package main

import (
    "fmt"
    "sync"
    "net/http"
    "log"
    "regexp"
    "io/ioutil"
)

type Crawler struct {
    urls map[string]bool
    mux sync.Mutex
    umatch *regexp.Regexp
}

func (c Crawler) parse(body string) (urls []string) {
   return c.umatch.FindAllString(body, -1)
}

func (c Crawler) fetch(url string) (urls []string) {
    res, err := http.Get(url)
    if err != nil {
        fmt.Println("Error in fetching %s: %s", url, err)
        log.Fatal(err)
    }
    defer res.Body.Close()
    body, err := ioutil.ReadAll(res.Body)
    if err != nil {
        log.Fatal(err)
    }
    urls = c.parse(string(body))
    return
}

func (c Crawler) Crawl(url string, depth int) {
    if depth <= 0 {
        return
    }

    c.mux.Lock()
    if c.urls[url] { //Already exists
        c.mux.Unlock()
        return
    }
    c.urls[url] = true
    c.mux.Unlock()

    log.Println("Fetching %s", url)
    fetched := c.fetch(url)
    for _, u := range fetched {
        go c.Crawl(u, depth - 1)
    }
    return
}

func main() {
    c := Crawler{urls : map[string]bool{}, umatch : regexp.MustCompile(`(http|ftp|https)://([w-_]+(?:(?:.[w-_]+)+))([w-.,@?^=%&:/~+#]*[w-@?^=%&/~+#])?`)}
    c.Crawl("http://www.yahoo.com", 3)
    for u, _ := range c.urls {
        fmt.Println(u)
    }
}

re := regexp.MustCompile("href="(.*?)"")
    subre := regexp.MustCompile(""/[\w]+")

    matchLink := re.FindAllStringSubmatch(string(*data), -1)