using PostSharp.Constraints;
using PostSharp.Extensibility;
using PostSharp.Reflection;
using PostSharp.Reflection.MethodBody;
using System;
using System.Reflection;
using System.Resources;
 
namespace PostSharp.Samples.ValidateResourceString
{
  /// <summary>
  ///   Custom attribute that, when applied to a <see cref="string" /> parameter, writes a warning at build-time that the
  ///   value passed to the parameter is a valid name for a string stored in
  ///   a managed resource.
  /// </summary>
  [AttributeUsage(AttributeTargets.Parameter)]
  [MulticastAttributeUsage(MulticastTargets.Parameter)]
  public sealed class ValidateResourceStringAttribute : ReferentialConstraint
  {
    private readonly string resourceBaseName;
 
    /// <summary>
    ///   Initializes a new <see cref="ValidateResourceStringAttribute" />.
    /// </summary>
    /// <param name="resourceBaseName">Name of the managed resource containing the string.</param>
    public ValidateResourceStringAttribute(string resourceBaseName)
    {
      this.resourceBaseName = resourceBaseName;
    }
 
    /// <summary>
    ///   Validates that the attribute has been applied to a valid parameter.
    /// </summary>
    /// <param name="target">The parameter to which the attribute has been applied.</param>
    /// <returns><c>true</c> if the attribute is applied to a valid parameter, otherwise <c>false</c>.</returns>
    public override bool ValidateConstraint(object target)
    {
      // Validate that the attribute has been applied to a parameter of type string.
      var parameter = (ParameterInfo) target;
 
      if (parameter.ParameterType != typeof(string))
      {
        Message.Write(parameter, SeverityType.Error, "VRN01",
          "Cannot use [ValidateResourceString] on parameter {0} because it is not of type string.", parameter);
        return false;
      }
 
      if (!(parameter.Member is MethodBase))
      {
        Message.Write(parameter, SeverityType.Error, "VRN02",
          "Cannot use [ValidateResourceString] on parameter {0} because the attribute can only be applied to method parameters.",
          parameter);
        return false;
      }
 
 
      // Validate that the current assembly contains a resource of the given name.
      var assembly = GetType().Assembly;
      try
      {
        new ResourceManager(resourceBaseName, assembly);
      }
      catch (Exception e)
      {
        Message.Write(parameter, SeverityType.Error, "VRN03",
          "Cannot load a managed resource named \"{1}\" from assembly \"{0}\": {2}", assembly.GetName().Name,
          resourceBaseName, e.Message);
        return false;
      }
 
      return true;
    }
 
    /// <summary>
    ///   Validates an <see cref="Assembly" /> against the current constraint.
    /// </summary>
    /// <param name="target">Parameter to which the current constraint has been applied.</param>
    /// <param name="assembly">Assembly being validated.</param>
    public override void ValidateCode(object target, Assembly assembly)
    {
      var parameter = (ParameterInfo) target;
      var resourceManager = new ResourceManager(resourceBaseName, assembly);
 
      // Get the list of methods referencing the parent method of the parameter.
      var reflectionService =
        PostSharpEnvironment.CurrentProject.GetService<IMethodBodyService>();
      var usages = ReflectionSearch.GetMethodsUsingDeclaration(parameter.Member);
 
 
      foreach (var usage in usages)
      {
        // Decompiles the method into expression trees.
        var methodBody = reflectionService.GetMethodBody(usage.UsingMethod,
          MethodBodyAbstractionLevel.ExpressionTree);
 
        // Visit the method body.
        var visitor = new Visitor(parameter, resourceManager);
        visitor.VisitMethodBody(methodBody);
      }
    }
 
    /// <summary>
    ///   Visits all expressions in the method body.
    /// </summary>
    private class Visitor : MethodBodyVisitor
    {
      private readonly ParameterInfo parameter;
      private readonly ResourceManager resourceManager;
 
      public Visitor(ParameterInfo parameter, ResourceManager resourceManager)
      {
        this.resourceManager = resourceManager;
        this.parameter = parameter;
      }
 
 
 
      /// <summary>
      ///   Visits a method call.
      /// </summary>
      /// <param name="expression"></param>
      /// <returns></returns>
      public override object VisitMethodCallExpression(IMethodCallExpression expression)
      {
        if (expression.Method == parameter.Member)
        {
          // We are inspecting the call to the method of interest.    
          var argument = expression.Arguments[parameter.Position];
          var constantExpression = argument as IConstantExpression;
 
          if (constantExpression != null)
          {
            var resourceName = (string) constantExpression.Value;
            if (resourceManager.GetString(resourceName) == null)
            {
              Message.Write(expression.ParentMethodBody.Method, SeverityType.Warning, "VRN04",
                "The string \"{0}\" in method {1} is not a valid resource name.", resourceName,
                expression.Method);
            }
          }
        }
 
        return base.VisitMethodCallExpression(expression);
      }
    }
  }
}