// Persistent completion records. recordAchievement is idempotent (a WHERE NOT EXISTS guard,
// not a unique-index/ON CONFLICT dance — simple and correct at this write volume) so calling it
// again for something already recorded is a safe no-op, not a duplicate row.

async function recordAchievement(pool, { studentId, type, curriculumPathId, curriculumVersion, stageId, assessmentSessionId, metadata }) {
  const { rows } = await pool.query(
    `INSERT INTO achievements (student_id, achievement_type, curriculum_path_id, curriculum_version, stage_id, assessment_session_id, metadata)
     SELECT $1, $2, $3, $4, $5, $6, $7
     WHERE NOT EXISTS (
       SELECT 1 FROM achievements
       WHERE student_id = $1 AND achievement_type = $2
         AND stage_id IS NOT DISTINCT FROM $5
         AND assessment_session_id IS NOT DISTINCT FROM $6
     )
     RETURNING *`,
    [studentId, type, curriculumPathId || null, curriculumVersion || null, stageId || null, assessmentSessionId || null, metadata ? JSON.stringify(metadata) : null]
  );
  return rows[0] || null; // null means it already existed — not an error
}

// Called after a progress update — checks whether this newly-completed scenario just finished
// a stage (and, transitively, the whole curriculum), recording achievements as needed. Cheap:
// only runs the curriculum-state computation the caller already has on hand.
async function checkStageAndCurriculumAchievements(pool, { studentId, path, curriculumState }) {
  for (const stage of curriculumState.stages) {
    if (stage.complete) {
      await recordAchievement(pool, {
        studentId, type: 'stage_completed', curriculumPathId: path.id, curriculumVersion: path.version,
        stageId: stage.id,
      });
    }
  }
  const allContentStagesComplete = curriculumState.stages.every((s) => s.complete);
  if (allContentStagesComplete) {
    await recordAchievement(pool, {
      studentId, type: 'curriculum_completed', curriculumPathId: path.id, curriculumVersion: path.version,
    });
  }
}

// Called when assessments.recordScenarioOutcome/submitSession finalizes a session — records
// 'capstone_completed' or 'assessment_completed' depending on the session's type. Only fires on
// an actual pass (defensive check — the only completion_rule implemented today is
// all_scenarios_passed, which already guarantees this, but a future threshold-based rule
// shouldn't silently start granting achievements for a partial result).
async function recordAssessmentAchievement(pool, session) {
  if (!session || !session.result?.passed) return null;
  const type = session.type === 'capstone' ? 'capstone_completed' : 'assessment_completed';
  return recordAchievement(pool, {
    studentId: session.student_id, type, assessmentSessionId: session.assessment_session_id,
    metadata: { assessment_definition_id: session.assessment_definition_id, title: session.title },
  });
}

async function listAchievements(pool, studentId) {
  const { rows } = await pool.query(`SELECT * FROM achievements WHERE student_id = $1 ORDER BY achieved_at DESC`, [studentId]);
  return rows;
}

module.exports = { recordAchievement, checkStageAndCurriculumAchievements, recordAssessmentAchievement, listAchievements };