1 files changed, 38 insertions, 0 deletions
diff --git a/plugins/base/viewer.go b/plugins/base/viewer.go
new file mode 100644
index 0000000..a76ecf9
--- /dev/null
+++ b/plugins/base/viewer.go
@@ -0,0 +1,38 @@
+package koushinbase
+
+import (
+	"fmt"
+
+	"git.sr.ht/~emersion/koushin"
+	"github.com/emersion/go-message"
+)
+
+// ErrViewUnsupported is returned by Viewer.ViewMessagePart when the message
+// part isn't supported.
+var ErrViewUnsupported = fmt.Errorf("cannot generate message view: unsupported part")
+
+// Viewer is a message part viewer.
+type Viewer interface {
+	// ViewMessagePart renders a message part. The returned value is displayed
+	// in a template. ErrViewUnsupported is returned if the message part isn't
+	// supported.
+	ViewMessagePart(*koushin.Context, *IMAPMessage, *message.Entity) (interface{}, error)
+}
+
+var viewers []Viewer
+
+// RegisterViewer registers a message part viewer.
+func RegisterViewer(viewer Viewer) {
+	viewers = append(viewers, viewer)
+}
+
+func viewMessagePart(ctx *koushin.Context, msg *IMAPMessage, part *message.Entity) (interface{}, error) {
+	for _, viewer := range viewers {
+		v, err := viewer.ViewMessagePart(ctx, msg, part)
+		if err == ErrViewUnsupported {
+			continue
+		}
+		return v, err
+	}
+	return nil, ErrViewUnsupported
+}