Read files from captured Git commits

internal/validation/tree.go

@@ -0,0 +1,72 @@
+package validation
+
+import (
+	"context"
+	"fmt"
+
+	"gitea.maximumdirect.net/eric/ReleaseKit/internal/git"
+)
+
+// CandidateTree is an inventory of one captured commit with blob contents
+// loaded lazily by object ID.
+type CandidateTree struct {
+	repositoryDir string
+	entries       []git.TreeEntry
+	byPath        map[string]int
+	blobs         map[string][]byte
+}
+
+// ReadCandidateTree enumerates the captured commit without reading from the
+// worktree.
+func ReadCandidateTree(ctx context.Context, repositoryDir, commit string) (*CandidateTree, error) {
+	entries, err := git.ReadTree(ctx, repositoryDir, commit)
+	if err != nil {
+		return nil, err
+	}
+	tree := &CandidateTree{
+		repositoryDir: repositoryDir,
+		entries:       entries,
+		byPath:        make(map[string]int, len(entries)),
+		blobs:         make(map[string][]byte),
+	}
+	for index, entry := range entries {
+		tree.byPath[entry.Path] = index
+	}
+	return tree, nil
+}
+
+// Entries returns the committed tree metadata in Git's tree order.
+func (tree *CandidateTree) Entries() []git.TreeEntry {
+	return append([]git.TreeEntry(nil), tree.entries...)
+}
+
+// ReadFile returns the committed blob bytes for path. Contents are cached by
+// object ID for later reads from this tree.
+func (tree *CandidateTree) ReadFile(ctx context.Context, path string) ([]byte, error) {
+	index, ok := tree.byPath[path]
+	if !ok {
+		return nil, fmt.Errorf("committed path %q does not exist", path)
+	}
+	entry := tree.entries[index]
+	if entry.Type != "blob" {
+		return nil, fmt.Errorf("committed path %q is a %s entry, not a blob", path, entry.Type)
+	}
+	if contents, ok := tree.blobs[entry.ObjectID]; ok {
+		return append([]byte(nil), contents...), nil
+	}
+	contents, err := git.ReadBlob(ctx, tree.repositoryDir, entry.ObjectID)
+	if err != nil {
+		return nil, fmt.Errorf("read committed path %q: %w", path, err)
+	}
+	tree.blobs[entry.ObjectID] = append([]byte(nil), contents...)
+	return contents, nil
+}
+
+// Entry returns the committed metadata for path when present.
+func (tree *CandidateTree) Entry(path string) (git.TreeEntry, bool) {
+	index, ok := tree.byPath[path]
+	if !ok {
+		return git.TreeEntry{}, false
+	}
+	return tree.entries[index], true
+}