Go language tour #73 solution

tour.golang.com#73.go

package main

import (
    "fmt"
)

type Fetcher interface {
    Fetch(url string) (body string, urls []string, err error)
}

type FetchResult struct {
    body string
    urls []string
    depth int
}

func FetchUrl(url string, depth int, resultc chan <- FetchResult) {
    body, urls, err := fetcher.Fetch(url)
    if err != nil {
        fmt.Println(err)
        resultc <- FetchResult{ body: "", urls: []string{}, depth: depth-1 }
    } else {
    	fmt.Printf("found: %s %q\n", url, body)
        resultc <- FetchResult{ body: body, urls: urls, depth: depth-1 }
    }
}

func Crawl(url string, depth int) {
    
    results := make(chan FetchResult)
    visited := make(map[string] bool)
    
    go FetchUrl(url, depth, results)
    outstanding := 1
    visited[url] = true
    
    for outstanding > 0 {
        result := <-results
        outstanding--
        if result.depth > 0 {
            for _, url := range result.urls {
                if visited[url] != true {
                    go FetchUrl(url, result.depth, results)
                    outstanding++
                    visited[url] = true
                }
            }
        }
    }
}

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

// 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/fmt/en",
            "http://golang.org/pkg/fmt/fr",
            "http://golang.org/pkg/fmt/es",
        },
    },
    "http://golang.org/pkg/fmt/en": &fakeResult{
        "Package English",
        []string {
            "http://golang.org/pkg/fmt/en/pineapple",
        },
    },
    "http://golang.org/pkg/fmt/fr": &fakeResult{
        "Package French",
        []string {
            "http://golang.org/pkg/fmt/en/ananas",
        },
    },
    "http://golang.org/pkg/fmt/es": &fakeResult{
        "Package Español",
        []string {
            "http://golang.org/pkg/fmt/en/piña",
        },
    },
    "http://golang.org/pkg/fmt/en/pineapple": &fakeResult{
        "Package Pineapple",
        []string {
        },
    },
    "http://golang.org/pkg/fmt/en/ananas": &fakeResult{
        "Package Ananas",
        []string {
        },
    },
    "http://golang.org/pkg/fmt/en/piña": &fakeResult{
        "Package Piña",
        []string {
        },
    },
    "http://golang.org/pkg/os/": &fakeResult{
        "Package os",
        []string{
            "http://golang.org/",
            "http://golang.org/pkg/",
        },
    },
}