/**
 * Identity Resolution Service
 *
 * Handles identity resolution (lookup) between local and remote instances.
 * Optimized for read-heavy operations.
 */

import { Injectable, Logger } from "@nestjs/common";
import { IdentityLinkingService } from "./identity-linking.service";
import type {
  IdentityResolutionResponse,
  BulkIdentityResolutionResponse,
} from "./types/identity-linking.types";

@Injectable()
export class IdentityResolutionService {
  private readonly logger = new Logger(IdentityResolutionService.name);

  constructor(private readonly identityLinkingService: IdentityLinkingService) {}

  /**
   * Resolve a remote user to a local user
   *
   * Looks up the identity mapping by remote instance and user ID.
   */
  async resolveIdentity(
    remoteInstanceId: string,
    remoteUserId: string
  ): Promise<IdentityResolutionResponse> {
    this.logger.debug(`Resolving identity: ${remoteUserId}@${remoteInstanceId}`);

    const identity = await this.identityLinkingService.resolveLocalIdentity(
      remoteInstanceId,
      remoteUserId
    );

    if (!identity) {
      return {
        found: false,
        remoteUserId,
        remoteInstanceId,
      };
    }

    return {
      found: true,
      localUserId: identity.localUserId,
      remoteUserId: identity.remoteUserId,
      remoteInstanceId: identity.remoteInstanceId,
      email: identity.email,
      metadata: identity.metadata,
    };
  }

  /**
   * Reverse resolve a local user to a remote identity
   *
   * Looks up the identity mapping by local user ID and remote instance.
   */
  async reverseResolveIdentity(
    localUserId: string,
    remoteInstanceId: string
  ): Promise<IdentityResolutionResponse> {
    this.logger.debug(`Reverse resolving identity: ${localUserId}@${remoteInstanceId}`);

    const identity = await this.identityLinkingService.resolveRemoteIdentity(
      localUserId,
      remoteInstanceId
    );

    if (!identity) {
      return {
        found: false,
        localUserId,
        remoteInstanceId,
      };
    }

    return {
      found: true,
      localUserId: identity.localUserId,
      remoteUserId: identity.remoteUserId,
      remoteInstanceId: identity.remoteInstanceId,
      email: identity.email,
      metadata: identity.metadata,
    };
  }

  /**
   * Bulk resolve multiple remote users to local users
   *
   * Efficient batch operation for resolving many identities at once.
   * Useful for aggregated dashboard views and multi-user operations.
   */
  async bulkResolveIdentities(
    remoteInstanceId: string,
    remoteUserIds: string[]
  ): Promise<BulkIdentityResolutionResponse> {
    this.logger.debug(
      `Bulk resolving ${remoteUserIds.length.toString()} identities for ${remoteInstanceId}`
    );

    if (remoteUserIds.length === 0) {
      return {
        mappings: {},
        notFound: [],
      };
    }

    const mappings: Record<string, string> = {};
    const notFound: string[] = [];

    // Resolve each identity
    // TODO: Optimize with a single database query using IN clause
    for (const remoteUserId of remoteUserIds) {
      const identity = await this.identityLinkingService.resolveLocalIdentity(
        remoteInstanceId,
        remoteUserId
      );

      if (identity) {
        mappings[remoteUserId] = identity.localUserId;
      } else {
        notFound.push(remoteUserId);
      }
    }

    this.logger.debug(
      `Bulk resolution complete: ${Object.keys(mappings).length.toString()} found, ${notFound.length.toString()} not found`
    );

    return {
      mappings,
      notFound,
    };
  }
}