////////////////////////////////////////////////////////////////////////////////
//
//  Microsoft Research Singularity
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
//  File:   ESet.ssc
//
//  Note: 
//        
//        
//
using System;
using Microsoft.SingSharp;
using Microsoft.Contracts;

namespace Microsoft.Singularity.Channels {

    using Microsoft.Singularity.V1.Threads;
    
    public class ESet<T, State> : ITracked, ISelectable where T: unmanaged struct, IEventCollectionElement {

        private AutoResetEventHandle evHandle;

        public SyncHandle GetWaitHandle() { return evHandle; }

        public void ResetWaitSignal() {
            AutoResetEventHandle.Reset(evHandle);
        }

        private Node! listHead;

        private Node? lookAside;

        private Node? nextScanStart;

        public ESet() {
            this.listHead = new Node(this);
            AutoResetEventHandle handleOnStack;
            if (!AutoResetEventHandle.Create(false, out handleOnStack)) {
                throw new System.Threading.HandleCreateException();
            }
            this.evHandle = handleOnStack;
        }


        private Node! GetFreshNode(T* in ExHeap opt(State) ep, ESet<T,State>! parent) {
            Node n = this.lookAside;
            if (n == null) {
                n = new Node(ep, parent);
            }
            else {
                this.lookAside = null;
                n.Init(ep, parent);
            }
            return n;
        }


        // we only want type visibility outside ESet, but not member accessibility
        private class Node {

            unsafe internal T* opt(ExHeap) opt(State) endpoint;
            unsafe private ESet<T,State>! parent;
            internal Node! next;
            internal Node! prev;

            internal Node([Delayed] ESet<T,State>! parent) {
                this.next = this;
                this.prev = this;
                this.parent = parent;
            }
            
            internal Node(T* opt(ExHeap) opt(State) ep, [Delayed] ESet<T,State>! parent) {
                this.next = this;
                this.prev = this;
                this.Init(ep, parent);
                this.parent = parent; // redundant, but to keep checker happy.
            }

            [Delayed]
            internal void Init(T* opt(ExHeap) opt(State) ep, [Delayed] ESet<T,State>! parent) {
                this.parent = parent;
                this.endpoint = ep;
            }

            internal T* in ExHeap opt(State) Unlink(ESet<T,State>! parent) {
                assert (parent == this.parent);
                this.prev.next = this.next;
                this.next.prev = this.prev;
                this.next = this;
                this.prev = this;
                T* in ExHeap opt(State) data = this.endpoint;
                assert data != null;
                this.endpoint = null;
                data->UnlinkFromCollection(parent.evHandle);
                parent.lookAside = this;
                return data;
            }

            internal void LinkAsNext(T*! opt(ExHeap) opt(State) ep, ESet<T,State>! parent) {
                Node next = parent.GetFreshNode(ep, parent);
                next.next = this.next;
                this.next = next;
                next.prev = this;
                next.next.prev = next;
                ep->LinkIntoCollection(parent.evHandle);
            }
        }

        #region ITracked members

        void ITracked.Release()
        {
            Node current = this.listHead.next;
            while (current != this.listHead) {
                // temporary hack until we fix the upcast in receiver context
                unsafe {
                    assert current.endpoint != null;
                    current.endpoint->Release();
                }
                current = current.next;
            }
        }

        void ITracked.Acquire()
        {
            Node current = this.listHead.next;
            while (current != this.listHead) {
                // temporary hack until we fix the upcast in receiver context
                unsafe {
                    assert current.endpoint != null;
                    current.endpoint->Acquire();
                }
                current = current.next;
            }
        }

        public void Dispose()
        {
            Node head = this.listHead;
            Node current = head.next;
            while (current != head) {
                Node next = current.next;
                T* opt(ExHeap) opt(State) ep = current.Unlink(this);
                // needed because delete does not add the call here due to generics
                ep->Dispose();
                delete ep;
                current = next;
            }
            head.next = head;
            head.prev = head;
            if (this.evHandle.id != UIntPtr.Zero) {
                AutoResetEventHandle.Dispose(this.evHandle);
                this.evHandle = new AutoResetEventHandle();
            }
        }

        void ITracked.Expose() {}
        void ITracked.UnExpose() {}

        #endregion

        public void Add([Claims] T*! opt(ExHeap) opt(State) ep) {
            this.listHead.LinkAsNext(ep, this);
        }


        public int Count {
            get {
                int count = 0;
                Node current = this.listHead.next;
                while (current != this.listHead) {
                    count++;
                    current = current.next;
                }
                return count;
            }
        }

        ///
        /// We have to be careful here. The node in nextScanStart might no longer
        /// be in the set. 
        ///
        /// The policy is to start scanning from the successor of the last scanned 
        /// point. 
        private Node! NextScanStart {
            get { 
                Node candidate = this.nextScanStart;
                if (candidate == null || candidate.endpoint == null) {
                    // node might no longer be in the set
                    return this.listHead;
                }
                return candidate;
            }
        }

        /// possible set to false when match not possible. Never set to true!
        public bool HeadMatches(int tag, ref bool possible, ref object setMatch)
        {
            // check if this tag is about the collection elements or about the collection itself:
            if ((tag & (~0xff)) != 0) {
              // about elements. Shift right 8 bits
              tag = tag>>8;

              // scan starting at different place each time
              Node scanStart = this.NextScanStart;

              bool setPossible = false;
              Node current = scanStart;
              do {
                  if (current != this.listHead) {
                      // ignore the dummy node
                      bool curPossible = true;
                      if (current.endpoint->HeadMatches(tag, ref curPossible, ref setMatch)) {
                          setMatch = current;
                          // set scan start point to be successor of this element
                          //
                          this.nextScanStart = current.next;
                          return true;
                      }
                      setPossible |= curPossible;
                  }
                  current = current.next;
              } while (current != scanStart);

              if (!setPossible) { possible = false; }
              return false;
            }
            else {
              // about the set itself.
              switch(tag) {
                case ESetReceiveTag.Empty:
                    if (this.listHead == null || this.listHead.next == this.listHead) {
                        return true;
                    }
                    possible = false; // can't match on this select receive
                    break;

                case ESetReceiveTag.Head:
                    if (this.listHead != null && this.listHead.next != this.listHead) {
                        return true;
                    }
                    possible = false; // can't match on this select receive
                    break;
              }
              return false;
            }
        }

        [Selectable((int)ESetReceiveTag.Empty)]
        public void RecvEmpty() {
        }

        [Selectable((int)ESetReceiveTag.Head)]
        public void RecvHead(out T*! in ExHeap opt(State) ep) {
            Node current = this.listHead.next;
            assert current != this.listHead;
            ep = (!)current.Unlink(this);
        }

        public T* opt(ExHeap) opt(State)! Extract(object setMatch) {
            assert setMatch != null;
            Node node = (Node)setMatch;
        
            T* opt(ExHeap) opt(State) result = node.Unlink(this);
            return (!)result;
        }
    }    



    internal enum ESetReceiveTag {
      Any = 1,
      Empty = 2,
      Head = 3,
    }
}