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// Exporting Monzo transactions to my YouNeedABudget.com (i.e. YNAB)
// account. YNAB unfortunately doesn't currently offer an Monzo integration. As
// a workaround and a practical excuse to learn Go, I decided to write one
// myself.
//
// This job is going to run N times per 24 hours. Monzo offers webhooks for
// reacting to certain types of events. I don't expect I'll need realtime data
// for my YNAB integration. That may change, however, so it's worth noting.
package main
import (
"bytes"
"encoding/json"
"fmt"
"log"
"net/http"
"net/http/httputil"
"net/url"
"strings"
"os"
"os/exec"
"utils"
)
////////////////////////////////////////////////////////////////////////////////
// Constants
////////////////////////////////////////////////////////////////////////////////
var (
accountId = os.Getenv("monzo_account_id")
clientId = os.Getenv("monzo_client_id")
clientSecret = os.Getenv("monzo_client_secret")
)
const (
redirectURI = "http://localhost:8080/authorization-code"
// TODO(wpcarro): Consider generating a random string for the state when the
// application starts instead of hardcoding it here.
state = "xyz123"
)
////////////////////////////////////////////////////////////////////////////////
// Business Logic
////////////////////////////////////////////////////////////////////////////////
// This is the response returned from Monzo when we exchange our authorization
// code for an access token. While Monzo returns additional fields, I'm only
// interested in AccessToken and RefreshToken.
type accessTokenResponse struct {
AccessToken string `json:"access_token"`
RefreshToken string `json:"refresh_token"`
ExpiresIn int `json:"expires_in"`
}
type setTokensRequest struct {
AccessToken string `json:"access_token"`
RefreshToken string `json:"refresh_token"`
ExpiresIn int `json:"expires_in"`
}
type Tokens struct {
AccessToken string `json:"access_token"`
RefreshToken string `json:"refresh_token"`
ExpiresIn int `json:"expires_in"`
}
// TODO(wpcarro): Replace http.PostForm and other similar calls with
// client.postForm. The default http.Get and other methods doesn't timeout, so
// it's better to create a configured client with a value for the timeout.
// Returns the access token and refresh tokens for the Monzo API.
func getTokens(code string) *Tokens {
res, err := http.PostForm("https://api.monzo.com/oauth2/token", url.Values{
"grant_type": {"authorization_code"},
"client_id": {clientId},
"client_secret": {clientSecret},
"redirect_uri": {redirectURI},
"code": {code},
})
utils.FailOn(err)
defer res.Body.Close()
payload := &accessTokenResponse{}
json.NewDecoder(res.Body).Decode(payload)
return &Tokens{payload.AccessToken, payload.RefreshToken, payload.ExpiresIn}
}
// TODO(wpcarro): Prefer using an environment variable for the web browser
// instead of assuming it will be google-chrome.
// Open a web browser to allow the user to authorize this application. Return
// the authorization code sent from Monzo.
func getAuthCode() string {
url := fmt.Sprintf("https://auth.monzo.com/?client_id=%s&redirect_uri=%s&response_type=code&state=%s", clientId, redirectURI, state)
exec.Command("google-chrome", url).Start()
authCode := make(chan string)
go func() {
log.Fatal(http.ListenAndServe(":8080", http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
// 1. Get authorization code from Monzo.
if req.URL.Path == "/authorization-code" {
params := req.URL.Query()
reqState := params["state"][0]
code := params["code"][0]
if reqState != state {
log.Fatalf("Value for state returned by Monzo does not equal our state. %s != %s", reqState, state)
}
authCode <- code
fmt.Fprintf(w, "Authorized!")
} else {
log.Printf("Unhandled request: %v\n", *req)
}
})))
}()
result := <-authCode
return result
}
// TODO(wpcarro): Move this logic out of here and into the tokens server.
func authorize() {
authCode := getAuthCode()
tokens := getTokens(authCode)
client := &http.Client{}
payload, _ := json.Marshal(setTokensRequest{
tokens.AccessToken,
tokens.RefreshToken,
tokens.ExpiresIn})
log.Printf("Access token: %s\n", tokens.AccessToken)
log.Printf("Refresh token: %s\n", tokens.RefreshToken)
log.Printf("Expires: %s\n", tokens.ExpiresIn)
req, _ := http.NewRequest("POST", "http://localhost:4242/set-tokens", bytes.NewBuffer(payload))
req.Header.Set("Content-Type", "application/json")
_, err := client.Do(req)
utils.FailOn(err)
}
// Retrieves the access token from the tokens server.
func getAccessToken() string {
return simpleGet("http://localhost:4242/token")
}
func main() {
accessToken := getAccessToken()
// authHeaders := map[string]string{
// "Authorization": fmt.Sprintf("Bearer %s", accessToken),
// }
client := &http.Client{}
form := url.Values{"account_id": {accountId}}
req, _ := http.NewRequest("GET", "https://api.monzo.com/transactions", strings.NewReader(form.Encode()))
req.Header.Add("Authorization", fmt.Sprintf("Bearer %s", accessToken))
req.Header.Add("Content-Type", "application/x-www-form-urlencoded")
bytes, _ := httputil.DumpRequest(req, true)
fmt.Println(string(bytes))
res, _ := client.Do(req)
bytes, _ = httputil.DumpResponse(res, true)
fmt.Println(string(bytes))
// res := simpleGet("https://api.monzo.com/accounts", authHeaders, true)
// fmt.Println(res)
os.Exit(0)
}
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