//
//  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.Editor;
    using Microsoft.VisualStudio.Text.Utilities;
    using Microsoft.VisualStudio.Utilities;
    using System;
    using System.Diagnostics;

    /// <summary>
    /// A per view manager for brace completion. This is called by the command filter in the 
    /// editor pkg.
    /// </summary>
    internal sealed class BraceCompletionManager : IBraceCompletionManager
    {
        #region Private Members

        private readonly IBraceCompletionStack _stack;
        private readonly IBraceCompletionAggregatorFactory _sessionFactory;
        private readonly IBraceCompletionAggregator _sessionAggregator;
        private readonly ITextView _textView;
        private readonly IGuardedOperations _guardedOperations;

        private bool _braceCompletionEnabled;

        private IBraceCompletionSession _postSession;
        private IBraceCompletionSession _waitingSession;
        private SnapshotPoint? _waitingSessionOpeningPoint;

        #endregion

        #region Constructors

        internal BraceCompletionManager(ITextView textView, IBraceCompletionStack stack, IBraceCompletionAggregatorFactory sessionFactory, IGuardedOperations guardedOperations)
        {
            _textView = textView;
            _stack = stack;
            _sessionFactory = sessionFactory;
            _guardedOperations = guardedOperations;
            _sessionAggregator = sessionFactory.CreateAggregator();

            GetOptions();
            RegisterEvents();
        }

        #endregion

        #region IBraceCompletionManager

        public bool Enabled
        {
            get
            {
                return _braceCompletionEnabled;
            }
        }

        public string ClosingBraces
        {
            get
            {
                return _sessionAggregator.ClosingBraces;
            }
        }

        public bool HasActiveSessions
        {
            get { return _stack.TopSession != null; }
        }

        public string OpeningBraces
        {
            get
            {
                return _sessionAggregator.OpeningBraces;
            }
        }

        public void PreTypeChar(char character, out bool handledCommand)
        {
            bool handled = false;

            bool hasSelection = HasSelection;

            Debug.Assert(_postSession == null, "_postSession should have been cleared");

            // give the existing session a chance to handle the character first

            if (_stack.TopSession != null && !hasSelection)
            {
                IBraceCompletionSession session = _stack.TopSession;

                // check for an existing session first
                _guardedOperations.CallExtensionPoint(() =>
                {
                    if (session.ClosingBrace.Equals(character) && IsCaretOnBuffer(session.SubjectBuffer))
                    {
                        session.PreOverType(out handled);

                        if (!handled)
                        {
                            _postSession = session;
                        }
                    }
                });
            }

            handledCommand = handled;

            // otherwise check if this starts a new session
            if (_postSession == null && !handled && Enabled && !hasSelection
                && _sessionAggregator.OpeningBraces.IndexOf(character) > -1 && !HasForwardTypingOnLine)
            {
                SnapshotPoint? openingPoint = _textView.Caret.Position.Point.GetInsertionPoint((b => _sessionAggregator.IsSupportedContentType(b.ContentType, character)));

                if (openingPoint.HasValue)
                {
                    IBraceCompletionSession session = null;
                    if (_sessionAggregator.TryCreateSession(_textView, openingPoint.Value, character, out session))
                    {
                        // add the session after the current keystroke completes
                        _waitingSession = session;
                        _waitingSessionOpeningPoint = openingPoint;
                    }
                }
            }
        }

        public void PostTypeChar(char character)
        {
            // check for any waiting sessions
            if (_waitingSession != null)
            {
                // Verify the session is still valid before starting it
                // and inserting the closing brace.
                if (ValidateStart(_waitingSessionOpeningPoint, character))
                {
                    _stack.PushSession(_waitingSession);
                }

                _waitingSession = null;
                _waitingSessionOpeningPoint = null;
            }
            else if (_postSession != null)
            {
                _guardedOperations.CallExtensionPoint(() =>
                {
                    if (_postSession.ClosingBrace.Equals(character))
                    {
                        _postSession.PostOverType();
                    }
                });

                _postSession = null;
            }
        }

        public void PreTab(out bool handledCommand)
        {
            bool handled = false;

            Debug.Assert(_postSession == null, "_postSession should have been cleared");

            // tab should only be handled by brace completion if there is no selection and both braces on the same line still
            if (_stack.TopSession != null && !HasSelection)
            {
                IBraceCompletionSession session = _stack.TopSession;

                _guardedOperations.CallExtensionPoint(() =>
                {
                    if (IsSingleLine(session.OpeningPoint, session.ClosingPoint))
                    {
                        session.PreTab(out handled);

                        if (!handled)
                        {
                            _postSession = session;
                        }
                    }
                });
            }

            handledCommand = handled;
        }

        public void PostTab()
        {
            if (_postSession != null)
            {
                _guardedOperations.CallExtensionPoint(() =>
                {
                    _postSession.PostTab();
                });

                _postSession = null;
            }
        }

        public void PreBackspace(out bool handledCommand)
        {
            bool handled = false;

            Debug.Assert(_postSession == null, "_postSession should have been cleared");

            if (_stack.TopSession != null && !HasSelection)
            {
                IBraceCompletionSession session = _stack.TopSession;

                _guardedOperations.CallExtensionPoint(() => 
                {
                    if (session.OpeningPoint != null && session.ClosingPoint != null)
                    {
                        session.PreBackspace(out handled);

                        if (!handled)
                        {
                            _postSession = session;
                        }
                    }
                });
            }

            handledCommand = handled;
        }

        public void PostBackspace()
        {
            if (_postSession != null)
            {
                _guardedOperations.CallExtensionPoint(() =>
                {
                    _postSession.PostBackspace();
                });

                _postSession = null;
            }
        }

        public void PreDelete(out bool handledCommand)
        {
            bool handled = false;

            Debug.Assert(_postSession == null, "_postSession should have been cleared");

            if (_stack.TopSession != null && !HasSelection)
            {
                IBraceCompletionSession session = _stack.TopSession;

                _guardedOperations.CallExtensionPoint(() =>
                {
                    if (session.OpeningPoint != null && session.ClosingPoint != null)
                    {
                        session.PreDelete(out handled);

                        if (!handled)
                        {
                            _postSession = session;
                        }
                    }
                });
            }

            handledCommand = handled;
        }

        public void PostDelete()
        {
            if (_postSession != null)
            {
                _guardedOperations.CallExtensionPoint(() =>
                {
                    _postSession.PostDelete();
                });

                _postSession = null;
            }
        }

        public void PreReturn(out bool handledCommand)
        {
            bool handled = false;

            Debug.Assert(_postSession == null, "_postSession should have been cleared");

            if (_stack.TopSession != null && !HasSelection)
            {
                IBraceCompletionSession session = _stack.TopSession;

                _guardedOperations.CallExtensionPoint(() =>
                {
                    if (IsSingleLine(session.OpeningPoint, session.ClosingPoint))
                    {
                        session.PreReturn(out handled);

                        if (!handled)
                        {
                            _postSession = session;
                        }
                    }
                });
            }

            handledCommand = handled;
        }

        public void PostReturn()
        {
            if (_postSession != null)
            {
                _guardedOperations.CallExtensionPoint(() =>
                {
                    _postSession.PostReturn();
                });

                _postSession = null;
            }
        }

        #endregion

        #region Events/Options

        private void RegisterEvents()
        {
            _textView.Closed += textView_Closed;
            _textView.Options.OptionChanged += Options_OptionChanged;
        }

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

        private void UnregisterEvents()
        {
            _textView.Closed -= textView_Closed;
            _textView.Options.OptionChanged -= Options_OptionChanged;
        }

        private void Options_OptionChanged(object sender, EditorOptionChangedEventArgs e)
        {
            GetOptions();
        }

        private void GetOptions()
        {
            bool beforeEnabled = _braceCompletionEnabled;

            _braceCompletionEnabled = _textView.Options.GetOptionValue(DefaultTextViewOptions.BraceCompletionEnabledOptionId);

            // if completion was disabled, clear out the stack
            if (beforeEnabled && !_braceCompletionEnabled)
            {
                _waitingSession = null;
                _postSession = null;
                _stack.Clear();
            }
        }

        #endregion

        #region Private Helpers

        private bool IsCaretOnBuffer(ITextBuffer buffer)
        {
            return _textView.Caret.Position.Point.GetPoint(buffer, PositionAffinity.Successor).HasValue;
        }

        private bool HasSelection
        {
            get
            {
                return !_textView.Selection.IsEmpty;
            }
        }

        // Determine if the line has text on it apart from any active braces in this view
        private bool HasForwardTypingOnLine
        {
            get
            {
                SnapshotPoint start = _textView.Caret.Position.BufferPosition;
                SnapshotPoint end = _textView.Caret.ContainingTextViewLine.End;

                if (start != end)
                {
                    // if we have an active session use that brace as the end
                    if (_stack.TopSession != null)
                    {
                        ITrackingPoint closingPoint = null;
                        IBraceCompletionSession session = _stack.TopSession;

                        _guardedOperations.CallExtensionPoint(() =>
                        {
                            // only set these if they are on the same buffer
                            if (session.OpeningPoint != null && session.ClosingPoint != null
                                && session.OpeningPoint.TextBuffer == session.ClosingPoint.TextBuffer)
                            {
                                closingPoint = session.ClosingPoint;
                            }
                        });

                        if (closingPoint != null)
                        {
                            SnapshotPoint? innerBraceEnd = closingPoint.GetPoint(closingPoint.TextBuffer.CurrentSnapshot);

                            if (innerBraceEnd.HasValue && _stack.TopSession.SubjectBuffer != _textView.TextBuffer)
                            {
                                // map the closing point to the text buffer for the check
                                innerBraceEnd = _textView.BufferGraph.MapUpToBuffer(innerBraceEnd.Value,
                                    closingPoint.TrackingMode, PositionAffinity.Predecessor, _textView.TextBuffer);
                            }

                            if (innerBraceEnd.HasValue && innerBraceEnd.Value.Position <= end && innerBraceEnd.Value.Position > 0)
                            {
                                end = innerBraceEnd.Value.Subtract(1);
                            }
                        }
                    }

                    // check if we aren't the last closing brace
                    if (start == end)
                    {
                        return false;
                    }
                    else if (start < end)
                    {
                        SnapshotSpan span = new SnapshotSpan(start, end);

                        if (!span.IsEmpty)
                        {
                            return !string.IsNullOrWhiteSpace(span.GetText());
                        }
                    }
                    else
                    {
                        Debug.Fail("unable to check for forward typing");
                        // shouldn't happen, but if it does count it as forward typing to avoid
                        // further action
                        return true;
                    }
                }

                return false;
            }
        }

        private static bool IsSingleLine(ITrackingPoint openingPoint, ITrackingPoint closingPoint)
        {
            if (openingPoint != null && closingPoint != null)
            {
                ITextSnapshot snapshot = openingPoint.TextBuffer.CurrentSnapshot;

                return openingPoint.GetPoint(snapshot).GetContainingLine().End.Position >= closingPoint.GetPoint(snapshot).Position;
            }

            return false;
        }

        // Verify that we are about to insert the closing brace right after the opening one
        private bool ValidateStart(SnapshotPoint? openingPoint, char openingChar)
        {
            if (openingPoint.HasValue)
            {
                ITextBuffer subjectBuffer = openingPoint.Value.Snapshot.TextBuffer;

                // Get the position based on the predecessor which should be the opening brace
                SnapshotPoint? caretPosition = _textView.Caret.Position.Point.GetPoint(subjectBuffer, PositionAffinity.Predecessor);

                // verify that the opening brace is right behind the caret
                if (caretPosition.HasValue && caretPosition.Value.Position > 0)
                {
                    SnapshotPoint openingBrace = caretPosition.Value.Subtract(1);
                    return (openingBrace.GetChar() == openingChar);
                }
            }

            return false;
        }

        #endregion
    }
}