refactor: own daily currency calculation lifetime

2026-10-16 14:59:00 +02:00
parent c8b2e8e0c5
commit a6ea75821b
5 changed files with 177 additions and 59 deletions
@@ -0,0 +1,81 @@
+import Foundation
+
+/// Owns shared daily rates and calculation state for one launcher lifetime.
+@MainActor
+public final class CurrencyCalculation {
+    public private(set) var result: CalculatorResult?
+    public private(set) var isCurrency = false
+    public var changed: (() -> Void)?
+
+    private let fetch: @MainActor () async throws -> CurrencyRates
+    private let now: () -> Date
+    private let calendar: Calendar
+    private var query = ""
+    private var rates: CurrencyRates?
+    private var fetchedAt: Date?
+    private var task: Task<Void, Never>?
+    private var error: String?
+    private var failureQuery: String?
+
+    public init(
+        now: @escaping () -> Date = Date.init,
+        calendar: Calendar = .current,
+        fetch: @escaping @MainActor () async throws -> CurrencyRates = { try await CurrencyAPI.fetch() }
+    ) {
+        self.now = now
+        self.calendar = calendar
+        self.fetch = fetch
+    }
+
+    deinit { task?.cancel() }
+
+    public func update(_ query: String) {
+        self.query = query
+        if failureQuery != query {
+            error = nil
+            failureQuery = nil
+        }
+        evaluate(allowingFetch: true)
+    }
+
+    private func evaluate(allowingFetch: Bool) {
+        isCurrency = Calculator.isCurrencyQuery(query, currencyRates: rates)
+        let stale = fetchedAt.map { !calendar.isDate($0, inSameDayAs: now()) } ?? true
+        if allowingFetch, isCurrency, stale, error == nil, task == nil { refresh() }
+        result = Calculator.evaluate(query, currencyRates: rates)
+        if isCurrency, let error {
+            let cached = rates.map { " Cached snapshot \($0.date) is not used." } ?? ""
+            result = CalculatorResult(displayValue: "Currency rates unavailable", copyValue: nil,
+                detail: "Daily rates: \(error). Change the query to retry.\(cached)")
+        } else if isCurrency, rates != nil, let answer = result {
+            let cacheStatus = stale
+                ? (task == nil ? "Stale cached daily rates" : "Stale cache; refreshing daily rates…")
+                : "Cached daily rates"
+            result = CalculatorResult(displayValue: answer.displayValue, copyValue: answer.copyValue,
+                detail: "\(answer.detail) · \(cacheStatus)")
+        }
+    }
+
+    private func refresh() {
+        let fetch = self.fetch
+        task = Task { [weak self] in
+            let response: Result<CurrencyRates, any Error>
+            do { response = .success(try await fetch()) }
+            catch { response = .failure(error) }
+            guard !Task.isCancelled, let self else { return }
+            self.task = nil
+            switch response {
+            case .success(let rates):
+                self.rates = rates
+                self.fetchedAt = self.now()
+                self.error = nil
+                self.failureQuery = nil
+            case .failure(let error):
+                self.error = error.localizedDescription
+                self.failureQuery = self.query
+            }
+            self.evaluate(allowingFetch: false)
+            self.changed?()
+        }
+    }
+}