package main

import (
	"fmt"
	"log"
	"net/http"
	"net/http/httputil"
	"net/url"
	"os"
)

type AutoRegistry struct {
	host               string
	port               string
	backendRegistryUrl string
	reverseProxy       *httputil.ReverseProxy
}

func NewAutoRegistry(host, port, backendRegistryUrl string) *AutoRegistry {
	proxy := AutoRegistry{
		host: host, port: port,
		backendRegistryUrl: backendRegistryUrl,
	}
	url, err := url.Parse(backendRegistryUrl)
	if err != nil {
		panic(err)
	}
	proxy.reverseProxy = httputil.NewSingleHostReverseProxy(url)
	return &proxy
}

func (autoProxy *AutoRegistry) setupHandler() {
	http.HandleFunc("/", autoProxy.requestHandler())
}

// ProxyRequestHandler handles the http request using proxy
func (autoProxy *AutoRegistry) requestHandler() func(http.ResponseWriter, *http.Request) {
	return func(w http.ResponseWriter, r *http.Request) {
		autoProxy.pushImageIfNeeded(r, autoProxy.host+":"+autoProxy.port)
		autoProxy.reverseProxy.ServeHTTP(w, r)
	}
}

func (autoProxy *AutoRegistry) pushImageIfNeeded(r *http.Request, registry string) {
	// below will catch error but can return old image to the user.
	// This will lead to a lot of troubleshooting. Better is to fail the request to the client
	// when there is a problem with docker.
	//defer func() {
	//	if r := recover(); r != nil {
	//		log.Println("ERROR: Docker interaction failed: ", r)
	//	}
	//}()

	log.Printf("Got request: %s, url: %s\n", r.Method, r.URL.Path)
	if r.Method != "HEAD" && r.Method != "GET" {
		return
	}
	image_name, tag_name, ok := ParseImage(r.URL.Path)
	if !ok {
		// not a manifest request
		return
	}
	docker_id, push_tag := GetDockerImageId(registry, image_name, tag_name)
	log.Printf("Docker id %s\n", docker_id)
	if docker_id == "" {
		return
	}
	registry_id := GetRegistryId(autoProxy.backendRegistryUrl, image_name, tag_name)
	if docker_id == registry_id {
		log.Printf("Image %s:%s is up to date in registry\n", image_name, tag_name)
	}
	log.Printf("image %s:%s is not up to date in registry, pushing it\n", image_name, tag_name)
	PushDockerImage(push_tag)
}

func printHelp() {
	fmt.Println("Usage: proxy <host> <port> <backendUrl>")
}

func main() {

	// make sure we can connect to docker and fail immediately otherwise
	CheckDockerAvailable()

	if len(os.Args) != 4 {
		printHelp()
	}
	host := os.Args[1]
	port := os.Args[2]
	backendRegistry := os.Args[3]

	log.Printf("Running with: host %s port %s backend %s\n", host, port, backendRegistry)

	proxy := NewAutoRegistry(host, port, backendRegistry)
	proxy.setupHandler()
	// handle all requests to your server using the proxy
	log.Fatal(http.ListenAndServe(":"+port, nil))
}