (transform(obj))
                {
                    sexpr.Add(obj);
                    inter.Remove(obj);
                }
            }
            return sexpr;
        }

        public string CarString() => Car() as string;

        public SExpression CarExpr() => Car() switch { SExpression sex => sex, IEnumerable<object> ie => new SExpression(ie), _ => null };

        public T Car<T>(T or = default) => Car() is T t ? t : or;

        public SExpression(params object[] initial)
        {
            inter.AddRange(initial);
        }

        public object[] Slice(int start,int length)
        {
            object[] slice = new object[length];
            inter.CopyTo(start, slice, 0, length);
            return slice;
        }

        public object Path(params int[] indecies)
        {
            IList<object> elements = this.inter;
            for (int i = 0; i < indecies.Length; i++)
            {
                int index = indecies[i];
                if (index < 0 || index >= elements.Count) throw new IndexOutOfRangeException("Index " + i + " (" + index + ") was out of bounds.");
                else
                {
                    if (elements[index] is IList<object> il)
                    {
                        elements = il;
                    }
                    else return elements[index];
                }
            }
            return elements;
        }

        public SExpression(IEnumerable<object> from)
        {
            inter.AddRange(from);
        }

        public override string ToString()
        {
            StringBuilder sb = new StringBuilder();

            //sb.Append("(");

            foreach (var item in inter)
            {
                if (item is SExpression se)
                    sb.Append("(" + se.ToString() + ")");
                else if (item is string str)
                    sb.Append(escape(str));
                else if (item is IEnumerable<object> il)
                    sb.Append("(" + new SExpression(il).ToString() + ")");
                else if (item is IEnumerable li)
                {
                    SExpression sex = new SExpression();
                    foreach (var o in li)
                    {
                        sex.inter.Add(o);
                    }
                    sb.Append("(" + sex.ToString() + ")");
                }
                else sb.Append(escape(item.ToString()));
                sb.Append(" ");
            }

            return sb.ToString().Trim();// + ")";
        }

        public SExpression FlattenTopLevel(bool full=false)
        {
            if (full) while (inter.Count == 1 && inter[0] is SExpression se)
                {
                    inter.Clear();
                    inter.AddRange(se.inter);
                }
            else if (inter.Count == 1 && inter[0] is SExpression se)
            {
                inter.Clear();
                inter.AddRange(se.inter);
            }
            return this;
        }

        private static readonly System.Text.RegularExpressions.Regex escape_re = new System.Text.RegularExpressions.Regex(@"[\s\(\)]", System.Text.RegularExpressions.RegexOptions.Compiled);
        private string escape(string str)
        {
            str = str.Replace("\\", "\\\\");
            str = str.Replace("\"", "\\\"");
            if (escape_re.IsMatch(str)) return $"\"{str}\"";
            else return str;
        }

        #region IList
        public object this[int index] { get => inter[index]; set => inter[index] = value; }

        public int Count => inter.Count;

        public bool IsReadOnly => false;

        public void Add(object item)
        {
            inter.Add(item);
        }

        public void Clear()
        {
            inter.Clear();
        }

        public bool Contains(object item)
        {
            return inter.Contains(item);
        }

        public void CopyTo(object[] array, int arrayIndex)
        {
            inter.CopyTo(array, arrayIndex);
        }

        public IEnumerator<object> GetEnumerator()
        {
            return inter.GetEnumerator();
        }

        public int IndexOf(object item)
        {
            return inter.IndexOf(item);
        }

        public void Insert(int index, object item)
        {
            inter.Insert(index, item);
        }

        public bool Remove(object item)
        {
           return inter.Remove(item);
        }

        public void RemoveAt(int index)
        {
            inter.RemoveAt(index);
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return (inter as IEnumerable).GetEnumerator();
        }
        #endregion

        private static async Task<SExpression> parse(AsyncConsumer<char> input)
        {
            SExpression main = new SExpression();
            var (isEscaped, isStringed) = (false, false);
            StringBuilder token = new StringBuilder();

            void addToken()
            {
                if (token.Length > 0)
                    main.inter.Add(token.ToString());
                token.Clear();
            }

            (char, bool) ok;
            while ((ok = await input.TryTake()).Item2)
            {
                var letter = ok.Item1;
                if (isEscaped)
                {
                    token.Append(letter);
                    isEscaped = false;
                }
                else if (letter == '\\')
                {
                    isEscaped = true;
                }
                else if (isStringed)
                {
                    if (letter == '"') isStringed = false;
                    else token.Append(letter);
                }
                else if (letter == '(')
                {
                    addToken();
                    main.inter.Add(await parse(input));
                }
                else if (letter == ')')
                {
                    addToken();
                    return main;
                }
                else if (letter == ' ' || letter == '\t' || letter == '\n' || letter == '\r' || letter == '\f')
                {
                    addToken();
                }
                else if (letter == '"')
                {
                    isStringed = true;
                }
                else token.Append(letter);
            }

            addToken();
            return main;
        }


        private static async IAsyncEnumerable<char> preprocess(IAsyncEnumerable<char> input)
        {
            var (isEscaped, isStringed, isCommented) = (false, false, false);
            await foreach (var letter in input)
            {
                if (isEscaped)
                {
                    yield return letter;
                    isEscaped = false;
                }
                else if (letter == '\\')
                {
                    isEscaped = true;
                    yield return letter;
                }
                else if (isStringed)
                {
                    yield return letter;
                    if (letter == '"') isStringed = false;
                }
                else if (isCommented)
                {
                    if (letter == '\n' || letter == '\r' || letter == '\f')
                    {
                        yield return '\n';
                        isCommented = false;
                    }
                }
                else if (letter == '"')
                {
                    isStringed = true;
                    yield return letter;
                }
                else if (letter == ';')
                {
                    isCommented = true;
                }
                else if (letter == '\t')
                {
                    yield return ' ';
                }
                else yield return letter;

            }
        }

        public static async Task<SExpression> ParseAsync(IAsyncEnumerable<char> str)
        {
            AsyncConsumer<char> s;
            var res = await parse(s = new AsyncConsumer<char>(preprocess(str)));
            await s.DisposeAsync();
            return res;
        }

        public static async IAsyncEnumerable<SExpression> ParseMultipleAsync(IAsyncEnumerable<char> str, [EnumeratorCancellation] CancellationToken token = default)
        {
            str = preprocess(str);

            await using var consumer = new AsyncConsumer<char>(str);

            (char, bool) cur = default;
            while ((await consumer.TryTake(token)).Item2)
            {
                if(cur.Item1 == '(')
                {
                    yield return await parse(consumer);
                }
            }
        }

        public static SExpression Parse(IEnumerable<char> str)
        {
            async IAsyncEnumerable<char> interop()
            {
                await Task.Yield();
                foreach (var s in str) yield return s;
            }
            try
            {
                var awaiter = ParseAsync(interop());
                awaiter.Wait();
                if (awaiter.IsFaulted) throw awaiter.Exception;
                return awaiter.Result;
            }
            catch (Exception ex) { throw ex; }
        }
    }


    class AsyncConsumer<T> : IAsyncDisposable
    {
        readonly IAsyncEnumerator<T> e;
        public AsyncConsumer(IAsyncEnumerable<T> input)
        {
            e = input.GetAsyncEnumerator();
        }

        public async ValueTask DisposeAsync()
        {
            await e.DisposeAsync();
        }

        public async ValueTask<(T, bool)> TryTake(CancellationToken token)
        {
            if (token == default) return await TryTake();

            TaskCompletionSource<bool> cancel = new TaskCompletionSource<bool>();
            using var _c = token.Register(() => cancel.SetResult(false));
            var res = e.MoveNextAsync().AsTask();
            if (await Task.WhenAny(res, cancel.Task) == res)
            {
                var ok = res.Result;
                if (ok)
                {
                    return (e.Current, true);
                }
                else return (default, false);
            }
            else
                throw new OperationCanceledException();
        }

        public async ValueTask<(T, bool)> TryTake()
        {
            var ok = await e.MoveNextAsync();
            if (ok)
            {
                return (e.Current, true);
            }
            else return (default, false);
        }
    }
}