Factor out resolution responsibilities

Sources/apk/Graph/ApkPackageGraphNode.swift

@@ -10,23 +10,10 @@ public class ApkPackageGraphNode {
   public var parentIDs = [ApkIndex.Index]()
   public var children: [ChildRef]
 
-  private weak var _graph: ApkPackageGraph?
-
-  public var package: ApkIndexPackage {
-    self._graph!.pkgIndex.packages[self.packageID]
-  }
-  public var parents: [ApkIndexPackage] {
-    self.parentIDs.map { index in self._graph!.pkgIndex.packages[index] }
-  }
-  public var childPackages: [ApkIndexPackage] {
-    self.children.map { child in self._graph!.pkgIndex.packages[child.packageID] }
-  }
-
   @inlinable public var isShallow: Bool { self.parentIDs.isEmpty }
   @inlinable public var isDeep: Bool { self.children.isEmpty }
 
   internal init(_ graph: ApkPackageGraph, id: Int, children: [ChildRef]) {
-    self._graph = graph
     self.packageID = id
     self.children = children
   }
@@ -54,31 +41,8 @@ extension ApkPackageGraphNode {
   }
 }
 
-extension ApkPackageGraphNode: CustomStringConvertible {
-  public var description: String {
-    let package = self.package
-    var result = "  \(package.nameDescription):\n"
-    if !self.parentIDs.isEmpty {
-      result += "    parents:\n"
-      for parent in self.parents {
-        result += "      \(parent.nameDescription)\n"
-      }
-    }
-    if !self.children.isEmpty {
-      result += "    children:\n"
-      for child in self.children {
-        let childPackage = self._graph!.pkgIndex.packages[child.packageID]
-        result += "      "
-        switch child.constraint {
-        case .dependency: result += "dep="
-        case .installIf: result += "installIf="
-        }
-        result += childPackage.nameDescription
-        result += ", "
-        result += child.versionSpec.description
-        result += "\n"
-      }
-    }
-    return result
+extension ApkIndex {
+  public func at(node: ApkPackageGraphNode) -> ApkIndexPackage {
+    self.packages[node.packageID]
   }
 }