package main

import (
	"bytes"
	"encoding/json"
	"embed"
	"flag"
	"fmt"
	"log"
	"net/http"
	"net/netip"
	"os"
	"text/template"
)

//go:embed simple.css/simple.css templates/index.html
var static embed.FS

type RuntimeConfig struct {
	Devices DevicesConfig
	Web     WebConfig
}

type DevicesConfig struct {
	Hs100 []Hs100Conf
}

type WebConfig struct {
	Listen netip.AddrPort
}

func main() {
	configPath := parseFlags()
	c := parseConfig(configPath)
	http.HandleFunc("/", index(c.Devices))
	http.HandleFunc("/api", api())
	http.Handle("/static/", http.StripPrefix("/static/",
		http.FileServer(http.FS(static))))
	fmt.Printf("Serving at http://%s\n", c.Web.Listen)
	log.Fatal(http.ListenAndServe(c.Web.Listen.String(), nil))
}

// parseFlags() handles command line interface (CLI) flags.
func parseFlags() string {

	var r string

	flag.StringVar(&r, "c", "/etc/webiot/config.json",
		"path to configuration file")
	flag.Parse()

	return r
}

// parseConfig() parses and validates the runtime configuration file and
// returns it as Go datastructure.
func parseConfig(path string) RuntimeConfig {
	data, err := os.ReadFile(path)
	if err != nil {
		log.Fatalf("Could not read '%s'!", path)
	}

	if !json.Valid(data) {
		log.Fatalf("%s contains invalid JSON!", path)
	}

	config := RuntimeConfig{}
	err = json.Unmarshal(data, &config)
	if err != nil {
		log.Fatalf("Could not parse configuration file:\n%s\n", err)
	}

	return config
}

// index() returns a HTTP handler for the index page.
func index(devices DevicesConfig) func(http.ResponseWriter, *http.Request) {
	tmpl, err := template.ParseFS(static, "templates/index.html")
	if err != nil {
		log.Fatal(err)
	}

	return func(w http.ResponseWriter, r *http.Request) {
		err = tmpl.Execute(w, devices)
		if err != nil {
			http.Error(w, fmt.Sprint(err), http.StatusInternalServerError)
			return
		}
	}
}

// mustRender() renders a template file with the given data and panics if this
// is not possible.
func mustRender(filepath string, data interface{}) string {
	file, err := os.ReadFile(filepath)
	if err != nil {
		log.Fatalf("Could not read '%s'!", filepath)
	}

	tmpl, err := template.New(filepath).Parse(string(file))
	var buffer bytes.Buffer
	err = tmpl.Execute(&buffer, data)
	if err != nil {
		fmt.Println(err)
		log.Fatalf("Could not execute template for %s!", filepath)
	}

	return buffer.String()
}

// api() returns the HTTP handler for the API endpoint.
func api() func(http.ResponseWriter, *http.Request) {
	return func(w http.ResponseWriter, r *http.Request) {

		// TODO assert correct HTTP method

		errHost, host := assertSingleParam(r, "host")
		errState, state := assertSingleParam(r, "state")
		if (errHost != nil) || (errState != nil) {
			http.Error(w,
				"Provide exactly one host and one state parameter!", 400)
			return
		}

		err := set(host, state)
		if err != nil {
			http.Error(w, "Could not set WiFi plug.", 500)
		} else {
			fmt.Fprint(w, "ok")
		}
	}
}

// assertSingleParam() returns the value of given URL key and panics if there
// is not exactly one match for this key.
func assertSingleParam(r *http.Request, key string) (error, string) {

	values := r.URL.Query()[key]
	if len(values) != 1 {
		return fmt.Errorf("Provide exactly one '%s' parameter!", key), ""
	}
	return nil, values[0]

}