/*
 * Copyright 2024, gRPC Authors All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import GRPCCore
import GRPCNIOTransportCore
import NIOCore
import NIOEmbedded
import Synchronization
import XCTest

@available(gRPCSwiftNIOTransport 2.0, *)
internal final class TimerTests: XCTestCase {
  fileprivate struct CounterTimerHandler: NIOScheduledCallbackHandler {
    let counter = AtomicCounter(0)

    func handleScheduledCallback(eventLoop: some EventLoop) {
      counter.increment()
    }
  }

  func testOneOffTimer() {
    let loop = EmbeddedEventLoop()
    defer { try! loop.close() }

    let handler = CounterTimerHandler()
    let timer = Timer(eventLoop: loop, duration: .seconds(1), repeating: false, handler: handler)
    timer.start()

    // Timer hasn't fired because we haven't reached the required duration.
    loop.advanceTime(by: .milliseconds(999))
    XCTAssertEqual(handler.counter.value, 0)

    // Timer has fired once.
    loop.advanceTime(by: .milliseconds(1))
    XCTAssertEqual(handler.counter.value, 1)

    // Timer does not repeat.
    loop.advanceTime(by: .seconds(1))
    XCTAssertEqual(handler.counter.value, 1)

    // Timer can be restarted and then fires again after the duration.
    timer.start()
    loop.advanceTime(by: .seconds(1))
    XCTAssertEqual(handler.counter.value, 2)

    // Timer can be cancelled before the duration and then does not fire.
    timer.start()
    loop.advanceTime(by: .milliseconds(999))
    timer.cancel()
    loop.advanceTime(by: .milliseconds(1))
    XCTAssertEqual(handler.counter.value, 2)

    // Timer can be restarted after being cancelled.
    timer.start()
    loop.advanceTime(by: .seconds(1))
    XCTAssertEqual(handler.counter.value, 3)
  }

  func testRepeatedTimer() {
    let loop = EmbeddedEventLoop()
    defer { try! loop.close() }

    let handler = CounterTimerHandler()
    let timer = Timer(eventLoop: loop, duration: .seconds(1), repeating: true, handler: handler)
    timer.start()

    // Timer hasn't fired because we haven't reached the required duration.
    loop.advanceTime(by: .milliseconds(999))
    XCTAssertEqual(handler.counter.value, 0)

    // Timer has fired once.
    loop.advanceTime(by: .milliseconds(1))
    XCTAssertEqual(handler.counter.value, 1)

    // Timer hasn't fired again because we haven't reached the required duration again.
    loop.advanceTime(by: .milliseconds(999))
    XCTAssertEqual(handler.counter.value, 1)

    // Timer has fired again.
    loop.advanceTime(by: .milliseconds(1))
    XCTAssertEqual(handler.counter.value, 2)

    // Timer continues to fire on each second.
    loop.advanceTime(by: .seconds(1))
    XCTAssertEqual(handler.counter.value, 3)
    loop.advanceTime(by: .seconds(1))
    XCTAssertEqual(handler.counter.value, 4)
    loop.advanceTime(by: .seconds(1))
    XCTAssertEqual(handler.counter.value, 5)
    loop.advanceTime(by: .seconds(5))
    XCTAssertEqual(handler.counter.value, 10)

    // Timer does not fire again, after being cancelled.
    timer.cancel()
    loop.advanceTime(by: .seconds(5))
    XCTAssertEqual(handler.counter.value, 10)

    // Timer can be restarted after being cancelled and continues to fire once per second.
    timer.start()
    loop.advanceTime(by: .seconds(5))
    XCTAssertEqual(handler.counter.value, 15)
  }
}