package main

import (
	"encoding/json"
	"fmt"
	"io/ioutil"
	"net/http"
	"strconv"
	"time"
)

// SiteAlertConfig is an instance of a site to be monitored
// in the config file
type SiteAlertConfig struct {
	URL string `json:"url"`
}

// Config is the config that we're running with
type Config struct {
	RefreshInterval int               `json:"refresh"`
	Alerts          []SiteAlertConfig `json:"alerts"`
}

var config *Config
var allAlerts []Alert

func main() {
	loadConfig()
	for {
		fmt.Println("Kicking off refresh.")
		for i := range allAlerts {
			fmt.Println("Checking URL: " + allAlerts[i].url + "...")
			if allAlerts[i].Refresh() {
				for j := 0; j < 25; j++ {
					fmt.Println(" CHANGE DETECTED!")
				}
			}
		}
		fmt.Println("Refresh Completed.")
		time.Sleep(time.Minute)
	}
}

func loadConfig() {
	fmt.Print("Loading Config...")
	jsonInp, err := ioutil.ReadFile("config.json")
	assertError(err)
	assertError(json.Unmarshal(jsonInp, &config))
	t, e := json.Marshal(config)
	if e != nil {
		fmt.Println(e)
	} else {
		fmt.Println(string(t))
	}
	for i := range config.Alerts {
		allAlerts = append(allAlerts, *CreateNewAlert(config.Alerts[i].URL))
	}
	fmt.Println("Found " + strconv.Itoa(len(allAlerts)) + " alerts")
}

// Alert is for monitoring a page
type Alert struct {
	url        string
	contents   string
	response   *http.Response
	err        error
	updateTime time.Time

	lastChangeContents string
	lastChangeResponse *http.Response
	lastChangeError    error
	lastChangeTime     time.Time
}

// CreateNewAlert returns an alert object for url 'u'
func CreateNewAlert(u string) *Alert {
	a := Alert{url: u}
	a.response, a.err = http.Get(u)
	return &a
}

// Refresh refetches the url for the alert and returns
// true if it changed.
func (a *Alert) Refresh() bool {
	var changed bool
	r, e := http.Get(a.url)
	if e != a.err {
		a.Update(r, "", e)
		return true
	}
	if body, err := ioutil.ReadAll(r.Body); err == nil {
		b := string(body)
		if b != a.contents {
			changed = true
			a.Update(r, b, e)
		}
	} else {
		e = err
	}
	r.Body.Close()
	if e != a.err {
		a.Update(r, "", e)
		return true
	}
	return changed
}

// Update updates the contents of the alert with the new changes
func (a *Alert) Update(r *http.Response, body string, e error) {
	a.lastChangeContents = a.contents
	a.lastChangeResponse = a.response
	a.lastChangeError = a.err
	a.lastChangeTime = a.updateTime

	a.contents = body
	a.response = r
	a.err = e
	a.updateTime = time.Now()
}

func assertError(err error) {
	if err != nil {
		panic(err)
	}
}