commit 8fe22415778bfdd9c2971f0efe7e71b7b068c392
Author: zonble <zonble@gmail.com>
Date:   Wed May 9 18:31:16 2018 +0800

    Initial commit.

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..357f152
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,5 @@
+.DS_Store
+/.build
+/Packages
+/*.xcodeproj
+.idea
diff --git a/Package.swift b/Package.swift
new file mode 100644
index 0000000..5c83cd5
--- /dev/null
+++ b/Package.swift
@@ -0,0 +1,28 @@
+// swift-tools-version:4.0
+// The swift-tools-version declares the minimum version of Swift required to build this package.
+
+import PackageDescription
+
+let package = Package(
+    name: "ActiveDays",
+    products: [
+        // Products define the executables and libraries produced by a package, and make them visible to other packages.
+        .library(
+            name: "ActiveDays",
+            targets: ["ActiveDays"]),
+    ],
+    dependencies: [
+        // Dependencies declare other packages that this package depends on.
+        // .package(url: /* package url */, from: "1.0.0"),
+    ],
+    targets: [
+        // Targets are the basic building blocks of a package. A target can define a module or a test suite.
+        // Targets can depend on other targets in this package, and on products in packages which this package depends on.
+        .target(
+            name: "ActiveDays",
+            dependencies: []),
+        .testTarget(
+            name: "ActiveDaysTests",
+            dependencies: ["ActiveDays"]),
+    ]
+)
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..af6da46
--- /dev/null
+++ b/README.md
@@ -0,0 +1,3 @@
+# ActiveDays
+
+A description of this package.
diff --git a/Sources/ActiveDays/ActiveDays.swift b/Sources/ActiveDays/ActiveDays.swift
new file mode 100644
index 0000000..70ebab0
--- /dev/null
+++ b/Sources/ActiveDays/ActiveDays.swift
@@ -0,0 +1,172 @@
+import Foundation
+
+public enum ActiveDaysCounterError: Error, LocalizedError {
+	case sessionUnstarted
+	case invalidDate
+	case needsNewSession
+
+	public var errorDescription: String? {
+		switch self {
+		case .sessionUnstarted:
+			return NSLocalizedString("You did not start a session.", comment: "")
+		case .invalidDate:
+			return NSLocalizedString("The incoming date is before the week.", comment: "")
+		case .needsNewSession:
+			return NSLocalizedString("The incoming date is not in the week. Please start a new session.", comment: "")
+		}
+	}
+}
+
+
+/// The result that you get when you commit a new access date to
+/// ActiveDaysPerWeekCounter.
+///
+/// - noEvent: you should not send anything to an analytics platform.
+/// - active: you should send an event to indicate how many days this
+///           user has been active.
+public enum ActiveDaysCounterResult {
+	case noEvent
+	case active(Int)
+}
+
+
+/// ActiveDaysPerWeekCounter is a class that we made to answer a
+/// challenge: how do we know about how many days does a user uses our
+/// app per week?
+///
+/// In KKBOX, we would like to find methods to measure how much does
+/// our app engadge with our users, and active days per week could be
+/// an indicator. However, it looks like most of the popular analytics
+/// platforms such as Firebase and so on do not provide such
+/// information.
+///
+/// Thus, we would like to make active days as "events" on analytics
+/// platforms, for example, "active for one day", "active for two
+/// days" could be events. ActiveDaysPerWeekCounter is a helper class
+/// to let us decide if we should send an event, and which event, to
+/// analytics platforms.
+///
+/// After creating an instance of ActiveDaysPerWeekCounter, you should
+/// ask it to start a session. And then you can get a result when you
+/// commit a new access date to the counter.
+
+public class ActiveDaysPerWeekCounter {
+	private var setingKey: String
+
+	/// Create an instance.
+	///
+	/// - Parameter setingKey: the key for helping storing data.
+	public init(setingKey: String) {
+		self.setingKey = setingKey
+	}
+
+	/// Remove all saved data.
+	public func reset() {
+		self.sessionBeginDate = nil
+		self.lastResult = nil
+		self.lastResultMadeDate = nil
+	}
+
+	public func startNewSessionIfNoExitingOne() -> Bool {
+		if let _ = self.sessionBeginDate {
+			return false
+		}
+		let date = Date()
+		self.startSession(date: date)
+		return true
+	}
+
+	/// Start a new session by a given date, and the base of the
+	/// session of be the start of the week where the given date is
+	/// in.
+	///
+	/// - Parameter date: the date for helping deciding the time base
+	///                   of the session.
+	public func startSession(date: Date) {
+		self.sessionBeginDate = date.weekBeginDay
+		self.lastResult = nil
+		self.lastResultMadeDate = nil
+	}
+
+	public func commit(accessDate: Date) throws -> ActiveDaysCounterResult {
+		guard let beginDate = self.sessionBeginDate else {
+			throw ActiveDaysCounterError.sessionUnstarted
+		}
+		if accessDate.compare(beginDate) == ComparisonResult.orderedAscending {
+			throw ActiveDaysCounterError.invalidDate
+		}
+		if accessDate.timeIntervalSince(beginDate) > 7 * 24 * 60 * 60 {
+			throw ActiveDaysCounterError.needsNewSession
+		}
+
+		guard let lastResultMadeDate = self.lastResultMadeDate,
+		      let lastResult = self.lastResult else {
+			self.lastResultMadeDate = accessDate
+			self.lastResult = 1
+			return .active(1)
+		}
+
+		if accessDate.compare(lastResultMadeDate) == ComparisonResult.orderedAscending {
+			throw ActiveDaysCounterError.invalidDate
+		}
+
+		if lastResultMadeDate.isInSameDay(with: accessDate) {
+			return .noEvent
+		}
+
+		let newResult = lastResult + 1
+		self.lastResult = newResult
+		self.lastResultMadeDate = accessDate
+		return .active(newResult)
+	}
+
+}
+
+
+private extension ActiveDaysPerWeekCounter {
+
+	private var sessionBeginDate: Date? {
+		get {
+			return UserDefaults.standard.object(forKey: setingKey + "-sessionBegin") as? Date
+		}
+		set {
+			guard let newValue = newValue else {
+				UserDefaults.standard.removeObject(forKey: setingKey + "-sessionBegin")
+				return
+			}
+			UserDefaults.standard.set(newValue, forKey: setingKey + "-sessionBegin")
+			UserDefaults.standard.synchronize()
+		}
+	}
+
+	private var lastResult: Int? {
+		get {
+			guard let int = UserDefaults.standard.object(forKey: setingKey + "-lastResult") as? Int else {
+				return nil
+			}
+			return int
+		}
+		set {
+			guard let newValue = newValue else {
+				UserDefaults.standard.removeObject(forKey: setingKey + "-lastResult")
+				return
+			}
+			UserDefaults.standard.set(newValue, forKey: setingKey + "-lastResult")
+			UserDefaults.standard.synchronize()
+		}
+	}
+
+	private var lastResultMadeDate: Date? {
+		get {
+			return UserDefaults.standard.object(forKey: setingKey + "-lastDate") as? Date
+		}
+		set {
+			guard let newValue = newValue else {
+				UserDefaults.standard.removeObject(forKey: setingKey + "-lastDate")
+				return
+			}
+			UserDefaults.standard.set(newValue, forKey: setingKey + "-lastDate")
+			UserDefaults.standard.synchronize()
+		}
+	}
+}
diff --git a/Sources/ActiveDays/DateExtensions.swift b/Sources/ActiveDays/DateExtensions.swift
new file mode 100644
index 0000000..e15f74c
--- /dev/null
+++ b/Sources/ActiveDays/DateExtensions.swift
@@ -0,0 +1,59 @@
+import Foundation
+
+extension Date {
+
+	/// Create a new date instance basing on Gregorian calendar and
+	/// GMT+0 timezone.
+	///
+	/// - Parameters:
+	///   - year: year
+	///   - month: month
+	///   - day: day
+	///   - hour: hour
+	///   - minute: minute
+	///   - second: second
+	/// - Returns: a date instance.
+	public static func from(year: Int, month: Int, day: Int, hour: Int, minute: Int, second: Int) -> Date? {
+		var components = DateComponents()
+		components.year = year
+		components.month = month
+		components.day = day
+		components.hour = hour
+		components.minute = minute
+		components.second = second
+		let gmt0 = TimeZone(secondsFromGMT: 0)!
+		var calendar = Calendar(identifier: .gregorian)
+		calendar.timeZone = gmt0
+		return calendar.date(from: components)
+	}
+
+	/// Return the day of the week where the date is at, basing on
+	/// GMT+-0 timezone.
+	public var weekBeginDay: Date? {
+		let gmt0 = TimeZone(secondsFromGMT: 0)!
+		var calendar = Calendar(identifier: .gregorian)
+		calendar.timeZone = gmt0
+		var components = calendar.dateComponents(in: gmt0, from: self)
+		components.hour = 0
+		components.minute = 0
+		components.second = 0
+		components.nanosecond = 0
+		components.day = components.day! - components.weekdayOrdinal!
+		components.weekdayOrdinal = 0
+		return calendar.date(from: components)
+	}
+
+	/// If the date and another date is in the same date.
+	public func isInSameDay(with date: Date) -> Bool {
+		let gmt0 = TimeZone(secondsFromGMT: 0)!
+		var calendar = Calendar(identifier: .gregorian)
+		calendar.timeZone = gmt0
+
+		let selfComponents = calendar.dateComponents(in: gmt0, from: self)
+		let incomingComponents = calendar.dateComponents(in: gmt0, from: date)
+		return selfComponents.year == incomingComponents.year &&
+				selfComponents.month == incomingComponents.month &&
+				selfComponents.day == incomingComponents.day
+	}
+
+}
diff --git a/Tests/ActiveDaysTests/ActiveDaysTests.swift b/Tests/ActiveDaysTests/ActiveDaysTests.swift
new file mode 100644
index 0000000..22fd4a9
--- /dev/null
+++ b/Tests/ActiveDaysTests/ActiveDaysTests.swift
@@ -0,0 +1,105 @@
+import XCTest
+@testable import ActiveDays
+
+final class ActiveDaysTests: XCTestCase {
+	var counter: ActiveDaysPerWeekCounter!
+
+	override func setUp() {
+		self.counter = ActiveDaysPerWeekCounter(setingKey: "com.kkbox.activedays")
+		self.counter.reset()
+	}
+
+	override func tearDown() {
+		self.counter.reset()
+		self.counter = nil
+	}
+
+	func testStartSession() {
+		XCTAssertTrue(self.counter.startNewSessionIfNoExitingOne())
+		XCTAssertFalse(self.counter.startNewSessionIfNoExitingOne())
+	}
+
+	func testUnstartedSession() {
+		do {
+			_ = try self.counter.commit(accessDate: Date())
+			XCTFail()
+		} catch {
+			XCTAssertNotNil(error)
+		}
+	}
+
+	func testOldDate() {
+		self.counter.startSession(date: Date.from(year: 2018, month: 5, day: 9, hour: 1, minute: 2, second: 3)!)
+		do {
+			_ = try self.counter.commit(accessDate: Date.from(year: 2018, month: 4, day: 15, hour: 1, minute: 2, second: 3)!)
+			XCTFail()
+		} catch ActiveDaysCounterError.invalidDate {
+		} catch {
+			XCTFail()
+		}
+	}
+
+	func testNeedNewSession() {
+		self.counter.startSession(date: Date.from(year: 2018, month: 5, day: 9, hour: 1, minute: 2, second: 3)!)
+		do {
+			_ = try self.counter.commit(accessDate: Date.from(year: 2018, month: 6, day: 15, hour: 1, minute: 2, second: 3)!)
+			XCTFail()
+		} catch ActiveDaysCounterError.needsNewSession {
+		} catch {
+			XCTFail()
+		}
+	}
+
+	func testCommit() {
+		self.counter.startSession(date: Date.from(year: 2018, month: 5, day: 9, hour: 1, minute: 2, second: 3)!)
+		var result = try! self.counter.commit(accessDate: Date.from(year: 2018, month: 5, day: 9, hour: 1, minute: 2, second: 3)!)
+		if case let .active(days) = result {
+			XCTAssertTrue(days == 1)
+		} else {
+			XCTFail()
+		}
+		result = try! self.counter.commit(accessDate: Date.from(year: 2018, month: 5, day: 9, hour: 2, minute: 2, second: 3)!)
+		if case .noEvent = result {
+		} else {
+			XCTFail()
+		}
+
+		result = try! self.counter.commit(accessDate: Date.from(year: 2018, month: 5, day: 11, hour: 2, minute: 2, second: 3)!)
+		if case let .active(days) = result {
+			XCTAssertTrue(days == 2)
+		} else {
+			XCTFail()
+		}
+
+		result = try! self.counter.commit(accessDate: Date.from(year: 2018, month: 5, day: 11, hour: 8, minute: 2, second: 3)!)
+		if case .noEvent = result {
+		} else {
+			XCTFail()
+		}
+
+
+		do {
+			_ = try self.counter.commit(accessDate: Date.from(year: 2018, month: 5, day: 9, hour: 1, minute: 2, second: 3)!)
+			XCTFail()
+		} catch ActiveDaysCounterError.invalidDate {
+		} catch {
+			XCTFail()
+		}
+
+		result = try! self.counter.commit(accessDate: Date.from(year: 2018, month: 5, day: 13, hour: 2, minute: 2, second: 3)!)
+		if case let .active(days) = result {
+			XCTAssertTrue(days == 3)
+		} else {
+			XCTFail()
+		}
+
+		do {
+			_ = try self.counter.commit(accessDate: Date.from(year: 2018, month: 5, day: 14, hour: 1, minute: 2, second: 3)!)
+			XCTFail()
+		} catch ActiveDaysCounterError.needsNewSession {
+		} catch {
+			XCTFail()
+		}
+	}
+
+}
diff --git a/Tests/ActiveDaysTests/DateExtensionTest.swift b/Tests/ActiveDaysTests/DateExtensionTest.swift
new file mode 100644
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--- /dev/null
+++ b/Tests/ActiveDaysTests/DateExtensionTest.swift
@@ -0,0 +1,56 @@
+import XCTest
+@testable import ActiveDays
+
+class DateExtensionTest: XCTestCase {
+
+	func testBeginOfTheWeek1() {
+		guard let date = Date.from(year: 2018, month: 5, day: 9, hour: 16, minute: 4, second: 0),
+		      let begin = date.weekBeginDay else {
+			return
+		}
+		let gmt0 = TimeZone(secondsFromGMT: 0)!
+		let calendar = Calendar(identifier: .gregorian)
+		let components = calendar.dateComponents(in: gmt0, from: begin)
+		XCTAssertTrue(components.year == 2018)
+		XCTAssertTrue(components.month == 5)
+		XCTAssertTrue(components.day == 7)
+		XCTAssertTrue(components.hour == 0)
+		XCTAssertTrue(components.second == 0)
+		XCTAssertTrue(components.minute == 0)
+	}
+
+	func testBeginOfTheWeek2() {
+		guard let date = Date.from(year: 2018, month: 5, day: 25, hour: 16, minute: 4, second: 0),
+		      let begin = date.weekBeginDay else {
+			return
+		}
+		let gmt0 = TimeZone(secondsFromGMT: 0)!
+		let calendar = Calendar(identifier: .gregorian)
+		let components = calendar.dateComponents(in: gmt0, from: begin)
+		XCTAssertTrue(components.year == 2018)
+		XCTAssertTrue(components.month == 5)
+		XCTAssertTrue(components.day == 21)
+		XCTAssertTrue(components.hour == 0)
+		XCTAssertTrue(components.second == 0)
+		XCTAssertTrue(components.minute == 0)
+	}
+
+	func testIsSameDay() {
+		guard let date1 = Date.from(year: 2018, month: 5, day: 25, hour: 16, minute: 4, second: 0),
+		      let date2 = Date.from(year: 2018, month: 5, day: 25, hour: 17, minute: 4, second: 0) else {
+			return
+		}
+		XCTAssertTrue(date1.isInSameDay(with: date2))
+	}
+
+	func testIsNotSameDay() {
+		guard let date1 = Date.from(year: 2018, month: 5, day: 25, hour: 16, minute: 4, second: 0),
+		      let date2 = Date.from(year: 2017, month: 5, day: 25, hour: 17, minute: 4, second: 0) else {
+			return
+		}
+		XCTAssertFalse(date1.isInSameDay(with: date2))
+
+	}
+
+
+}
diff --git a/Tests/ActiveDaysTests/XCTestManifests.swift b/Tests/ActiveDaysTests/XCTestManifests.swift
new file mode 100644
index 0000000..8355395
--- /dev/null
+++ b/Tests/ActiveDaysTests/XCTestManifests.swift
@@ -0,0 +1,9 @@
+import XCTest
+
+#if !os(macOS)
+public func allTests() -> [XCTestCaseEntry] {
+	return [
+		testCase(ActiveDaysTests.allTests),
+	]
+}
+#endif
diff --git a/Tests/LinuxMain.swift b/Tests/LinuxMain.swift
new file mode 100644
index 0000000..44d8b6c
--- /dev/null
+++ b/Tests/LinuxMain.swift
@@ -0,0 +1,7 @@
+import XCTest
+
+import ActiveDaysTests
+
+var tests = [XCTestCaseEntry]()
+tests += ActiveDaysTests.allTests()
+XCTMain(tests)
\ No newline at end of file