WIP: More core models.

Sources/ManualDCore/EffectiveLengthGroup.swift

@@ -0,0 +1,30 @@
+import Foundation
+
+public struct EffectiveLengthGroup: Codable, Equatable {
+  public let group: Int
+  public let letter: String
+  public let effectiveLength: Int
+  public let category: Category
+  public var label: String { "\(group)\(letter.uppercased())" }
+
+  public init(
+    group: Int,
+    letter: String,
+    effectiveLength: Int,
+    category: Category
+  ) {
+    self.group = group
+    self.letter = letter
+    self.effectiveLength = effectiveLength
+    self.category = category
+  }
+}
+
+extension EffectiveLengthGroup {
+
+  public enum Category: String, Codable, Equatable {
+    case supply
+    case `return`
+  }
+
+}