///////////////////////////////////////////////////////////////////////////////
//
//  Microsoft Research Singularity
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
//  File:   PacketFifo.sg
//

namespace Microsoft.Singularity.Io.Net
{
    using System;
    using System.Runtime.InteropServices;
    using Microsoft.Contracts;
    using Microsoft.SingSharp;
    using Microsoft.Singularity;
    using Microsoft.Singularity.Channels;

    public rep struct PacketFifo : ITracked
    {
        private Packet*[]! in ExHeap packets;
        private int head;
        private int length;

        public PacketFifo(int capacity)
        {
            this.packets = new [ExHeap] Packet* [capacity];
            this.head   = 0;
            this.length = 0;
        }

        public int Capacity
        {
            get { expose (this) { return this.packets.Length; } }
        }

        public int Count
        {
            get { expose (this) { return this.length; } }
        }

        public void Push([Claims] Packet*! in ExHeap p)
            requires this.Count < this.Capacity;
        {
            expose (this) {
                int index = this.head;
                expose (this.packets[index]) {
                    assert this.packets[index] == null;
                    delete this.packets[index];
                    this.packets[index] = p;
                }
                this.head = (this.head + 1) % this.Capacity;
                this.length++;
            }
        }

        public void Push(PacketFifo*! in ExHeap donor, int count)
            requires this.Count + count <= this.Capacity;
        {
            count = Math.Min(donor->Count, count);
            while (count-- > 0) {
                this.Push(donor->Pop());
            }
        }

        public void Push(PacketFifo*! in ExHeap donor)
            requires this.Count + donor->Count <= this.Capacity;
        {
            Push(donor, donor->Count);
        }

        public Packet*! in ExHeap Pop()
            requires this.Count > 0;
        {
            expose (this) {
                Packet*! in ExHeap packet;
                int index = (this.Capacity + this.head - this.length) % this.Capacity;
                expose (this.packets[index]) {
                    packet = (!)packets[index];
                    this.packets[index] = null;
                }
                this.length--;
                return packet;
            }
        }
    }
}