package main

import (
    "log"
    "net/http"

    "github.com/mileusna/facebook-messenger"
)

func main() {
    msng := &messenger.Messenger{
        AccessToken:     "YOUR_ACCESS_TOKEN_THAT_YOU_WILL_GENERATE_FOR_YOUR_PAGE_ON_FACEBOOK",
        VerifyToken:     "YOUR_SECRET_TOKEN_FOR_VERIFYING_WEBHOOK_PUT_THE_SAME_VALUE_HERE_AND_ON_FB",
        PageID:          "YOUR_PAGE_ID",
        MessageReceived: messageReceived, // your function for handling received messages, defined below
    }

    // in init or afterwards, you can also specify events when receiving postbacks and message delivery reports from Facebook
    // if you don't want to manage this events, just comment/don't use this receivers
    msng.PostbackReceived = postbackReceived // comment/delete if not used
    // msng.DeliveryReceived = deliveryReceived // comment/delete if not used

    // set URL for your webhook and directly use msng as http Handler
    http.Handle("/mychatbot", msng)
    http.ListenAndServe(":8008", nil)
}

// messageReceived is called when you receive message on you webhook i.e. when someone sends message to your chat bot
// params: messenger that received the message, then the user id that sent us message and message data itself
func messageReceived(msng *messenger.Messenger, userID int64, m messenger.FacebookMessage) {

    // message received, now lets check what user has sent to us
    switch m.Text {
    case "hello", "hi":
        // someone sent hello or hi, reply with simple text message
        msng.SendTextMessage(userID, "Hello there")

    case "send me website":
        // now lets send him some structured message with image and link
        gm := msng.NewGenericMessage(userID)
        gm.AddNewElement("Title", "Subtitle", "http://mysite.com", "http://mysite.com/some-photo.jpeg", nil)

        // GenericMessage can contain up to 10 elements, they are represented as cards and can be scoreled horicontally in messenger
        // So lets add one more element, this time with buttons
        btn1 := msng.NewWebURLButton("Contact US", "http://mysite.com/contact")
        btn2 := msng.NewPostbackButton("Ok", "THIS_DATA_YOU_WILL_RECEIVE_AS_POSTBACK_WHEN_USER_CLICK_THE_BUTTON")
        gm.AddNewElement("Site title", "Subtitle", "http://mysite.com", "http://mysite.com/some-photo.jpeg", []messenger.Button{btn1, btn2})

        // ok, message is ready, lets send
        msng.SendMessage(gm)

    default:
        // upthere we haven't check for errors and responses for cleaner example code
        // but keep in mind that SendMessage returns FacebookResponse struct and error
        // errors are received from Facebook if sometnihg went wrong with message sending
        resp, err := msng.SendTextMessage(userID, m.Text) // echo, send back to user the same text he sent to us
        if err != nil {
            log.Println(err)
            return // if there is an error, resp is empty struct, useless
        }
        log.Println("Message ID", resp.MessageID, "sent to user", resp.RecipientID)
        // store resp.MessageID if you want to track delivery reports that will be sent later from Facebook
    }
}

// postbackReceived is called when you reiceive postback event from Facebook server
func postbackReceived(msng *messenger.Messenger, userID int64, p messenger.FacebookPostback) {
    if p.Payload == "THIS_DATA_YOU_WILL_RECEIVE_AS_POSTBACK_WHEN_USER_CLICK_THE_BUTTON" {
        // user just clicked Ok button from previouse example, lets just send him a message
        msng.SendTextMessage(userID, "Ok, I'm always online, chat with me anytime :)")
    }
}

// deliveryReceived is used if you want to track delivery reports for sent messages
func deliveryReceived(msng *messenger.Messenger, userID int64, d messenger.FacebookDelivery) {
    for _, mid := range d.Mids {
        log.Println("Message delivered, msgID:", mid)
    }
}