refactor: consolidate download domain into download package

internal/download/hash.go

@@ -0,0 +1,69 @@
+package download
+
+import (
+	"context"
+	"crypto/sha256"
+	"encoding/hex"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+)
+
+func hashFile(path string) (string, error) {
+	file, err := os.Open(path)
+	if err != nil {
+		return "", err
+	}
+	defer file.Close()
+
+	h := sha256.New()
+	if _, err := io.Copy(h, file); err != nil {
+		return "", err
+	}
+
+	return hex.EncodeToString(h.Sum(nil)), nil
+}
+
+type hashIndex struct {
+	files map[string]string
+}
+
+func newHashIndex(ctx context.Context, root string) (*hashIndex, error) {
+	index := &hashIndex{files: make(map[string]string)}
+
+	err := filepath.WalkDir(root, func(path string, d fs.DirEntry, err error) error {
+		if ctx.Err() != nil {
+			return ctx.Err()
+		}
+		if err != nil || d.IsDir() {
+			return nil
+		}
+
+		hash, err := hashFile(path)
+		if err != nil {
+			return nil
+		}
+
+		index.files[hash] = path
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	return index, nil
+}
+
+func (h *hashIndex) find(hash string) (string, bool) {
+	path, ok := h.files[hash]
+	return path, ok
+}
+
+func (d *Downloader) initHashIndex(ctx context.Context) error {
+	d.hashIndexOnce.Do(func() {
+		d.hashIndex, d.hashIndexErr = newHashIndex(ctx, d.appConfig.OutputDir)
+	})
+
+	return d.hashIndexErr
+}