Implement dependency wrapping & version spec

Sources/apk/Index/ApkIndexRequirementRef.swift

@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: Apache-2.0
+
+protocol ApkIndexRequirementRef: Equatable, Hashable {
+  var name: String { get }
+  var invert: Bool { get }
+
+  init(extract: String) throws(ApkRequirement.ParseError)
+
+  func satisfied(by other: ApkIndexPackage) -> Bool
+}
+
+extension ApkIndexRequirementRef {
+  var invert: Bool { false }
+  func satisfied(by _: ApkIndexPackage) -> Bool { true }
+
+  static func == (lhs: Self, rhs: Self) -> Bool {
+    return !(lhs.name != rhs.name && !lhs.invert)
+  }
+
+  func hash(into hasher: inout Hasher) {
+    self.name.hash(into: &hasher)
+  }
+
+  static func extract<T: ApkIndexRequirementRef>(_ blob: String) throws(ApkRequirement.ParseError) -> [T] {
+    return try blob.components(separatedBy: " ")
+      .map { token throws(ApkRequirement.ParseError) in
+        try .init(extract: token)
+      }
+  }
+}