import * as plugins from './smartstate.plugins.js';
import { StatePart } from './smartstate.classes.statepart.js';
import { computed } from './smartstate.classes.computed.js';

export type TInitMode = 'soft' | 'mandatory' | 'force' | 'persistent';

/**
 * Smartstate takes care of providing state
 */
export class Smartstate<StatePartNameType extends string> {
  public statePartMap: { [key in StatePartNameType]?: StatePart<StatePartNameType, any> } = {};

  private pendingStatePartCreation: Map<string, Promise<StatePart<StatePartNameType, any>>> = new Map();

  // Batch support
  private batchDepth = 0;
  private isFlushing = false;
  private pendingNotifications = new Set<StatePart<any, any>>();

  constructor() {}

  /**
   * whether state changes are currently being batched
   */
  public get isBatching(): boolean {
    return this.batchDepth > 0;
  }

  /**
   * registers a state part for deferred notification during a batch
   */
  public registerPendingNotification(statePart: StatePart<any, any>): void {
    this.pendingNotifications.add(statePart);
  }

  /**
   * batches multiple state updates so subscribers are only notified once all updates complete
   */
  public async batch(updateFn: () => Promise<void> | void): Promise<void> {
    this.batchDepth++;
    try {
      await updateFn();
    } finally {
      this.batchDepth--;
      if (this.batchDepth === 0 && !this.isFlushing) {
        this.isFlushing = true;
        try {
          while (this.pendingNotifications.size > 0) {
            const pending = [...this.pendingNotifications];
            this.pendingNotifications.clear();
            for (const sp of pending) {
              await sp.notifyChange();
            }
          }
        } finally {
          this.isFlushing = false;
        }
      }
    }
  }

  /**
   * creates a computed observable derived from multiple state parts
   */
  public computed<TResult>(
    sources: StatePart<StatePartNameType, any>[],
    computeFn: (...states: any[]) => TResult,
  ): plugins.smartrx.rxjs.Observable<TResult> {
    return computed(sources, computeFn);
  }

  /**
   * Allows getting and initializing a new statepart
   */
  public async getStatePart<PayloadType>(
    statePartNameArg: StatePartNameType,
    initialArg?: PayloadType,
    initMode: TInitMode = 'soft'
  ): Promise<StatePart<StatePartNameType, PayloadType>> {
    // Return pending creation if one exists to prevent duplicate state parts
    const pending = this.pendingStatePartCreation.get(statePartNameArg);
    if (pending) {
      return pending as Promise<StatePart<StatePartNameType, PayloadType>>;
    }

    const existingStatePart = this.statePartMap[statePartNameArg];

    if (existingStatePart) {
      switch (initMode) {
        case 'mandatory':
          throw new Error(
            `State part '${statePartNameArg}' already exists, but initMode is 'mandatory'`
          );
        case 'force':
          existingStatePart.dispose();
          break;
        case 'soft':
        case 'persistent':
        default:
          return existingStatePart as StatePart<StatePartNameType, PayloadType>;
      }
    } else {
      if (initialArg === undefined) {
        throw new Error(
          `State part '${statePartNameArg}' does not exist and no initial state provided`
        );
      }
    }

    const creationPromise = this.createStatePart<PayloadType>(statePartNameArg, initialArg, initMode);
    this.pendingStatePartCreation.set(statePartNameArg, creationPromise);

    try {
      const result = await creationPromise;
      return result;
    } finally {
      this.pendingStatePartCreation.delete(statePartNameArg);
    }
  }

  /**
   * Creates a statepart
   */
  private async createStatePart<PayloadType>(
    statePartName: StatePartNameType,
    initialPayloadArg: PayloadType,
    initMode: TInitMode = 'soft'
  ): Promise<StatePart<StatePartNameType, PayloadType>> {
    const newState = new StatePart<StatePartNameType, PayloadType>(
      statePartName,
      initMode === 'persistent'
        ? {
            dbName: 'smartstate',
            storeName: statePartName,
          }
        : null
    );
    newState.smartstateRef = this;
    await newState.init();
    const currentState = newState.getState();

    if (initMode === 'persistent' && currentState !== undefined) {
      await newState.setState({
        ...initialPayloadArg,
        ...currentState,
      });
    } else {
      await newState.setState(initialPayloadArg);
    }

    this.statePartMap[statePartName] = newState;
    return newState;
  }
}