1 files changed, 45 insertions, 0 deletions
diff --git a/avatar.go b/avatar.go
new file mode 100644
index 0000000..4342890
--- /dev/null
+++ b/avatar.go
@@ -0,0 +1,45 @@
+package main
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"net/http"
+	"strings"
+)
+
+// An avatar is drawn from the name alone: fetching one tells somewhere else
+// who reads what, and an upload needs a parser.
+func avatarSVG(name string) []byte {
+	sum := sha256.Sum256([]byte(name))
+	// Fixed saturation and lightness, so every one is readable.
+	hue := int(sum[0]) * 360 / 256
+	var b strings.Builder
+	fmt.Fprintf(&b, `<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 5 5" width="20" height="20" role="img" aria-label="%s">`, name)
+	fmt.Fprintf(&b, `<rect width="5" height="5" fill="#eee"/>`)
+	fmt.Fprintf(&b, `<g fill="hsl(%d,45%%,35%%)">`, hue)
+	// Three columns mirrored into five.
+	for x := range 3 {
+		for y := range 5 {
+			if sum[1+x*5+y]&1 == 0 {
+				continue
+			}
+			fmt.Fprintf(&b, `<rect x="%d" y="%d" width="1" height="1"/>`, x, y)
+			if x < 2 {
+				fmt.Fprintf(&b, `<rect x="%d" y="%d" width="1" height="1"/>`, 4-x, y)
+			}
+		}
+	}
+	b.WriteString(`</g></svg>`)
+	return []byte(b.String())
+}
+
+func (f *Forge) handleAvatar(w http.ResponseWriter, r *http.Request) {
+	name := r.PathValue("name")
+	if !accountNameRE.MatchString(name) {
+		http.NotFound(w, r)
+		return
+	}
+	w.Header().Set("Content-Type", "image/svg+xml")
+	w.Header().Set("Cache-Control", "max-age=86400")
+	w.Write(avatarSVG(name))
+}