Restructurised Statistics.

internal/statistics/db/sqlite/db.go

@@ -2,11 +2,9 @@ package sqlite
 
 import (
 	"database/sql"
-	"dwelling-radio/internal/radio"
 	"dwelling-radio/internal/statistics"
 	_ "embed"
 	"fmt"
-	"time"
 
 	_ "github.com/mattn/go-sqlite3"
 	"github.com/pkg/errors"
@@ -32,52 +30,8 @@ var (
 	queryMostSimultaneousListeners string
 )
 
-var (
-	stmtSongAdd                   *sql.Stmt
-	stmtHistoryAdd                *sql.Stmt
-	stmtLastNSongs                *sql.Stmt
-	stmtMostPopularSongs          *sql.Stmt
-	stmtMostSimultaneousListeners *sql.Stmt
-)
-
 type SQLiteStatistics struct {
-	db *sql.DB
-}
-
-func initDBStatements(db *sql.DB) error {
-	db.Exec("PRAGMA foreign_keys = ON;")
-
-	_, err := db.Exec(querySchema)
-	if err != nil {
-		return errors.Wrap(err, "failed to init schema")
-	}
-
-	stmtSongAdd, err = db.Prepare(querySongAdd)
-	if err != nil {
-		return errors.Wrap(err, "failed to prepare querySongAdd")
-	}
-
-	stmtHistoryAdd, err = db.Prepare(queryHistoryAdd)
-	if err != nil {
-		return errors.Wrap(err, "failed to prepare queryHistoryAdd")
-	}
-
-	stmtLastNSongs, err = db.Prepare(queryLastNSongs)
-	if err != nil {
-		return errors.Wrap(err, "failed to prepare queryLastNSongs")
-	}
-
-	stmtMostPopularSongs, err = db.Prepare(queryMostPopularSongs)
-	if err != nil {
-		return errors.Wrap(err, "failed to prepare queryMostPopularSongs")
-	}
-
-	stmtMostSimultaneousListeners, err = db.Prepare(queryMostSimultaneousListeners)
-	if err != nil {
-		return errors.Wrap(err, "failed to prepare queryMostSimultaneousListeners")
-	}
-
-	return nil
+	statistics.BaseStatistics
 }
 
 func New(path string) (statistics.Statistics, error) {
@@ -86,106 +40,51 @@ func New(path string) (statistics.Statistics, error) {
 		return nil, err
 	}
 
-	if err := initDBStatements(db); err != nil {
-		return nil, err
-	}
+	stats := &SQLiteStatistics{
+		BaseStatistics: statistics.BaseStatistics{
+			Db: db, DbDateFormat: dbDateFormat}}
 
-	return &SQLiteStatistics{db: db}, nil
-}
+	db.Exec("PRAGMA foreign_keys = ON;")
 
-func (s *SQLiteStatistics) Add(song *radio.Song) error {
-	if song == nil || song.Artist == "" || song.Title == "" {
-		return errors.New("No song or an empty one was passed.")
-	}
-
-	tx, err := s.db.Begin()
+	_, err = db.Exec(querySchema)
 	if err != nil {
-		return err
-	}
-	defer tx.Rollback()
-
-	row := tx.Stmt(stmtSongAdd).QueryRow(song.Artist, song.Title)
-	if row.Err() != nil {
-		return row.Err()
+		return nil, errors.Wrap(err,
+			statistics.ErrPrepareStmt{Name: "initial schema"}.Error())
 	}
 
-	var songID int64
-	if err := row.Scan(&songID); err != nil {
-		return err
-	}
-
-	res, err := tx.Stmt(stmtHistoryAdd).Exec(song.StartAt.UTC().Format(dbDateFormat),
-		songID, song.Listeners, song.PeakListeners)
+	stats.BaseStatistics.StmtSongAdd, err = db.Prepare(querySongAdd)
 	if err != nil {
-		return err
-	} else if ra, err := res.RowsAffected(); ra == 0 || err != nil {
-		return errors.New("a song wasn't added to history, but there were no errors")
+		return nil, errors.Wrap(err,
+			statistics.ErrPrepareStmt{Name: "song_add"}.Error())
 	}
 
-	tx.Commit()
-
-	return nil
-}
-
-func (s *SQLiteStatistics) LastNSongs(n int64) ([]radio.Song, error) {
-	if n == 0 {
-		return nil, nil
-	}
-
-	tx, err := s.db.Begin()
+	stats.BaseStatistics.StmtHistoryAdd, err = db.Prepare(queryHistoryAdd)
 	if err != nil {
-		return nil, err
+		return nil, errors.Wrap(err,
+			statistics.ErrPrepareStmt{Name: "history_add"}.Error())
 	}
-	defer tx.Rollback()
 
-	rows, err := tx.Stmt(stmtLastNSongs).Query(n)
+	stats.BaseStatistics.StmtLastNSongs, err = db.Prepare(queryLastNSongs)
 	if err != nil {
-		return nil, err
+		return nil, errors.Wrap(err,
+			statistics.ErrPrepareStmt{Name: "last N songs"}.Error())
 	}
 
-	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(dbDateFormat, startAt)
-		if err != nil {
-			return nil, err
-		}
-
-		i++
+	stats.BaseStatistics.StmtMostPopularSongs, err = db.Prepare(queryMostPopularSongs)
+	if err != nil {
+		return nil, errors.Wrap(err,
+			statistics.ErrPrepareStmt{Name: "most popular song"}.Error())
 	}
 
-	tx.Commit()
-
-	if i == 0 {
-		return nil, nil
+	stats.BaseStatistics.StmtMostSimultaneousListeners, err = db.Prepare(queryMostSimultaneousListeners)
+	if err != nil {
+		return nil, errors.Wrap(err,
+			statistics.ErrPrepareStmt{Name: "most simultaneous listeners"}.Error())
 	}
 
-	lst := make([]radio.Song, i)
-	copy(lst, songs[:])
-
-	return lst, nil
-}
-
-func (s *SQLiteStatistics) MostNPopularSongs(n int64) ([]radio.Song, error) {
-	if n == 0 {
-		return nil, nil
-	}
-
-	return nil, nil
-}
-
-func (s *SQLiteStatistics) MostSimultaneousListeners() (radio.Song, error) {
-	return radio.Song{}, nil
+	return stats, nil
 }
 
 func (s *SQLiteStatistics) Close() error {
-	return s.db.Close()
+	return s.BaseStatistics.Close()
 }

internal/statistics/statistics.go

@@ -1,6 +1,13 @@
 package statistics
 
-import "dwelling-radio/internal/radio"
+import (
+	"database/sql"
+	"dwelling-radio/internal/radio"
+	"fmt"
+	"time"
+
+	"github.com/pkg/errors"
+)
 
 const MostListenedDateFormat string = "02 January 2006 at 15:04:05 MST"
 
@@ -11,3 +18,121 @@ type Statistics interface {
 	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()
+}