//
//  Copyright (c) Microsoft Corporation. All rights reserved.
//  Licensed under the MIT License. See License.txt in the project root for license information.
//
// This file contain implementations details that are subject to change without notice.
// Use at your own risk.
//
namespace Microsoft.VisualStudio.Text.BraceCompletion.Implementation
{
    using Microsoft.VisualStudio.Text;
    using Microsoft.VisualStudio.Text.BraceCompletion;
    using Microsoft.VisualStudio.Text.Editor;
    using Microsoft.VisualStudio.Text.Utilities;
    using System;
    using System.Collections.Generic;
    using System.Collections.ObjectModel;

    /// <summary>
    /// Represents the stack of active brace completion sessions.
    /// The stack handles removing sessions no longer in focus as
    /// well as marking the inner most closing brace with the 
    /// adornment.
    /// </summary>
    internal class BraceCompletionStack : IBraceCompletionStack
    {
        #region Private Members
        private Stack<IBraceCompletionSession> _stack;

        private ITextView _textView;
        private ITextBuffer _currentSubjectBuffer;

        private IBraceCompletionAdornmentServiceFactory _adornmentServiceFactory;
        private IBraceCompletionAdornmentService _adornmentService;
        private GuardedOperations _guardedOperations;
        #endregion

        #region Constructors
        public BraceCompletionStack(ITextView textView, IBraceCompletionAdornmentServiceFactory adornmentFactory, GuardedOperations guardedOperations)
        {
            _adornmentServiceFactory = adornmentFactory;
            _stack = new Stack<IBraceCompletionSession>();

            _textView = textView;
            _guardedOperations = guardedOperations;

            RegisterEvents();
        }
        #endregion

        #region IBraceCompletionStack
        public IBraceCompletionSession TopSession
        {
            get
            {
                return (_stack.Count > 0 ? _stack.Peek() : null);
            }
        }

        public void PushSession(IBraceCompletionSession session)
        {
            ITextView view = null;
            ITextBuffer buffer = null;

            _guardedOperations.CallExtensionPoint(() =>
            {
                view = session.TextView;
                buffer = session.SubjectBuffer;
            });

            if (view != null && buffer != null)
            {
                SetCurrentBuffer(buffer);
                bool validStart = false;

                // start the session to add the closing brace
                _guardedOperations.CallExtensionPoint(() =>
                {
                    session.Start();

                    // verify the session is valid before going on.
                    // some sessions may want to leave the stack at this point
                    validStart = (session.OpeningPoint != null && session.ClosingPoint != null);
                });

                if (validStart)
                {
                    // highlight the brace
                    ITrackingPoint closingPoint = null;
                    _guardedOperations.CallExtensionPoint(() =>
                    {
                        closingPoint = session.ClosingPoint;
                    });

                    HighlightSpan(closingPoint);

                    // put it on the stack for tracking
                    _stack.Push(session);
                }
            }
        }

        public ReadOnlyObservableCollection<IBraceCompletionSession> Sessions
        {
            get
            {
                return new ReadOnlyObservableCollection<IBraceCompletionSession>(new ObservableCollection<IBraceCompletionSession>(_stack));
            }
        }

        public void RemoveOutOfRangeSessions(SnapshotPoint point)
        {
            bool updateHighlightSpan = false;

            while (_stack.Count > 0 && !Contains(TopSession, point))
            {
                updateHighlightSpan = true;

                // remove the session and call Finish
                PopSession();
            }

            if (updateHighlightSpan)
            {
                HighlightSpan(TopSession != null ? TopSession.ClosingPoint : null);
            }
        }

        public void Clear()
        {
            while (_stack.Count > 0)
            {
                PopSession();
            }

            SetCurrentBuffer(null);
            HighlightSpan(null);
        }

        #endregion

        #region Events

        private void RegisterEvents()
        {
            if (_adornmentServiceFactory != null)
            {
                _adornmentService = _adornmentServiceFactory.GetOrCreateService(_textView);
            }

            _textView.Caret.PositionChanged += Caret_PositionChanged;
            _textView.Closed += TextView_Closed;
        }

        private void UnregisterEvents()
        {
            _textView.Caret.PositionChanged -= Caret_PositionChanged;
            _textView.Closed -= TextView_Closed;

            // unhook subject buffer
            SetCurrentBuffer(null);

            _textView = null;
        }

        public void ConnectSubjectBuffer(ITextBuffer subjectBuffer)
        {
            subjectBuffer.PostChanged += SubjectBuffer_PostChanged;
        }

        public void DisconnectSubjectBuffer(ITextBuffer subjectBuffer)
        {
            subjectBuffer.PostChanged -= SubjectBuffer_PostChanged;
        }

        private void TextView_Closed(object sender, EventArgs e)
        {
            UnregisterEvents();
        }

        // Remove any sessions that no longer contain the caret
        private void Caret_PositionChanged(object sender, CaretPositionChangedEventArgs e)
        {
            if (_stack.Count > 0)
            {
                // use the new position if possible, otherwise map to the subject buffer
                if (_currentSubjectBuffer != null && e.TextView.TextBuffer != _currentSubjectBuffer)
                {
                    SnapshotPoint? newPosition = e.NewPosition.Point.GetPoint(_currentSubjectBuffer, PositionAffinity.Successor);

                    if (newPosition.HasValue)
                    {
                        RemoveOutOfRangeSessions(newPosition.Value);
                    }
                    else
                    {
                        // caret is no longer in the subject buffer. probably
                        // moved to different buffer in the same view.
                        // clear all tracks
                        _stack.Clear();
                    }
                }
                else
                {
                    RemoveOutOfRangeSessions(e.NewPosition.BufferPosition);
                }
            }
        }

        // Verify that the top most session is still valid after a buffer change
        // This handles any issues that could result from text being replaced
        // or multi view scenarios where the caret is not being moved in the 
        // current view.
        private void SubjectBuffer_PostChanged(object sender, EventArgs e)
        {
            bool updateHighlightSpan = false;

            // only check the top most session
            // outer sessions could become invalid while the inner most
            // sessions stay valid, but there is no reason to check them every time
            while (_stack.Count > 0 && !IsSessionValid(TopSession))
            {
                updateHighlightSpan = true;
                _stack.Pop().Finish();
            }

            if (updateHighlightSpan)
            {
                ITrackingPoint closingPoint = null;

                if (TopSession != null)
                {
                    _guardedOperations.CallExtensionPoint(() => closingPoint = TopSession.ClosingPoint);
                }

                HighlightSpan(closingPoint);
            }
        }

        private bool IsSessionValid(IBraceCompletionSession session)
        {
            bool isValid = false;

            _guardedOperations.CallExtensionPoint(() =>
            {
                if (session.ClosingPoint != null && session.OpeningPoint != null && session.SubjectBuffer != null)
                {
                    ITextSnapshot snapshot = session.SubjectBuffer.CurrentSnapshot;
                    SnapshotPoint closingSnapshotPoint = session.ClosingPoint.GetPoint(snapshot);
                    SnapshotPoint openingSnapshotPoint = session.OpeningPoint.GetPoint(snapshot);

                    // Verify that the closing and opening points still match the expected braces
                    isValid = closingSnapshotPoint.Position > 1
                        && openingSnapshotPoint.Position <= (closingSnapshotPoint.Position - 2)
                        && openingSnapshotPoint.GetChar() == session.OpeningBrace
                        && closingSnapshotPoint.Subtract(1).GetChar() == session.ClosingBrace;
                }
            });

            return isValid;
        }

        #endregion

        #region Private Helpers

        private void SetCurrentBuffer(ITextBuffer buffer)
        {
            // Connect to the subject buffer of the session
            if (_currentSubjectBuffer != buffer)
            {
                if (_currentSubjectBuffer != null)
                {
                    DisconnectSubjectBuffer(_currentSubjectBuffer);
                }

                _currentSubjectBuffer = buffer;

                if (_currentSubjectBuffer != null)
                {
                    ConnectSubjectBuffer(_currentSubjectBuffer);
                }
            }
        }

        private void PopSession()
        {
            IBraceCompletionSession session = _stack.Pop();
            ITextBuffer nextSubjectBuffer = null;

            _guardedOperations.CallExtensionPoint(() =>
            {
                // call finish to allow the session to do any cleanup
                session.Finish();

                if (TopSession != null)
                {
                    nextSubjectBuffer = TopSession.SubjectBuffer;
                }
            });

            SetCurrentBuffer(nextSubjectBuffer);
        }

        private void HighlightSpan(ITrackingPoint point)
        {
            if (_adornmentService != null)
            {
                _adornmentService.Point = point;
            }
        }

        private bool Contains(IBraceCompletionSession session, SnapshotPoint point)
        {
            bool contains = false;

            _guardedOperations.CallExtensionPoint(() =>
            {
                // remove any sessions with nulls, if they decide they need to get off the stack
                // they can do it this way.
                if (session.OpeningPoint != null && session.ClosingPoint != null
                    && session.OpeningPoint.TextBuffer == session.ClosingPoint.TextBuffer
                    && point.Snapshot.TextBuffer == session.OpeningPoint.TextBuffer)
                {
                    ITextSnapshot snapshot = point.Snapshot;

                    contains = session.OpeningPoint.GetPosition(snapshot) < point.Position
                        && session.ClosingPoint.GetPosition(snapshot) > point.Position;
                }
            });

            return contains;
        }
        #endregion
    }
}