Added the catalogue models and seed to support phase 3 of the POC prototype in the Persistence package.

Packages/Persistence/Sources/Public/Models/Listing.swift

@@ -51,6 +51,8 @@ public struct Listing: Sendable, Equatable {
     public let cover: Cover
     /// When the copy was listed.
     public let listedAt: Date
+    /// When a sale of the copy was agreed, or `nil` while it is for sale.
+    public let soldAt: Date?
 
     // MARK: Initializers
 
@@ -77,7 +79,8 @@ public struct Listing: Sendable, Equatable {
         shippingCents: Int,
         acceptsOffers: Bool,
         cover: Cover,
-        listedAt: Date
+        listedAt: Date,
+        soldAt: Date? = nil
     ) {
         self.slug = slug
         self.shop = shop
@@ -102,6 +105,7 @@ public struct Listing: Sendable, Equatable {
         self.acceptsOffers = acceptsOffers
         self.cover = cover
         self.listedAt = listedAt
+        self.soldAt = soldAt
     }
 
 }
@@ -112,6 +116,20 @@ public extension Listing {
 
     // MARK: Computed
 
+    /// The grade or condition in a few words: `CGC 9.8` for a slab, `Raw · NM` for a raw issue, the condition alone for a collected edition.
+    var gradeLabel: String {
+        if let grader, let grade {
+            return "\(grader) \(String(format: "%.1f", grade))"
+        }
+
+        return format == "single-issues" ? "Raw · \(condition)" : condition
+    }
+
+    /// Whether the copy is still for sale.
+    var isAvailable: Bool {
+        soldAt == nil
+    }
+
     /// Whether the issue is a key.
     var isKey: Bool {
         keyNotes != nil