﻿// 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.

using System.Collections.Immutable;
using System.Linq;
using System.Threading;

namespace Microsoft.CodeAnalysis.Completion
{
    /// <summary>
    /// The description of a <see cref="CompletionItem"/>.
    /// </summary>
    public sealed class CompletionDescription
    {
        private string? _text;

        /// <summary>
        /// The <see cref="CompletionDescription"/> used when there is no description.
        /// </summary>
        public static readonly CompletionDescription Empty = new(ImmutableArray<TaggedText>.Empty);

        /// <summary>
        /// The individual tagged parts of the description.
        /// </summary>
        public ImmutableArray<TaggedText> TaggedParts { get; }

        private CompletionDescription(ImmutableArray<TaggedText> taggedParts)
            => TaggedParts = taggedParts.NullToEmpty();

        /// <summary>
        /// Creates a new instance of <see cref="CompletionDescription"/> with the specified <see cref="TaggedText"/> parts.
        /// </summary>
        /// <param name="taggedParts">The individual tagged parts of the description.</param>
        public static CompletionDescription Create(ImmutableArray<TaggedText> taggedParts)
            => new(taggedParts);

        /// <summary>
        /// Creates a new instance of <see cref="CompletionDescription"/> from untagged text.
        /// </summary>
        public static CompletionDescription FromText(string text)
            => new(ImmutableArray.Create(new TaggedText(TextTags.Text, text)));

        /// <summary>
        /// Creates a copy of this <see cref="CompletionDescription"/> with the <see cref="TaggedParts"/> property changed.
        /// </summary>
        public CompletionDescription WithTaggedParts(ImmutableArray<TaggedText> taggedParts)
        {
            if (taggedParts != TaggedParts)
            {
                return new CompletionDescription(taggedParts);
            }
            else
            {
                return this;
            }
        }

        /// <summary>
        /// The text of the description without tags.
        /// </summary>
        public string Text
        {
            get
            {
                if (_text == null)
                {
                    Interlocked.CompareExchange(ref _text, string.Concat(TaggedParts.Select(p => p.Text)), null);
                }

                return _text;
            }
        }
    }
}
