feat: list and show quizzes over MCP for their owner

- quizzes_list_quizzes and quizzes_show_quiz bound to GET /api/v1/quizzes
  and /api/v1/quizzes/{slug} behind user.api_token, the per-user
  golem15.quizzes.manage throttle, a scope and the access_quizzes permission
- the permission is grantable through pact.HasFrontendPermissions
- owner JSON shapes with solutions in manage_json.go, never used by a
  student route

classes/manage.go

@@ -0,0 +1,97 @@
+package classes
+
+// Owner-side management behind the manage routes under /api/v1/quizzes,
+// which the MCP quiz tools bind. There is no owner column: a user whose
+// groups grant golem15.quizzes.access_quizzes manages every quiz, as in the
+// admin (A7). Quizzes are addressed by slug.
+
+import (
+	"context"
+	"errors"
+
+	"git.golem15.com/golem15/sm-quizzes-plugin/models"
+	"gorm.io/gorm"
+)
+
+// ManagedQuizRow is one quiz of the owner list with its question count and
+// the number of completed attempts (of every user).
+type ManagedQuizRow struct {
+	Quiz          models.Quiz
+	QuestionCount int
+	AttemptsCount int
+}
+
+// ListManagedQuizzes returns every quiz, published or not, optionally only
+// those whose context equals quizContext, ordered by context (quizzes
+// without one last), title and id.
+func ListManagedQuizzes(ctx context.Context, db *gorm.DB, quizContext string) ([]ManagedQuizRow, error) {
+	db = db.WithContext(ctx)
+	q := db.Model(&models.Quiz{})
+	if quizContext != "" {
+		q = q.Where("context = ?", quizContext)
+	}
+	var quizzes []models.Quiz
+	if err := q.Order("context ASC NULLS LAST, title ASC, id ASC").Find(&quizzes).Error; err != nil {
+		return nil, err
+	}
+	out := make([]ManagedQuizRow, 0, len(quizzes))
+	if len(quizzes) == 0 {
+		return out, nil
+	}
+	ids := make([]uint, len(quizzes))
+	for i, quiz := range quizzes {
+		ids[i] = quiz.ID
+	}
+	type countRow struct {
+		QuizID uint
+		N      int
+	}
+	var questions, attempts []countRow
+	if err := db.Model(&models.Question{}).Select("quiz_id, COUNT(*) AS n").
+		Where("quiz_id IN ?", ids).Group("quiz_id").Scan(&questions).Error; err != nil {
+		return nil, err
+	}
+	if err := db.Model(&models.Attempt{}).Select("quiz_id, COUNT(*) AS n").
+		Where("quiz_id IN ? AND completed_at IS NOT NULL", ids).Group("quiz_id").Scan(&attempts).Error; err != nil {
+		return nil, err
+	}
+	questionsBy := map[uint]int{}
+	for _, c := range questions {
+		questionsBy[c.QuizID] = c.N
+	}
+	attemptsBy := map[uint]int{}
+	for _, c := range attempts {
+		attemptsBy[c.QuizID] = c.N
+	}
+	for _, quiz := range quizzes {
+		out = append(out, ManagedQuizRow{Quiz: quiz, QuestionCount: questionsBy[quiz.ID], AttemptsCount: attemptsBy[quiz.ID]})
+	}
+	return out, nil
+}
+
+// ManagedQuiz loads a quiz, published or not, with every question in sort
+// order and every answer of each, solutions included. A missing slug is
+// ErrNotFound.
+func ManagedQuiz(ctx context.Context, db *gorm.DB, slug string) (*models.Quiz, error) {
+	var quiz models.Quiz
+	err := db.WithContext(ctx).
+		Preload("Questions", func(tx *gorm.DB) *gorm.DB { return tx.Order("sort_order ASC, id ASC") }).
+		Preload("Questions.Answers", func(tx *gorm.DB) *gorm.DB { return tx.Order("sort_order ASC, id ASC") }).
+		Where("slug = ?", slug).Take(&quiz).Error
+	if errors.Is(err, gorm.ErrRecordNotFound) {
+		return nil, ErrNotFound
+	}
+	if err != nil {
+		return nil, err
+	}
+	return &quiz, nil
+}
+
+// CompletedAttemptCount counts the completed attempts of every user on a
+// quiz.
+func CompletedAttemptCount(ctx context.Context, db *gorm.DB, quizID uint) (int, error) {
+	var n int64
+	err := db.WithContext(ctx).Model(&models.Attempt{}).
+		Where("quiz_id = ? AND completed_at IS NOT NULL", quizID).Count(&n).Error
+	return int(n), err
+}