Initial version of global entry notifier

* Location defaults to AUS airport.
* Support MacOS native notifications.

Author: Rajath Agasthya

README.md

@@ -1,2 +1,29 @@
 # global-entry-notifier
-Script to notify of available Global Entry enrollment appointments at a particular location
+Script to notify of available Global Entry enrollment appointments at a particular location. Only supports running on MacOS.
+
+## Prerequisites
+
+* MacOS (for notifications).
+* Install [Go](https://go.dev) (if building from source).
+
+## Usage
+
+```shell
+$ ./global-entry-notifier -h
+Usage of ./global-entry-notifier:
+  -days int
+        number of days from today to filter slots; use 1 for current day (default 1)
+  -interval duration
+        polling interval for available slots e.g. 1m, 1h, 1h10m, 1d, 1d1h10m (default 1m0s)
+  -limit int
+        number of slots to notify (default 1)
+  -location-id int
+        ID of the Global Entry Enrollment Center; defaults to AUS airport (default 7820)
+```
+
+1. Find your desired enrollment
+   center [here](https://ttp.cbp.dhs.gov/schedulerapi/locations/?temporary=false&inviteOnly=false&operational=true&serviceName=Global%20Entry)
+   and copy its `id` field. For example: ID
+   of San Francisco Global Entry Enrollment Center is `5446`.
+2. Use the binary from [releases page](https://github.com/rajathagasthya/global-entry-notifier/releases) or build binary from source using `go build -o global-entry-notifier ./main.go`.
+3. Run the binary with the arguments shown above. Use `Ctrl+C` to exit.

go.mod

@@ -0,0 +1,3 @@
+module github.com/rajathagasthya/global-entry-notifier
+
+go 1.21.6

main.go

@@ -0,0 +1,142 @@
+package main
+
+import (
+	"encoding/json"
+	"flag"
+	"fmt"
+	"log"
+	"net/http"
+	"net/url"
+	"os"
+	"os/exec"
+	"os/signal"
+	"syscall"
+	"time"
+)
+
+type Slot struct {
+	LocationId     int  `json:"locationId"`
+	StartTimestamp Time `json:"startTimestamp"`
+	EndTimestamp   Time `json:"endTimestamp"`
+	Active         bool `json:"active"`
+}
+
+type Time struct {
+	time.Time `json:"-"`
+}
+
+// UnmarshalJSON implements the json.Unmarshaller interface.
+func (t *Time) UnmarshalJSON(data []byte) error {
+	if string(data) == "null" {
+		return nil
+	}
+	var str string
+	err := json.Unmarshal(data, &str)
+	if err != nil {
+		return err
+	}
+	pt, err := time.LoadLocation("America/Los_Angeles")
+	if err != nil {
+		return err
+	}
+	t.Time, err = time.ParseInLocation("2006-01-02T15:04", str, pt)
+	return err
+}
+
+func getSlots(u *url.URL) ([]Slot, error) {
+	resp, err := http.Get(u.String())
+	if err != nil {
+		return nil, fmt.Errorf("response error: %w", err)
+	}
+	defer resp.Body.Close()
+
+	var slots []Slot
+	err = json.NewDecoder(resp.Body).Decode(&slots)
+	if err != nil {
+		return nil, fmt.Errorf("error decoding response: %w", err)
+	}
+	return slots, nil
+}
+
+func filterSlots(slots []Slot, days int) []Slot {
+	if len(slots) == 0 || days < 0 {
+		return nil
+	}
+	var result []Slot
+	deadline := time.Now().AddDate(0, 0, int(days))
+	for _, s := range slots {
+		if s.StartTimestamp.IsZero() {
+			continue
+		}
+		if s.Active && (s.StartTimestamp.Before(deadline) || s.StartTimestamp.Equal(deadline)) {
+			result = append(result, s)
+		}
+	}
+	return result
+}
+
+func notify(slots []Slot) error {
+	if len(slots) == 0 {
+		return nil
+	}
+	for _, s := range slots {
+		script := fmt.Sprintf("display notification \"%s\" with title \"Global Entry Slot Available\" sound name \"Purr\"", s.StartTimestamp.Format("Mon Jan 2 15:04"))
+		cmd := exec.Command("/usr/bin/osascript", "-e", script)
+		cmd.Stderr = os.Stderr
+		if err := cmd.Run(); err != nil {
+			return fmt.Errorf("failed to notify: %w", err)
+		}
+	}
+	return nil
+}
+
+func main() {
+	locationID := flag.Int("location-id", 7820, "ID of the Global Entry Enrollment Center; defaults to AUS airport")
+	limit := flag.Int("limit", 1, "number of slots to notify")
+	days := flag.Int("days", 1, "number of days from today to filter slots; use 1 for current day")
+	interval := flag.Duration("interval", 1*time.Minute, "polling interval for available slots e.g. 1m, 1h, 1h10m, 1d, 1d1h10m")
+	flag.Parse()
+
+	if *locationID < 1 {
+		log.Fatal("location-id cannot be < 1")
+	}
+	if *days < 1 {
+		log.Fatal("days cannot be < 1")
+	}
+	if *limit < 1 {
+		log.Fatal("limit cannot be < 1")
+	}
+
+	// List of locations can be found at https://ttp.cbp.dhs.gov/schedulerapi/locations/?temporary=false&inviteOnly=false&operational=true&serviceName=Global%20Entry
+	u, err := url.Parse(fmt.Sprintf("https://ttp.cbp.dhs.gov/schedulerapi/slots?orderBy=soonest&limit=%d&locationId=%d", *limit, *locationID))
+	if err != nil {
+		log.Fatalf("error parsing url: %v", err)
+	}
+
+	fmt.Printf("Waiting for available appointments at location %d\n", *locationID)
+
+	sigs := make(chan os.Signal, 1)
+	signal.Notify(sigs, syscall.SIGINT, syscall.SIGTERM)
+
+	tickDuration := *interval
+	ticker := time.NewTicker(tickDuration)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-sigs:
+			log.Println("shutting down on signal")
+			return
+		case <-ticker.C:
+			slots, err := getSlots(u)
+			if err != nil {
+				log.Fatal(err)
+			}
+			if len(slots) == 0 {
+				break
+			}
+			if err := notify(filterSlots(slots, *days)); err != nil {
+				log.Fatal(err)
+			}
+		}
+	}
+}