import type { IRouteContext } from '../../core/models/route-context.js';
import type { ILogger } from './models/types.js';

/**
 * Interface for cached function result
 */
interface ICachedResult<T> {
  value: T;
  expiry: number;
  hash: string;
}

/**
 * Function cache for NetworkProxy function-based targets
 * 
 * This cache improves performance for function-based targets by storing
 * the results of function evaluations and reusing them for similar contexts.
 */
export class FunctionCache {
  // Cache storage
  private hostCache: Map<string, ICachedResult<string | string[]>> = new Map();
  private portCache: Map<string, ICachedResult<number>> = new Map();
  
  // Maximum number of entries to store in each cache
  private maxCacheSize: number;
  
  // Default TTL for cache entries in milliseconds (default: 5 seconds)
  private defaultTtl: number;
  
  // Logger
  private logger: ILogger;
  
  /**
   * Creates a new function cache
   * 
   * @param logger Logger for debug output
   * @param options Cache options
   */
  constructor(
    logger: ILogger,
    options: {
      maxCacheSize?: number;
      defaultTtl?: number;
    } = {}
  ) {
    this.logger = logger;
    this.maxCacheSize = options.maxCacheSize || 1000;
    this.defaultTtl = options.defaultTtl || 5000; // 5 seconds default
    
    // Start the cache cleanup timer
    setInterval(() => this.cleanupCache(), 30000); // Cleanup every 30 seconds
  }
  
  /**
   * Compute a hash for a context object
   * This is used to identify similar contexts for caching
   * 
   * @param context The route context to hash
   * @param functionId Identifier for the function (usually route name or ID)
   * @returns A string hash
   */
  private computeContextHash(context: IRouteContext, functionId: string): string {
    // Extract relevant properties for the hash
    const hashBase = {
      functionId,
      port: context.port,
      domain: context.domain,
      clientIp: context.clientIp,
      path: context.path,
      query: context.query,
      isTls: context.isTls,
      tlsVersion: context.tlsVersion
    };
    
    // Generate a hash string
    return JSON.stringify(hashBase);
  }
  
  /**
   * Get cached host result for a function and context
   * 
   * @param context Route context
   * @param functionId Identifier for the function
   * @returns Cached host value or undefined if not found
   */
  public getCachedHost(context: IRouteContext, functionId: string): string | string[] | undefined {
    const hash = this.computeContextHash(context, functionId);
    const cached = this.hostCache.get(hash);
    
    // Return if no cached value or expired
    if (!cached || cached.expiry < Date.now()) {
      if (cached) {
        // If expired, remove from cache
        this.hostCache.delete(hash);
        this.logger.debug(`Cache miss (expired) for host function: ${functionId}`);
      } else {
        this.logger.debug(`Cache miss for host function: ${functionId}`);
      }
      return undefined;
    }
    
    this.logger.debug(`Cache hit for host function: ${functionId}`);
    return cached.value;
  }
  
  /**
   * Get cached port result for a function and context
   * 
   * @param context Route context
   * @param functionId Identifier for the function
   * @returns Cached port value or undefined if not found
   */
  public getCachedPort(context: IRouteContext, functionId: string): number | undefined {
    const hash = this.computeContextHash(context, functionId);
    const cached = this.portCache.get(hash);
    
    // Return if no cached value or expired
    if (!cached || cached.expiry < Date.now()) {
      if (cached) {
        // If expired, remove from cache
        this.portCache.delete(hash);
        this.logger.debug(`Cache miss (expired) for port function: ${functionId}`);
      } else {
        this.logger.debug(`Cache miss for port function: ${functionId}`);
      }
      return undefined;
    }
    
    this.logger.debug(`Cache hit for port function: ${functionId}`);
    return cached.value;
  }
  
  /**
   * Store a host function result in the cache
   * 
   * @param context Route context
   * @param functionId Identifier for the function
   * @param value Host value to cache
   * @param ttl Optional TTL in milliseconds
   */
  public cacheHost(
    context: IRouteContext,
    functionId: string,
    value: string | string[],
    ttl?: number
  ): void {
    const hash = this.computeContextHash(context, functionId);
    const expiry = Date.now() + (ttl || this.defaultTtl);
    
    // Check if we need to prune the cache before adding
    if (this.hostCache.size >= this.maxCacheSize) {
      this.pruneOldestEntries(this.hostCache);
    }
    
    // Store the result
    this.hostCache.set(hash, { value, expiry, hash });
    this.logger.debug(`Cached host function result for: ${functionId}`);
  }
  
  /**
   * Store a port function result in the cache
   * 
   * @param context Route context
   * @param functionId Identifier for the function
   * @param value Port value to cache
   * @param ttl Optional TTL in milliseconds
   */
  public cachePort(
    context: IRouteContext,
    functionId: string,
    value: number,
    ttl?: number
  ): void {
    const hash = this.computeContextHash(context, functionId);
    const expiry = Date.now() + (ttl || this.defaultTtl);
    
    // Check if we need to prune the cache before adding
    if (this.portCache.size >= this.maxCacheSize) {
      this.pruneOldestEntries(this.portCache);
    }
    
    // Store the result
    this.portCache.set(hash, { value, expiry, hash });
    this.logger.debug(`Cached port function result for: ${functionId}`);
  }
  
  /**
   * Remove expired entries from the cache
   */
  private cleanupCache(): void {
    const now = Date.now();
    let expiredCount = 0;
    
    // Clean up host cache
    for (const [hash, cached] of this.hostCache.entries()) {
      if (cached.expiry < now) {
        this.hostCache.delete(hash);
        expiredCount++;
      }
    }
    
    // Clean up port cache
    for (const [hash, cached] of this.portCache.entries()) {
      if (cached.expiry < now) {
        this.portCache.delete(hash);
        expiredCount++;
      }
    }
    
    if (expiredCount > 0) {
      this.logger.debug(`Cleaned up ${expiredCount} expired cache entries`);
    }
  }
  
  /**
   * Prune oldest entries from a cache map
   * Used when the cache exceeds the maximum size
   * 
   * @param cache The cache map to prune
   */
  private pruneOldestEntries<T>(cache: Map<string, ICachedResult<T>>): void {
    // Find the oldest entries
    const now = Date.now();
    const itemsToRemove = Math.floor(this.maxCacheSize * 0.2); // Remove 20% of the cache
    
    // Convert to array for sorting
    const entries = Array.from(cache.entries());
    
    // Sort by expiry (oldest first)
    entries.sort((a, b) => a[1].expiry - b[1].expiry);
    
    // Remove oldest entries
    const toRemove = entries.slice(0, itemsToRemove);
    for (const [hash] of toRemove) {
      cache.delete(hash);
    }
    
    this.logger.debug(`Pruned ${toRemove.length} oldest cache entries`);
  }
  
  /**
   * Get current cache stats
   */
  public getStats(): { hostCacheSize: number; portCacheSize: number } {
    return {
      hostCacheSize: this.hostCache.size,
      portCacheSize: this.portCache.size
    };
  }
  
  /**
   * Clear all cached entries
   */
  public clearCache(): void {
    this.hostCache.clear();
    this.portCache.clear();
    this.logger.info('Function cache cleared');
  }
}