URL Shortener - Goland assignment

urlshortener.go

package main

import (
	"flag"
	"fmt"
	"gopkg.in/yaml.v2"
	"io/ioutil"
	"log"
	"net/http"
	"os"
	"strconv"
)

type Redirect struct {
	Slug string `yaml:"slug"`
	Link string `yaml:"link"`
}

type Config struct {
	Redirects [] Redirect `yaml:"redirects"`
}

func main()  {
	slug := flag.String("a", "", "The short link. Must be unique.")
	link := flag.String("u", "", "The URI of the deep link.")
	list := flag.Bool("l", false, "List redirections.")
	help := flag.Bool("h", false, "Print usage info.")
	run := flag.Bool("r", false, "Start HTTP server.")
	port := flag.Int64("p", 8080, "The port to listen on for HTTP requests.")

	flag.Usage = func() {
		fmt.Fprintf(os.Stderr, "Usage: %s Options are:\n ", os.Args)
		flag.PrintDefaults()
	}
	flag.Parse()

	if *help == true {
		flag.Usage()
	}

	if *slug != "" && *link != "" {
		addConfig(*slug, *link)
	}

	if *list {
		c, err := loadConfig()
		check(err)
		for i, r := range (*c).Redirects {
			fmt.Println(i, r.Slug, r.Link)
		}
	}

	if *run {
		runServer(*port)
	}
}

func check(err error) {
	if err != nil {
		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
		os.Exit(1)
	}
}

func runServer(port int64) {
	log.Printf("Server started on %v port", strconv.FormatInt(port, 10))
	c, err := loadConfig()
	check(err)
	h := func (w http.ResponseWriter, r *http.Request) {
		slug := r.URL.Path[1:]
		i := find((*c).Redirects, slug)
		if i < len((*c).Redirects) {
			http.Redirect(w, r, (*c).Redirects[i].Link, 307)
		} else {
			fmt.Fprintf(w, "No redirection found for '%s'!", r.URL.Path[1:])
		}
	}

	http.HandleFunc("/", h)
	log.Fatal(http.ListenAndServe(":" + strconv.FormatInt(port, 10), nil))

}

func find(rs []Redirect, s string) int {
	for i, r := range rs {
		if r.Slug == s {
			return i
		}
	}
	return len(rs)
}

func addConfig(slug string, link string) {
	c, err := loadConfig()
	check(err)

	i := find((*c).Redirects, slug)
	if i < len((*c).Redirects) {
		(*c).Redirects[i] = Redirect {
			slug,
			link,
		}
	} else {
		(*c).Redirects = append((*c).Redirects, Redirect{
			slug,
			link,
		})
	}
	err = c.saveConfig()
	check(err)
}

func loadConfig() (*Config, error) {
	c :=Config{}
	cYaml, err := ioutil.ReadFile("config.yaml")
	if err != nil {
		return &c, err
	}
	err = yaml.Unmarshal(cYaml, &c)
	return &c, err
}

func (c *Config) saveConfig() error {
	cYaml, err := yaml.Marshal(c)
	if err != nil {
		return err
	}
	err = ioutil.WriteFile("config.yaml", cYaml, 0664)
	return err
}