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();
		}
	}
}

