// 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.Generic;
using System.Collections.Immutable;
using System.Diagnostics;
using System.Linq;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.Diagnostics;
 
namespace Microsoft.CodeAnalysis.CodeFixes
{
    /// <summary>
    /// Represents a single fix. This is essentially a tuple
    /// that holds on to a <see cref="CodeAction"/> and the set of
    /// <see cref="Diagnostic"/>s that this <see cref="CodeAction"/> will fix.
    /// </summary>
    internal sealed class CodeFix
    {
        internal readonly Project Project;
        internal readonly CodeAction Action;
        internal readonly ImmutableArray<Diagnostic> Diagnostics;
 
        /// <summary>
        /// This is the diagnostic that will show up in the preview pane header when a particular fix
        /// is selected in the light bulb menu. We also group all fixes with the same <see cref="PrimaryDiagnostic"/>
        /// together (into a single SuggestedActionSet) in the light bulb menu.
        /// </summary>
        /// <remarks>
        /// A given fix can fix one or more diagnostics. However, our light bulb UI (preview pane, grouping
        /// of fixes in the light bulb menu etc.) currently keeps things simple and pretends that
        /// each fix fixes a single <see cref="PrimaryDiagnostic"/>.
        /// 
        /// Implementation-wise the <see cref="PrimaryDiagnostic"/> is always the first diagnostic that
        /// the <see cref="CodeFixProvider"/> supplied when registering the fix (<see 
        /// cref="CodeFixContext.RegisterCodeFix(CodeAction, IEnumerable{Diagnostic})"/>). This could change
        /// in the future, if we decide to change the UI to depict the true mapping between fixes and diagnostics
        /// or if we decide to use some other heuristic to determine the <see cref="PrimaryDiagnostic"/>.
        /// </remarks>
        internal Diagnostic PrimaryDiagnostic => Diagnostics[0];
 
        internal CodeFix(Project project, CodeAction action, Diagnostic diagnostic)
        {
            Project = project;
            Action = action;
            Diagnostics = ImmutableArray.Create(diagnostic);
        }
 
        internal CodeFix(Project project, CodeAction action, ImmutableArray<Diagnostic> diagnostics)
        {
            Debug.Assert(!diagnostics.IsDefaultOrEmpty);
            Project = project;
            Action = action;
            Diagnostics = diagnostics;
        }
 
        internal DiagnosticData GetPrimaryDiagnosticData()
        {
            var diagnostic = PrimaryDiagnostic;
 
            if (diagnostic.Location.IsInSource)
            {
                var document = Project.GetDocument(diagnostic.Location.SourceTree);
                if (document != null)
                {
                    return DiagnosticData.Create(diagnostic, document);
                }
            }
            else if (diagnostic.Location.Kind == LocationKind.ExternalFile)
            {
                var document = Project.Documents.FirstOrDefault(d => d.FilePath == diagnostic.Location.GetLineSpan().Path);
                if (document != null)
                {
                    return DiagnosticData.Create(diagnostic, document);
                }
            }
 
            return DiagnosticData.Create(Project.Solution, diagnostic, Project);
        }
    }
}