// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for more information.

#nullable disable

using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Threading;
using Microsoft.CodeAnalysis.CSharp.Extensions;
using Microsoft.CodeAnalysis.CSharp.Syntax;
using Microsoft.CodeAnalysis.Shared.Extensions;
using Roslyn.Utilities;

namespace Microsoft.CodeAnalysis.CSharp.Organizing.Organizers;

internal static partial class MemberDeclarationsOrganizer
{
    public static SyntaxList<MemberDeclarationSyntax> Organize(
        SyntaxList<MemberDeclarationSyntax> members,
        CancellationToken cancellationToken)
    {
        // Break the list of members up into groups based on the PP 
        // directives between them.
        var groups = members.SplitNodesOnPreprocessorBoundaries(cancellationToken);

        // Go into each group and organize them.  We'll then have a list of 
        // lists.  Flatten that list and return that.
        var sortedGroups = groups.Select(OrganizeMemberGroup).Flatten().ToList();

        if (sortedGroups.SequenceEqual(members))
        {
            return members;
        }

        return [.. sortedGroups];
    }

    private static void TransferTrivia<TSyntaxNode>(
        IList<TSyntaxNode> originalList,
        IList<TSyntaxNode> finalList) where TSyntaxNode : SyntaxNode
    {
        Debug.Assert(originalList.Count == finalList.Count);

        if (originalList.Count >= 2)
        {
            // Ok, we wanted to reorder the list.  But we're definitely not done right now. While
            // most of the list will look fine, we will have issues with the first node.  First,
            // we don't want to move any pp directives or banners that are on the first node.
            // Second, it can often be the case that the node doesn't even have any trivia.  We
            // want to follow the user's style.  So we find the node that was in the index that
            // the first node moved to, and we attempt to keep an appropriate amount of
            // whitespace based on that.

            // If the first node didn't move, then we don't need to do any of this special fixup
            // logic.
            if (originalList[0] != finalList[0])
            {
                // First. Strip any pp directives or banners on the first node.  They have to
                // move to the first node in the final list.
                CopyBanner(originalList, finalList);

                // Now, we need to fix up the first node wherever it is in the final list.  We
                // need to strip it of its banner, and we need to add additional whitespace to
                // match the user's style

                FixupOriginalFirstNode(originalList, finalList);
            }
        }
    }

    private static void FixupOriginalFirstNode<TSyntaxNode>(IList<TSyntaxNode> originalList, IList<TSyntaxNode> finalList) where TSyntaxNode : SyntaxNode
    {
        // Now, find the original node in the final list.
        var originalFirstNode = originalList[0];
        var indexInFinalList = finalList.IndexOf(originalFirstNode);

        // Find the initial node we had at that same index.
        var originalNodeAtThatIndex = originalList[indexInFinalList];

        // If that node had blank lines above it, then place that number of blank
        // lines before the first node in the final list.
        var blankLines = originalNodeAtThatIndex.GetLeadingBlankLines();

        originalFirstNode = originalFirstNode.GetNodeWithoutLeadingBannerAndPreprocessorDirectives()
            .WithPrependedLeadingTrivia(blankLines);

        finalList[indexInFinalList] = originalFirstNode;
    }

    private static void CopyBanner<TSyntaxNode>(
        IList<TSyntaxNode> originalList,
        IList<TSyntaxNode> finalList) where TSyntaxNode : SyntaxNode
    {
        // First. Strip any pp directives or banners on the first node.  They
        // have to stay at the top of the list.
        var banner = originalList[0].GetLeadingBannerAndPreprocessorDirectives();

        // Now, we want to remove any blank lines from the new first node and then 
        // reattach the banner. 
        var finalFirstNode = finalList[0];
        finalFirstNode = finalFirstNode.GetNodeWithoutLeadingBlankLines();
        finalFirstNode = finalFirstNode.WithLeadingTrivia(banner.Concat(finalFirstNode.GetLeadingTrivia()));

        // Place the updated first node back in the result list
        finalList[0] = finalFirstNode;
    }

    private static IList<MemberDeclarationSyntax> OrganizeMemberGroup(IList<MemberDeclarationSyntax> members)
    {
        if (members.Count > 1)
        {
            var initialList = new List<MemberDeclarationSyntax>(members);

            var finalList = initialList.OrderBy(new Comparer()).ToList();

            if (!finalList.SequenceEqual(initialList))
            {
                // Ok, we wanted to reorder the list.  But we're definitely not done right now.
                // While most of the list will look fine, we will have issues with the first 
                // node.  First, we don't want to move any pp directives or banners that are on
                // the first node.  Second, it can often be the case that the node doesn't even
                // have any trivia.  We want to follow the user's style.  So we find the node that
                // was in the index that the first node moved to, and we attempt to keep an
                // appropriate amount of whitespace based on that.
                TransferTrivia(initialList, finalList);

                return finalList;
            }
        }

        return members;
    }
}
