dwelling-radio/internal/statistics/statistics.go

package statistics

import (
	"database/sql"
	"dwelling-radio/internal/radio"
	"fmt"
	"time"

	"github.com/pkg/errors"
)

const MostListenedDateFormat string = "02 January 2006 at 15:04:05 MST"

type Statistics interface {
	Add(*radio.Song) error
	LastNSongs(n int64) ([]radio.Song, error)
	MostNPopularSongs(n int64) ([]radio.Song, error)
	MostSimultaneousListeners() (radio.Song, error)
	Close() error
}

type ErrPrepareStmt struct {
	Name string
}

func (e ErrPrepareStmt) Error() string {
	return fmt.Sprintf("failed to prepare an SQL statement '%s'", e.Name)
}

var ErrNoSong = errors.New("no song was passed (a struct is nil or empty)")
var ErrSongNotAdded = errors.New("song was not added")

type BaseStatistics struct {
	Db           *sql.DB
	DbDateFormat string

	StmtHistoryAdd *sql.Stmt
	StmtSongAdd    *sql.Stmt

	StmtLastNSongs                *sql.Stmt
	StmtMostPopularSongs          *sql.Stmt
	StmtMostSimultaneousListeners *sql.Stmt
}

func (s *BaseStatistics) Add(song *radio.Song) error {
	if song == nil || song.Artist == "" || song.Title == "" {
		return ErrNoSong
	}

	tx, err := s.Db.Begin()
	if err != nil {
		return err
	}
	defer tx.Rollback()

	row := tx.Stmt(s.StmtSongAdd).QueryRow(song.Artist, song.Title)
	if row.Err() != nil {
		return row.Err()
	}

	var songID int64
	if err := row.Scan(&songID); err != nil {
		return err
	}

	_, err = tx.Stmt(s.StmtHistoryAdd).Exec(song.StartAt.UTC().Format(s.DbDateFormat),
		songID, song.Listeners, song.PeakListeners)
	if err != nil {
		return errors.Wrap(err, ErrSongNotAdded.Error())
	}

	tx.Commit()

	return nil
}

func (s *BaseStatistics) LastNSongs(n int64) ([]radio.Song, error) {
	if n == 0 {
		return nil, nil
	}

	tx, err := s.Db.Begin()
	if err != nil {
		return nil, err
	}
	defer tx.Rollback()

	rows, err := tx.Stmt(s.StmtLastNSongs).Query(n)
	if err != nil {
		return nil, err
	}

	songs := make([]radio.Song, n)

	i := 0
	for rows.Next() {
		var startAt string

		if err := rows.Scan(&startAt, &songs[i].Artist, &songs[i].Title,
			&songs[i].Listeners, &songs[i].PeakListeners); err != nil {
			return nil, err
		}

		songs[i].StartAt, err = time.Parse(s.DbDateFormat, startAt)
		if err != nil {
			return nil, err
		}

		i++
	}

	tx.Commit()

	if i == 0 {
		return nil, nil
	}

	lst := make([]radio.Song, i)
	copy(lst, songs[:])

	return lst, nil
}

func (s *BaseStatistics) MostNPopularSongs(n int64) ([]radio.Song, error) {
	if n == 0 {
		return nil, nil
	}

	return nil, nil
}

func (s *BaseStatistics) MostSimultaneousListeners() (radio.Song, error) {
	return radio.Song{}, nil
}

func (s *BaseStatistics) Close() error {
	return s.Db.Close()
}