aplus/aplus.go

package main

import (
	"encoding/json"
	"fmt"
	"html"
	"io"
	"net/http"
	"net/url"
	"strings"
)

func submit_code(course_code int, attendance_code string) {
	cur_body := launch_aplus(course_code)

	fmt.Printf("%s", cur_body)

	current_url := fmt.Sprintf("%s/student/", base_aplus_link)
	// the links to submit the code for a class is under the dayPanel div
	daypanel_start := strings.Index(cur_body, "<div class=\"dayPanel\"")

	// link_start - link_end is to extract the URL
	// TODO: make this more elegant to allow multiple of these links
	//       (maybe use an html parser)
	// 	 or at least use extract_attribute()
	link_start := daypanel_start
	link_start += strings.Index(cur_body[link_start:], "<a href=\"./?module")
	link_start += len("<a href=\"")
	link_end := link_start
	link_end += strings.Index(cur_body[link_end:], "\"")

	link_url := current_url + cur_body[link_start:link_end]
	link_url = html.UnescapeString(link_url)

	fmt.Println("!!!")
	fmt.Printf("%i %i %i\n", daypanel_start, link_start, link_end)
	fmt.Println(link_url)
	fmt.Println("!!!")

	resp, _ := client.Get(link_url)
	body, _ := io.ReadAll(resp.Body)

	form_str := get_form_from_request_body(body)
	form_values := parse_form(form_str)
	form_values["ctl01$sessionCode"][0] = attendance_code

	resp, _ = client.PostForm(link_url, form_values)
	body, _ = io.ReadAll(resp.Body)

	if strings.Index(string(body), "ctl01_errorMessage") != -1 {
		errormsg_start := strings.Index(string(body), "ctl01_errorMessage")
		errormsg_start += strings.Index(string(body)[errormsg_start:], "Text\">")
		errormsg_start += len("Text\">")
		errormsg_end := errormsg_start
		errormsg_end += strings.Index(string(body)[errormsg_start:], "<")
		fmt.Println(string(body)[errormsg_start:errormsg_end])
	} else if strings.Index(string(body), "ctl02_codeSuccessMessage") != -1 {
		fmt.Println("Code successfully recorded")
	}
}

func launch_aplus(course_code int) string {
	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)

	resp, _ := client.Get(aplus)
	body, _ := io.ReadAll(resp.Body)

	form_str := get_form_from_request_body(body)
	form_values := parse_form(form_str)

	resp, _ = client.PostForm(base_aplus_link, form_values)
	body, _ = io.ReadAll(resp.Body)
	return string(body)
}

func get_aplus(token string, link string, client http.Client) string {
	resp, _ := client.Get(link)

	body, _ := io.ReadAll(resp.Body)

	var aplus Aplus
	json.Unmarshal(body, &aplus)

	return aplus.URL
}

func get_form_from_request_body(req_body []byte) string {
	body_str := string(req_body)
	form_start := strings.Index(body_str, "<form")
	form_end := strings.Index(body_str, "</form>") + 7
	form_html := req_body[form_start:form_end]

	return string(form_html)
}

// parse_form extracts form fields and values from the given HTML form string.
func parse_form(form_html string) url.Values {
	form_values := make(url.Values)
	inputs := strings.Split(form_html, "<input")

	for _, input := range inputs {
		// Extract field name and value
		name := extract_attribute(input, "name")
		value := html.UnescapeString(extract_attribute(input, "value"))

		if name != "" {
			form_values.Add(name, value)
		}
	}

	return form_values
}

func extract_attribute(input string, attribute string) string {
	start := strings.Index(input, attribute+"=\"")
	if start == -1 {
		start = strings.Index(input, attribute+"='")
	}

	if start == -1 {
		return ""
	}

	start += len(attribute) + 2

	end := strings.Index(input[start:], "\"")
	if end == -1 {
		end = strings.Index(input[start:], "'")
	}

	if end == -1 {
		return ""
	}

	return input[start : start+end]
}