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