////////////////////////////////////////////////////////////////////////////////
//
//  Microsoft Research Singularity
//
//  Copyright (c) Microsoft Corporation.  All rights reserved.
//
//  Note:   Implements a selectable abstraction that looks ahead on a pipe channels
//          for control-C and exports separate logical receivable messages for
//          non-control-C characters and control-C, effectively allowing one to
//          consume Ctrl-C's out of order.
//

using System;
using Microsoft.SingSharp;
using Microsoft.Singularity;
using Microsoft.Singularity.Channels;
using Microsoft.Singularity.V1.Threads;
using Tty = Microsoft.Singularity.Io.Tty;

namespace Microsoft.Singularity.Io
{

    public sealed class PipeLookAhead : ITracked, ISelectable {

        private struct CircularBuffer : ITracked {

            private char[]! in ExHeap buffer; // circular buffer
            private int nextReadIndex;
            private int nextWriteIndex;
            private int controlC_Count; // ctrl-c's in buffer
            private int controlC_Consumed; // ctrl-c's consumed in buffer
            private int controlZ_Count; // ctrl-z's in buffer
            private int controlZ_Consumed; // ctrl-z's consumed in buffer

            public bool HasControlC {
                get { return controlC_Count > 0; }
            }

            public bool HasControlZ {
                get { return controlZ_Count > 0; }
            }

            private int CharsInBuffer {
                get {
                    if (nextWriteIndex >= nextReadIndex) {
                        return nextWriteIndex - nextReadIndex;
                    }
                    else {
                        expose (this) {
                            return buffer.Length - nextReadIndex + nextWriteIndex;
                        }
                    }
                }
            }

            public int CharsAvailable {
                get {
                    int available = CharsInBuffer - controlC_Consumed - controlZ_Consumed;
                    return available;
                }
            }


            public CircularBuffer(int lookAhead) {
                this.buffer = new[ExHeap] char[lookAhead+256];
                this.nextReadIndex = 0;
                this.nextWriteIndex = 0;
                this.controlC_Count = 0;
                this.controlC_Consumed = 0;
                this.controlZ_Count = 0;
                this.controlZ_Consumed = 0;
            }

            private int FreeSpace {
                get {
                    // Careful, circular buffer can't be filled completely.
                    // Need 1 extra space to distinguish full from empty buffer.
                    expose (this) {
                        return this.buffer.Length - this.CharsInBuffer - 1;
                    }
                }
            }
            public void Add(char[]! in ExHeap buffer, int index, int count) {
                EnsureCapacity(count);
                for (int i = 0; i < count; i++) {
                    Add(buffer[index++]);
                }
            }

            private void Add(char c) {
                expose (this) {
                    this.buffer[this.nextWriteIndex++] = c;
                    if (this.nextWriteIndex == this.buffer.Length) {
                        this.nextWriteIndex = 0; // wrap around
                    }
                    if (c == (int)Tty.ControlCodes.CTRL_C) {
                        this.controlC_Count++;
                    }
                    if (c == (int)Tty.ControlCodes.CTRL_Z) {
                        this.controlZ_Count++;
                    }
                    //
                    //DebugStub.WriteLine("Add {0} writeIndex={1} readIndex={2}",
                    //                  __arglist(c, this.nextWriteIndex,
                    //                            this.nextReadIndex));
                    //
                }
            }

            private void EnsureCapacity(int count) {
                int freeSpace = this.FreeSpace;
                int charsBuffered = this.CharsInBuffer;

                if (freeSpace < count) {
                    expose (this) {
                        int newSize =  this.buffer.Length + count;
                        char[] in ExHeap newBuffer = new[ExHeap] char[newSize];
                        char[] in ExHeap oldBuffer = this.buffer;
                        if (this.nextWriteIndex >= this.nextReadIndex) {
                            // copy area between indices
                            Bitter.Copy(newBuffer, 0, charsBuffered,
                                        oldBuffer, this.nextReadIndex);
                        }
                        else {
                            // copy areas from read to end and from start to write.
                            int suffix = this.buffer.Length - this.nextReadIndex;
                            Bitter.Copy(newBuffer, 0, suffix,
                                        oldBuffer, this.nextReadIndex);
                            Bitter.Copy(newBuffer, suffix, this.nextWriteIndex,
                                        oldBuffer, 0);
                        }
                        delete this.buffer;
                        this.buffer = newBuffer;
                        this.nextReadIndex = 0;
                        this.nextWriteIndex = charsBuffered;
                    }
                }
            }

            public void Dispose()
            {
                delete this.buffer;
            }

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

            public void GetChar(out char ch) {
                expose (this) {
                tryAgain:
                    assert CharsAvailable > 0;
                    ch = this.buffer[this.nextReadIndex++];
                    if (this.nextReadIndex == this.buffer.Length) {
                        this.nextReadIndex = 0; // wrap around
                    }
                    if (ch == (int)Tty.ControlCodes.CTRL_C) {
                        if (this.controlC_Consumed > 0) {
                            // filter. already consumed via Ctrl_C
                            this.controlC_Consumed--;
                            goto tryAgain;
                        }
                        else {
                            this.controlC_Count--;
                        }
                    }
                    if (ch == (int)Tty.ControlCodes.CTRL_Z) {
                        if (this.controlZ_Consumed > 0) {
                            // filter. already consumed via Ctrl_Z
                            this.controlZ_Consumed--;
                            goto tryAgain;
                        }
                        else {
                            this.controlZ_Count--;
                        }
                    }
                    //
                    //char c = ch;
                    //DebugStub.WriteLine("GetChar {0} writeIndex={1} readIndex={2} CtrlC={3} CtrlZ={4} C-Used={5} Z-Used={6}",
                    //                  __arglist(c, this.nextWriteIndex,
                    //                            this.nextReadIndex,
                    //                            this.controlC_Count,
                    //                            this.controlZ_Count,
                    //                            this.controlC_Consumed,
                    //                            this.controlZ_Consumed
                    //                            ));
                    //

                }
            }

            public void ConsumeControlC() {
                assert this.controlC_Count > 0;
                this.controlC_Count--;
                this.controlC_Consumed++;
            }

            public void ConsumeControlZ() {
                assert this.controlZ_Count > 0;
                this.controlZ_Count--;
                this.controlZ_Consumed++;
            }
        }

        private UnicodePipeContract.Exp pipe; // null when pipe is closed

        private int lookAhead;
        private CircularBuffer buffer;
        AutoResetEventHandle evHandle;

        public PipeLookAhead([Claims] UnicodePipeContract.Exp pipe, int lookAhead)
        {
            this.pipe = pipe;
            this.lookAhead = lookAhead;
            this.buffer = new CircularBuffer(lookAhead);

            // We allocate an autoreset event handle for the case
            // when the underlying pipe is closed.
            AutoResetEventHandle handleOnStack;
            if (!AutoResetEventHandle.Create(false, out handleOnStack)) {
                throw new System.Threading.HandleCreateException();
            }
            this.evHandle = handleOnStack;
        }

        public void Dispose()
        {
            this.buffer.Dispose();
            delete this.pipe;
            if (this.evHandle.id != UIntPtr.Zero) {
                AutoResetEventHandle.Dispose(this.evHandle);
                this.evHandle = new AutoResetEventHandle();
            }
        }

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


        SyncHandle ISelectable.GetWaitHandle() {
            expose (this) {
                // non-null checker was right in pointing out issue if pipe is null.
                // Design problem: what handle do we return in this case?
                if (this.pipe != null) {
                    return this.pipe.GetWaitHandle();
                }
                else {
                    return this.evHandle;
                }
            }
        }

        void ISelectable.ResetWaitSignal() {
            // dummy
        }

        private void FillToLookAheadWithoutBlock()
        {
            expose (this) {
                UnicodePipeContract.Exp pipe = this.pipe;
                if (pipe == null) return;
                while (this.buffer.CharsAvailable < this.lookAhead) {
                    switch receive {
                    case pipe.Write(buffer,index,count):
                        this.buffer.Add(buffer, index, count);
                        pipe.SendAckWrite(buffer);
                        break;

                    case pipe.ChannelClosed():
                        delete pipe;
                        this.pipe = null;
                        return;

                    case timeout:
                        return;
                    }
                }
            } //expose
        }

        public bool IsClosed {
            get {
                expose(this) {
                    return (this.pipe == null && this.buffer.CharsAvailable==0);
                }
            }
        }

        private bool HasCharacter {
            get {
                expose(this) {
                    return this.buffer.CharsAvailable > 0;
                }
            }
        }

        private int CharsAvailable {
            get {
                expose(this) {
                    return this.buffer.CharsAvailable;
                }
            }
        }

        private bool HasControlC {
            get {
                expose(this) {
                    return this.buffer.HasControlC;
                }
            }
        }

        private bool HasControlZ {
            get {
                expose(this) {
                    return this.buffer.HasControlZ;
                }
            }
        }

        enum SelectTag {
            ChannelClosed = -1,
            Any = 1,
            Char = 2,
            ControlC = 3,
            ControlZ = 4,
        }

        /// <summary>
        /// blocks until a character is available
        /// </summary>
        public int ReadChar() {
            PipeLookAhead pipe = this;
            switch receive {
                case pipe.Char(ch):
                    return ch;
                case pipe.ChannelClosed():
                    return -1;
            }
        }

        public bool HeadMatches(int tag, ref bool possible, ref object setMatch) {

            this.FillToLookAheadWithoutBlock();

            switch ((SelectTag)tag) {
            case SelectTag.ChannelClosed:
                if (this.IsClosed) {
                    return true;
                }
                if (this.HasCharacter) {
                    possible = false;
                }
                return false;

            case SelectTag.Char:
                if (this.HasCharacter) {
                    return true;
                }
                if (this.IsClosed) {
                    possible = false;
                }
                return false;

            case SelectTag.ControlC:
                if (this.HasControlC) {
                    return true;
                }
                if (this.IsClosed) {
                    possible = false;
                }
                return false;

            case SelectTag.ControlZ:
                if (this.HasControlZ) {
                    return true;
                }
                if (this.IsClosed) {
                    possible = false;
                }
                return false;

            }
            return false;
        }

        [Selectable((int)SelectTag.Char)]
        public void RecvChar(out char ch) {
            expose(this) {
                this.buffer.GetChar(out ch);
            }
        }

        [Selectable((int)SelectTag.ControlC)]
        public void RecvControlC() {
            expose(this) {
                this.buffer.ConsumeControlC();
            }
        }

        [Selectable((int)SelectTag.ControlZ)]
        public void RecvControlZ() {
            expose(this) {
                this.buffer.ConsumeControlZ();
            }
        }

    }
}