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

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

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+import Foundation
+
+/// A `Sendable` snapshot of a buyer's offer on a listing.
+public struct Offer: Sendable, Equatable {
+
+    // MARK: Constants
+
+    /// The share of the asking price under which an offer is declined outright.
+    public static let floorShare = 0.8
+
+    /// How long an offer binds its buyer: 48 hours.
+    public static let lifetime: TimeInterval = 172_800
+
+    // MARK: Properties
+
+    /// The offer's identifier.
+    public let id: UUID
+    /// The identifier of the conversation the offer was made in.
+    public let conversationID: UUID
+    /// The listing offered on.
+    public let listing: Listing
+    /// The account offering.
+    public let buyer: User
+    /// The amount offered, in euro cents.
+    public let amountCents: Int
+    /// Where the offer stands; an open offer past its expiry reads as expired.
+    public let status: Status
+    /// When the offer was made.
+    public let createdAt: Date
+    /// When the offer stops binding its buyer.
+    public let expiresAt: Date
+
+    // MARK: Initializers
+
+    public init(
+        id: UUID,
+        conversationID: UUID,
+        listing: Listing,
+        buyer: User,
+        amountCents: Int,
+        status: Status,
+        createdAt: Date,
+        expiresAt: Date
+    ) {
+        self.id = id
+        self.conversationID = conversationID
+        self.listing = listing
+        self.buyer = buyer
+        self.amountCents = amountCents
+        self.status = status
+        self.createdAt = createdAt
+        self.expiresAt = expiresAt
+    }
+
+}
+
+// MARK: - Enumerations
+
+public extension Offer {
+    /// Where an offer stands.
+    enum Status: String, Sendable {
+        /// Waiting for the seller's answer.
+        case open
+        /// Accepted: a sale record was opened.
+        case accepted
+        /// Declined by the seller.
+        case declined
+        /// Left unanswered past its expiry, or overtaken by a sale of the listing.
+        case expired
+    }
+}
+
+// MARK: - Extensions
+
+public extension Offer {
+
+    // MARK: Methods
+
+    /// The lowest offer a listing's seller hears, in euro cents: ``floorShare`` of the asking price, rounded up to a whole euro.
+    /// - Parameter askingCents: the listing's asking price, in euro cents.
+    static func floor(
+        forAsking askingCents: Int
+    ) -> Int {
+        Int((Double(askingCents) * floorShare / 100).rounded(.up)) * 100
+    }
+
+}