import * as plugins from './smartstate.plugins.js';
import { Observable, shareReplay, takeUntil } from 'rxjs';
import { StateAction, type IActionDef } from './smartstate.classes.stateaction.js';
import type { Smartstate } from './smartstate.classes.smartstate.js';

export type TMiddleware<TPayload> = (
  newState: TPayload,
  oldState: TPayload | undefined,
) => TPayload | Promise<TPayload>;

/**
 * creates an Observable that emits once when the given AbortSignal fires
 */
function fromAbortSignal(signal: AbortSignal): Observable<void> {
  return new Observable<void>((subscriber) => {
    if (signal.aborted) {
      subscriber.next();
      subscriber.complete();
      return;
    }
    const handler = () => {
      subscriber.next();
      subscriber.complete();
    };
    signal.addEventListener('abort', handler);
    return () => signal.removeEventListener('abort', handler);
  });
}

export class StatePart<TStatePartName, TStatePayload> {
  public name: TStatePartName;
  public state = new plugins.smartrx.rxjs.Subject<TStatePayload>();
  public stateStore: TStatePayload | undefined;
  public smartstateRef?: Smartstate<any>;
  private cumulativeDeferred = plugins.smartpromise.cumulativeDefer();

  private mutationQueue: Promise<any> = Promise.resolve();
  private pendingCumulativeNotification: ReturnType<typeof setTimeout> | null = null;

  private webStoreOptions: plugins.webstore.IWebStoreOptions;
  private webStore: plugins.webstore.WebStore<TStatePayload> | null = null;

  private middlewares: TMiddleware<TStatePayload>[] = [];

  // Selector memoization
  private selectorCache = new WeakMap<Function, plugins.smartrx.rxjs.Observable<any>>();
  private defaultSelectObservable: plugins.smartrx.rxjs.Observable<TStatePayload> | null = null;

  constructor(nameArg: TStatePartName, webStoreOptionsArg?: plugins.webstore.IWebStoreOptions) {
    this.name = nameArg;

    if (webStoreOptionsArg) {
      this.webStoreOptions = webStoreOptionsArg;
    }
  }

  /**
   * initializes the webstore
   */
  public async init() {
    if (this.webStoreOptions) {
      this.webStore = new plugins.webstore.WebStore<TStatePayload>(this.webStoreOptions);
      await this.webStore.init();
      const storedState = await this.webStore.get(String(this.name));
      if (storedState && this.validateState(storedState)) {
        this.stateStore = storedState;
        await this.notifyChange();
      }
    }
  }

  /**
   * gets the state from the state store
   */
  public getState(): TStatePayload | undefined {
    return this.stateStore;
  }

  /**
   * adds a middleware that intercepts setState calls.
   * middleware can transform the state or throw to reject it.
   * returns a removal function.
   */
  public addMiddleware(middleware: TMiddleware<TStatePayload>): () => void {
    this.middlewares.push(middleware);
    return () => {
      const idx = this.middlewares.indexOf(middleware);
      if (idx !== -1) {
        this.middlewares.splice(idx, 1);
      }
    };
  }

  /**
   * sets the stateStore to the new state (serialized via mutation queue)
   */
  public async setState(newStateArg: TStatePayload): Promise<TStatePayload> {
    return this.mutationQueue = this.mutationQueue.then(
      () => this.applyState(newStateArg),
      () => this.applyState(newStateArg),
    );
  }

  /**
   * applies the state change (middleware → validate → persist → notify)
   */
  private async applyState(newStateArg: TStatePayload): Promise<TStatePayload> {
    // Run middleware chain
    let processedState = newStateArg;
    for (const mw of this.middlewares) {
      processedState = await mw(processedState, this.stateStore);
    }

    // Validate state structure
    if (!this.validateState(processedState)) {
      throw new Error(`Invalid state structure for state part '${this.name}'`);
    }

    // Save to WebStore first to ensure atomicity
    if (this.webStore) {
      await this.webStore.set(String(this.name), processedState);
    }

    // Update in-memory state after successful persistence
    this.stateStore = processedState;
    await this.notifyChange();

    return this.stateStore;
  }

  /**
   * Validates state structure - can be overridden for custom validation
   */
  protected validateState(stateArg: any): stateArg is TStatePayload {
    return stateArg !== null && stateArg !== undefined;
  }

  /**
   * notifies of a change on the state
   */
  public async notifyChange() {
    const snapshot = this.stateStore;
    if (snapshot === undefined) {
      return;
    }

    // If inside a batch, defer the notification
    if (this.smartstateRef?.isBatching) {
      this.smartstateRef.registerPendingNotification(this);
      return;
    }

    const createStateHash = async (stateArg: any) => {
      return await plugins.smarthashWeb.sha256FromString(plugins.smartjson.stableOneWayStringify(stateArg));
    };
    try {
      const currentHash = await createStateHash(snapshot);
      if (
        this.lastStateNotificationPayloadHash &&
        currentHash === this.lastStateNotificationPayloadHash
      ) {
        return;
      }
      this.lastStateNotificationPayloadHash = currentHash;
    } catch (err) {
      console.error(`State hash computation failed for '${this.name}':`, err);
    }
    this.state.next(snapshot);
  }
  private lastStateNotificationPayloadHash: any;

  /**
   * creates a cumulative notification by adding a change notification at the end of the call stack
   */
  public notifyChangeCumulative() {
    if (this.pendingCumulativeNotification) {
      clearTimeout(this.pendingCumulativeNotification);
    }

    this.pendingCumulativeNotification = setTimeout(() => {
      this.pendingCumulativeNotification = null;
      if (this.stateStore !== undefined) {
        this.notifyChange().catch((err) => {
          console.error(`notifyChangeCumulative failed for '${this.name}':`, err);
        });
      }
    }, 0);
  }

  /**
   * selects a state or a substate.
   * supports an optional AbortSignal for automatic unsubscription.
   * memoizes observables by selector function reference.
   */
  public select<T = TStatePayload>(
    selectorFn?: (state: TStatePayload) => T,
    options?: { signal?: AbortSignal }
  ): plugins.smartrx.rxjs.Observable<T> {
    const hasSignal = options?.signal != null;

    // Check memoization cache (only for non-signal selects)
    if (!hasSignal) {
      if (!selectorFn) {
        if (this.defaultSelectObservable) {
          return this.defaultSelectObservable as unknown as plugins.smartrx.rxjs.Observable<T>;
        }
      } else if (this.selectorCache.has(selectorFn)) {
        return this.selectorCache.get(selectorFn)!;
      }
    }

    const effectiveSelectorFn = selectorFn || ((state: TStatePayload) => <T>(<any>state));

    let mapped = this.state.pipe(
      plugins.smartrx.rxjs.ops.startWith(this.getState()),
      plugins.smartrx.rxjs.ops.filter((stateArg): stateArg is TStatePayload => stateArg !== undefined),
      plugins.smartrx.rxjs.ops.map((stateArg) => {
        try {
          return effectiveSelectorFn(stateArg);
        } catch (e) {
          console.error(`Selector error in state part '${this.name}':`, e);
          return undefined;
        }
      })
    );

    if (hasSignal) {
      mapped = mapped.pipe(takeUntil(fromAbortSignal(options.signal)));
      return mapped;
    }

    // Apply shareReplay for caching and store in memo cache
    const shared = mapped.pipe(shareReplay({ bufferSize: 1, refCount: true }));
    if (!selectorFn) {
      this.defaultSelectObservable = shared as unknown as plugins.smartrx.rxjs.Observable<TStatePayload>;
    } else {
      this.selectorCache.set(selectorFn, shared);
    }

    return shared;
  }

  /**
   * creates an action capable of modifying the state
   */
  public createAction<TActionPayload>(
    actionDef: IActionDef<TStatePayload, TActionPayload>
  ): StateAction<TStatePayload, TActionPayload> {
    return new StateAction(this, actionDef);
  }

  /**
   * dispatches an action on the statepart level
   */
  public async dispatchAction<T>(stateAction: StateAction<TStatePayload, T>, actionPayload: T): Promise<TStatePayload> {
    await this.cumulativeDeferred.promise;
    return this.mutationQueue = this.mutationQueue.then(
      async () => {
        const newState = await stateAction.actionDef(this, actionPayload);
        return this.applyState(newState);
      },
      async () => {
        const newState = await stateAction.actionDef(this, actionPayload);
        return this.applyState(newState);
      },
    );
  }

  /**
   * waits until a certain part of the state becomes available.
   * supports optional timeout and AbortSignal.
   */
  public async waitUntilPresent<T = TStatePayload>(
    selectorFn?: (state: TStatePayload) => T,
    optionsOrTimeout?: number | { timeoutMs?: number; signal?: AbortSignal }
  ): Promise<T> {
    // Parse backward-compatible args
    let timeoutMs: number | undefined;
    let signal: AbortSignal | undefined;
    if (typeof optionsOrTimeout === 'number') {
      timeoutMs = optionsOrTimeout;
    } else if (optionsOrTimeout) {
      timeoutMs = optionsOrTimeout.timeoutMs;
      signal = optionsOrTimeout.signal;
    }

    const done = plugins.smartpromise.defer<T>();
    const selectedObservable = this.select(selectorFn);
    let resolved = false;

    // Check if already aborted
    if (signal?.aborted) {
      throw new Error('Aborted');
    }

    const subscription = selectedObservable.subscribe((value) => {
      if (value !== undefined && value !== null && !resolved) {
        resolved = true;
        done.resolve(value);
      }
    });

    let timeoutId: ReturnType<typeof setTimeout> | undefined;
    if (timeoutMs) {
      timeoutId = setTimeout(() => {
        if (!resolved) {
          resolved = true;
          subscription.unsubscribe();
          done.reject(new Error(`waitUntilPresent timed out after ${timeoutMs}ms`));
        }
      }, timeoutMs);
    }

    // Handle abort signal
    const abortHandler = signal ? () => {
      if (!resolved) {
        resolved = true;
        subscription.unsubscribe();
        if (timeoutId) clearTimeout(timeoutId);
        done.reject(new Error('Aborted'));
      }
    } : undefined;

    if (signal && abortHandler) {
      signal.addEventListener('abort', abortHandler);
    }

    try {
      const result = await done.promise;
      return result;
    } finally {
      subscription.unsubscribe();
      if (timeoutId) clearTimeout(timeoutId);
      if (signal && abortHandler) {
        signal.removeEventListener('abort', abortHandler);
      }
    }
  }

  /**
   * is executed
   */
  public async stateSetup(
    funcArg: (statePartArg?: StatePart<any, TStatePayload>) => Promise<TStatePayload>
  ) {
    const resultPromise = funcArg(this);
    this.cumulativeDeferred.addPromise(resultPromise);
    await this.setState(await resultPromise);
  }

  /**
   * disposes the state part, completing the Subject and cleaning up resources
   */
  public dispose(): void {
    this.state.complete();
    if (this.pendingCumulativeNotification) {
      clearTimeout(this.pendingCumulativeNotification);
      this.pendingCumulativeNotification = null;
    }
    this.middlewares.length = 0;
    this.selectorCache = new WeakMap();
    this.defaultSelectObservable = null;
    this.webStore = null;
    this.smartstateRef = undefined;
  }
}