use the Canvas API to get A+ tool ID and URL

Was previously hardcoded.

README.md

@@ -2,7 +2,7 @@
 
 This is an cli utility initially created for students at Florida Polytechnic University to submit their aplus codes. 
 In time, we intend to generalize this utility to all universities.
-In the meantime however, any students from other universities wishing to use the utility may change the base_link and external_tools_code (you see this in the URL when you navigate to Aplus attendance within your course) variables.
+In the meantime however, any students from other universities wishing to use the utility may change the instance_url (the main URL you see before the / when you use Canvas) variables.
 
 ## Usage
 

aplus.go

@@ -7,6 +7,7 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"os"
 	"strings"
 )
 
@@ -60,6 +61,12 @@ func submit_code(course_code int, attendance_code string) {
 }
 
 func launch_aplus(course_code int) string {
+	err := init_aplus_toolid(course_code)
+	if err != nil {
+		fmt.Println("Failed to get A+ base URL and tool ID")
+		os.Exit(1)
+	}
+
 	aplus_link := fmt.Sprintf("%s/courses/%d/external_tools/sessionless_launch?id=%d&access_token=%s",
 		base_link, course_code, external_tools_code, token)
 	aplus := get_aplus(token, aplus_link, client)

canvas.go

@@ -2,20 +2,21 @@ package main
 
 import (
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
 	"net/http/cookiejar"
 	"os"
+	"strings"
 
 	"golang.org/x/net/publicsuffix"
 )
 
 func initialize() {
-	base_link = "https://floridapolytechnic.instructure.com/api/v1"
-	base_aplus_link = "https://floridapoly.aplusattendance.com/canvas"
+	instance_url := "https://floridapolytechnic.instructure.com"
+	base_link = instance_url + "/api/v1"
 	token = os.Getenv("CANVAS_API_KEY")
-	external_tools_code = 913
 	jar, _ := cookiejar.New(&cookiejar.Options{
 		PublicSuffixList: publicsuffix.List,
 	})
@@ -49,6 +50,31 @@ func get_courses(token string, link string, client http.Client) []CanvasCourse {
 	return canvas_courses
 }
 
+func init_aplus_toolid(course_id int) error {
+	link := fmt.Sprintf("%s/courses/%d/external_tools?access_token=%s&search_term=aplus&include_parents=true", base_link, course_id, token)
+	resp, err := client.Get(link)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+	body, _ := io.ReadAll(resp.Body)
+
+	var external_tools []ExternalTool
+	err = json.Unmarshal(body, &external_tools)
+	if err != nil && !strings.Contains(string(body), "\"unauthorized\"") {
+		return err
+	}
+
+	for _, tool := range external_tools {
+		if strings.Contains(tool.URL, ".aplusattendance.com/") && base_aplus_link == "" {
+			base_aplus_link = tool.URL
+			external_tools_code = tool.ID
+		}
+	}
+
+	return errors.New("Could not find A+ link and tool ID")
+}
+
 func list_all_courses() {
 	all_courses := fmt.Sprintf("%s/courses?access_token=%s&per_page=100", base_link, token)
 

main.go

@@ -9,9 +9,7 @@ import (
 )
 
 var base_link string
-var base_aplus_link string
 var token string
-var external_tools_code int
 var client http.Client
 
 func main() {

structs.go

@@ -54,3 +54,9 @@ type Enrollment struct {
 	EnrollmentState                string `json:"enrollment_state"`
 	LimitPrivilegesToCourseSection bool   `json:"limit_privileges_to_course_section"`
 }
+
+type ExternalTool struct {
+	ID     int    `json:"id"`
+	URL    string `json:"url"`
+	Status string `json:"status"`
+}