Refactor Store into SessionStore; move domain SQL onto User/Question/Answer.

internal/store/answer.go

@@ -0,0 +1,57 @@
+package store
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"strings"
+	"time"
+)
+
+// Answer is an admin reply to a question.
+type Answer struct {
+	QuestionID string
+	AuthorID   string
+	AuthorName string
+	Body       string
+	CreatedAt  string
+	UpdatedAt  string
+	db         *sql.DB
+}
+
+// NewAnswer returns an Answer bound to db.
+func NewAnswer(db *sql.DB) *Answer {
+	return &Answer{db: db}
+}
+
+// Upsert inserts or updates the answer for QuestionID.
+func (a *Answer) Upsert(ctx context.Context) error {
+	if a == nil || a.db == nil {
+		return fmt.Errorf("answer: no database")
+	}
+	a.Body = strings.TrimSpace(a.Body)
+	now := time.Now().UTC().Format(time.RFC3339)
+	if a.CreatedAt == "" {
+		a.CreatedAt = now
+	}
+	a.UpdatedAt = now
+	_, err := a.db.ExecContext(ctx, `
+INSERT INTO answers (question_id, author_id, body, created_at, updated_at) VALUES ($1, $2, $3, $4, $5)
+ON CONFLICT (question_id) DO UPDATE SET body = excluded.body, author_id = excluded.author_id, updated_at = excluded.updated_at`,
+		a.QuestionID, a.AuthorID, a.Body, a.CreatedAt, a.UpdatedAt)
+	return err
+}
+
+func GetAnswer(ctx context.Context, db *sql.DB, questionID string) (*Answer, error) {
+	var a Answer
+	err := db.QueryRowContext(ctx, `
+SELECT a.question_id, a.author_id, u.name, a.body, a.created_at, a.updated_at
+FROM answers a
+JOIN users u ON u.id = a.author_id
+WHERE a.question_id = $1`, questionID).Scan(&a.QuestionID, &a.AuthorID, &a.AuthorName, &a.Body, &a.CreatedAt, &a.UpdatedAt)
+	if err != nil {
+		return nil, err
+	}
+	a.db = db
+	return &a, nil
+}