feat: remote taskfile improvements (cache/expiry) (#2176)

* feat: cache as node, RemoteNode and cache-first approach

* feat: cache expiry

* feat: pass ctx into reader methods instead of timeout

* docs: updated remote taskfiles experiment doc

* feat: use cache if download fails

taskfile/node_cache.go

@@ -0,0 +1,113 @@
+package taskfile
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"os"
+	"path/filepath"
+	"time"
+)
+
+const remoteCacheDir = "remote"
+
+type CacheNode struct {
+	*BaseNode
+	source RemoteNode
+}
+
+func NewCacheNode(source RemoteNode, dir string) *CacheNode {
+	return &CacheNode{
+		BaseNode: &BaseNode{
+			dir: filepath.Join(dir, remoteCacheDir),
+		},
+		source: source,
+	}
+}
+
+func (node *CacheNode) Read() ([]byte, error) {
+	return os.ReadFile(node.Location())
+}
+
+func (node *CacheNode) Write(data []byte) error {
+	if err := node.CreateCacheDir(); err != nil {
+		return err
+	}
+	return os.WriteFile(node.Location(), data, 0o644)
+}
+
+func (node *CacheNode) ReadTimestamp() time.Time {
+	b, err := os.ReadFile(node.timestampPath())
+	if err != nil {
+		return time.Time{}.UTC()
+	}
+	timestamp, err := time.Parse(time.RFC3339, string(b))
+	if err != nil {
+		return time.Time{}.UTC()
+	}
+	return timestamp.UTC()
+}
+
+func (node *CacheNode) WriteTimestamp(t time.Time) error {
+	if err := node.CreateCacheDir(); err != nil {
+		return err
+	}
+	return os.WriteFile(node.timestampPath(), []byte(t.Format(time.RFC3339)), 0o644)
+}
+
+func (node *CacheNode) ReadChecksum() string {
+	b, _ := os.ReadFile(node.checksumPath())
+	return string(b)
+}
+
+func (node *CacheNode) WriteChecksum(checksum string) error {
+	if err := node.CreateCacheDir(); err != nil {
+		return err
+	}
+	return os.WriteFile(node.checksumPath(), []byte(checksum), 0o644)
+}
+
+func (node *CacheNode) CreateCacheDir() error {
+	if err := os.MkdirAll(node.dir, 0o755); err != nil {
+		return err
+	}
+	return nil
+}
+
+func (node *CacheNode) ChecksumPrompt(checksum string) string {
+	cachedChecksum := node.ReadChecksum()
+	switch {
+
+	// If the checksum doesn't exist, prompt the user to continue
+	case cachedChecksum == "":
+		return taskfileUntrustedPrompt
+
+	// If there is a cached hash, but it doesn't match the expected hash, prompt the user to continue
+	case cachedChecksum != checksum:
+		return taskfileChangedPrompt
+
+	default:
+		return ""
+	}
+}
+
+func (node *CacheNode) Location() string {
+	return node.filePath("yaml")
+}
+
+func (node *CacheNode) checksumPath() string {
+	return node.filePath("checksum")
+}
+
+func (node *CacheNode) timestampPath() string {
+	return node.filePath("timestamp")
+}
+
+func (node *CacheNode) filePath(suffix string) string {
+	return filepath.Join(node.dir, fmt.Sprintf("%s.%s", node.source.CacheKey(), suffix))
+}
+
+func checksum(b []byte) string {
+	h := sha256.New()
+	h.Write(b)
+	return fmt.Sprintf("%x", h.Sum(nil))
+}