Add Timer library

Author: Vladislav Alekseev

.gitignore

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+.DS_Store
+/.build
+/Packages
+/*.xcodeproj

Makefile

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+generate: 
+	swift package generate-xcodeproj --xcconfig-overrides Package.xcconfig --enable-code-coverage
+.PHONY: generate
+
+open: generate
+	open *.xcodeproj
+.PHONY: open
+
+clean:
+	rm -rf .build/
+.PHONY: clean
+
+build:
+	swift build -Xswiftc "-target" -Xswiftc "x86_64-apple-macosx10.13" --static-swift-stdlib
+
+run:
+	swift run -Xswiftc "-target" -Xswiftc "x86_64-apple-macosx10.13" --static-swift-stdlib
+
+test:
+	swift test -Xswiftc "-target" -Xswiftc "x86_64-apple-macosx10.13" --parallel

Package.swift

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+// swift-tools-version:4.2
+
+import PackageDescription
+
+let package = Package(
+    name: "AvitoSharedUtils",
+    products: [
+        .library(
+            name: "Timer",
+            targets: [
+                "Timer"
+            ]
+        )
+    ],
+    dependencies: [],
+    targets: [
+        .target(
+            // MARK: Timer
+            name: "Timer",
+            dependencies: [
+            ]
+        ),
+    ]
+)

Package.xcconfig

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+MACOSX_DEPLOYMENT_TARGET=10.13
+SUPPORTED_PLATFORMS=macosx

README.md

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-ios-shared-utils
+# Avito Shared Utils
+
+Swift package that provides some basic shareable utility classes.
+
+## Developing
+
+- `make open` to generate Xcode project and open it in Xcode
+- `make test` to run all unit tests using SPM
+- `make build` to build all products using SPM
+
+## Timer
+
+A GCD-based timer.
+
+```swift
+let timer = DispatchBasedTimer.startedTimer(repeating: .seconds(1), leeway: .seconds(1)) { [weak self] timer in
+    guard let strongSelf = self else {
+        timer.stop()
+        return
+    }
+    strongSelf.handleTimerTick()
+}
+```
+

Sources/Timer/DispatchBasedTimer.swift

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+import Dispatch
+import Foundation
+
+public final class DispatchBasedTimer {
+    private var timer: DispatchSourceTimer?
+    private let queue = DispatchQueue(label: "DispatchBasedTimer.queue")
+    private let deadline: DispatchTime
+    private let repeating: DispatchTimeInterval
+    private let leeway: DispatchTimeInterval
+
+    public init(deadline: DispatchTime = .now(), repeating: DispatchTimeInterval, leeway: DispatchTimeInterval) {
+        self.deadline = deadline
+        self.repeating = repeating
+        self.leeway = leeway
+    }
+    
+    public static func startedTimer(
+        deadline: DispatchTime = .now(),
+        repeating: DispatchTimeInterval,
+        leeway: DispatchTimeInterval,
+        handler: @escaping (DispatchBasedTimer) -> ())
+        -> DispatchBasedTimer
+    {
+        let timer = DispatchBasedTimer(deadline: deadline, repeating: repeating, leeway: leeway)
+        timer.start(handler: handler)
+        return timer
+    }
+    
+    deinit {
+        stop()
+    }
+    
+    public func start(handler: @escaping (DispatchBasedTimer) -> ()) {
+        stop()
+        
+        let timer = DispatchSource.makeTimerSource(queue: queue)
+        timer.schedule(deadline: deadline, repeating: repeating, leeway: leeway)
+        timer.setEventHandler(handler: { handler(self) })
+        timer.resume()
+        self.timer = timer
+    }
+    
+    public func stop() {
+        timer?.cancel()
+        timer?.setEventHandler(handler: nil)
+    }
+    
+    public func pause() {
+        timer?.suspend()
+    }
+    
+    public func resume() {
+        timer?.resume()
+    }
+}