Create a simple Pagination - golang programming

paginator.go

package main

import (
	"database/sql"
	"encoding/json"
	"flag"
	"fmt"
	"log"
	"net/http"
	"os"
	"strconv"

	"github.com/bmizerany/pat"
	_ "github.com/mattn/go-sqlite3"
)

// DB connection
var DB *sql.DB

func main() {
	var err error
	// Define a new command-line flag with the name 'addr', a default value of ":4000"
	// and some short help text explaining what the flag controls. The value of the
	// flag will be stored in the addr variable at runtime.
	addr := flag.String("addr", ":8080", "HTTP network address")

	// Use log.New() to create a logger for writing information messages. This takes
	// three parameters: the destination to write the logs to (os.Stdout), a string
	// prefix for message (INFO followed by a tab), and flags to indicate what
	// additional information to include (local date and time). Note that the flags
	// are joined using the bitwise OR operator |.
	// InfoLog = log.New(os.Stdout, "INFO\t", log.Ldate|log.Ltime|log.Lshortfile)
	infoLog := log.New(os.Stdout, "INFO\t", log.Ldate|log.Ltime|log.Llongfile)

	// Create a logger for writing error messages in the same way, but use stderr as
	// the destination and use the log.Lshortfile flag to include the relevant
	// file name and line number.
	errLog := log.New(os.Stderr, "ERROR\t", log.Ldate|log.Ltime|log.Llongfile)

	mux := pat.New()

	// userHandler
	// mux.Get("/user", http.HandlerFunc(user.Get))
	mux.Get("/user/create", http.HandlerFunc(CreateUser))
	mux.Get("/user", http.HandlerFunc(GetUser))

	// Importantly, we use the flag.Parse() function to parse the command-line flag.
	// This reads in the command-line flag value and assigns it to the addr
	// variable. You need to call this *before* you use the addr variable
	// otherwise it will always contain the default value of ":4000". If any errors are
	// encountered during parsing the application will be terminated.
	flag.Parse()

	// sqlite
	DB, err = sql.Open("sqlite3", "alochym.db")

	if err != nil {
		panic(err)
	}
	defer DB.Close()

	infoLog.Println("starting server on", *addr)
	err = http.ListenAndServe(*addr, mux)
	errLog.Fatal(err)
}

// User models
type User struct {
	ID       int
	Name     string
	Email    string
	Password string
}

// Pagination Object
type Pagination struct {
	Next          int
	Previous      int
	RecordPerPage int
	CurrentPage   int
	TotalPage     int
}

// Get all User accounts
func (u User) Get(page int) (interface{}, error) {
	var (
		// Create empty Album
		record = User{}
		// Create empty slice Album
		users = []User{}
		data  = map[string]interface{}{}
	)

	limit := 10
	offset := limit * (page - 1)
	data["Page"] = *pagination("users", limit, page)

	// sqlstmt - Avoid SQL Injection Attack
	// Using limit and offset to get records
	sqlstmt := fmt.Sprintf("SELECT id, name, email FROM users order by id desc limit %d offset %d", limit, offset)

	fmt.Println(sqlstmt)

	rows, _ := DB.Query(sqlstmt)
	// close rows query
	defer rows.Close()

	for rows.Next() {
		err := rows.Scan(&record.ID, &record.Name, &record.Email)
		if err != nil {
			// check server err
			return nil, err
		}

		// append record to albums slice
		users = append(users, record)
	}

	data["Records"] = users

	return data, nil
}

// GetUser return all user records
func GetUser(w http.ResponseWriter, r *http.Request) {
	u := User{}
	page, _ := strconv.Atoi(r.URL.Query().Get("page"))

	if page == 0 {
		page = 1
	}

	result, _ := u.Get(page)
	w.Header().Set("Content-Type", "application/json")
  // Transform to JSON response
	json.NewEncoder(w).Encode(result)
}

// CreateUser mock data
func CreateUser(w http.ResponseWriter, r *http.Request) {
	sqldroptable := fmt.Sprint("DROP TABLE users;")
	DB.Exec(sqldroptable)

	sqltable := fmt.Sprintf("CREATE TABLE users (id INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT, name VARCHAR(255) NOT NULL, email VARCHAR(255) NOT NULL, password CHAR(60) NOT NULL, created  datetime default current_timestamp)")

	// Execute SQL Statements
	_, err := DB.Exec(sqltable)

	if err != nil {
		fmt.Println(err.Error())
	}

	fmt.Println("User table created")

	var users = []User{
		{Name: "Alice Jones", Email: "alice@example.com", Password: "alochym@123"},
		{Name: "Do Nguyen Ha", Email: "hadn4@fpt.com.vn", Password: "alochym@123"},
		{Name: "Ngo Thi To Nhu", Email: "nhuntt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Hiep", Email: "hiepdt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Kim Hoa", Email: "hoadtk@nhs.com.vn", Password: "alochym@123"},
		{Name: "Alice Jones", Email: "alice@example.com", Password: "alochym@123"},
		{Name: "Do Nguyen Ha", Email: "hadn4@fpt.com.vn", Password: "alochym@123"},
		{Name: "Ngo Thi To Nhu", Email: "nhuntt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Hiep", Email: "hiepdt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Kim Hoa", Email: "hoadtk@nhs.com.vn", Password: "alochym@123"},
		{Name: "Alice Jones", Email: "alice@example.com", Password: "alochym@123"},
		{Name: "Do Nguyen Ha", Email: "hadn4@fpt.com.vn", Password: "alochym@123"},
		{Name: "Ngo Thi To Nhu", Email: "nhuntt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Hiep", Email: "hiepdt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Kim Hoa", Email: "hoadtk@nhs.com.vn", Password: "alochym@123"},
		{Name: "Alice Jones", Email: "alice@example.com", Password: "alochym@123"},
		{Name: "Do Nguyen Ha", Email: "hadn4@fpt.com.vn", Password: "alochym@123"},
		{Name: "Ngo Thi To Nhu", Email: "nhuntt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Hiep", Email: "hiepdt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Kim Hoa", Email: "hoadtk@nhs.com.vn", Password: "alochym@123"},
		{Name: "Alice Jones", Email: "alice@example.com", Password: "alochym@123"},
		{Name: "Do Nguyen Ha", Email: "hadn4@fpt.com.vn", Password: "alochym@123"},
		{Name: "Ngo Thi To Nhu", Email: "nhuntt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Hiep", Email: "hiepdt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Kim Hoa", Email: "hoadtk@nhs.com.vn", Password: "alochym@123"},
		{Name: "Alice Jones", Email: "alice@example.com", Password: "alochym@123"},
		{Name: "Do Nguyen Ha", Email: "hadn4@fpt.com.vn", Password: "alochym@123"},
		{Name: "Ngo Thi To Nhu", Email: "nhuntt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Hiep", Email: "hiepdt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Kim Hoa", Email: "hoadtk@nhs.com.vn", Password: "alochym@123"},
		{Name: "Alice Jones", Email: "alice@example.com", Password: "alochym@123"},
		{Name: "Do Nguyen Ha", Email: "hadn4@fpt.com.vn", Password: "alochym@123"},
		{Name: "Ngo Thi To Nhu", Email: "nhuntt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Hiep", Email: "hiepdt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Kim Hoa", Email: "hoadtk@nhs.com.vn", Password: "alochym@123"},
		{Name: "Alice Jones", Email: "alice@example.com", Password: "alochym@123"},
		{Name: "Do Nguyen Ha", Email: "hadn4@fpt.com.vn", Password: "alochym@123"},
		{Name: "Ngo Thi To Nhu", Email: "nhuntt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Hiep", Email: "hiepdt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Kim Hoa", Email: "hoadtk@nhs.com.vn", Password: "alochym@123"},
		{Name: "Alice Jones", Email: "alice@example.com", Password: "alochym@123"},
		{Name: "Do Nguyen Ha", Email: "hadn4@fpt.com.vn", Password: "alochym@123"},
		{Name: "Ngo Thi To Nhu", Email: "nhuntt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Hiep", Email: "hiepdt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Kim Hoa", Email: "hoadtk@nhs.com.vn", Password: "alochym@123"},
		{Name: "Alice Jones", Email: "alice@example.com", Password: "alochym@123"},
		{Name: "Do Nguyen Ha", Email: "hadn4@fpt.com.vn", Password: "alochym@123"},
		{Name: "Ngo Thi To Nhu", Email: "nhuntt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Hiep", Email: "hiepdt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Kim Hoa", Email: "hoadtk@nhs.com.vn", Password: "alochym@123"},
		{Name: "Alice Jones", Email: "alice@example.com", Password: "alochym@123"},
		{Name: "Do Nguyen Ha", Email: "hadn4@fpt.com.vn", Password: "alochym@123"},
		{Name: "Ngo Thi To Nhu", Email: "nhuntt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Hiep", Email: "hiepdt@fpt.com.vn", Password: "alochym@123"},
		{Name: "Do Thi Kim Hoa", Email: "hoadtk@nhs.com.vn", Password: "alochym@123"},
	}

	for _, v := range users {
		sqlstmt := fmt.Sprintf("INSERT INTO users(name, email, password) VALUES(\"%s\", \"%s\", \"%s\")",
			v.Name,
			v.Email,
			v.Password,
		)
		DB.Exec(sqlstmt)
	}
	w.Write([]byte("Get All Snippet"))
}

// sqlHelper
// running sql command and return error
func sqlHelper(db *sql.DB, sqlstmt string) error {
	// Execute SQL Statements
	fmt.Println(sqlstmt)

	result, err := db.Exec(sqlstmt)

	// err check for DB operation
	if err != nil {
		return err
	}

	rowCount, err := result.RowsAffected()

	// error check for RowsAffected function
	if err != nil {
		return err
	}

	// there is no row found
	if rowCount == 0 {
		return sql.ErrNoRows
	}

	return nil
}

// Generated Pagination Meta data
func pagination(table string, limit, page int) *Pagination {
	var (
		tmpl        = Pagination{}
		recordcount int
	)

	// Count all record
	sqltable := fmt.Sprintf("SELECT count(id) FROM %s", table)

	DB.QueryRow(sqltable).Scan(&recordcount)

	total := (recordcount / limit)

	// Calculator Total Page
	remainder := (recordcount % limit)
	if remainder == 0 {
		tmpl.TotalPage = total
	} else {
		tmpl.TotalPage = total + 1
	}

	// Set current/record per page meta data
	tmpl.CurrentPage = page
	tmpl.RecordPerPage = limit

	// Calculator the Next/Previous Page
	if page <= 0 {
		tmpl.Next = page + 1
	} else if page < tmpl.TotalPage {
		tmpl.Previous = page - 1
		tmpl.Next = page + 1
	} else if page == tmpl.TotalPage {
		tmpl.Previous = page - 1
		tmpl.Next = 0
	}

	return &tmpl
}