package main

import (
	"flag"
	"fmt"
	"log"
	"net/url"
)

func main() {
	maxConcurrency := flag.Int("c", 0, "Maximum number of concurrent queue pushes")
	startRawURL := flag.String("url", "", "Entry-point URL")
	flag.Parse()

	if *maxConcurrency == 0 {
		log.Fatal("Missing -c argument")
	}

	if *startRawURL == "" {
		log.Fatal("Missing -url argument")
	}

	startURL, err := url.Parse(*startRawURL)
	if err != nil {
		log.Fatal(err)
	}

	/* Main logic starts here. */

	worklist := make(chan []url.URL)
	go func() {
		worklist <- []url.URL{*startURL}
	}()

	seen := make(map[url.URL]bool)
	for list := range worklist {
		for _, u := range list {
			if !seen[u] {
				fmt.Printf("%s\n", &u)
				seen[u] = true

				go func() {
					more := crawl(u)
					worklist <- more
				}()
			}
		}
	}
}

func crawl(u url.URL) []url.URL {
	doc, err := fetch(u)
	if err != nil {
		log.Print(err)
		return nil
	}

	return findURLs(u, doc)
}