Feature 02 task 1: SQLite connection and embedded migration runner (#10)

Co-authored-by: dev_agent <dev_agent@cubecraftlabs.com>
Co-committed-by: dev_agent <dev_agent@cubecraftlabs.com>

internal/store/store.go

@@ -0,0 +1,79 @@
+// Package store owns the MealQuest SQLite database: one writer connection,
+// a read pool, and the embedded schema migrations.
+package store
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"fmt"
+	"net/url"
+	"path/filepath"
+
+	_ "modernc.org/sqlite" // registers the "sqlite" database/sql driver
+)
+
+// FileName is the database file inside the data directory.
+const FileName = "mealquest.db"
+
+// readPoolSize is the maximum number of open read connections.
+const readPoolSize = 4
+
+// connPragmas are applied by the driver to every new connection.
+var connPragmas = []string{
+	"busy_timeout(5000)",
+	"journal_mode(WAL)",
+	"foreign_keys(1)",
+}
+
+// Store holds the database handles. All writes go through Writer, which has
+// exactly one connection; Reader is a pool of read-only connections.
+type Store struct {
+	Writer *sql.DB
+	Reader *sql.DB
+}
+
+// Open opens <dataDir>/mealquest.db, creating it if absent, and verifies both
+// handles can connect. It does not apply migrations; call Migrate for that.
+func Open(ctx context.Context, dataDir string) (*Store, error) {
+	path, err := filepath.Abs(filepath.Join(dataDir, FileName))
+	if err != nil {
+		return nil, fmt.Errorf("store: resolve database path: %w", err)
+	}
+
+	// The writer is opened and pinged first so the file exists and is in WAL
+	// mode before any read-only connection touches it.
+	writer, err := openDB(ctx, path, 1, url.Values{"_txlock": {"immediate"}})
+	if err != nil {
+		return nil, fmt.Errorf("store: open writer: %w", err)
+	}
+	reader, err := openDB(ctx, path, readPoolSize, url.Values{"_pragma": {"query_only(1)"}})
+	if err != nil {
+		return nil, errors.Join(fmt.Errorf("store: open reader: %w", err), writer.Close())
+	}
+	return &Store{Writer: writer, Reader: reader}, nil
+}
+
+// Close closes both handles.
+func (s *Store) Close() error {
+	return errors.Join(s.Reader.Close(), s.Writer.Close())
+}
+
+func openDB(ctx context.Context, path string, maxConns int, extra url.Values) (*sql.DB, error) {
+	q := url.Values{"_pragma": connPragmas}
+	for k, vs := range extra {
+		q[k] = append(q[k], vs...)
+	}
+	dsn := (&url.URL{Scheme: "file", Path: path, RawQuery: q.Encode()}).String()
+
+	db, err := sql.Open("sqlite", dsn)
+	if err != nil {
+		return nil, err
+	}
+	db.SetMaxOpenConns(maxConns)
+	db.SetMaxIdleConns(maxConns)
+	if err := db.PingContext(ctx); err != nil {
+		return nil, errors.Join(err, db.Close())
+	}
+	return db, nil
+}