package main

import (
	"log"
	"fmt"
	"path/filepath"
	"io"
	"os"
	"os/signal"
	"os/user"
	"os/exec"
	"strconv"
	"syscall"
	"database/sql"

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

const databaseSchemaVersion int = 2  // this defines the needed version for the
                                     // executable

func setupDatabase() *sql.DB {

	u,err := user.Current()
	if err != nil {
		log.Fatal(err)
	}
	target := fmt.Sprintf("%s@unix(%s)/%s", u.Username, config.Database.Socket,
	                      config.Database.Database)

	db,err := sql.Open("mysql", target)
	if err != nil {
		log.Fatal(err)
	}

	err = db.Ping()
	if err != nil {
		log.Fatal(err)
	}

	migrate(db)

	// allow graceful shutdown
	var listener = make(chan os.Signal)
	signal.Notify(listener, syscall.SIGTERM)
	signal.Notify(listener, syscall.SIGINT)
	go func() {
		signal := <-listener
		log.Printf("\nGot signal '%+v'. Shutting down ...\n", signal)
		dbCleanup(db)
		os.Exit(0)  // TODO this does not belong to a database - write utils file 'shutdown.go'
	}()

	return db
}

func migrate(db *sql.DB) {

	const t = databaseSchemaVersion  // targeted database schema version

	for {
		v := schemaVersion(db)  // read schema version from DB table

		// handle current database schema which is newer than targeted one
		if v > t {
			log.Fatalf(
			    "Current database schema version is %d but newest is %d!", v, t)
		}

		// break if targeted version is already reached
		if v == t {
			break
		}

		// execute migration
		log.Printf("Starting database schema migration to version %d.\n", v+1)
		path := filepath.Join(config.Database.Migrations,
		                      fmt.Sprintf("%04d_migration.sql", v+1))
		RunSqlScript(path)
		log.Printf("Finished database schema migration to version %d.\n", v+1)
	}
}

func RunSqlScript(path string) {

	script, err := os.Open(path)
	if err != nil {
		log.Fatalf("Could not open SQL script '%s'!\n", path)
	}

	cmd := exec.Command("mariadb")
	stdin, err := cmd.StdinPipe()
	if err != nil {
		log.Fatalf("Could not open stdin of mariadb process!\n%v", err)
	}

	err = cmd.Start()
	if err != nil {
		log.Fatalf("Could not start mariadb process!\n%v", err)
	}
	io.Copy(stdin, script)
	stdin.Close()

	err = cmd.Wait()
	if err != nil {
		log.Fatalf("Failed to wait for SQL script to finish!\n%v", err)
	}
}

func schemaVersion(db *sql.DB) int {

	// ask database for schema version
	cmd := "SELECT value FROM meta WHERE (identifier='version');"
	rows, err := db.Query(cmd)

	// handle missing meta table
	if err != nil {
		log.Fatal(err)
	}

	// handle successful schema version query
	defer rows.Close()
	rows.Next()
	var version string
	err = rows.Scan(&version)

	// handle missing version field in meta table
	if err != nil {
		log.Fatal(err)
	}

	// convert to integer and handle error
	v, err := strconv.Atoi(version)
	if err != nil {
		log.Fatalf("Could not convert database schema version '%s' to int.\n",
		           version)
	}

	return v
}

func dbCleanup(db *sql.DB) {
	err := db.Close()
	if err != nil {
		log.Println("Could not close database connection")
	} else {
		log.Println("Closed database connection")
	}
}