import { Injectable, Logger, OnModuleInit } from "@nestjs/common";
import { PrismaService } from "../prisma/prisma.service";
import type { LlmProviderInstance } from "@prisma/client";
import type {
  LlmProviderInterface,
  LlmProviderHealthStatus,
} from "./providers/llm-provider.interface";
import { OllamaProvider, type OllamaProviderConfig } from "./providers/ollama.provider";

/**
 * Provider information returned by getAllProviders
 */
export interface ProviderInfo {
  id: string;
  name: string;
  provider: string;
  endpoint?: string;
  userId?: string | null;
  isDefault: boolean;
}

/**
 * Provider health status with instance ID
 */
export interface ProviderHealthInfo extends LlmProviderHealthStatus {
  id: string;
}

/**
 * LLM Manager Service
 *
 * Manages multiple LLM provider instances and routes requests.
 * Supports hot reload, provider selection, and health monitoring.
 *
 * @example
 * ```typescript
 * // Get default provider
 * const provider = await llmManager.getDefaultProvider();
 *
 * // Get user-specific provider
 * const userProvider = await llmManager.getUserProvider("user-123");
 *
 * // Register new provider dynamically
 * await llmManager.registerProvider(providerInstance);
 *
 * // Reload from database
 * await llmManager.reloadFromDatabase();
 * ```
 */
@Injectable()
export class LlmManagerService implements OnModuleInit {
  private readonly logger = new Logger(LlmManagerService.name);
  private readonly providers = new Map<string, LlmProviderInterface>();
  private readonly instanceMetadata = new Map<string, LlmProviderInstance>();

  constructor(private readonly prisma: PrismaService) {}

  /**
   * Initialize the service by loading all enabled providers from the database.
   * Called automatically by NestJS during module initialization.
   *
   * @throws {Error} If database connection fails
   */
  async onModuleInit(): Promise<void> {
    this.logger.log("Initializing LLM Manager Service...");
    try {
      await this.loadProvidersFromDatabase();
      this.logger.log(`Loaded ${String(this.providers.size)} provider(s)`);
    } catch (error: unknown) {
      const errorMessage = error instanceof Error ? error.message : String(error);
      this.logger.error(`Failed to initialize LLM Manager: ${errorMessage}`);
      throw new Error(`Failed to load providers from database: ${errorMessage}`);
    }
  }

  /**
   * Register a new provider instance or update an existing one.
   * Supports hot reload - no restart required.
   *
   * @param instance - Provider instance from database
   * @throws {Error} If provider type is unknown or initialization fails
   */
  async registerProvider(instance: LlmProviderInstance): Promise<void> {
    try {
      this.logger.log(`Registering provider: ${instance.displayName} (${instance.id})`);

      // Create provider instance based on type
      const provider = this.createProvider(instance);

      // Initialize the provider
      await provider.initialize();

      // Store in registry
      this.providers.set(instance.id, provider);
      this.instanceMetadata.set(instance.id, instance);

      this.logger.log(`Provider registered successfully: ${instance.displayName}`);
    } catch (error: unknown) {
      const errorMessage = error instanceof Error ? error.message : String(error);
      this.logger.error(`Failed to register provider ${instance.id}: ${errorMessage}`);
      throw error;
    }
  }

  /**
   * Unregister a provider instance from the registry.
   * Supports hot reload - no restart required.
   *
   * @param instanceId - Provider instance ID
   */
  // eslint-disable-next-line @typescript-eslint/require-await
  async unregisterProvider(instanceId: string): Promise<void> {
    if (this.providers.has(instanceId)) {
      this.logger.log(`Unregistering provider: ${instanceId}`);
      this.providers.delete(instanceId);
      this.instanceMetadata.delete(instanceId);
    }
  }

  /**
   * Get a provider by its instance ID.
   *
   * @param instanceId - Provider instance ID
   * @returns Provider interface
   * @throws {Error} If provider not found
   */
  // eslint-disable-next-line @typescript-eslint/require-await
  async getProviderById(instanceId: string): Promise<LlmProviderInterface> {
    const provider = this.providers.get(instanceId);
    if (!provider) {
      throw new Error(`Provider with ID ${instanceId} not found`);
    }
    return provider;
  }

  /**
   * Get all active provider instances.
   *
   * @returns Array of provider information
   */
  // eslint-disable-next-line @typescript-eslint/require-await
  async getAllProviders(): Promise<ProviderInfo[]> {
    const providers: ProviderInfo[] = [];

    for (const [id, provider] of this.providers.entries()) {
      const metadata = this.instanceMetadata.get(id);
      const config = provider.getConfig();

      providers.push({
        id,
        name: metadata?.displayName ?? provider.name,
        provider: provider.type,
        endpoint: config.endpoint,
        userId: metadata?.userId ?? null,
        isDefault: metadata?.isDefault ?? false,
      });
    }

    return providers;
  }

  /**
   * Get the default system-level provider.
   * Default provider is identified by isDefault=true and userId=null.
   *
   * @returns Default provider interface
   * @throws {Error} If no default provider configured
   */
  // eslint-disable-next-line @typescript-eslint/require-await
  async getDefaultProvider(): Promise<LlmProviderInterface> {
    // Find default system-level provider (userId = null, isDefault = true)
    for (const [id, metadata] of this.instanceMetadata.entries()) {
      if (metadata.isDefault && metadata.userId === null) {
        const provider = this.providers.get(id);
        if (provider) {
          return provider;
        }
      }
    }

    throw new Error("No default provider configured");
  }

  /**
   * Get a provider for a specific user.
   * Prioritizes user-level providers over system default.
   *
   * Selection logic:
   * 1. User-specific provider (userId matches)
   * 2. System default provider (userId = null, isDefault = true)
   *
   * @param userId - User ID
   * @returns Provider interface
   * @throws {Error} If no provider available for user
   */
  async getUserProvider(userId: string): Promise<LlmProviderInterface> {
    // First, try to find user-specific provider
    for (const [id, metadata] of this.instanceMetadata.entries()) {
      if (metadata.userId === userId) {
        const provider = this.providers.get(id);
        if (provider) {
          return provider;
        }
      }
    }

    // Fall back to default provider
    try {
      return await this.getDefaultProvider();
    } catch {
      throw new Error(`No provider available for user ${userId}`);
    }
  }

  /**
   * Check health of all registered providers.
   *
   * @returns Array of health status information
   */
  async checkAllProvidersHealth(): Promise<ProviderHealthInfo[]> {
    const healthStatuses: ProviderHealthInfo[] = [];

    for (const [id, provider] of this.providers.entries()) {
      try {
        const health = await provider.checkHealth();
        healthStatuses.push({ id, ...health });
      } catch (error: unknown) {
        const errorMessage = error instanceof Error ? error.message : String(error);
        this.logger.warn(`Health check failed for provider ${id}: ${errorMessage}`);

        // Include failed health check in results
        healthStatuses.push({
          id,
          healthy: false,
          provider: provider.type,
          error: errorMessage,
        });
      }
    }

    return healthStatuses;
  }

  /**
   * Reload all providers from the database.
   * Clears existing providers and loads fresh state from database.
   * Supports hot reload - no restart required.
   *
   * @throws {Error} If database connection fails
   */
  async reloadFromDatabase(): Promise<void> {
    this.logger.log("Reloading providers from database...");

    // Clear existing providers
    this.providers.clear();
    this.instanceMetadata.clear();

    // Reload from database
    await this.loadProvidersFromDatabase();

    this.logger.log(`Reloaded ${String(this.providers.size)} provider(s)`);
  }

  /**
   * Load all enabled providers from the database.
   * Private helper method called during initialization and reload.
   *
   * @throws {Error} If database query fails
   */
  private async loadProvidersFromDatabase(): Promise<void> {
    const instances = await this.prisma.llmProviderInstance.findMany({
      where: { isEnabled: true },
    });

    // Register each provider instance
    for (const instance of instances) {
      try {
        await this.registerProvider(instance);
      } catch (error: unknown) {
        const errorMessage = error instanceof Error ? error.message : String(error);
        this.logger.warn(`Skipping provider ${instance.id} due to error: ${errorMessage}`);
      }
    }
  }

  /**
   * Create a provider instance based on provider type.
   * Factory method for instantiating provider implementations.
   *
   * @param instance - Provider instance from database
   * @returns Provider interface implementation
   * @throws {Error} If provider type is unknown
   */
  private createProvider(instance: LlmProviderInstance): LlmProviderInterface {
    switch (instance.providerType) {
      case "ollama":
        return new OllamaProvider(instance.config as OllamaProviderConfig);

      // Future providers:
      // case "claude":
      //   return new ClaudeProvider(instance.config);
      // case "openai":
      //   return new OpenAIProvider(instance.config);

      default:
        throw new Error(`Unknown provider type: ${instance.providerType}`);
    }
  }
}