Set a theme cookie

2 files changed, 56 insertions, 0 deletions

diff --git a/middleware/pipe.go b/middleware/pipe.go
new file mode 100644
index 0000000..4b5064d
--- /dev/null
+++ b/middleware/pipe.go
@@ -0,0 +1,14 @@
+package middleware
+
+import "net/http"
+
+type Middleware func(http.Handler) http.Handler
+
+func Pipe(xs ...Middleware) Middleware {
+	return func(next http.Handler) http.Handler {
+		for i := len(xs) - 1; i >= 0; i-- {
+			next = xs[i](next)
+		}
+		return next
+	}
+}
diff --git a/middleware/theme.go b/middleware/theme.go
new file mode 100644
index 0000000..4f14c97
--- /dev/null
+++ b/middleware/theme.go
@@ -0,0 +1,42 @@
+package middleware
+
+import (
+	"cmp"
+	"context"
+	"math"
+	"net/http"
+)
+
+const defaultTheme = "dark"
+
+func Theme(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		var userTheme string
+
+		/* Grab the ‘theme’ cookie to figure out what the users current
+		   theme is and add it to the context.  If the user doesn’t yet
+		   have a theme cookie or the cookie they have contains an
+		   invalid theme then we fallback to the default theme and
+		   (re)set the cookie. */
+
+		c, err := r.Cookie("theme")
+		if err == nil {
+			switch c.Value {
+			case "dark", "light":
+				userTheme = c.Value
+			}
+		}
+
+		theme := cmp.Or(userTheme, defaultTheme)
+		if userTheme == "" {
+			http.SetCookie(w, &http.Cookie{
+				Name:   "theme",
+				Value:  theme,
+				MaxAge: math.MaxInt32,
+			})
+		}
+
+		ctx := context.WithValue(r.Context(), "theme", theme)
+		next.ServeHTTP(w, r.WithContext(ctx))
+	})
+}