import { Injectable, Logger } from '@nestjs/common';
import { Knex } from 'knex';
import { ModelClass } from 'objection';
import { BaseModel } from './base.model';
import { ModelRegistry } from './model.registry';
import { ObjectMetadata } from './dynamic-model.factory';
import { TenantDatabaseService } from '../../tenant/tenant-database.service';
import { UserModel, RoleModel, PermissionModel } from './system-models';

/**
 * Service to manage dynamic models for a specific tenant
 */
@Injectable()
export class ModelService {
  private readonly logger = new Logger(ModelService.name);
  private tenantRegistries = new Map<string, ModelRegistry>();

  constructor(private tenantDbService: TenantDatabaseService) {}

  /**
   * Get or create a registry for a tenant
   */
  getTenantRegistry(tenantId: string): ModelRegistry {
    if (!this.tenantRegistries.has(tenantId)) {
      const registry = new ModelRegistry();
      
      // Register system models that are defined as static Objection models
      this.registerSystemModels(registry);
      
      this.tenantRegistries.set(tenantId, registry);
    }
    return this.tenantRegistries.get(tenantId)!;
  }

  /**
   * Register static system models in the registry
   * Uses simplified models without complex relationMappings to avoid modelPath issues
   */
  private registerSystemModels(registry: ModelRegistry): void {
    // Register system models by their API name (used in referenceObject fields)
    // These are simplified versions without relationMappings to avoid dependency issues
    registry.registerModel('User', UserModel as any);
    registry.registerModel('Role', RoleModel as any);
    registry.registerModel('Permission', PermissionModel as any);
    
    this.logger.debug('Registered system models: User, Role, Permission');
  }

  /**
   * Create and register a model for a tenant
   */
  async createModelForObject(
    tenantId: string,
    objectMetadata: ObjectMetadata,
  ): Promise<ModelClass<BaseModel>> {
    const registry = this.getTenantRegistry(tenantId);
    const model = registry.createAndRegisterModel(objectMetadata);

    this.logger.log(
      `Registered model for ${objectMetadata.apiName} in tenant ${tenantId}`,
    );

    return model;
  }

  /**
   * Get a model for a tenant and object
   */
  getModel(tenantId: string, objectApiName: string): ModelClass<BaseModel> {
    const registry = this.getTenantRegistry(tenantId);
    return registry.getModel(objectApiName);
  }

  /**
   * Get a bound model (with knex connection) for a tenant and object
   */
  async getBoundModel(
    tenantId: string,
    objectApiName: string,
  ): Promise<ModelClass<BaseModel>> {
    const knex = await this.tenantDbService.getTenantKnexById(tenantId);
    const model = this.getModel(tenantId, objectApiName);
    
    // Bind knex to the model and also to all models in the registry
    // This ensures system models also have knex bound when they're used in relations
    const registry = this.getTenantRegistry(tenantId);
    const allModels = registry.getAllModelNames();
    
    // Bind knex to all models to ensure relations work
    for (const modelName of allModels) {
      try {
        const m = registry.getModel(modelName);
        if (m && !m.knex()) {
          m.knex(knex);
        }
      } catch (error) {
        // Ignore errors for models that don't need binding
      }
    }
    
    return model.bindKnex(knex);
  }

  /**
   * Check if a model exists for a tenant
   */
  hasModel(tenantId: string, objectApiName: string): boolean {
    const registry = this.getTenantRegistry(tenantId);
    return registry.hasModel(objectApiName);
  }

  /**
   * Get all model names for a tenant
   */
  getAllModelNames(tenantId: string): string[] {
    const registry = this.getTenantRegistry(tenantId);
    return registry.getAllModelNames();
  }

  /**
   * Ensure a model is registered with all its dependencies.
   * This method handles recursive model creation for related objects.
   * 
   * @param tenantId - The tenant ID
   * @param objectApiName - The object API name to ensure registration for
   * @param fetchMetadata - Callback function to fetch object metadata (provided by ObjectService)
   * @param visited - Set to track visited models and prevent infinite loops
   */
  async ensureModelWithDependencies(
    tenantId: string,
    objectApiName: string,
    fetchMetadata: (apiName: string) => Promise<ObjectMetadata>,
    visited: Set<string> = new Set(),
  ): Promise<void> {
    // Prevent infinite recursion
    if (visited.has(objectApiName)) {
      return;
    }
    visited.add(objectApiName);

    // Check if model already exists
    if (this.hasModel(tenantId, objectApiName)) {
      return;
    }

    try {
      // Fetch the object metadata
      const objectMetadata = await fetchMetadata(objectApiName);

      // Extract lookup fields to find dependencies
      const lookupFields = objectMetadata.fields.filter(
        f => f.type === 'LOOKUP' && f.referenceObject
      );

      // Recursively ensure all dependent models are registered first
      for (const field of lookupFields) {
        if (field.referenceObject) {
          try {
            await this.ensureModelWithDependencies(
              tenantId,
              field.referenceObject,
              fetchMetadata,
              visited,
            );
          } catch (error) {
            // If related object doesn't exist (e.g., system tables), skip it
            this.logger.debug(
              `Skipping registration of related model ${field.referenceObject}: ${error.message}`
            );
          }
        }
      }

      if (objectMetadata.relations) {
        for (const relation of objectMetadata.relations) {
          if (relation.targetObjectApiName) {
            try {
              await this.ensureModelWithDependencies(
                tenantId,
                relation.targetObjectApiName,
                fetchMetadata,
                visited,
              );
            } catch (error) {
              this.logger.debug(
                `Skipping registration of related model ${relation.targetObjectApiName}: ${error.message}`
              );
            }
          }
        }
      }

      // Now create and register this model (all dependencies are ready)
      await this.createModelForObject(tenantId, objectMetadata);
      this.logger.log(`Registered model for ${objectApiName} in tenant ${tenantId}`);
    } catch (error) {
      this.logger.warn(
        `Failed to ensure model for ${objectApiName}: ${error.message}`
      );
      throw error;
    }
  }
}