First pass implementation of an SQLite backing store for fetched opportunities

internal/store/common.go

@@ -0,0 +1,43 @@
+package store
+
+import (
+	"database/sql"
+	"fmt"
+)
+
+// Option configures Open.
+type Option func(*options)
+
+type options struct {
+	autoMigrate bool
+}
+
+// OpenDB opens the SQLite database at path with the store's connection
+// settings (foreign keys, WAL, busy timeout, immediate transactions). The
+// file is created on first use. Use it for anything that works on the store's
+// database directly, such as running migrations.
+func OpenDB(path string) (*sql.DB, error) {
+	return sql.Open("sqlite3", dsn(path))
+}
+
+// WithAutoMigrate makes Open apply pending migrations instead of returning
+// ErrNeedsMigration. Intended for tests and throwaway databases; applications
+// should migrate explicitly with the migrate command.
+func WithAutoMigrate() Option {
+	return func(o *options) { o.autoMigrate = true }
+}
+
+// dsn builds the mattn/go-sqlite3 connection string.
+//
+//   - _foreign_keys: SQLite ignores REFERENCES clauses unless this is on.
+//   - _journal_mode=WAL: readers don't block the writer or each other.
+//   - _busy_timeout: wait for a lock rather than failing immediately.
+//   - _txlock=immediate: transactions take the write lock at BEGIN, so a
+//     read-then-write transaction (as in SaveOpportunity) can't fail with
+//     SQLITE_BUSY halfway through.
+func dsn(path string) string {
+	return fmt.Sprintf(
+		"file:%s?_foreign_keys=on&_journal_mode=WAL&_busy_timeout=5000&_txlock=immediate",
+		path,
+	)
+}