//
//  RetryPolicy.swift
//  Zyquo Router
//
//  Author: Simon-Pierre Boucher
//  Mail: contact@spboucher.ai
//
//  Exponential backoff with jitter for transient upstream failures (429/5xx,
//  timeouts). Never retries once the first streamed byte has been forwarded
//  to the client — enforced by the caller in Phase 3's UpstreamCall path.
//

import Foundation

struct RetryPolicy: Sendable {
    var maxAttempts = 3
    var baseDelay: TimeInterval = 0.5
    var maxDelay: TimeInterval = 8.0

    /// Whether a failed attempt with this upstream status is worth retrying.
    func shouldRetry(status: Int, attempt: Int) -> Bool {
        guard attempt < maxAttempts else { return false }
        return status == 429 || (500...599).contains(status)
    }

    /// Full-jitter exponential backoff; honors an upstream Retry-After when given.
    func delay(attempt: Int, retryAfter: TimeInterval? = nil) -> TimeInterval {
        if let retryAfter, retryAfter > 0 {
            return min(retryAfter, maxDelay)
        }
        let exponential = min(baseDelay * pow(2, Double(attempt - 1)), maxDelay)
        return Double.random(in: 0...exponential)
    }
}