feat: add PostgreSQL persistence layer with Neon DB support

internal/interview/store_pg.go

@@ -0,0 +1,77 @@
+package interview
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+type PostgresStore struct {
+	pool *pgxpool.Pool
+}
+
+func NewPostgresStore(pool *pgxpool.Pool) *PostgresStore {
+	return &PostgresStore{pool: pool}
+}
+
+func toJSON(v any) string {
+	b, _ := json.Marshal(v)
+	return string(b)
+}
+
+func (s *PostgresStore) Create(session Session) (Session, error) {
+	_, err := s.pool.Exec(context.Background(),
+		`INSERT INTO interview_sessions (id, user_id, target_role, stack, interview_timeline, questions, answers, created_at)
+		 VALUES ($1, $2, $3, $4::jsonb, $5, $6::jsonb, $7::jsonb, $8)
+		 ON CONFLICT (id) DO UPDATE SET
+		   user_id = EXCLUDED.user_id,
+		   target_role = EXCLUDED.target_role,
+		   stack = EXCLUDED.stack,
+		   interview_timeline = EXCLUDED.interview_timeline,
+		   questions = EXCLUDED.questions,
+		   answers = EXCLUDED.answers,
+		   created_at = EXCLUDED.created_at`,
+		session.ID, session.UserID, session.TargetRole, toJSON(session.Stack),
+		session.InterviewTimeline, toJSON(session.Questions), toJSON(session.Answers), session.CreatedAt,
+	)
+	if err != nil {
+		return Session{}, fmt.Errorf("insert session: %w", err)
+	}
+	return session, nil
+}
+
+func (s *PostgresStore) Get(id string) (Session, error) {
+	var session Session
+	var stackJSON, questionsJSON, answersJSON string
+
+	err := s.pool.QueryRow(context.Background(),
+		`SELECT id, user_id, target_role, stack, interview_timeline, questions, answers, created_at
+		 FROM interview_sessions WHERE id = $1`, id,
+	).Scan(&session.ID, &session.UserID, &session.TargetRole, &stackJSON,
+		&session.InterviewTimeline, &questionsJSON, &answersJSON, &session.CreatedAt)
+	if err != nil {
+		return Session{}, ErrSessionNotFound
+	}
+
+	json.Unmarshal([]byte(stackJSON), &session.Stack)
+	json.Unmarshal([]byte(questionsJSON), &session.Questions)
+	json.Unmarshal([]byte(answersJSON), &session.Answers)
+	return session, nil
+}
+
+func (s *PostgresStore) Update(session Session) (Session, error) {
+	_, err := s.pool.Exec(context.Background(),
+		`UPDATE interview_sessions SET
+		   user_id = $2, target_role = $3, stack = $4::jsonb, interview_timeline = $5,
+		   questions = $6::jsonb, answers = $7::jsonb, created_at = $8
+		 WHERE id = $1`,
+		session.ID, session.UserID, session.TargetRole, toJSON(session.Stack),
+		session.InterviewTimeline, toJSON(session.Questions), toJSON(session.Answers), session.CreatedAt,
+	)
+	if err != nil {
+		return Session{}, fmt.Errorf("update session: %w", err)
+	}
+	return session, nil
+}