swiftapp/swift/Sources/App/AppControlService.swift

import Foundation

protocol AppControlServicing {
    func commands() -> AsyncStream<AppNavigationCommand>
}

struct MockBackendControlService: AppControlServicing {
    static let controlFileEnvironmentKey = "SOCIALIO_CONTROL_FILE"
    static let pollingIntervalEnvironmentKey = "SOCIALIO_CONTROL_POLL_MS"

    private let environment: [String: String]

    init(environment: [String: String] = ProcessInfo.processInfo.environment) {
        self.environment = environment
    }

    func commands() -> AsyncStream<AppNavigationCommand> {
        guard let controlFilePath = environment[Self.controlFileEnvironmentKey]?
            .trimmingCharacters(in: .whitespacesAndNewlines),
            !controlFilePath.isEmpty else {
            return AsyncStream { continuation in
                continuation.finish()
            }
        }

        let controlFileURL = URL(fileURLWithPath: controlFilePath)
        let pollingInterval = pollingIntervalDuration

        return AsyncStream { continuation in
            let task = Task.detached(priority: .background) {
                var lastAppliedPayload: String?

                while !Task.isCancelled {
                    if let payload = try? String(contentsOf: controlFileURL, encoding: .utf8) {
                        let trimmedPayload = payload.trimmingCharacters(in: .whitespacesAndNewlines)

                        if !trimmedPayload.isEmpty,
                           trimmedPayload != lastAppliedPayload,
                           let command = AppNavigationCommand.parse(trimmedPayload) {
                            lastAppliedPayload = trimmedPayload
                            continuation.yield(command)
                        }
                    }

                    try? await Task.sleep(for: pollingInterval)
                }

                continuation.finish()
            }

            continuation.onTermination = { _ in
                task.cancel()
            }
        }
    }

    private var pollingIntervalDuration: Duration {
        guard let rawValue = environment[Self.pollingIntervalEnvironmentKey],
              let milliseconds = Int(rawValue),
              milliseconds > 0 else {
            return .milliseconds(600)
        }

        return .milliseconds(milliseconds)
    }
}