1 files changed, 71 insertions, 0 deletions
diff --git a/apidiff/report.go b/apidiff/report.go
new file mode 100644
index 0000000..ce79e27
--- /dev/null
+++ b/apidiff/report.go
@@ -0,0 +1,71 @@
+package apidiff
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+)
+
+// Report describes the changes detected by Changes.
+type Report struct {
+	Changes []Change
+}
+
+// A Change describes a single API change.
+type Change struct {
+	Message    string
+	Compatible bool
+}
+
+func (r Report) messages(compatible bool) []string {
+	var msgs []string
+	for _, c := range r.Changes {
+		if c.Compatible == compatible {
+			msgs = append(msgs, c.Message)
+		}
+	}
+	return msgs
+}
+
+func (r Report) String() string {
+	var buf bytes.Buffer
+	if err := r.Text(&buf); err != nil {
+		return fmt.Sprintf("!!%v", err)
+	}
+	return buf.String()
+}
+
+func (r Report) Text(w io.Writer) error {
+	if err := r.TextIncompatible(w, true); err != nil {
+		return err
+	}
+	return r.TextCompatible(w)
+}
+
+func (r Report) TextIncompatible(w io.Writer, withHeader bool) error {
+	if withHeader {
+		return r.writeMessages(w, "Incompatible changes:", r.messages(false))
+	}
+	return r.writeMessages(w, "", r.messages(false))
+}
+
+func (r Report) TextCompatible(w io.Writer) error {
+	return r.writeMessages(w, "Compatible changes:", r.messages(true))
+}
+
+func (r Report) writeMessages(w io.Writer, header string, msgs []string) error {
+	if len(msgs) == 0 {
+		return nil
+	}
+	if header != "" {
+		if _, err := fmt.Fprintf(w, "%s\n", header); err != nil {
+			return err
+		}
+	}
+	for _, m := range msgs {
+		if _, err := fmt.Fprintf(w, "- %s\n", m); err != nil {
+			return err
+		}
+	}
+	return nil
+}