refactor: make migration process more intelligent, add test coverage

pkg/db/pragma_fk_check.go

@@ -0,0 +1,42 @@
+package db
+
+import (
+	"fmt"
+	"strings"
+
+	"github.com/jmoiron/sqlx"
+
+	"git.offline-twitter.com/offline-labs/gas-stack/pkg/must"
+)
+
+// PragmaFKViolation is a result row of SQLite's `pragma foreign_key_check`.
+type PragmaFKViolation struct {
+	SrcTable      string `db:"table"`
+	SrcRowid      int    `db:"rowid"`
+	DstTable      string `db:"parent"`
+	ForeignKeyIdx int    `db:"fkid"`
+}
+
+// PragmaFKViolations is a slice of FK violations.  It also implements the `error` interface.
+type PragmaFKViolations []PragmaFKViolation
+
+func (v PragmaFKViolations) Error() string {
+	var b strings.Builder
+	for i, fkv := range v {
+		if i > 0 {
+			b.WriteString("\n")
+		}
+		fmt.Fprintf(&b, "Item #%d in table %q has invalid reference to table %q", fkv.SrcRowid, fkv.SrcTable, fkv.DstTable)
+	}
+	return b.String()
+}
+
+// PragmaForeignKeyCheck uses `pragma foreign_key_check` to do a full database check for any FK violations.
+func PragmaForeignKeyCheck(q sqlx.Queryer) error {
+	var ret PragmaFKViolations
+	must.Do(sqlx.Select(q, &ret, `pragma foreign_key_check`))
+	if len(ret) == 0 {
+		return nil
+	}
+	return ret
+}