// 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.Threading;
using System.Threading.Tasks;

namespace Microsoft.CodeAnalysis;

internal sealed partial class SolutionCompilationState
{
    /// <summary>
    /// Represents a change that needs to be made to a <see cref="Compilation"/>, <see cref="GeneratorDriver"/>, or both
    /// in response to some user edit.
    /// </summary>
    private abstract partial class TranslationAction
    {
        /// <summary>
        /// The original state of the project prior to the user edit.
        /// </summary>
        public readonly ProjectState OldProjectState;

        /// <summary>
        /// The state of the project after the user edit was made.
        /// </summary>
        public readonly ProjectState NewProjectState;

        protected TranslationAction(ProjectState oldProjectState, ProjectState newProjectState)
        {
            OldProjectState = oldProjectState;
            NewProjectState = newProjectState;
        }

        public abstract Task<Compilation> TransformCompilationAsync(Compilation oldCompilation, CancellationToken cancellationToken);

        /// <summary>
        /// Whether or not <see cref="TransformCompilationAsync" /> can be called on Compilations that may contain
        /// generated documents.
        /// </summary>
        /// <remarks>
        /// Most translation actions add or remove a single syntax tree which means we can do the "same" change
        /// to a compilation that contains the generated files and one that doesn't; however some translation actions
        /// (like <see cref="ReplaceAllSyntaxTreesAction"/>) will unilaterally remove all trees, and would have unexpected
        /// side effects. This opts those out of operating on ones with generated documents where there would be side effects.
        /// </remarks>
        public abstract bool CanUpdateCompilationWithStaleGeneratedTreesIfGeneratorsGiveSameOutput { get; }

        public abstract GeneratorDriver TransformGeneratorDriver(GeneratorDriver generatorDriver);

        /// <summary>
        /// When changes are made to a solution, we make a list of translation actions. If multiple similar changes happen in rapid
        /// succession, we may be able to merge them without holding onto intermediate state.
        /// </summary>
        /// <param name="priorAction">The action prior to this one. May be a different type.</param>
        /// <returns>A non-null <see cref="TranslationAction" /> if we could create a merged one, null otherwise.</returns>
        public virtual TranslationAction? TryMergeWithPrior(TranslationAction priorAction)
            => null;
    }
}