MusicServer/internal/backend/statistics.go

package backend

import (
	"context"
	"encoding/json"
	"time"

	"music-server/internal/db/repository"

	"github.com/google/uuid"
)

// SoundtrackWithSongs represents a soundtrack with its songs for statistics
type SoundtrackWithSongs struct {
	SoundtrackID         int32              `json:"soundtrack_id"`
	SoundtrackUuid       uuid.UUID          `json:"soundtrack_uuid"`
	SoundtrackName       string             `json:"soundtrack_name"`
	SoundtrackPlayed     int32              `json:"soundtrack_played"`
	SoundtrackLastPlayed *time.Time         `json:"soundtrack_last_played,omitempty"`
	Songs                []SongInfoForStats `json:"songs"`
}

// SongInfoForStats represents a song with soundtrack info for statistics.
// The field order matches the generated query rows so they can be converted directly.
type SongInfoForStats struct {
	SoundtrackID   int32     `json:"soundtrack_id"`
	SoundtrackUuid uuid.UUID `json:"soundtrack_uuid"`
	SongUuid       uuid.UUID `json:"song_uuid"`
	SoundtrackName string    `json:"soundtrack_name"`
	SongName       string    `json:"song_name"`
	Path           string    `json:"path"`
	TimesPlayed    int32     `json:"times_played"`
	FileName       *string   `json:"file_name,omitempty"`
}

// StatisticsSummary holds overall statistics
type StatisticsSummary struct {
	TotalSoundtracks       int64   `json:"total_soundtracks"`
	PlayedSoundtracks      int64   `json:"played_soundtracks"`
	NeverPlayedSoundtracks int64   `json:"never_played_soundtracks"`
	TotalSoundtrackPlays   int64   `json:"total_soundtrack_plays"`
	AvgSoundtrackPlays     float64 `json:"avg_soundtrack_plays"`
	MaxSoundtrackPlays     int64   `json:"max_soundtrack_plays"`
	MinSoundtrackPlays     int64   `json:"min_soundtrack_plays"`
}

// StatisticsService reads play statistics.
type StatisticsService struct {
	q repository.Querier
}

// NewStatisticsService creates a StatisticsService.
func NewStatisticsService(q repository.Querier) *StatisticsService {
	return &StatisticsService{q: q}
}

// soundtrackRow covers the generated rows that share the soundtrack-with-songs shape.
type soundtrackRow interface {
	repository.GetMostPlayedSoundtracksWithSongsRow |
		repository.GetLeastPlayedSoundtracksWithSongsRow |
		repository.GetLastPlayedSoundtracksRow |
		repository.GetOldestPlayedSoundtracksRow
}

func toSoundtracks[R soundtrackRow](rows []R, err error) ([]SoundtrackWithSongs, error) {
	if err != nil {
		return nil, err
	}
	var result []SoundtrackWithSongs
	for _, r := range rows {
		row := repository.GetMostPlayedSoundtracksWithSongsRow(r)
		result = append(result, SoundtrackWithSongs{
			SoundtrackID:         row.SoundtrackID,
			SoundtrackUuid:       row.SoundtrackUuid,
			SoundtrackName:       row.SoundtrackName,
			SoundtrackPlayed:     row.SoundtrackPlayed,
			SoundtrackLastPlayed: row.SoundtrackLastPlayed,
			Songs:                parseSongs(row.Songs),
		})
	}
	return result, nil
}

type songRow interface {
	repository.GetMostPlayedSongsWithSoundtrackRow | repository.GetLeastPlayedSongsWithSoundtrackRow
}

func toSongs[R songRow](rows []R, err error) ([]SongInfoForStats, error) {
	if err != nil {
		return nil, err
	}
	var result []SongInfoForStats
	for _, r := range rows {
		result = append(result, SongInfoForStats(repository.GetMostPlayedSongsWithSoundtrackRow(r)))
	}
	return result, nil
}

func parseSongs(data []byte) []SongInfoForStats {
	songs := []SongInfoForStats{}
	if data != nil {
		if err := json.Unmarshal(data, &songs); err != nil {
			return []SongInfoForStats{}
		}
	}
	return songs
}

// MostPlayedSoundtracks returns the top N most played soundtracks with their songs
func (s *StatisticsService) MostPlayedSoundtracks(ctx context.Context, limit int32) ([]SoundtrackWithSongs, error) {
	return toSoundtracks(s.q.GetMostPlayedSoundtracksWithSongs(ctx, limit))
}

// LeastPlayedSoundtracks returns the top N least played soundtracks with their songs
func (s *StatisticsService) LeastPlayedSoundtracks(ctx context.Context, limit int32) ([]SoundtrackWithSongs, error) {
	return toSoundtracks(s.q.GetLeastPlayedSoundtracksWithSongs(ctx, limit))
}

// LastPlayedSoundtracks returns the most recently played soundtracks
func (s *StatisticsService) LastPlayedSoundtracks(ctx context.Context, limit int32) ([]SoundtrackWithSongs, error) {
	return toSoundtracks(s.q.GetLastPlayedSoundtracks(ctx, limit))
}

// OldestPlayedSoundtracks returns the least recently played soundtracks
func (s *StatisticsService) OldestPlayedSoundtracks(ctx context.Context, limit int32) ([]SoundtrackWithSongs, error) {
	return toSoundtracks(s.q.GetOldestPlayedSoundtracks(ctx, limit))
}

// NeverPlayedSoundtracks returns soundtracks that have never been played
func (s *StatisticsService) NeverPlayedSoundtracks(ctx context.Context) ([]SoundtrackWithSongs, error) {
	rows, err := s.q.GetNeverPlayedSoundtracks(ctx)
	if err != nil {
		return nil, err
	}
	var result []SoundtrackWithSongs
	for _, row := range rows {
		result = append(result, SoundtrackWithSongs{
			SoundtrackID:     row.SoundtrackID,
			SoundtrackUuid:   row.SoundtrackUuid,
			SoundtrackName:   row.SoundtrackName,
			SoundtrackPlayed: row.SoundtrackPlayed,
			Songs:            parseSongs(row.Songs),
		})
	}
	return result, nil
}

// MostPlayedSongs returns the top N most played songs with their soundtrack info
func (s *StatisticsService) MostPlayedSongs(ctx context.Context, limit int32) ([]SongInfoForStats, error) {
	return toSongs(s.q.GetMostPlayedSongsWithSoundtrack(ctx, limit))
}

// LeastPlayedSongs returns the top N least played songs with their soundtrack info
func (s *StatisticsService) LeastPlayedSongs(ctx context.Context, limit int32) ([]SongInfoForStats, error) {
	return toSongs(s.q.GetLeastPlayedSongsWithSoundtrack(ctx, limit))
}

// Summary returns overall statistics
func (s *StatisticsService) Summary(ctx context.Context) (StatisticsSummary, error) {
	row, err := s.q.GetStatisticsSummary(ctx)
	if err != nil {
		return StatisticsSummary{}, err
	}
	return StatisticsSummary(row), nil
}