From 049b70f23d0783c51a300da4cf87fa86e626a052 Mon Sep 17 00:00:00 2001
From: "Gustavo \"Guz\" L de Mello" <contact@guz.one>
Date: Mon, 24 Feb 2025 08:04:28 -0300
Subject: [PATCH] feat(smalltrip): cache middleware

---
 middleware/cache.go | 181 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 181 insertions(+)
 create mode 100644 middleware/cache.go

diff --git a/middleware/cache.go b/middleware/cache.go
new file mode 100644
index 0000000..b7aef61
--- /dev/null
+++ b/middleware/cache.go
@@ -0,0 +1,181 @@
+package middleware
+
+import (
+	"fmt"
+	"net/http"
+	"strings"
+	"time"
+)
+
+func Cache(options ...CacheOption) Middleware {
+	d := defaultCacheDirectives
+
+	for _, option := range options {
+		option(&d)
+	}
+
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Set("Cache-Control", d.String())
+			next.ServeHTTP(w, r)
+		})
+	}
+}
+
+
+type CacheOption func(*directives)
+
+func CacheMaxAge(t time.Duration) CacheOption {
+	return func(d *directives) { d.maxAge = &t }
+}
+
+func CacheSMaxAge(t time.Duration) CacheOption {
+	return func(d *directives) { d.sMaxage = &t }
+}
+
+func CacheNoCache(b ...bool) CacheOption {
+	bool := optionalTrue(b)
+	return func(d *directives) { d.noCache = &bool }
+}
+
+func CacheNoStore(b ...bool) CacheOption {
+	bool := optionalTrue(b)
+	return func(d *directives) { d.noStore = &bool }
+}
+
+func CacheNoTransform(b ...bool) CacheOption {
+	bool := optionalTrue(b)
+	return func(d *directives) { d.noTransform = &bool }
+}
+
+func CacheMustRevalidate(b ...bool) CacheOption {
+	bool := optionalTrue(b)
+	return func(d *directives) { d.mustRevalidate = &bool }
+}
+
+func CacheProxyRevalidate(b ...bool) CacheOption {
+	bool := optionalTrue(b)
+	return func(d *directives) { d.proxyRevalidate = &bool }
+}
+
+func CacheMustUnderstand(b ...bool) CacheOption {
+	bool := optionalTrue(b)
+	return func(d *directives) { d.mustUnderstand = &bool }
+}
+
+func CachePrivate(b ...bool) CacheOption {
+	bool := optionalTrue(b)
+	return func(d *directives) { d.private = &bool }
+}
+
+func CachePublic(b ...bool) CacheOption {
+	bool := optionalTrue(b)
+	return func(d *directives) { d.public = &bool }
+}
+
+func CacheImmutable(b ...bool) CacheOption {
+	bool := optionalTrue(b)
+	return func(d *directives) { d.immutable = &bool }
+}
+
+func CacheStaleWhileRevalidate(t time.Duration) CacheOption {
+	return func(d *directives) { d.staleWhileRevalidate = &t }
+}
+
+func CacheStaleIfError(t time.Duration) CacheOption {
+	return func(d *directives) { d.staleIfError = &t }
+}
+
+func optionalTrue(b []bool) bool {
+	bool := true
+	if len(b) > 0 {
+		bool = b[1]
+	}
+	return bool
+}
+
+var (
+	defaultCacheDirectives = directives{
+		maxAge:  &day,
+		sMaxage: &day,
+
+		mustRevalidate: &tru,
+		private:        &tru,
+
+		staleWhileRevalidate: &twoDays,
+		staleIfError:         &twoDays,
+	}
+	tru, fals = true, false
+	day       = time.Duration(time.Hour * 24)
+	twoDays   = time.Duration(time.Hour * 48)
+)
+
+type directives struct {
+	maxAge  *time.Duration
+	sMaxage *time.Duration
+
+	noCache     *bool
+	noStore     *bool
+	noTransform *bool
+
+	mustRevalidate  *bool
+	proxyRevalidate *bool
+	mustUnderstand  *bool
+
+	private   *bool
+	public    *bool
+	immutable *bool
+
+	staleWhileRevalidate *time.Duration
+	staleIfError         *time.Duration
+}
+
+func (d directives) String() string {
+	ds := []string{}
+
+	if d.maxAge != nil {
+		ds = append(ds, fmt.Sprintf("max-age=%d", d.maxAge.Seconds()))
+	}
+	if d.sMaxage != nil {
+		ds = append(ds, fmt.Sprintf("s-maxage=%d", d.sMaxage.Seconds()))
+	}
+
+	if d.noCache != nil && *d.noCache {
+		ds = append(ds, "no-cache")
+	}
+	if d.noStore != nil && *d.noStore {
+		ds = append(ds, "no-store")
+	}
+	if d.noTransform != nil && *d.noTransform {
+		ds = append(ds, "no-transform")
+	}
+
+	if d.mustRevalidate != nil && *d.mustRevalidate {
+		ds = append(ds, "must-revalidate")
+	}
+	if d.proxyRevalidate != nil && *d.proxyRevalidate {
+		ds = append(ds, "proxy-revalidate")
+	}
+	if d.mustUnderstand != nil && *d.mustRevalidate {
+		ds = append(ds, "must-understand")
+	}
+
+	if d.private != nil && *d.private {
+		ds = append(ds, "private")
+	}
+	if d.public != nil && *d.public {
+		ds = append(ds, "public")
+	}
+	if d.immutable != nil && *d.immutable {
+		ds = append(ds, "immutable")
+	}
+
+	if d.staleWhileRevalidate != nil {
+		ds = append(ds, fmt.Sprintf("stale-while-revalidate=%d", d.staleWhileRevalidate.Seconds()))
+	}
+	if d.staleIfError != nil {
+		ds = append(ds, fmt.Sprintf("stale-if-error=%d", d.staleIfError.Seconds()))
+	}
+
+	return strings.Join(ds, ", ")
+}