package main

import (
	"fmt"
	"log"

	"github.com/tidwall/buntdb"
)

var dbFile = "data.db"
var key = "test"
var value = "bla"
var nonExistingKey = "doesnotexist"

func main() {
	data, _ := readDbObject(dbFile, key)
	fmt.Printf("read key: %s\n", data)

	_ = writeDbObject(dbFile, key, value)
	fmt.Println("written key")

	data, _ = readDbObject(dbFile, key)
	fmt.Printf("read key: %s\n", data)

	_ = deleteDbObject(dbFile, key)
	fmt.Println("deleted existing key")

	data, _ = readDbObject(dbFile, key)
	fmt.Printf("read key: %s\n", data)

	_ = writeDbObject(dbFile, key, value)
	fmt.Println("written key again")

	_ = shrinkDb(dbFile)
	fmt.Println("shrunk database")

	data, _ = readDbObject(dbFile, key)
	fmt.Printf("read key: %s\n", data)

	data, err := readDbObject(dbFile, nonExistingKey)
	if err != nil {
		fmt.Println(err)
	}
	fmt.Printf("read non existing key: %s\n", data)

}

func shrinkDb(dbFile string) (err error) {
	// connect to database
	db, err := buntdb.Open(dbFile)
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	// shrink database
	err = db.Shrink()
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	return nil
}

// readDbObject reads an object from a database
func readDbObject(dbFile string, key string) (value string, err error) {
	// connect to database
	db, err := buntdb.Open(dbFile)
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	// get object
	err = db.View(func(tx *buntdb.Tx) error {
		value, err = tx.Get(key)
		if err != nil {
			return err
		}
		return err
	})
	// return object
	return
}

// writeDbObject writes an object to a database
func writeDbObject(dbFile string, key string, value string) (err error) {
	// connect to database
	db, err := buntdb.Open(dbFile)
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	// write object
	err = db.Update(func(tx *buntdb.Tx) error {
		_, _, err := tx.Set(key, value, nil)
		return err
	})
	return nil
}

// deleteDbObject deletes an object to a database
func deleteDbObject(dbFile string, dbObject string) (err error) {
	// connect to database
	db, err := buntdb.Open(dbFile)
	if err != nil {
		log.Fatal(err)
	}
	defer db.Close()

	// write object
	err = db.Update(func(tx *buntdb.Tx) error {
		_, err := tx.Delete(dbObject)
		return err
	})
	return nil
}