/*
Copyright 2022 Splunk Inc.

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 Foundation

class BandwidthTracker {
    private let maxSamples: Int
    private let timeWindowNanos: UInt64
    private var samples: [(Int, UInt64)] = []

    init(timeWindowMillis: UInt64 = 30_000, maxSamples: Int = 60) {
        self.maxSamples = maxSamples
        self.timeWindowNanos = timeWindowMillis * 1_000_000
    }

    func add(bytes: Int, timeNanos: UInt64) {
        if samples.count >= maxSamples {
            samples.removeFirst()
        }

        samples.append((bytes, timeNanos))
    }

    /// Returns bandwidth in KiB/s
    func bandwidth(timeNanosNow: UInt64) -> Double {
        let samplesInWindow = samples.filter { (_, ts) in
            timeNanosNow >= ts && timeNanosNow - ts <= timeWindowNanos
        }

        if samplesInWindow.isEmpty {
            return 0.0
        }

        let transferredBytes = samplesInWindow.reduce(0, { total, sample in
            let (bytes, _) = sample
            return total + bytes
        })

        let beginTime = timeNanosNow >= timeWindowNanos ? timeNanosNow - timeWindowNanos : 0
        let intervalSeconds = Double(timeNanosNow - beginTime) / 1e9
        return Double(transferredBytes) / 1024.0 / intervalSeconds
    }
}