import { Exception, ensureErrorOrException, IDisposable } from "./Util.ts";

export interface AsyncReplyChannel<Reply> {
  reply(value: Reply): void
}

export type Continuation<T> = (x: T) => void;

export type Continuations<T> = [
  Continuation<T>,
  Continuation<Exception>,
  Continuation<OperationCanceledException>
];

export class CancellationToken implements IDisposable {
  private _id: number;
  private _cancelled: boolean;
  private _listeners: Map<number, () => void>;
  constructor(cancelled = false) {
    this._id = 0;
    this._cancelled = cancelled;
    this._listeners = new Map();
  }
  get isCancelled() {
    return this._cancelled;
  }
  public cancel() {
    if (!this._cancelled) {
      this._cancelled = true;
      for (const [, listener] of this._listeners) {
        listener();
      }
    }
  }
  public addListener(f: () => void) {
    const id = this._id;
    this._listeners.set(this._id++, f);
    return id;
  }
  public removeListener(id: number) {
    return this._listeners.delete(id);
  }
  public register(f: (state?: any) => void, state?: any) {
    const $ = this;
    const id = this.addListener(state == null ? f : () => f(state));
    return { Dispose() { $.removeListener(id); } };
  }
  public Dispose() {
    // Implement IDisposable for compatibility but do nothing
    // According to docs, calling Dispose does not trigger cancellation
    // https://docs.microsoft.com/en-us/dotnet/api/system.threading.cancellationtokensource.dispose?view=net-6.0
  }
}

export class OperationCanceledException extends Exception {
  constructor(msg?: string) {
    super(msg ?? "The operation was canceled");
    // Object.setPrototypeOf(this, OperationCanceledException.prototype);
  }
}

export class Trampoline {
  static get maxTrampolineCallCount() {
    return 2000;
  }
  private callCount: number;
  constructor() {
    this.callCount = 0;
  }
  public incrementAndCheck() {
    return this.callCount++ > Trampoline.maxTrampolineCallCount;
  }
  public hijack(f: () => void) {
    this.callCount = 0;
    setTimeout(f, 0);
  }
}

export interface IAsyncContext<T> {
  onSuccess: Continuation<T>;
  onError: Continuation<Exception>;
  onCancel: Continuation<OperationCanceledException>;

  cancelToken: CancellationToken;
  trampoline: Trampoline;
}

export type Async<T> = (x: IAsyncContext<T>) => void;

export function protectedCont<T>(f: Async<T>) {
  return (ctx: IAsyncContext<T>) => {
    if (ctx.cancelToken.isCancelled) {
      ctx.onCancel(new OperationCanceledException());
    } else if (ctx.trampoline.incrementAndCheck()) {
      ctx.trampoline.hijack(() => {
        try {
          f(ctx);
        } catch (err) {
          ctx.onError(ensureErrorOrException(err));
        }
      });
    } else {
      try {
        f(ctx);
      } catch (err) {
        ctx.onError(ensureErrorOrException(err));
      }
    }
  };
}

export function protectedBind<T, U>(computation: Async<T>, binder: (x: T) => Async<U>) {
  return protectedCont((ctx: IAsyncContext<U>) => {
    computation({
      onSuccess: (x: T) => {
        try {
          binder(x)(ctx);
        } catch (err) {
          ctx.onError(ensureErrorOrException(err));
        }
      },
      onError: ctx.onError,
      onCancel: ctx.onCancel,
      cancelToken: ctx.cancelToken,
      trampoline: ctx.trampoline,
    });
  });
}

export function protectedReturn<T>(value: T) {
  return protectedCont((ctx: IAsyncContext<T>) => ctx.onSuccess(value));
}

export class AsyncBuilder {
  public Bind<T, U>(computation: Async<T>, binder: (x: T) => Async<U>) {
    return protectedBind(computation, binder);
  }

  public Combine<T>(computation1: Async<void>, computation2: Async<T>) {
    return this.Bind(computation1, () => computation2);
  }

  public Delay<T>(generator: () => Async<T>) {
    return protectedCont((ctx: IAsyncContext<T>) => generator()(ctx));
  }

  public For<T>(sequence: Iterable<T>, body: (x: T) => Async<void>) {
    const iter = sequence[Symbol.iterator]();
    let cur = iter.next();
    return this.While(() => !cur.done, this.Delay(() => {
      const res = body(cur.value);
      cur = iter.next();
      return res;
    }));
  }

  public Return<T>(value: T) {
    return protectedReturn(value);
  }

  public ReturnFrom<T>(computation: Async<T>) {
    return computation;
  }

  public TryFinally<T>(computation: Async<T>, compensation: () => void) {
    return protectedCont((ctx: IAsyncContext<T>) => {
      computation({
        onSuccess: (x: T) => {
          compensation();
          ctx.onSuccess(x);
        },
        onError: (x: any) => {
          compensation();
          ctx.onError(x);
        },
        onCancel: (x: any) => {
          compensation();
          ctx.onCancel(x);
        },
        cancelToken: ctx.cancelToken,
        trampoline: ctx.trampoline,
      });
    });
  }

  public TryWith<T>(computation: Async<T>, catchHandler: (e: any) => Async<T>) {
    return protectedCont((ctx: IAsyncContext<T>) => {
      computation({
        onSuccess: ctx.onSuccess,
        onCancel: ctx.onCancel,
        cancelToken: ctx.cancelToken,
        trampoline: ctx.trampoline,
        onError: (ex: any) => {
          try {
            catchHandler(ex)(ctx);
          } catch (err) {
            ctx.onError(ensureErrorOrException(err));
          }
        },
      });
    });
  }

  public Using<T extends IDisposable, U>(resource: T, binder: (x: T) => Async<U>) {
    return this.TryFinally(binder(resource), () => resource.Dispose());
  }

  public While(guard: () => boolean, computation: Async<void>): Async<void> {
    if (guard()) {
      return this.Bind(computation, () => this.While(guard, computation));
    } else {
      return this.Return(void 0);
    }
  }

  public Zero() {
    return protectedCont((ctx: IAsyncContext<void>) => ctx.onSuccess(void 0));
  }
}

export const singleton = new AsyncBuilder();