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/migrate.go

@@ -0,0 +1,105 @@
+package store
+
+import (
+	"context"
+	"database/sql"
+	"fmt"
+	"io/fs"
+	"strings"
+	"time"
+)
+
+const createSchemaMigrations = `CREATE TABLE IF NOT EXISTS schema_migrations (
+	version    TEXT PRIMARY KEY,
+	applied_at TEXT NOT NULL
+)`
+
+// Migrate applies every *.sql file at the root of migrations that is not yet
+// recorded in schema_migrations, in filename order. Each migration runs in its
+// own transaction together with the insert that records it, so a failing
+// migration leaves the database at the previous version. A version is the
+// file name without its .sql extension.
+//
+// The database must not hold a version unknown to migrations: that means it
+// was migrated by a newer build, and Migrate refuses to continue.
+func Migrate(ctx context.Context, db *sql.DB, migrations fs.FS) error {
+	files, err := fs.Glob(migrations, "*.sql")
+	if err != nil {
+		return fmt.Errorf("migrate: list migrations: %w", err)
+	}
+	if len(files) == 0 {
+		return fmt.Errorf("migrate: no migrations found")
+	}
+
+	if _, err := db.ExecContext(ctx, createSchemaMigrations); err != nil {
+		return fmt.Errorf("migrate: create schema_migrations: %w", err)
+	}
+	applied, err := appliedVersions(ctx, db)
+	if err != nil {
+		return err
+	}
+
+	known := make(map[string]bool, len(files))
+	for _, name := range files {
+		known[strings.TrimSuffix(name, ".sql")] = true
+	}
+	for version := range applied {
+		if !known[version] {
+			return fmt.Errorf("migrate: database has version %q, which this build does not know", version)
+		}
+	}
+
+	for _, name := range files { // fs.Glob returns names in lexical order
+		version := strings.TrimSuffix(name, ".sql")
+		if applied[version] {
+			continue
+		}
+		body, err := fs.ReadFile(migrations, name)
+		if err != nil {
+			return fmt.Errorf("migrate: read %s: %w", name, err)
+		}
+		if err := apply(ctx, db, version, string(body)); err != nil {
+			return fmt.Errorf("migrate: apply %s: %w", name, err)
+		}
+	}
+	return nil
+}
+
+func appliedVersions(ctx context.Context, db *sql.DB) (map[string]bool, error) {
+	rows, err := db.QueryContext(ctx, `SELECT version FROM schema_migrations`)
+	if err != nil {
+		return nil, fmt.Errorf("migrate: read schema_migrations: %w", err)
+	}
+	defer rows.Close()
+	applied := make(map[string]bool)
+	for rows.Next() {
+		var v string
+		if err := rows.Scan(&v); err != nil {
+			return nil, fmt.Errorf("migrate: read schema_migrations: %w", err)
+		}
+		applied[v] = true
+	}
+	if err := rows.Err(); err != nil {
+		return nil, fmt.Errorf("migrate: read schema_migrations: %w", err)
+	}
+	return applied, nil
+}
+
+func apply(ctx context.Context, db *sql.DB, version, body string) error {
+	tx, err := db.BeginTx(ctx, nil)
+	if err != nil {
+		return err
+	}
+	defer tx.Rollback() // no-op once committed
+
+	if _, err := tx.ExecContext(ctx, body); err != nil {
+		return err
+	}
+	if _, err := tx.ExecContext(ctx,
+		`INSERT INTO schema_migrations (version, applied_at) VALUES (?, ?)`,
+		version, time.Now().UTC().Format(time.RFC3339),
+	); err != nil {
+		return err
+	}
+	return tx.Commit()
+}