// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.

using System.Collections.Generic;
using System.Linq;
using Microsoft.Build.Framework;
using Microsoft.Build.Utilities;

namespace Microsoft.DotNet.Arcade.Sdk;

/// <summary>
/// Groups items by ItemSpec.
/// 
/// Given the following items:
/// <![CDATA[
/// <ItemGroup>
///   <Stuff Include="A" Value="X"/>
///   <Stuff Include="A" Value="Y"/>
///   <Stuff Include="B" Value="Z"/>
/// </ItemGroup>
/// ]]>
/// 
/// produces
/// 
/// <![CDATA[
/// <ItemGroup>
///   <Stuff Include="A" Value="X;Y"/>
///   <Stuff Include="B" Value="Z"/>
/// </ItemGroup>
/// ]]>
/// 
/// </summary>
[MSBuildMultiThreadableTask]
public sealed class GroupItemsBy : Task
{
    /// <summary>
    /// Items to group by their ItemSpec.
    /// </summary>
    [Required]
    public ITaskItem[] Items { get; set; }

    /// <summary>
    /// Names of custom metadata to group (e.g. "Value" in the example above).
    /// When merging two items the values of metadata in this set are merged into a list, 
    /// while the first value is used for metadata not in this set.
    /// </summary>
    [Required]
    public string[] GroupMetadata { get; set; }

    /// <summary>
    /// Items with grouped metadata values.
    /// </summary>
    [Output]
    public ITaskItem[] GroupedItems { get; set; }

    public override bool Execute()
    {
        ITaskItem mergeItems(IEnumerable<ITaskItem> items)
        {
            var result = items.First();

            foreach (var item in items.Skip(1))
            {
                foreach (string metadataName in GroupMetadata)
                {
                    var left = result.GetMetadata(metadataName);
                    var right = item.GetMetadata(metadataName);

                    result.SetMetadata(metadataName, 
                        (string.IsNullOrEmpty(left) || left == right) ? right : string.IsNullOrEmpty(right) ? left : left + ";" + right);
                }
            }

            return result;
        }

        GroupedItems = (from item in Items
                        group item by item.ItemSpec
                        into itemsWithEqualKey
                        select mergeItems(itemsWithEqualKey)).ToArray();

        return true;
    }
}