import Foundation
import JavaScriptCore

private let contextLock = NSRecursiveLock()

final class JavaScriptWorker {
    private let processQueue = DispatchQueue(label: "DispatchQueue.JavaScriptWorker")
    private let virtualMachine: JSVirtualMachine
    @SyncAccess(lock: contextLock) private var commonContext: JSContext? = nil

    init() {
        virtualMachine = processQueue.sync { JSVirtualMachine()! }
    }

    private func createContext() -> JSContext {
        let context = JSContext(virtualMachine: virtualMachine)!
        context.exceptionHandler = { _, exception in
            if let error = exception?.toString() {
                print(error)
            }
        }
        return context
    }

    @discardableResult func evaluate(script: Script) -> JSValue! {
        evaluate(string: script.body)
    }

    private func evaluate(string: String) -> JSValue! {
        let ctx = commonContext ?? createContext()
        return ctx.evaluateScript(string)
    }

    private func json(for string: String) -> JSON {
        evaluate(string: "JSON.stringify(\(string));")!.toString()!
    }

    func call(function: String, with arguments: [JSON]) -> JSON {
        let joined = arguments.map(\.string).joined(separator: ",")
        return json(for: "\(function)(\(joined))")
    }

    func inCommonContext<Value>(execute: (JavaScriptWorker) -> Value) -> Value {
        commonContext = createContext()
        defer {
            commonContext = nil
        }
        return execute(self)
    }
}