import * as plugins from '../plugins.js';
import type {
  IUpstreamRegistryConfig,
  IUpstreamAuthConfig,
  IUpstreamCacheConfig,
  IUpstreamResilienceConfig,
  IUpstreamResult,
  IUpstreamFetchContext,
  IProtocolUpstreamConfig,
  IUpstreamScopeRule,
  TCircuitState,
} from './interfaces.upstream.js';
import {
  DEFAULT_CACHE_CONFIG,
  DEFAULT_RESILIENCE_CONFIG,
} from './interfaces.upstream.js';
import { CircuitBreaker, CircuitOpenError, withCircuitBreaker } from './classes.circuitbreaker.js';
import { UpstreamCache } from './classes.upstreamcache.js';

/**
 * Base class for protocol-specific upstream implementations.
 *
 * Provides:
 * - Multi-upstream routing with priority
 * - Scope-based filtering (glob patterns)
 * - Authentication handling
 * - Circuit breaker per upstream
 * - Caching with TTL
 * - Retry with exponential backoff
 * - 429 rate limit handling
 */
export abstract class BaseUpstream {
  /** Protocol name for logging */
  protected abstract readonly protocolName: string;

  /** Upstream configuration */
  protected readonly config: IProtocolUpstreamConfig;

  /** Resolved cache configuration */
  protected readonly cacheConfig: IUpstreamCacheConfig;

  /** Resolved resilience configuration */
  protected readonly resilienceConfig: IUpstreamResilienceConfig;

  /** Circuit breakers per upstream */
  protected readonly circuitBreakers: Map<string, CircuitBreaker> = new Map();

  /** Upstream cache */
  protected readonly cache: UpstreamCache;

  /** Logger instance */
  protected readonly logger: plugins.smartlog.Smartlog;

  constructor(config: IProtocolUpstreamConfig, logger?: plugins.smartlog.Smartlog) {
    this.config = config;
    this.cacheConfig = { ...DEFAULT_CACHE_CONFIG, ...config.cache };
    this.resilienceConfig = { ...DEFAULT_RESILIENCE_CONFIG, ...config.resilience };
    this.cache = new UpstreamCache(this.cacheConfig);
    this.logger = logger || new plugins.smartlog.Smartlog({
      logContext: {
        company: 'smartregistry',
        companyunit: 'upstream',
        environment: 'production',
        runtime: 'node',
      }
    });

    // Initialize circuit breakers for each upstream
    for (const upstream of config.upstreams) {
      const upstreamResilience = { ...this.resilienceConfig, ...upstream.resilience };
      this.circuitBreakers.set(upstream.id, new CircuitBreaker(upstream.id, upstreamResilience));
    }
  }

  /**
   * Check if upstream is enabled.
   */
  public isEnabled(): boolean {
    return this.config.enabled;
  }

  /**
   * Get all configured upstreams.
   */
  public getUpstreams(): IUpstreamRegistryConfig[] {
    return this.config.upstreams;
  }

  /**
   * Get circuit breaker state for an upstream.
   */
  public getCircuitState(upstreamId: string): TCircuitState | null {
    const breaker = this.circuitBreakers.get(upstreamId);
    return breaker ? breaker.getState() : null;
  }

  /**
   * Get cache statistics.
   */
  public getCacheStats() {
    return this.cache.getStats();
  }

  /**
   * Fetch a resource from upstreams.
   * Tries upstreams in priority order, respecting circuit breakers and scope rules.
   */
  public async fetch(context: IUpstreamFetchContext): Promise<IUpstreamResult | null> {
    if (!this.config.enabled) {
      return null;
    }

    // Get applicable upstreams sorted by priority
    const applicableUpstreams = this.getApplicableUpstreams(context.resource);

    if (applicableUpstreams.length === 0) {
      return null;
    }

    // Use the first applicable upstream's URL for cache key
    const primaryUpstreamUrl = applicableUpstreams[0]?.url;

    // Check cache first
    const cached = await this.cache.get(context, primaryUpstreamUrl);
    if (cached && !cached.stale) {
      return {
        success: true,
        status: 200,
        headers: cached.headers,
        body: cached.data,
        upstreamId: cached.upstreamId,
        fromCache: true,
        latencyMs: 0,
      };
    }

    // Check for negative cache (recent 404)
    if (await this.cache.hasNegative(context, primaryUpstreamUrl)) {
      return {
        success: false,
        status: 404,
        headers: {},
        upstreamId: 'cache',
        fromCache: true,
        latencyMs: 0,
      };
    }

    // If we have stale cache, return it immediately and revalidate in background
    if (cached?.stale && this.cacheConfig.staleWhileRevalidate) {
      // Fire and forget revalidation
      this.revalidateInBackground(context, applicableUpstreams);
      return {
        success: true,
        status: 200,
        headers: cached.headers,
        body: cached.data,
        upstreamId: cached.upstreamId,
        fromCache: true,
        latencyMs: 0,
      };
    }

    // Try each upstream in order
    let lastError: Error | null = null;

    for (const upstream of applicableUpstreams) {
      const breaker = this.circuitBreakers.get(upstream.id);
      if (!breaker) continue;

      try {
        const result = await withCircuitBreaker(
          breaker,
          () => this.fetchFromUpstream(upstream, context),
        );

        // Cache successful responses
        if (result.success && result.body) {
          await this.cache.set(
            context,
            Buffer.isBuffer(result.body) ? result.body : Buffer.from(JSON.stringify(result.body)),
            result.headers['content-type'] || 'application/octet-stream',
            result.headers,
            upstream.id,
            upstream.url,
          );
        }

        // Cache 404 responses
        if (result.status === 404) {
          await this.cache.setNegative(context, upstream.id, upstream.url);
        }

        return result;
      } catch (error) {
        if (error instanceof CircuitOpenError) {
          this.logger.log('debug', `Circuit open for upstream ${upstream.id}, trying next`);
        } else {
          this.logger.log('warn', `Upstream ${upstream.id} failed: ${(error as Error).message}`);
        }
        lastError = error as Error;
        // Continue to next upstream
      }
    }

    // All upstreams failed
    if (lastError) {
      this.logger.log('error', `All upstreams failed for ${context.resource}: ${lastError.message}`);
    }

    return null;
  }

  /**
   * Invalidate cache for a resource pattern.
   */
  public async invalidateCache(pattern: RegExp): Promise<number> {
    return this.cache.invalidatePattern(pattern);
  }

  /**
   * Clear all cache entries.
   */
  public async clearCache(): Promise<void> {
    await this.cache.clear();
  }

  /**
   * Stop the upstream (cleanup resources).
   */
  public stop(): void {
    this.cache.stop();
  }

  /**
   * Get upstreams that apply to a resource, sorted by priority.
   */
  protected getApplicableUpstreams(resource: string): IUpstreamRegistryConfig[] {
    return this.config.upstreams
      .filter(upstream => {
        if (!upstream.enabled) return false;

        // Check circuit breaker
        const breaker = this.circuitBreakers.get(upstream.id);
        if (breaker && !breaker.canRequest()) return false;

        // Check scope rules
        return this.matchesScopeRules(resource, upstream.scopeRules);
      })
      .sort((a, b) => a.priority - b.priority);
  }

  /**
   * Check if a resource matches scope rules.
   * Empty rules = match all.
   */
  protected matchesScopeRules(resource: string, rules?: IUpstreamScopeRule[]): boolean {
    if (!rules || rules.length === 0) {
      return true;
    }

    // Process rules in order
    // Start with default exclude (nothing matches)
    let matched = false;

    for (const rule of rules) {
      const isMatch = plugins.minimatch(resource, rule.pattern);
      if (isMatch) {
        matched = rule.action === 'include';
      }
    }

    return matched;
  }

  /**
   * Fetch from a specific upstream with retry logic.
   */
  protected async fetchFromUpstream(
    upstream: IUpstreamRegistryConfig,
    context: IUpstreamFetchContext,
  ): Promise<IUpstreamResult> {
    const upstreamResilience = { ...this.resilienceConfig, ...upstream.resilience };
    const startTime = Date.now();

    let lastError: Error | null = null;

    for (let attempt = 0; attempt <= upstreamResilience.maxRetries; attempt++) {
      try {
        const result = await this.executeRequest(upstream, context, upstreamResilience.timeoutMs);
        return {
          ...result,
          upstreamId: upstream.id,
          fromCache: false,
          latencyMs: Date.now() - startTime,
        };
      } catch (error) {
        lastError = error as Error;

        // Don't retry on 4xx errors (except 429)
        if (this.isNonRetryableError(error)) {
          break;
        }

        // Calculate delay with exponential backoff and jitter
        if (attempt < upstreamResilience.maxRetries) {
          const delay = this.calculateBackoffDelay(
            attempt,
            upstreamResilience.retryDelayMs,
            upstreamResilience.retryMaxDelayMs,
          );
          await this.sleep(delay);
        }
      }
    }

    throw lastError || new Error('Request failed');
  }

  /**
   * Execute a single HTTP request to an upstream.
   */
  protected async executeRequest(
    upstream: IUpstreamRegistryConfig,
    context: IUpstreamFetchContext,
    timeoutMs: number,
  ): Promise<Omit<IUpstreamResult, 'upstreamId' | 'fromCache' | 'latencyMs'>> {
    // Build the full URL
    const url = this.buildUpstreamUrl(upstream, context);

    // Build headers with auth
    const headers = this.buildHeaders(upstream, context);

    // Make the request using SmartRequest
    const request = plugins.smartrequest.SmartRequest.create()
      .url(url)
      .method(context.method as any)
      .headers(headers)
      .timeout(timeoutMs)
      .handle429Backoff({ maxRetries: 3, fallbackDelay: 1000, maxWaitTime: 30000 });

    // Add query params if present
    if (Object.keys(context.query).length > 0) {
      request.query(context.query);
    }

    let response: plugins.smartrequest.ICoreResponse;

    switch (context.method.toUpperCase()) {
      case 'GET':
        response = await request.get();
        break;
      case 'HEAD':
        // SmartRequest doesn't have head(), use options
        response = await request.method('HEAD').get();
        break;
      default:
        response = await request.get();
    }

    // Parse response
    const responseHeaders: Record<string, string> = {};
    for (const [key, value] of Object.entries(response.headers)) {
      responseHeaders[key.toLowerCase()] = Array.isArray(value) ? value[0] : value;
    }

    let body: Buffer | any;
    const contentType = responseHeaders['content-type'] || '';

    if (response.ok) {
      if (contentType.includes('application/json')) {
        body = await response.json();
      } else {
        const arrayBuffer = await response.arrayBuffer();
        body = Buffer.from(arrayBuffer);
      }
    }

    return {
      success: response.ok,
      status: response.status,
      headers: responseHeaders,
      body,
    };
  }

  /**
   * Build the full URL for an upstream request.
   * Subclasses can override for protocol-specific URL building.
   */
  protected buildUpstreamUrl(upstream: IUpstreamRegistryConfig, context: IUpstreamFetchContext): string {
    // Remove leading slash if URL already has trailing slash
    let path = context.path;
    if (upstream.url.endsWith('/') && path.startsWith('/')) {
      path = path.slice(1);
    }
    return `${upstream.url}${path}`;
  }

  /**
   * Build headers including authentication.
   */
  protected buildHeaders(
    upstream: IUpstreamRegistryConfig,
    context: IUpstreamFetchContext,
  ): Record<string, string> {
    const headers: Record<string, string> = { ...context.headers };

    // Remove host header (will be set by HTTP client)
    delete headers['host'];

    // Add authentication
    this.addAuthHeaders(headers, upstream.auth);

    return headers;
  }

  /**
   * Add authentication headers based on auth config.
   */
  protected addAuthHeaders(headers: Record<string, string>, auth: IUpstreamAuthConfig): void {
    switch (auth.type) {
      case 'basic':
        if (auth.username && auth.password) {
          const credentials = Buffer.from(`${auth.username}:${auth.password}`).toString('base64');
          headers['authorization'] = `Basic ${credentials}`;
        }
        break;
      case 'bearer':
        if (auth.token) {
          headers['authorization'] = `Bearer ${auth.token}`;
        }
        break;
      case 'api-key':
        if (auth.token) {
          const headerName = auth.headerName || 'authorization';
          headers[headerName.toLowerCase()] = auth.token;
        }
        break;
      case 'none':
      default:
        // No authentication
        break;
    }
  }

  /**
   * Check if an error should not be retried.
   */
  protected isNonRetryableError(error: unknown): boolean {
    // Check for HTTP status errors
    if (error && typeof error === 'object' && 'status' in error) {
      const status = (error as { status: number }).status;
      // Don't retry 4xx errors except 429 (rate limited)
      if (status >= 400 && status < 500 && status !== 429) {
        return true;
      }
    }
    return false;
  }

  /**
   * Calculate backoff delay with exponential backoff and jitter.
   */
  protected calculateBackoffDelay(
    attempt: number,
    baseDelayMs: number,
    maxDelayMs: number,
  ): number {
    // Exponential backoff: delay = base * 2^attempt
    const exponentialDelay = baseDelayMs * Math.pow(2, attempt);

    // Cap at max delay
    const cappedDelay = Math.min(exponentialDelay, maxDelayMs);

    // Add jitter (±25%)
    const jitter = cappedDelay * 0.25 * (Math.random() * 2 - 1);

    return Math.floor(cappedDelay + jitter);
  }

  /**
   * Sleep for a specified duration.
   */
  protected sleep(ms: number): Promise<void> {
    return new Promise(resolve => setTimeout(resolve, ms));
  }

  /**
   * Revalidate cache in background.
   */
  protected async revalidateInBackground(
    context: IUpstreamFetchContext,
    upstreams: IUpstreamRegistryConfig[],
  ): Promise<void> {
    try {
      for (const upstream of upstreams) {
        const breaker = this.circuitBreakers.get(upstream.id);
        if (!breaker || !breaker.canRequest()) continue;

        try {
          const result = await withCircuitBreaker(
            breaker,
            () => this.fetchFromUpstream(upstream, context),
          );

          if (result.success && result.body) {
            await this.cache.set(
              context,
              Buffer.isBuffer(result.body) ? result.body : Buffer.from(JSON.stringify(result.body)),
              result.headers['content-type'] || 'application/octet-stream',
              result.headers,
              upstream.id,
              upstream.url,
            );
            return; // Successfully revalidated
          }
        } catch {
          // Continue to next upstream
        }
      }
    } catch (error) {
      this.logger.log('debug', `Background revalidation failed: ${(error as Error).message}`);
    }
  }
}