refactor: taskfile/ast package (#1450)

* refactor: ast package

* feat: read -> taskfile

* refactor: taskfile.Taskfile -> taskfile.Read

* refactor: move merge function back into taskfile package

* refactor: rename taskfile.go to read.go

taskfile/cache.go

@@ -0,0 +1,58 @@
+package taskfile
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+)
+
+type Cache struct {
+	dir string
+}
+
+func NewCache(dir string) (*Cache, error) {
+	dir = filepath.Join(dir, "remote")
+	if err := os.MkdirAll(dir, 0o755); err != nil {
+		return nil, err
+	}
+	return &Cache{
+		dir: dir,
+	}, nil
+}
+
+func checksum(b []byte) string {
+	h := sha256.New()
+	h.Write(b)
+	return fmt.Sprintf("%x", h.Sum(nil))
+}
+
+func (c *Cache) write(node Node, b []byte) error {
+	return os.WriteFile(c.cacheFilePath(node), b, 0o644)
+}
+
+func (c *Cache) read(node Node) ([]byte, error) {
+	return os.ReadFile(c.cacheFilePath(node))
+}
+
+func (c *Cache) writeChecksum(node Node, checksum string) error {
+	return os.WriteFile(c.checksumFilePath(node), []byte(checksum), 0o644)
+}
+
+func (c *Cache) readChecksum(node Node) string {
+	b, _ := os.ReadFile(c.checksumFilePath(node))
+	return string(b)
+}
+
+func (c *Cache) key(node Node) string {
+	return strings.TrimRight(checksum([]byte(node.Location())), "=")
+}
+
+func (c *Cache) cacheFilePath(node Node) string {
+	return filepath.Join(c.dir, fmt.Sprintf("%s.yaml", c.key(node)))
+}
+
+func (c *Cache) checksumFilePath(node Node) string {
+	return filepath.Join(c.dir, fmt.Sprintf("%s.checksum", c.key(node)))
+}