package main

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

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

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

const (
	queryInsert = "INSERT INTO Punkte (Matrnr, Aufgabe, Punkte) VALUES(?,?,?)"
)

// This function  assumes it input to be only one float
func convertFloat(input string) string {
	// replace all , with .
	return strings.Replace(input, ",", ".", -1)
}

func YesNo() bool {
	reader := bufio.NewReader(os.Stdin)
	for {
		line, _, err := reader.ReadLine()
		if err != nil {
			return false
		}

		// default case
		if len(line) == 0 {
			return true
		}

		switch line[0] {
		case 'Y':
			fallthrough
		case 'y':
			return true
		case 'N':
			fallthrough
		case 'n':
			return false
		}
	}
}

func main() {
	flag.Parse()

	files := flag.Args()
	if len(files) == 0 {
		log.Fatal("no files given!")
	}

	db, err := sql.Open("mysql", *dbURL)
	if err != nil {
		log.Fatal("error connecting to Database:", err)
	}
	defer db.Close()

	for _, f := range files {
		log.Println("importing", f)
		file, err := os.Open(f)
		if err != nil {
			log.Println("could not open file:", f+":", err)
			continue
		}

		reader := csv.NewReader(file)
		transaction, err := db.Begin()
		if err != nil {
			log.Fatal("cannot prepare statement:", err)
		}

		stmt, err := transaction.Prepare(queryInsert)
		if err != nil {
			log.Fatal("could not prepare insert statement:", err)
		}
		defer stmt.Close()

		var (
			line      []string
			count     = 0
			linecount = 0

			ID      int
			Aufgabe = 1
			points  float64
		)

		for {
			linecount++
			line, err = reader.Read()
			if err != nil || line == nil {
				break
			}

			if len(line) < 2 {
				log.Println(linecount, ": malformed line")
				continue
			}

			if ID, err = strconv.Atoi(line[0]); err != nil {
				log.Println(linecount, ": no ID given, could not convert:", err)
				continue
			}

			fmt.Print(ID, " ")

			Aufgabe = 1
			for _, p := range line[1:] {
				if points, err = strconv.ParseFloat(convertFloat(p), 32); err != nil {
					log.Println(linecount, "A", Aufgabe, ": could not parse points:", err)
				}
				fmt.Print(points, " ")

				if _, err = stmt.Exec(ID, Aufgabe, points); err != nil {
					log.Println(linecount, ": error inserting:", err)
				}
				Aufgabe++
			}
			fmt.Println()
			count++
		}
		fmt.Println("read", count, "Students")
		fmt.Println("commit changes? (Y/n)")
		if YesNo() {
			transaction.Commit()
		}
	}
}