package repository

import (
	"context"
	"errors"
	"fmt"
	"strings"

	"github.com/google/uuid"
	"github.com/jackc/pgx/v5"
	"github.com/jackc/pgx/v5/pgxpool"

	"learning-service/internal/model"
)

type LessonRepository struct {
	pool *pgxpool.Pool
}

func NewLessonRepository(pool *pgxpool.Pool) *LessonRepository {
	return &LessonRepository{pool: pool}
}

const lessonCols = `
	id, course_id, position, title, markdown, video_key, video_duration_sec,
	test_id, is_required, created_at, updated_at
`

func scanLesson(scan func(...any) error) (*model.Lesson, error) {
	var l model.Lesson
	if err := scan(
		&l.ID, &l.CourseID, &l.Position, &l.Title, &l.Markdown,
		&l.VideoKey, &l.VideoDurationSec, &l.TestID, &l.IsRequired,
		&l.CreatedAt, &l.UpdatedAt,
	); err != nil {
		return nil, err
	}
	return &l, nil
}

func (r *LessonRepository) ListByCourse(ctx context.Context, courseID uuid.UUID) ([]model.Lesson, error) {
	rows, err := r.pool.Query(ctx,
		`SELECT `+lessonCols+` FROM lessons
		 WHERE course_id = $1
		 ORDER BY position, created_at`, courseID)
	if err != nil {
		return nil, err
	}
	defer rows.Close()
	out := []model.Lesson{}
	for rows.Next() {
		l, err := scanLesson(rows.Scan)
		if err != nil {
			return nil, err
		}
		out = append(out, *l)
	}
	return out, rows.Err()
}

func (r *LessonRepository) Get(ctx context.Context, id uuid.UUID) (*model.Lesson, error) {
	l, err := scanLesson(r.pool.QueryRow(ctx,
		`SELECT `+lessonCols+` FROM lessons WHERE id = $1`, id).Scan)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, ErrNotFound
		}
		return nil, err
	}
	return l, nil
}

func (r *LessonRepository) Create(ctx context.Context, courseID uuid.UUID, req model.CreateLessonRequest) (*model.Lesson, error) {
	isRequired := true
	if req.IsRequired != nil {
		isRequired = *req.IsRequired
	}
	if strings.TrimSpace(req.Title) == "" {
		return nil, fmt.Errorf("title is required")
	}
	var id uuid.UUID
	err := r.pool.QueryRow(ctx, `
		INSERT INTO lessons (course_id, position, title, markdown, test_id, is_required)
		VALUES ($1, $2, $3, $4, $5, $6)
		RETURNING id`,
		courseID, req.Position, req.Title, req.Markdown, req.TestID, isRequired,
	).Scan(&id)
	if err != nil {
		return nil, err
	}
	return r.Get(ctx, id)
}

func (r *LessonRepository) Update(ctx context.Context, id uuid.UUID, req model.UpdateLessonRequest) (*model.Lesson, error) {
	sets := []string{}
	args := []any{}
	add := func(col string, val any) {
		args = append(args, val)
		sets = append(sets, fmt.Sprintf("%s = $%d", col, len(args)))
	}
	if req.Position != nil {
		add("position", *req.Position)
	}
	if req.Title != nil {
		add("title", *req.Title)
	}
	if req.Markdown != nil {
		add("markdown", *req.Markdown)
	}
	if req.VideoKey != nil {
		add("video_key", *req.VideoKey)
	}
	if req.VideoDurationSec != nil {
		add("video_duration_sec", *req.VideoDurationSec)
	}
	if req.TestID != nil {
		// req.TestID == &uuid.Nil → сбросить связь. Стандартное поведение
		// «явный null» делается отдельным эндпоинтом — здесь Update только
		// устанавливает не-nil значение.
		add("test_id", *req.TestID)
	}
	if req.IsRequired != nil {
		add("is_required", *req.IsRequired)
	}
	if len(sets) == 0 {
		return r.Get(ctx, id)
	}
	sets = append(sets, "updated_at = NOW()")
	args = append(args, id)
	q := fmt.Sprintf(`UPDATE lessons SET %s WHERE id = $%d`, strings.Join(sets, ", "), len(args))
	tag, err := r.pool.Exec(ctx, q, args...)
	if err != nil {
		return nil, err
	}
	if tag.RowsAffected() == 0 {
		return nil, ErrNotFound
	}
	return r.Get(ctx, id)
}

// SetVideo — отдельный helper для post-upload UPDATE: ставит video_key
// и duration после успешного PutObject в MinIO. Возвращает старый key
// (если был) — handler удалит его из MinIO best-effort'ом, чтобы не
// плодить «висящие» объекты при замене видео.
func (r *LessonRepository) SetVideo(ctx context.Context, id uuid.UUID, key string, durationSec int) (oldKey string, err error) {
	err = r.pool.QueryRow(ctx, `
		UPDATE lessons
		   SET video_key = $2, video_duration_sec = $3, updated_at = NOW()
		 WHERE id = $1
		 RETURNING (SELECT video_key FROM lessons WHERE id = $1)`,
		id, key, durationSec).Scan(&oldKey)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return "", ErrNotFound
		}
		return "", err
	}
	return oldKey, nil
}

func (r *LessonRepository) Delete(ctx context.Context, id uuid.UUID) (videoKey string, err error) {
	// Возвращаем video_key чтобы handler мог удалить объект из MinIO.
	err = r.pool.QueryRow(ctx, `
		DELETE FROM lessons WHERE id = $1
		RETURNING video_key`, id).Scan(&videoKey)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return "", ErrNotFound
		}
		return "", err
	}
	return videoKey, nil
}

// ReorderInCourse — батч-апдейт position'ов одного курса через UNNEST.
// Тот же паттерн что у TestRepository.ReorderQuestions.
func (r *LessonRepository) ReorderInCourse(ctx context.Context, courseID uuid.UUID, items []struct {
	ID       uuid.UUID
	Position int
}) error {
	if len(items) == 0 {
		return nil
	}
	ids := make([]uuid.UUID, len(items))
	positions := make([]int, len(items))
	for i, it := range items {
		ids[i] = it.ID
		positions[i] = it.Position
	}
	_, err := r.pool.Exec(ctx, `
		UPDATE lessons l
		   SET position = u.pos, updated_at = NOW()
		  FROM UNNEST($1::uuid[], $2::int[]) AS u(id, pos)
		 WHERE l.id = u.id AND l.course_id = $3`,
		ids, positions, courseID)
	return err
}