From b59ed0b70f86c0dc1496c3145fa114bc38965f51 Mon Sep 17 00:00:00 2001
From: Nick Bourdakos <bourdakos@google.com>
Date: Tue, 21 Feb 2023 08:00:31 -0800
Subject: [PATCH] Add Apple implementation for timer

PiperOrigin-RevId: 511201457
---
 .../platform/implementation/apple/platform.mm |  1 -
 .../platform/implementation/apple/timer.h     |  8 ++-
 .../platform/implementation/apple/timer.mm    | 63 ++++++++++++++++++-
 3 files changed, 67 insertions(+), 5 deletions(-)

diff --git a/internal/platform/implementation/apple/platform.mm b/internal/platform/implementation/apple/platform.mm
index 2e442403..bc038d6a 100644
--- a/internal/platform/implementation/apple/platform.mm
+++ b/internal/platform/implementation/apple/platform.mm
@@ -224,7 +224,6 @@ absl::StatusOr<WebResponse> ImplementationPlatform::SendRequest(const WebRequest
   return webResponse;
 }
 
-// TODO(b/261511529): Add implementation.
 std::unique_ptr<Timer> ImplementationPlatform::CreateTimer() {
   return std::make_unique<apple::Timer>();
 }
diff --git a/internal/platform/implementation/apple/timer.h b/internal/platform/implementation/apple/timer.h
index 068629f5..26090e84 100644
--- a/internal/platform/implementation/apple/timer.h
+++ b/internal/platform/implementation/apple/timer.h
@@ -15,6 +15,8 @@
 #ifndef PLATFORM_IMPL_APPLE_TIMER_H_
 #define PLATFORM_IMPL_APPLE_TIMER_H_
 
+#import <Foundation/Foundation.h>
+
 #include <utility>
 
 #include "internal/platform/implementation/timer.h"
@@ -25,7 +27,7 @@ namespace apple {
 class Timer : public api::Timer {
  public:
   Timer() = default;
-  ~Timer() override = default;
+  ~Timer() override;
 
   bool Create(int delay, int interval,
               absl::AnyInvocable<void()> callback) override;
@@ -33,6 +35,10 @@ class Timer : public api::Timer {
   bool Stop() override;
 
   bool FireNow() override;
+
+ private:
+  absl::AnyInvocable<void()> callback_;
+  dispatch_source_t timer_;
 };
 
 }  // namespace apple
diff --git a/internal/platform/implementation/apple/timer.mm b/internal/platform/implementation/apple/timer.mm
index 252f063d..7ea292e7 100644
--- a/internal/platform/implementation/apple/timer.mm
+++ b/internal/platform/implementation/apple/timer.mm
@@ -17,15 +17,72 @@
 #include <utility>
 
 #include "internal/platform/implementation/timer.h"
+#import "GoogleToolboxForMac/GTMLogger.h"
+
+// The leeway parameter is a hint from the application as to the amount of time, in nanoseconds, up
+// to which the system can defer the timer to align with other system activity for improved system
+// performance or power consumption. For example, an application might perform a periodic task every
+// 5 minutes, with a leeway of up to 30 seconds. Note that some latency is to be expected for all
+// timers, even when a leeway value of zero is specified.
+uint64_t const GNCTimerLeewayInNanoseconds = 0;
 
 namespace nearby {
 namespace apple {
 
-bool Timer::Create(int delay, int interval, absl::AnyInvocable<void()> callback) { return true; }
+Timer::~Timer() { Stop(); }
 
-bool Timer::Stop() { return true; }
+bool Timer::Create(int delay, int interval, absl::AnyInvocable<void()> callback) {
+  if (delay < 0 || interval < 0) {
+    GTMLoggerError(@"Delay and interval must be positive or zero.");
+    return false;
+  }
 
-bool Timer::FireNow() { return true; }
+  if (timer_ != nil) {
+    GTMLoggerError(@"Timer has already started.");
+    return false;
+  }
+
+  uint64_t delayInNanoseconds = delay * NSEC_PER_MSEC;
+  // If `interval` is 0, it means we only want the timer to fire once. We map this to
+  // `DISPATCH_TIME_FOREVER` to have this effect.
+  uint64_t intervalInNanoseconds = interval == 0 ? DISPATCH_TIME_FOREVER : interval * NSEC_PER_MSEC;
+  callback_ = std::move(callback);
+
+  timer_ = dispatch_source_create(DISPATCH_SOURCE_TYPE_TIMER, /*handle=*/0, /*mask=*/0,
+                                  dispatch_get_main_queue());
+
+  dispatch_source_set_event_handler(timer_, ^{
+    if (callback_ != nil) {
+      callback_();
+    }
+    // If our interval is `DISPATCH_TIME_FOREVER`, it means we only want the timer to fire once.
+    if (intervalInNanoseconds == DISPATCH_TIME_FOREVER) {
+      Stop();
+    }
+  });
+
+  dispatch_source_set_timer(timer_, dispatch_time(DISPATCH_TIME_NOW, delayInNanoseconds),
+                            intervalInNanoseconds, GNCTimerLeewayInNanoseconds);
+  dispatch_resume(timer_);
+  return true;
+}
+
+bool Timer::Stop() {
+  if (timer_ != nil) {
+    dispatch_source_cancel(timer_);
+  }
+  timer_ = nil;
+  callback_ = nil;
+  return true;
+}
+
+bool Timer::FireNow() {
+  if (callback_ != nil) {
+    callback_();
+    return true;
+  }
+  return false;
+}
 
 }  // namespace apple
 }  // namespace nearby