Implemented phase 3 for the POC prototype in the Website service.

Services/Website/Sources/Library/Internal/Extensions/Date+Stamps.swift

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+import Foundation
+
+extension Date {
+
+    // MARK: Methods
+
+    /// How long until the date, in a few words: `47 h left`, `2 days left`, `under an hour left`.
+    /// - Parameter now: the moment counted from.
+    func countdown(
+        from now: Date
+    ) -> String {
+        let hours = Int(timeIntervalSince(now) / 3_600)
+
+        switch hours {
+        case ..<1: return "under an hour left"
+        case ..<48: return "\(hours) h left"
+        default: return "\(hours / 24) days left"
+        }
+    }
+
+    /// The date as a stamp on a record: `today, 09:14`, `yesterday, 21:38`, `20 Sep, 14:05`, or with the year once it differs.
+    ///
+    /// Read on Amsterdam's clock: the marketplace is NL-first.
+    /// - Parameter now: the moment "today" is judged from.
+    func stamp(
+        relativeTo now: Date
+    ) -> String {
+        let time = formatted(Self.style.hour(.twoDigits(amPM: .omitted)).minute(.twoDigits))
+
+        if Self.calendar.isDate(self, inSameDayAs: now) {
+            return "today, \(time)"
+        }
+
+        if
+            let yesterday = Self.calendar.date(byAdding: .day, value: -1, to: now),
+            Self.calendar.isDate(self, inSameDayAs: yesterday)
+        {
+            return "yesterday, \(time)"
+        }
+
+        let isSameYear = Self.calendar.isDate(self, equalTo: now, toGranularity: .year)
+        let day = formatted(isSameYear ? Self.style.day().month(.abbreviated) : Self.style.day().month(.abbreviated).year())
+
+        return "\(day), \(time)"
+    }
+
+}
+
+// MARK: - Helpers
+
+private extension Date {
+
+    // MARK: Constants
+
+    /// The calendar days are told apart by, on Amsterdam's clock.
+    static let calendar: Calendar = {
+        var calendar = Calendar(identifier: .gregorian)
+
+        calendar.timeZone = timeZone
+
+        return calendar
+    }()
+
+    /// The base format style: British English, on Amsterdam's clock.
+    static let style = Date.FormatStyle(
+        locale: .init(identifier: "en_GB"),
+        calendar: calendar,
+        timeZone: timeZone
+    )
+
+    static let timeZone = TimeZone(identifier: "Europe/Amsterdam") ?? .gmt
+
+}