Generic dialect support. (MySQL and Postgres)

visitor.go

@@ -0,0 +1,63 @@
+package jet
+
+type visitor interface {
+	visit(element acceptsVisitor)
+}
+
+type acceptsVisitor interface {
+	accept(visitor visitor)
+}
+
+type noOpVisitorImpl struct {
+}
+
+func (n *noOpVisitorImpl) accept(visitor visitor) {
+	// NO OP
+}
+
+// --------------- dialect finder -----------------//
+
+type DialectFinder struct {
+	dialects map[string]Dialect
+}
+
+func newDialectFinder() *DialectFinder {
+	return &DialectFinder{
+		dialects: make(map[string]Dialect),
+	}
+}
+
+func (f *DialectFinder) dialect() Dialect {
+	if len(f.dialects) == 0 {
+		panic("jet: can't detect dialect")
+	}
+
+	if len(f.dialects) > 1 {
+		panic("jet: more than one dialect detected")
+	}
+
+	for _, dialect := range f.dialects {
+		return dialect
+	}
+
+	panic("jet: internal error")
+}
+
+func (f *DialectFinder) visit(element acceptsVisitor) {
+
+	if table, ok := element.(table); ok {
+		dialect := table.dialect()
+		f.dialects[dialect.Name] = dialect
+	}
+}
+
+func detectDialect(element acceptsVisitor, dialectOverride ...Dialect) Dialect {
+	if len(dialectOverride) > 0 {
+		return dialectOverride[0]
+	}
+
+	dialectFinder := newDialectFinder()
+	element.accept(dialectFinder)
+
+	return dialectFinder.dialect()
+}