import type { SynclinkTask } from "./task";

export const createEndpoint = Symbol("Synclink.endpoint");
export const releaseProxy = Symbol("Synclink.releaseProxy");
export const proxyMarker = Symbol("Synclink.proxy");

/**
 * Interface of values that were marked to be proxied with `synclink.proxy()`.
 * Can also be implemented by classes.
 */
export interface ProxyMarked {
  [proxyMarker]: true;
}

/**
 * Takes a type and wraps it in a Promise, if it not already is one.
 * This is to avoid `Promise<Promise<T>>`.
 *
 * This is the inverse of `Unpromisify<T>`.
 */
type Promisify<T> = T extends Promise<unknown> ? T : Promise<T>;
/**
 * Takes a type that may be Promise and unwraps the Promise type.
 * If `P` is not a Promise, it returns `P`.
 *
 * This is the inverse of `Promisify<T>`.
 */
type Unpromisify<P> = P extends Promise<infer T> ? T : P;

/**
 * Takes the raw type of a remote property and returns the type that is visible to the local thread on the proxy.
 *
 * Note: This needs to be its own type alias, otherwise it will not distribute over unions.
 * See https://www.typescriptlang.org/docs/handbook/2/conditional-types.html#distributive-conditional-types
 */
type RemoteProperty<T> =
  // If the value is a method, synclink will proxy it automatically.
  // Objects are only proxied if they are marked to be proxied.
  // Otherwise, the property is converted to a Promise that resolves the cloned value.
  T extends Function | ProxyMarked ? Remote<T> : SynclinkTask<T>;

/**
 * Takes the raw type of a property as a remote thread would see it through a proxy (e.g. when passed in as a function
 * argument) and returns the type that the local thread has to supply.
 *
 * This is the inverse of `RemoteProperty<T>`.
 *
 * Note: This needs to be its own type alias, otherwise it will not distribute over unions. See
 * https://www.typescriptlang.org/docs/handbook/advanced-types.html#distributive-conditional-types
 */
type LocalProperty<T> = T extends Function | ProxyMarked ? Local<T> : UnTask<T>;

/**
 * Proxies `T` if it is a `ProxyMarked`, clones it otherwise (as handled by structured cloning and transfer handlers).
 */
export type ProxyOrClone<T> = T extends ProxyMarked ? Remote<T> : T;
/**
 * Inverse of `ProxyOrClone<T>`.
 */
export type UnproxyOrClone<T> = T extends RemoteObject<ProxyMarked>
  ? Local<T>
  : T;

/**
 * Takes the raw type of a remote object in the other thread and returns the type as it is visible to the local thread
 * when proxied with `Synclink.proxy()`.
 *
 * This does not handle call signatures, which is handled by the more general `Remote<T>` type.
 *
 * @template T The raw type of a remote object as seen in the other thread.
 */
export type RemoteObject<T> = { [P in keyof T]: RemoteProperty<T[P]> };
/**
 * Takes the type of an object as a remote thread would see it through a proxy (e.g. when passed in as a function
 * argument) and returns the type that the local thread has to supply.
 *
 * This does not handle call signatures, which is handled by the more general `Local<T>` type.
 *
 * This is the inverse of `RemoteObject<T>`.
 *
 * @template T The type of a proxied object.
 */
export type LocalObject<T> = { [P in keyof T]: LocalProperty<T[P]> };

/**
 * Additional special synclink methods available on each proxy returned by `Synclink.wrap()`.
 */
export interface ProxyMethods {
  [createEndpoint]: () => Promise<MessagePort>;
  [releaseProxy]: () => SynclinkTask<void>;
}

type UnTask<T> = T extends SynclinkTask<infer S> ? S : T;
type MaybePromise<T> = Promise<T> | T;

/**
 * Takes the raw type of a remote object, function or class in the other thread and returns the type as it is visible to
 * the local thread from the proxy return value of `Synclink.wrap()` or `Synclink.proxy()`.
 */
export type Remote<T> =
  // Handle properties
  RemoteObject<T> &
    // Handle call signature (if present)
    (T extends (...args: infer TArguments) => infer TReturn
      ? (
          ...args: { [I in keyof TArguments]: UnproxyOrClone<TArguments[I]> }
        ) => SynclinkTask<ProxyOrClone<Unpromisify<TReturn>>>
      : unknown) &
    // Handle construct signature (if present)
    // The return of construct signatures is always proxied (whether marked or not)
    (T extends { new (...args: infer TArguments): infer TInstance }
      ? {
          new (
            ...args: {
              [I in keyof TArguments]: UnproxyOrClone<TArguments[I]>;
            }
          ): SynclinkTask<Remote<TInstance>>;
        }
      : unknown) &
    // Include additional special synclink methods available on the proxy.
    ProxyMethods;

/**
 * Takes the raw type of a remote object, function or class as a remote thread would see it through a proxy (e.g. when
 * passed in as a function argument) and returns the type the local thread has to supply.
 *
 * This is the inverse of `Remote<T>`. It takes a `Remote<T>` and returns its original input `T`.
 */
export type Local<T> =
  // Omit the special proxy methods (they don't need to be supplied, synclink adds them)
  Omit<LocalObject<T>, keyof ProxyMethods> &
    // Handle call signatures (if present)
    (T extends (...args: infer TArguments) => infer TReturn
      ? (
          ...args: { [I in keyof TArguments]: ProxyOrClone<TArguments[I]> }
        ) => // The raw function could either be sync or async, but is always proxied automatically
        MaybePromise<UnproxyOrClone<UnTask<TReturn>>>
      : unknown) &
    // Handle construct signature (if present)
    // The return of construct signatures is always proxied (whether marked or not)
    (T extends { new (...args: infer TArguments): infer TInstance }
      ? {
          new (
            ...args: {
              [I in keyof TArguments]: ProxyOrClone<TArguments[I]>;
            }
          ): // The raw constructor could either be sync or async, but is always proxied automatically
          MaybePromise<Local<UnTask<TInstance>>>;
        }
      : unknown);