// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.ComponentModel.Composition;
using System.Linq;
using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.Text;
using Microsoft.VisualStudio.Editor.Razor;
using Microsoft.VisualStudio.Text;
using Microsoft.VisualStudio.Text.Projection;

namespace Microsoft.VisualStudio.LanguageServices.Razor
{
    [System.Composition.Shared]
    [Export(typeof(VisualStudioWorkspaceAccessor))]
    internal class DefaultVisualStudioWorkspaceAccessor : VisualStudioWorkspaceAccessor
    {
        private readonly IBufferGraphFactoryService _bufferGraphService;
        private readonly TextBufferProjectService _projectService;
        private readonly Workspace _defaultWorkspace;

        [ImportingConstructor]
        public DefaultVisualStudioWorkspaceAccessor(
            IBufferGraphFactoryService bufferGraphService,
            TextBufferProjectService projectService,
            [Import(typeof(VisualStudioWorkspace))] Workspace defaultWorkspace)
        {
            if (bufferGraphService == null)
            {
                throw new ArgumentNullException(nameof(bufferGraphService));
            }

            if (projectService == null)
            {
                throw new ArgumentNullException(nameof(projectService));
            }

            if (defaultWorkspace == null)
            {
                throw new ArgumentNullException(nameof(defaultWorkspace));
            }

            _bufferGraphService = bufferGraphService;
            _projectService = projectService;
            _defaultWorkspace = defaultWorkspace;
        }

        public override Workspace Workspace => _defaultWorkspace;

        public override bool TryGetWorkspace(ITextBuffer textBuffer, out Workspace workspace)
        {
            if (textBuffer == null)
            {
                throw new ArgumentNullException(nameof(textBuffer));
            }

            // We do a best effort approach in this method to get the workspace that belongs to the TextBuffer.
            // The approaches we take to find the workspace are:
            //
            // 1. Look for a C# projection buffer associated with the Razor buffer. If we can find one we let
            //    Roslyn take control of finding the Workspace (projectionBuffer.GetWorkspace()). If not,
            //    fall back to determining if we can use the default workspace.
            // 2. Look to see if this ITextBuffer is associated with a host project. If we find that our Razor
            //    buffer has a host project, we make the assumption that we should use the default VisualStudioWorkspace.

            if (TryGetWorkspaceFromProjectionBuffer(textBuffer, out workspace))
            {
                return true;
            }

            if (TryGetWorkspaceFromHostProject(textBuffer, out workspace))
            {
                return true;
            }

            workspace = null;
            return false;
        }

        // Internal virtual for testing
        internal virtual bool TryGetWorkspaceFromProjectionBuffer(ITextBuffer textBuffer, out Workspace workspace)
        {
            var graph = _bufferGraphService.CreateBufferGraph(textBuffer);
            var projectedCSharpBuffer = graph.GetTextBuffers(buffer => buffer.ContentType.IsOfType("CSharp")).FirstOrDefault();

            if (projectedCSharpBuffer == null)
            {
                workspace = null;
                return false;
            }

            workspace = projectedCSharpBuffer.GetWorkspace();
            if (workspace == null)
            {
                // Couldn't resolve a workspace for the projected csharp buffer.
                return false;
            }

            return true;
        }

        // Internal virtual for testing
        internal virtual bool TryGetWorkspaceFromHostProject(ITextBuffer textBuffer, out Workspace workspace)
        {
            var project = _projectService.GetHostProject(textBuffer);

            if (project == null)
            {
                // Could not locate a project for the given text buffer.
                workspace = null;
                return false;
            }

            // We have a host project, assume default workspace.
            workspace = _defaultWorkspace;
            return true;
        }
    }
}