RateLimit.swift

import Foundation

private let log = Log(topic: .rateLimit)

/// Timeout based rate limit helper class.
final class RateLimit {

    // MARK: - Private

    private let timeout: TimeInterval
    private var lastExecutionTimestamp: Date?

    // MARK: - Public

    init(timeout: TimeInterval) {
        self.timeout = timeout
    }

    /// Calls the passed in block in case the timeout
    /// is reached since the last call to this method.
    ///
    /// - Parameter block: The block that should be executed.
    /// - Returns: Whether the timeout has been reached and the block was called.
    @discardableResult
    func perform(_ block: () -> Void) -> Bool {
        if let lastTimestamp = lastExecutionTimestamp {
            let timeoutDiff = abs(lastTimestamp.timeIntervalSinceNow) - timeout
            log.info("Difference until timeout: \(timeoutDiff)")
            if timeoutDiff < 0 {
                log.info("Skipping perform, timeout not reached.")
                return false
            } else {
                lastExecutionTimestamp = Date()
                block()
                log.info("Timeout reached, updating timestamp.")
                return true
            }
        } else {
            lastExecutionTimestamp = Date()
            block()
            log.info("First execution, storing initial timestamp.")
            return true
        }
    }

}