package main

import (
	"log"
	"net/http"
	"net/http/httputil"
	"net/url"
)

// startProxy starts an HTTP reverse proxy that forwards requests to workers.
// It acquires a worker from the pool for each request and releases it when done.
func startProxy(listenAddr string, pool *WorkerPool) {
	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		// Acquire a worker (blocks if none available)
		workerAddr, ok := pool.Acquire()
		if !ok {
			http.Error(w, "Service unavailable", http.StatusServiceUnavailable)
			return
		}

		// Ensure we release the worker when done
		defer pool.Release(workerAddr)

		// Create reverse proxy to the worker
		targetURL, err := url.Parse("http://" + workerAddr)
		if err != nil {
			log.Printf("[proxy] Failed to parse worker URL %s: %v", workerAddr, err)
			http.Error(w, "Internal server error", http.StatusInternalServerError)
			return
		}

		proxy := httputil.NewSingleHostReverseProxy(targetURL)

		// Custom error handler
		proxy.ErrorHandler = func(w http.ResponseWriter, r *http.Request, err error) {
			log.Printf("[proxy] Error proxying to %s: %v", workerAddr, err)
			http.Error(w, "Bad gateway", http.StatusBadGateway)
		}

		log.Printf("[proxy] %s %s -> %s", r.Method, r.URL.Path, workerAddr)
		proxy.ServeHTTP(w, r)
	})

	log.Printf("[proxy] Listening on %s", listenAddr)
	if err := http.ListenAndServe(listenAddr, handler); err != nil {
		log.Fatalf("[proxy] Failed to start: %v", err)
	}
}