From ce4f44ec256fe0a9ff08384ec1d86cbf1420a67f Mon Sep 17 00:00:00 2001
From: Egor Kovetskiy <e.kovetskiy@gmail.com>
Date: Tue, 4 Jul 2023 06:49:25 +0000
Subject: [PATCH] add cache for namespaces for one hour

Signed-off-by: Egor Kovetskiy <e.kovetskiy@gmail.com>
---
 cmd/tubectl/cache.go    | 102 ++++++++++++++++++++++++++++++++++++++++
 cmd/tubectl/complete.go |   2 +-
 cmd/tubectl/kube.go     |  14 ++++++
 3 files changed, 117 insertions(+), 1 deletion(-)
 create mode 100644 cmd/tubectl/cache.go

diff --git a/cmd/tubectl/cache.go b/cmd/tubectl/cache.go
new file mode 100644
index 0000000..fa4f7b5
--- /dev/null
+++ b/cmd/tubectl/cache.go
@@ -0,0 +1,102 @@
+package main
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"time"
+
+	"github.com/reconquest/karma-go"
+)
+
+// useCache executes do() function and caches its result in path.
+// if cache is older than ttl, do() function is executed again.
+// if do() function returns error, cache is not updated.
+func useCache[T any](
+	do func() (T, error),
+	path string,
+	ttl time.Duration,
+) (T, error) {
+	var result T
+
+	userCacheDir, err := os.UserCacheDir()
+	if err != nil {
+		return result, karma.Format(
+			err,
+			"unable to get user cache dir",
+		)
+	}
+
+	cacheDir := filepath.Join(userCacheDir, "tubekit")
+
+	cachePath := filepath.Join(cacheDir, path)
+
+	cacheFile, err := os.OpenFile(cachePath, os.O_RDWR, 0644)
+	switch {
+	case err == nil:
+		defer cacheFile.Close()
+
+		stat, err := cacheFile.Stat()
+		if err != nil {
+			return result, karma.Format(
+				err,
+				"unable to stat cache file: %s", cachePath,
+			)
+		}
+
+		if time.Since(stat.ModTime()) < ttl {
+			var result T
+			err := json.NewDecoder(cacheFile).Decode(&result)
+			if err != nil {
+				return result, karma.Format(
+					err,
+					"unable to decode cache file: %s", cachePath,
+				)
+			}
+
+			return result, nil
+		}
+
+	case os.IsNotExist(err):
+		err = os.MkdirAll(filepath.Dir(cachePath), 0755)
+		if err != nil {
+			return result, karma.Format(
+				err,
+				"unable to create cache dir for: %s", cachePath,
+			)
+		}
+
+		cacheFile, err = os.Create(cachePath)
+		if err != nil {
+			return result, karma.Format(
+				err,
+				"unable to create cache file: %s", cachePath,
+			)
+		}
+
+		defer cacheFile.Close()
+
+	default:
+		return result, karma.Format(
+			err,
+			"unable to open cache file: %s", cachePath,
+		)
+	}
+
+	result, err = do()
+	if err != nil {
+		return result, err
+	}
+
+	encoder := json.NewEncoder(cacheFile)
+
+	err = encoder.Encode(result)
+	if err != nil {
+		return result, karma.Format(
+			err,
+			"unable to encode cache file: %s", path,
+		)
+	}
+
+	return result, nil
+}
diff --git a/cmd/tubectl/complete.go b/cmd/tubectl/complete.go
index a0f1373..68f122b 100644
--- a/cmd/tubectl/complete.go
+++ b/cmd/tubectl/complete.go
@@ -47,7 +47,7 @@ func completeParams(client string, params *Params) (*Params, error) {
 	}
 
 	if params.CompleteNamespace {
-		namespaces, err := requestNamespaces(client, params)
+		namespaces, err := requestNamespacesWithCache(client, params)
 		if err != nil {
 			return params, karma.Format(
 				err,
diff --git a/cmd/tubectl/kube.go b/cmd/tubectl/kube.go
index 6f5b26c..8db3ce5 100644
--- a/cmd/tubectl/kube.go
+++ b/cmd/tubectl/kube.go
@@ -6,6 +6,7 @@ import (
 	"os"
 	"os/exec"
 	"sort"
+	"time"
 
 	"github.com/reconquest/karma-go"
 	clientcmdapi "k8s.io/client-go/tools/clientcmd"
@@ -44,6 +45,19 @@ func parseKubernetesContexts(kubeconfig string) ([]string, error) {
 	return contexts, nil
 }
 
+// requestNamespacesWithCache returns list of namespaces available in current context.
+// it uses requestNamespaces() to retrieve list of namespaces from kubernetes
+// but caches the result in XDG_CACHE_HOME/tubekit/{current-context}/namespaces.json
+func requestNamespacesWithCache(client string, params *Params) ([]string, error) {
+	return useCache(
+		func() ([]string, error) {
+			return requestNamespaces(client, params)
+		},
+		fmt.Sprintf("%s/namespaces.json", params.Context),
+		time.Hour,
+	)
+}
+
 func requestNamespaces(client string, params *Params) ([]string, error) {
 	// omit namespace argument because requesting list of them
 	cmd, args := getCommand(