[Analytics Hub] Add helpers for creating the delta percentage text

WooCommerce/Classes/ViewRelated/Dashboard/Factories/StatsDataTextFormatter.swift

@@ -24,6 +24,16 @@ struct StatsDataTextFormatter {
         }
     }
 
+    /// Creates the text to display for the total revenue delta.
+    ///
+    static func createTotalRevenueDelta(from previousPeriod: OrderStatsV4?, to currentPeriod: OrderStatsV4?) -> String {
+        if let previousRevenue = totalRevenue(at: nil, orderStats: previousPeriod), let currentRevenue = totalRevenue(at: nil, orderStats: currentPeriod) {
+            return createDeltaText(from: previousRevenue, to: currentRevenue)
+        } else {
+            return Constants.placeholderText
+        }
+    }
+
     // MARK: Orders Stats
 
     /// Creates the text to display for the order count.
@@ -36,6 +46,16 @@ struct StatsDataTextFormatter {
         }
     }
 
+    /// Creates the text to display for the order count delta.
+    ///
+    static func createOrderCountDelta(from previousPeriod: OrderStatsV4?, to currentPeriod: OrderStatsV4?) -> String {
+        if let previousCount = orderCount(at: nil, orderStats: previousPeriod), let currentCount = orderCount(at: nil, orderStats: currentPeriod) {
+            return createDeltaText(from: previousCount, to: currentCount)
+        } else {
+            return Constants.placeholderText
+        }
+    }
+
     /// Creates the text to display for the average order value.
     ///
     static func createAverageOrderValueText(orderStats: OrderStatsV4?, currencyFormatter: CurrencyFormatter, currencyCode: String) -> String {
@@ -48,6 +68,16 @@ struct StatsDataTextFormatter {
         }
     }
 
+    /// Creates the text to display for the average order value delta.
+    ///
+    static func createAverageOrderValueDelta(from previousPeriod: OrderStatsV4?, to currentPeriod: OrderStatsV4?) -> String {
+        if let previousAverage = averageOrderValue(orderStats: previousPeriod), let currentAverage = averageOrderValue(orderStats: currentPeriod) {
+            return createDeltaText(from: previousAverage, to: currentAverage)
+        } else {
+            return Constants.placeholderText
+        }
+    }
+
     // MARK: Views and Visitors Stats
 
     /// Creates the text to display for the visitor count.
@@ -60,6 +90,16 @@ struct StatsDataTextFormatter {
         }
     }
 
+    /// Creates the text to display for the visitor count delta.
+    ///
+    static func createVisitorCountDelta(from previousPeriod: SiteVisitStats?, to currentPeriod: SiteVisitStats?) -> String {
+        if let previousCount = visitorCount(at: nil, siteStats: previousPeriod), let currentCount = visitorCount(at: nil, siteStats: currentPeriod) {
+            return createDeltaText(from: previousCount, to: currentCount)
+        } else {
+            return Constants.placeholderText
+        }
+    }
+
     // MARK: Conversion Stats
 
     /// Creates the text to display for the conversion rate.
@@ -82,6 +122,28 @@ struct StatsDataTextFormatter {
             return Constants.placeholderText
         }
     }
+}
+
+extension StatsDataTextFormatter {
+
+    // MARK: Delta Calculations
+
+    /// Creates the text showing the percent change from the previous `Decimal` value to the current `Decimal` value
+    ///
+    static func createDeltaText(from previousValue: Decimal, to currentValue: Decimal) -> String {
+        guard previousValue > 0 else {
+            return deltaNumberFormatter.string(from: 1) ?? "+100%"
+        }
+
+        let deltaValue = ((currentValue - previousValue) / previousValue)
+        return deltaNumberFormatter.string(from: deltaValue as NSNumber) ?? Constants.placeholderText
+    }
+
+    /// Creates the text showing the percent change from the previous `Double` value to the current `Double` value
+    ///
+    static func createDeltaText(from previousValue: Double, to currentValue: Double) -> String {
+        createDeltaText(from: Decimal(previousValue), to: Decimal(currentValue))
+    }
 
     // MARK: Stats Intervals
 
@@ -98,6 +160,16 @@ struct StatsDataTextFormatter {
 // MARK: - Private helpers
 
 private extension StatsDataTextFormatter {
+
+    /// Number formatter for delta percentages, e.g. `+36%` or `-16%`.
+    ///
+    static let deltaNumberFormatter: NumberFormatter = {
+        let numberFormatter = NumberFormatter()
+        numberFormatter.numberStyle = .percent
+        numberFormatter.positivePrefix = numberFormatter.plusSign
+        return numberFormatter
+    }()
+
     /// Retrieves the visitor count for the provided order stats and, optionally, a specific interval.
     ///
     static func visitorCount(at selectedIndex: Int?, siteStats: SiteVisitStats?) -> Double? {

WooCommerce/WooCommerceTests/ViewRelated/Dashboard/StatsDataTextFormatterTests.swift

@@ -62,6 +62,18 @@ final class StatsDataTextFormatterTests: XCTestCase {
         XCTAssertEqual(totalRevenue, "$25")
     }
 
+    func test_createTotalRevenueDelta_returns_expected_delta_text() {
+        // Given
+        let previousOrderStats = OrderStatsV4.fake().copy(totals: .fake().copy(grossRevenue: 10))
+        let currentOrderStats = OrderStatsV4.fake().copy(totals: .fake().copy(grossRevenue: 15))
+
+        // When
+        let totalRevenueDelta = StatsDataTextFormatter.createTotalRevenueDelta(from: previousOrderStats, to: currentOrderStats)
+
+        // Then
+        XCTAssertEqual(totalRevenueDelta, "+50%")
+    }
+
     // MARK: Orders Stats
 
     func test_createOrderCountText_returns_expected_order_count() {
@@ -94,6 +106,18 @@ final class StatsDataTextFormatterTests: XCTestCase {
         XCTAssertEqual(orderCount, "1")
     }
 
+    func test_createOrderCountDelta_returns_expected_delta_text() {
+        // Given
+        let previousOrderStats = OrderStatsV4.fake().copy(totals: .fake().copy(totalOrders: 10))
+        let currentOrderStats = OrderStatsV4.fake().copy(totals: .fake().copy(totalOrders: 15))
+
+        // When
+        let orderCountDelta = StatsDataTextFormatter.createOrderCountDelta(from: previousOrderStats, to: currentOrderStats)
+
+        // Then
+        XCTAssertEqual(orderCountDelta, "+50%")
+    }
+
     func test_createAverageOrderValueText_does_not_return_decimal_points_for_integer_value() {
         // Given
         let orderStats = OrderStatsV4.fake().copy(totals: .fake().copy(averageOrderValue: 62))
@@ -120,6 +144,18 @@ final class StatsDataTextFormatterTests: XCTestCase {
         XCTAssertEqual(averageOrderValue, "$62.86")
     }
 
+    func test_createAverageOrderValueDelta_returns_expected_delta_text() {
+        // Given
+        let previousOrderStats = OrderStatsV4.fake().copy(totals: .fake().copy(averageOrderValue: 10.00))
+        let currentOrderStats = OrderStatsV4.fake().copy(totals: .fake().copy(averageOrderValue: 15.00))
+
+        // When
+        let averageOrderValueDelta = StatsDataTextFormatter.createAverageOrderValueDelta(from: previousOrderStats, to: currentOrderStats)
+
+        // Then
+        XCTAssertEqual(averageOrderValueDelta, "+50%")
+    }
+
     // MARK: Views and Visitors Stats
 
     // This test reflects the current method for computing total visitor count.
@@ -150,6 +186,18 @@ final class StatsDataTextFormatterTests: XCTestCase {
         XCTAssertEqual(visitorCount, "17")
     }
 
+    func test_createVisitorCountDelta_returns_expected_delta_text() {
+        // Given
+        let previousSiteStats = SiteVisitStats.fake().copy(items: [.fake().copy(period: "0", visitors: 10)])
+        let currentSiteStats = SiteVisitStats.fake().copy(items: [.fake().copy(period: "0", visitors: 15)])
+
+        // When
+        let visitorCountDelta = StatsDataTextFormatter.createVisitorCountDelta(from: previousSiteStats, to: currentSiteStats)
+
+        // Then
+        XCTAssertEqual(visitorCountDelta, "+50%")
+    }
+
     // MARK: Conversion Stats
 
     func test_createConversionRateText_returns_placeholder_when_visitor_count_is_zero() {
@@ -200,4 +248,54 @@ final class StatsDataTextFormatterTests: XCTestCase {
         // Then
         XCTAssertEqual(conversionRate, "10%")
     }
+
+    // MARK: Delta Calculations
+
+    func test_createDeltaText_returns_expected_positive_text() {
+        // Given
+        let previousValue: Double = 100
+        let currentValue: Double = 150
+
+        // When
+        let deltaText = StatsDataTextFormatter.createDeltaText(from: previousValue, to: currentValue)
+
+        // Then
+        XCTAssertEqual(deltaText, "+50%")
+    }
+
+    func test_createDeltaText_returns_expected_negative_text() {
+        // Given
+        let previousValue: Double = 150
+        let currentValue: Double = 100
+
+        // When
+        let deltaText = StatsDataTextFormatter.createDeltaText(from: previousValue, to: currentValue)
+
+        // Then
+        XCTAssertEqual(deltaText, "-33%")
+    }
+
+    func test_createDeltaText_returns_100_percent_change_when_previous_value_is_zero() {
+        // Given
+        let previousValue: Double = 0
+        let currentValue: Double = 10
+
+        // When
+        let deltaText = StatsDataTextFormatter.createDeltaText(from: previousValue, to: currentValue)
+
+        // Then
+        XCTAssertEqual(deltaText, "+100%")
+    }
+
+    func test_createDeltaText_returns_negative_100_percent_change_when_current_value_is_zero() {
+        // Given
+        let previousValue: Double = 10
+        let currentValue: Double = 0
+
+        // When
+        let deltaText = StatsDataTextFormatter.createDeltaText(from: previousValue, to: currentValue)
+
+        // Then
+        XCTAssertEqual(deltaText, "-100%")
+    }
 }