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

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

@@ -0,0 +1,131 @@
+import Foundation
+
+/// A `Sendable` snapshot of a conversation between a buyer and a shop, as one of them sees it.
+public struct Conversation: Sendable, Equatable {
+
+    // MARK: Properties
+
+    /// The conversation's identifier.
+    public let id: UUID
+    /// The account buying.
+    public let buyer: User
+    /// The shop selling.
+    public let shop: Shop
+    /// The listing the conversation is about, or `nil` when it is about the shop at large.
+    public let listing: Listing?
+    /// Which side of the conversation the viewer is on.
+    public let side: Side
+    /// What was said, offered, and stamped, oldest first.
+    public let entries: [Entry]
+    /// The number of entries from the other side the viewer has not seen yet.
+    public let unreadCount: Int
+    /// The number of the sale agreed in the conversation, or `nil` when none was.
+    public let saleNumber: Int?
+
+    // MARK: Initializers
+
+    public init(
+        id: UUID,
+        buyer: User,
+        shop: Shop,
+        listing: Listing?,
+        side: Side,
+        entries: [Entry],
+        unreadCount: Int,
+        saleNumber: Int?
+    ) {
+        self.id = id
+        self.buyer = buyer
+        self.shop = shop
+        self.listing = listing
+        self.side = side
+        self.entries = entries
+        self.unreadCount = unreadCount
+        self.saleNumber = saleNumber
+    }
+
+}
+
+// MARK: - Structs
+
+public extension Conversation {
+    /// One thing in a conversation: something said, an offer made, or an event stamped.
+    struct Entry: Sendable, Equatable {
+
+        // MARK: Properties
+
+        /// What the entry is.
+        public let kind: Kind
+        /// Who wrote the message, made the offer, or caused the event.
+        public let sender: User
+        /// The message, the offer's note, or the event in a sentence.
+        public let body: String
+        /// The offer made, for an offer entry.
+        public let offer: Offer?
+        /// The number of the sale an event opened, or `nil`.
+        public let saleNumber: Int?
+        /// When the entry was made.
+        public let createdAt: Date
+
+        // MARK: Initializers
+
+        public init(
+            kind: Kind,
+            sender: User,
+            body: String,
+            offer: Offer? = nil,
+            saleNumber: Int? = nil,
+            createdAt: Date
+        ) {
+            self.kind = kind
+            self.sender = sender
+            self.body = body
+            self.offer = offer
+            self.saleNumber = saleNumber
+            self.createdAt = createdAt
+        }
+
+        // MARK: Enumerations
+
+        /// What a conversation entry is.
+        public enum Kind: String, Sendable {
+            /// Something a party wrote.
+            case text
+            /// An offer, with its optional note.
+            case offer
+            /// Something that happened: an offer answered, a sale agreed, a step of the handshake taken.
+            case event
+        }
+
+    }
+}
+
+// MARK: - Enumerations
+
+public extension Conversation {
+    /// A side of a conversation.
+    enum Side: String, Sendable {
+        case buying
+        case selling
+    }
+}
+
+// MARK: - Extensions
+
+public extension Conversation {
+
+    // MARK: Computed
+
+    /// The latest entry, or `nil` in a conversation nothing was said in yet.
+    var latest: Entry? {
+        entries.last
+    }
+
+    /// The offer still waiting for an answer, or `nil` when there is none.
+    var openOffer: Offer? {
+        entries
+            .compactMap(\.offer)
+            .last { $0.status == .open }
+    }
+
+}