Solution to go tutorial #70

go#70.go

package main

import (
    "fmt"
)

type Fetcher interface {
    // Fetch returns the body of URL and
    // a slice of URLs found on that page.
    Fetch(url string) (body string, urls []string, err error)
}

type fetchQueueItem struct{
  url string
  depth int
}

// Crawl uses fetcher to recursively crawl
// pages starting with url, to a maximum of depth.
func Crawl(url string, depth int, fetcher Fetcher) {

    // This implementation doesn't do either:
    if depth <= 0 {
        return
    }
    
    chAddOne := make(chan fetchQueueItem)
    chResolveOne := make(chan string)    
    
    fnDoFetch := func(url string, depth int, chAddOne chan fetchQueueItem, chResolveOne chan string) { 
        body, urls, err := fetcher.Fetch(url)
        if err != nil {
            fmt.Println(err)
            chResolveOne <- url
            return
        }
        fmt.Printf("found: %s %q\n", url, body)
        for _, u := range urls {
            chAddOne <- fetchQueueItem{u, depth - 1}                    
        }
        chResolveOne <- url
    }
    
    
    urlPending := make(map[string] int)
    urlPending[url] = 1
    
    go fnDoFetch(url, depth, chAddOne, chResolveOne)
    
    for i := 0; i < 100; i++ {
        select{
          case toAdd := <- chAddOne:
            if urlPending[toAdd.url] == 0{
              urlPending[toAdd.url] = 1
              go fnDoFetch(toAdd.url, toAdd.depth, chAddOne, chResolveOne)
            }
            
          case toResolve := <- chResolveOne:
            
            urlPending[toResolve] = 2

            allDone := true
            for _, completedLevel := range(urlPending){
                if completedLevel != 2{
                allDone = false
                }
                
            }
            if allDone{
              return
            }
        }
        
        
    }

}

func main() {
    Crawl("http://golang.org/", 4, fetcher)
}

// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult

type fakeResult struct {
    body string
    urls []string
}

func (f *fakeFetcher) Fetch(url string) (string, []string, error) {
    if res, ok := (*f)[url]; ok {
        return res.body, res.urls, nil
    }
    
    return "", nil, fmt.Errorf("not found: %s", url)
}

// fetcher is a populated fakeFetcher.
var fetcher = &fakeFetcher{
    "http://golang.org/": &fakeResult{
        "The Go Programming Language",
        []string{
            "http://golang.org/pkg/",
            "http://golang.org/cmd/",
        },
    },
    "http://golang.org/pkg/": &fakeResult{
        "Packages",
        []string{
            "http://golang.org/",
            "http://golang.org/cmd/",
            "http://golang.org/pkg/fmt/",
            "http://golang.org/pkg/os/",
        },
    },
    "http://golang.org/pkg/fmt/": &fakeResult{
        "Package fmt",
        []string{
            "http://golang.org/",
            "http://golang.org/pkg/",
        },
    },
    "http://golang.org/pkg/os/": &fakeResult{
        "Package os",
        []string{
            "http://golang.org/",
            "http://golang.org/pkg/",
        },
    },
}