Update

+config.json
+credentials.json
+token.json
\ No newline at end of file

@@ -3,17 +3,19 @@ module classroom
 go 1.14
 
 require (
+	classroom/endpoints v0.0.0
+	classroom/functions v0.0.0
+	classroom/models v0.0.0
+	classroom/utils v0.0.0
 	github.com/go-sql-driver/mysql v1.5.0
 	github.com/julienschmidt/httprouter v1.3.0
 	github.com/rs/cors v1.7.0
-
-	classroom/endpoints v0.0.0
-	classroom/models v0.0.0
-	classroom/functions v0.0.0
+	google.golang.org/api v0.36.0
 )
 
 replace (
 	classroom/endpoints v0.0.0 => ./endpoints
-	classroom/models v0.0.0 => ./models
 	classroom/functions v0.0.0 => ./functions
-)
\ No newline at end of file
+	classroom/models v0.0.0 => ./models
+	classroom/utils v0.0.0 => ./utils
+)

+module classroom
+
+go 1.14
+
+require (
+	golang.org/x/net v0.0.0-20201031054903-ff519b6c9102
+	golang.org/x/oauth2 v0.0.0-20201109201403-9fd604954f58
+	google.golang.org/api v0.36.0
+)

+package utils
+
+import (
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"os"
+
+	"golang.org/x/net/context"
+	"golang.org/x/oauth2"
+)
+
+// Retrieve a token, saves the token, then returns the generated client.
+func getClient(config *oauth2.Config) *http.Client {
+	// The file token.json stores the user's access and refresh tokens, and is
+	// created automatically when the authorization flow completes for the first
+	// time.
+	tokFile := "token.json"
+	tok, err := tokenFromFile(tokFile)
+	if err != nil {
+		tok = getTokenFromWeb(config)
+		saveToken(tokFile, tok)
+	}
+	return config.Client(context.Background(), tok)
+}
+
+// Request a token from the web, then returns the retrieved token.
+func getTokenFromWeb(config *oauth2.Config) *oauth2.Token {
+	authURL := config.AuthCodeURL("state-token", oauth2.AccessTypeOffline)
+	fmt.Printf("Go to the following link in your browser then type the "+
+		"authorization code: \n%v\n", authURL)
+
+	var authCode string
+	if _, err := fmt.Scan(&authCode); err != nil {
+		log.Fatalf("Unable to read authorization code: %v", err)
+	}
+
+	tok, err := config.Exchange(context.TODO(), authCode)
+	if err != nil {
+		log.Fatalf("Unable to retrieve token from web: %v", err)
+	}
+	return tok
+}
+
+// Retrieves a token from a local file.
+func tokenFromFile(file string) (*oauth2.Token, error) {
+	f, err := os.Open(file)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	tok := &oauth2.Token{}
+	err = json.NewDecoder(f).Decode(tok)
+	return tok, err
+}
+
+// Saves a token to a file path.
+func saveToken(path string, token *oauth2.Token) {
+	fmt.Printf("Saving credential file to: %s\n", path)
+	f, err := os.OpenFile(path, os.O_RDWR|os.O_CREATE|os.O_TRUNC, 0600)
+	if err != nil {
+		log.Fatalf("Unable to cache oauth token: %v", err)
+	}
+	defer f.Close()
+	json.NewEncoder(f).Encode(token)
+}

+package utils
+
+import (
+	"strings"
+)
+
+func A1ToInt(val string) int64 {
+	upperVal := strings.ToUpper(val)
+	idx := 0
+	for i := range upperVal {
+		idx += 26*i + (int(upperVal[i]) - 65)
+	}
+	return int64(idx)
+}

+package utils
+
+import (
+	"context"
+	"fmt"
+	"io/ioutil"
+	"log"
+
+	"golang.org/x/oauth2/google"
+	"google.golang.org/api/option"
+	"google.golang.org/api/sheets/v4"
+)
+
+type SheetsService struct {
+	srv *sheets.Service
+	ctx context.Context
+}
+
+func NewSheetsService(credentialsPath string) (*SheetsService, error) {
+	b, err := ioutil.ReadFile(credentialsPath)
+	if err != nil {
+		log.Fatalf("Unable to read client secret file: %v", err)
+	}
+
+	// If modifying these scopes, delete your previously saved token.json.
+	config, err := google.ConfigFromJSON(b, "https://www.googleapis.com/auth/spreadsheets")
+	if err != nil {
+		log.Fatalf("Unable to parse client secret file to config: %v", err)
+	}
+	client := getClient(config)
+
+	ctx := context.Background()
+	sheetsService, err := sheets.NewService(ctx,
+		option.WithHTTPClient(client),
+		option.WithScopes(sheets.SpreadsheetsScope),
+	)
+	if err != nil {
+		return nil, err
+	}
+
+	srv := &SheetsService{
+		srv: sheetsService,
+		ctx: ctx,
+	}
+
+	return srv, nil
+}
+
+func (s *SheetsService) WriteAndMerge(sr SheetsRequest) error {
+	req := &sheets.Request{}
+	req.MergeCells = &sheets.MergeCellsRequest{
+		MergeType: "MERGE_ALL",
+		Range:     sr.Range,
+	}
+
+	rb := &sheets.BatchUpdateSpreadsheetRequest{
+		Requests: []*sheets.Request{req},
+	}
+
+	_, err := s.srv.Spreadsheets.BatchUpdate(sr.SpreadSheetID, rb).Context(s.ctx).Do()
+	if err != nil {
+		return err
+	}
+
+	var vr sheets.ValueRange
+	val := []interface{}{sr.Value}
+	vr.Values = append(vr.Values, val)
+	_, err = s.srv.Spreadsheets.Values.Append(sr.SpreadSheetID, sr.RangeStr, &vr).ValueInputOption("RAW").Do()
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (s *SheetsService) RemoveValue(sr SheetsRequest) error {
+	req := &sheets.Request{}
+	req.UnmergeCells = &sheets.UnmergeCellsRequest{
+		Range: sr.Range,
+	}
+
+	req2 := &sheets.Request{}
+	req2.UpdateBorders = &sheets.UpdateBordersRequest{
+		Range: sr.Range,
+		InnerHorizontal: &sheets.Border{
+			Color: &sheets.Color{
+				Blue:  0.0,
+				Green: 0.0,
+				Red:   0.0,
+			},
+			Style: "SOLID",
+		},
+	}
+
+	rb := &sheets.BatchUpdateSpreadsheetRequest{
+		Requests: []*sheets.Request{req, req2},
+	}
+
+	_, err := s.srv.Spreadsheets.BatchUpdate(sr.SpreadSheetID, rb).Context(s.ctx).Do()
+	if err != nil {
+		return err
+	}
+
+	_, err = s.srv.Spreadsheets.Values.Clear(sr.SpreadSheetID, sr.RangeStr, &sheets.ClearValuesRequest{}).Do()
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+type SheetsRequest struct {
+	SpreadSheetID string
+	SheetID       int64
+	Range         *sheets.GridRange
+	RangeStr      string
+	Value         string
+}
+
+func NewSheetsRequest(
+	spreadSheetID string, sheetID int64, column string, start, end int64, value string) SheetsRequest {
+	colIndex := A1ToInt(column)
+
+	req := SheetsRequest{}
+	req.SpreadSheetID = spreadSheetID
+	req.SheetID = sheetID
+	req.Range = &sheets.GridRange{
+		SheetId:          sheetID,
+		StartColumnIndex: colIndex,
+		EndColumnIndex:   colIndex + 1,
+		StartRowIndex:    start - 1,
+		EndRowIndex:      end,
+	}
+	req.RangeStr = fmt.Sprintf("%s%d:%s%d", column, start, column, end)
+	req.Value = value
+	return req
+}