1 files changed, 121 insertions, 0 deletions
diff --git a/object/resolve/treefs_open.go b/object/resolve/treefs_open.go
new file mode 100644
index 00000000..76bd5e4f
--- /dev/null
+++ b/object/resolve/treefs_open.go
@@ -0,0 +1,121 @@
+package resolve
+
+import (
+	"fmt"
+	"io"
+	"io/fs"
+
+	"codeberg.org/lindenii/furgit/object"
+)
+
+func (treeFS *TreeFS) Open(name string) (fs.File, error) {
+	entry, err := treeFS.resolvePath(treeFSOpOpen, name)
+	if err != nil {
+		return nil, err
+	}
+
+	info, err := treeFS.statEntry(entry)
+	if err != nil {
+		return nil, treeFSPathError(treeFSOpOpen, name, err)
+	}
+
+	if entry.isDir() {
+		treeID, err := entry.subtreeID()
+		if err != nil {
+			return nil, treeFSPathError(treeFSOpOpen, name, err)
+		}
+
+		tree, err := treeFS.resolver.ExactTree(treeID)
+		if err != nil {
+			return nil, treeFSPathError(treeFSOpOpen, name, err)
+		}
+
+		entries := make([]fs.DirEntry, 0, len(tree.Object().Entries))
+		for _, child := range tree.Object().Entries {
+			childEntry := treeEntryValue{
+				name:      string(child.Name),
+				mode:      child.Mode,
+				objectID:  child.ID,
+				treeEntry: &child,
+			}
+
+			childInfo, err := treeFS.statEntry(childEntry)
+			if err != nil {
+				return nil, treeFSPathError(treeFSOpOpen, name, err)
+			}
+
+			entries = append(entries, childInfo)
+		}
+
+		return &treeFSDir{
+			info:    info,
+			entries: entries,
+		}, nil
+	}
+
+	if entry.mode == object.FileModeGitlink {
+		return nil, treeFSPathError(treeFSOpOpen, name, fmt.Errorf("object/resolve: gitlink entries are not readable as files"))
+	}
+
+	reader, _, err := treeFS.resolver.ExactBlobReader(entry.objectID)
+	if err != nil {
+		return nil, treeFSPathError(treeFSOpOpen, name, err)
+	}
+
+	return &treeFSBlob{
+		info:   info,
+		reader: reader,
+	}, nil
+}
+
+type treeFSBlob struct {
+	info   *treeFSInfo
+	reader io.ReadCloser
+}
+
+var _ fs.File = (*treeFSBlob)(nil)
+
+func (file *treeFSBlob) Stat() (fs.FileInfo, error) { return file.info, nil }
+func (file *treeFSBlob) Read(p []byte) (int, error) { return file.reader.Read(p) }
+func (file *treeFSBlob) Close() error               { return file.reader.Close() }
+
+type treeFSDir struct {
+	info    *treeFSInfo
+	entries []fs.DirEntry
+	offset  int
+}
+
+var (
+	_ fs.File        = (*treeFSDir)(nil)
+	_ fs.ReadDirFile = (*treeFSDir)(nil)
+)
+
+func (dir *treeFSDir) Stat() (fs.FileInfo, error) { return dir.info, nil }
+func (dir *treeFSDir) Close() error               { return nil }
+
+func (dir *treeFSDir) Read(_ []byte) (int, error) {
+	return 0, fs.ErrInvalid
+}
+
+func (dir *treeFSDir) ReadDir(n int) ([]fs.DirEntry, error) {
+	if dir.offset >= len(dir.entries) && n > 0 {
+		return nil, io.EOF
+	}
+
+	if n <= 0 {
+		out := append([]fs.DirEntry(nil), dir.entries[dir.offset:]...)
+		dir.offset = len(dir.entries)
+
+		return out, nil
+	}
+
+	end := dir.offset + n
+	if end > len(dir.entries) {
+		end = len(dir.entries)
+	}
+
+	out := append([]fs.DirEntry(nil), dir.entries[dir.offset:end]...)
+	dir.offset = end
+
+	return out, nil
+}