NDEPEND Namespace Dependency Cycles

// <Name>Avoid namespaces dependency cycles</Name>
warnif count > 0
// This query lists all application namespace dependency cycles.
// Each row shows a different cycle, prefixed with a namespace entangled in the cycle.
//
// To browse a cycle on the dependency graph or the dependency matrix, right click
// a cycle cell and export the matched namespaces to the dependency graph or matrix!
//
// In the matrix, dependency cycles are represented with red squares and black cells.
// To easily browse dependency cycles, the Matrix comes with an option:
//   --> Display Direct and Indirect Dependencies
//
// Read our white books relative to partitioning code,
// to know more about namespaces dependency cycles, and why avoiding them
// is a simple but efficient solution to architecture for your code base.
// http://www.ndepend.com/WhiteBooks.aspx


// Optimization: restraint application assemblies set
// If some namespaces are mutually dependent
//  - They must be declared in the same assembly
//  - The parent assembly must ContainsNamespaceDependencyCycle
from assembly in Application.Assemblies
                 .Where(a => a.ContainsNamespaceDependencyCycle != null &&
                             a.ContainsNamespaceDependencyCycle.Value)

// Optimization: restraint namespaces set
// A namespace involved in a cycle necessarily have a null Level.
let namespacesSuspect = assembly.ChildNamespaces.Where(n => n.Level == null)

// hashset is used to avoid iterating again on namespaces already caught in a cycle.
let hashset = new HashSet<INamespace>()


from suspect in namespacesSuspect
   // By commenting in this line, the query matches all namespaces involved in a cycle.
   where !hashset.Contains(suspect)

   // Define 2 code metrics
   // - Namespaces depth of is using indirectly the suspect namespace.
   // - Namespaces depth of is used by the suspect namespace indirectly.
   // Note: for direct usage the depth is equal to 1.
   let namespacesUserDepth = namespacesSuspect.DepthOfIsUsing(suspect)
   let namespacesUsedDepth = namespacesSuspect.DepthOfIsUsedBy(suspect)

   // Select namespaces that are both using and used by namespaceSuspect
   let usersAndUsed = from n in namespacesSuspect where
                         namespacesUserDepth[n] > 0 &&
                         namespacesUsedDepth[n] > 0
                      select n

   where usersAndUsed.Count() > 0

   // Here we've found namespace(s) both using and used by the suspect namespace.
   // A cycle involving the suspect namespace is found!
   let cycle = usersAndUsed.Append(suspect)

   // Fill hashset with namespaces in the cycle.
   // .ToArray() is needed to force the iterating process.
   let unused1 = (from n in cycle let unused2 = hashset.Add(n) select n).ToArray()

select new { suspect, cycle }