package main

import (
	"database/sql"
	"encoding/csv"
	"flag"
	"log"
	"os"
	"strconv"

	_ "github.com/go-sql-driver/mysql"
)

// Student from Database
type Student struct {
	Vorname, Nachname string
	Matrikelnummer    int
	StudiengangID     int
}

var (
	databaseURL = flag.String("db", "julian:hi@/test", "The Database url")
)

const (
	insertQuery = "INSERT INTO Teilnehmer (Nachname, Vorname, Matrnr, Studiengang) VALUES(?,?,?,?)"
)

// Main Function
func main() {
	flag.Parse()

	if flag.NArg() == 0 {
		log.Fatal("no file(s) given!")
	}

	// try to open file
	file, err := os.Open(flag.Arg(0))
	if err != nil {
		log.Fatal("could not open file:", err)
	}
	defer file.Close()

	reader := csv.NewReader(file)

	defer log.Println("shutdown completed")
	// list all Database providers
	log.Println("Database providers:", sql.Drivers())

	// connect to database
	db, err := sql.Open("mysql", *databaseURL)

	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()
	log.Println("mysql connection established")
	// prepare Queries
	newStudent, err := db.Prepare(insertQuery)
	if err != nil {
		log.Fatal("Error preparing statement:", insertQuery+":", err)
	}

	defer newStudent.Close()

	// init completed
	defer log.Println("shutting down")

	var (
		line       []string
		linenumber = 0
		count      = 0
	)

	for ; err == nil; line, err = reader.Read() {
		linenumber++
		if len(line) < 4 {
			log.Println("line", linenumber, "malformed")
			continue
		}

		number, err := strconv.Atoi(line[2])
		if err != nil {
			log.Println("line", linenumber, ":could not convert ID:"+line[2]+":", err)
			continue
		}
		if number < 0 {
			log.Println("line", linenumber, ":ID invalid:", number)
			continue
		}

		studiengang, err := strconv.Atoi(line[3])
		if err != nil {
			log.Println("line", linenumber, ":studiengang could not be converted:", err)
			continue
		}
		if studiengang < 0 || studiengang > 2 {
			log.Println("line", linenumber, ":Studiengang does not exist:", studiengang)
			continue
		}

		if _, err := newStudent.Exec(line[0], line[1], number, studiengang); err != nil {
			log.Println("line", linenumber, ":could not execute INSERT:", err)
			continue
		}

		count++
	}

	log.Println("done, inserted", count, "records")
}