using Microsoft.CodeAnalysis;
using Microsoft.CodeAnalysis.CodeActions;
using Microsoft.CodeAnalysis.Formatting;
using Microsoft.CodeAnalysis.Simplification;
using System.Collections.Generic;
using System.Linq;
using System.Threading;

namespace TestHelper {
  /// <summary>
  /// Diagnostic Producer class with extra methods dealing with applying codefixes
  /// All methods are static
  /// </summary>
  public abstract partial class CodeFixVerifier : DiagnosticVerifier {
    /// <summary>
    /// Apply the inputted CodeAction to the inputted document.
    /// Meant to be used to apply codefixes.
    /// </summary>
    /// <param name="document">The Document to apply the fix on</param>
    /// <param name="codeAction">A CodeAction that will be applied to the Document.</param>
    /// <returns>A Document with the changes from the CodeAction</returns>
    private static Document ApplyFix(Document document, CodeAction codeAction) {
      var operations = codeAction.GetOperationsAsync(CancellationToken.None).Result;
      var solution = operations.OfType<ApplyChangesOperation>().Single().ChangedSolution;
      return solution.GetDocument(document.Id);
    }

    /// <summary>
    /// Compare two collections of Diagnostics,and return a list of any new diagnostics that appear only in the second collection.
    /// Note: Considers Diagnostics to be the same if they have the same Ids.  In the case of multiple diagnostics with the same Id in a row,
    /// this method may not necessarily return the new one.
    /// </summary>
    /// <param name="diagnostics">The Diagnostics that existed in the code before the CodeFix was applied</param>
    /// <param name="newDiagnostics">The Diagnostics that exist in the code after the CodeFix was applied</param>
    /// <returns>A list of Diagnostics that only surfaced in the code after the CodeFix was applied</returns>
    private static IEnumerable<Diagnostic> GetNewDiagnostics(IEnumerable<Diagnostic> diagnostics, IEnumerable<Diagnostic> newDiagnostics) {
      var oldArray = diagnostics.OrderBy(d => d.Location.SourceSpan.Start).ToArray();
      var newArray = newDiagnostics.OrderBy(d => d.Location.SourceSpan.Start).ToArray();

      int oldIndex = 0;
      int newIndex = 0;

      while (newIndex < newArray.Length) {
        if (oldIndex < oldArray.Length && oldArray[oldIndex].Id == newArray[newIndex].Id) {
          ++oldIndex;
          ++newIndex;
        } else {
          yield return newArray[newIndex++];
        }
      }
    }

    /// <summary>
    /// Get the existing compiler diagnostics on the inputted document.
    /// </summary>
    /// <param name="document">The Document to run the compiler diagnostic analyzers on</param>
    /// <returns>The compiler diagnostics that were found in the code</returns>
    private static IEnumerable<Diagnostic> GetCompilerDiagnostics(Document document) {
      return document.GetSemanticModelAsync().Result.GetDiagnostics();
    }

    /// <summary>
    /// Given a document, turn it into a string based on the syntax root
    /// </summary>
    /// <param name="document">The Document to be converted to a string</param>
    /// <returns>A string containing the syntax of the Document after formatting</returns>
    private static string GetStringFromDocument(Document document) {
      var simplifiedDoc = Simplifier.ReduceAsync(document, Simplifier.Annotation).Result;
      var root = simplifiedDoc.GetSyntaxRootAsync().Result;
      root = Formatter.Format(root, Formatter.Annotation, simplifiedDoc.Project.Solution.Workspace);
      return root.GetText().ToString();
    }
  }
}