1 files changed, 124 insertions, 0 deletions
diff --git a/obj_commit.go b/obj_commit.go
new file mode 100644
index 00000000..100c6b35
--- /dev/null
+++ b/obj_commit.go
@@ -0,0 +1,124 @@
+package furgit
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+)
+
+// Commit mirrors the structure of a Git commit object.
+type Commit struct {
+	objectBase
+
+	Tree         Hash
+	Parents      []Hash
+	Author       Ident
+	Committer    Ident
+	Message      []byte
+	ExtraHeaders []ExtraHeader
+}
+
+// ObjType allows Commit to satisfy the Object interface.
+func (*Commit) ObjType() ObjType {
+	return ObjCommit
+}
+
+func parseCommit(id Hash, body []byte) (*Commit, error) {
+	c := new(Commit)
+	c.objectBase = objectBase{Hash: id}
+	i := 0
+	for i < len(body) {
+		rel := bytes.IndexByte(body[i:], '\n')
+		if rel < 0 {
+			return nil, errors.New("furgit: commit: missing newline")
+		}
+		line := body[i : i+rel]
+		i += rel + 1
+		if len(line) == 0 {
+			break
+		}
+
+		switch {
+		case bytes.HasPrefix(line, []byte("tree ")):
+			treeID, err := ParseHash(string(line[5:]))
+			if err != nil {
+				return nil, fmt.Errorf("furgit: commit: tree: %w", err)
+			}
+			c.Tree = treeID
+		case bytes.HasPrefix(line, []byte("parent ")):
+			parent, err := ParseHash(string(line[7:]))
+			if err != nil {
+				return nil, fmt.Errorf("furgit: commit: parent: %w", err)
+			}
+			c.Parents = append(c.Parents, parent)
+		case bytes.HasPrefix(line, []byte("author ")):
+			idt, err := parseIdent(line[7:])
+			if err != nil {
+				return nil, fmt.Errorf("furgit: commit: author: %w", err)
+			}
+			c.Author = *idt
+		case bytes.HasPrefix(line, []byte("committer ")):
+			idt, err := parseIdent(line[10:])
+			if err != nil {
+				return nil, fmt.Errorf("furgit: commit: committer: %w", err)
+			}
+			c.Committer = *idt
+		case bytes.HasPrefix(line, []byte("gpgsig ")), bytes.HasPrefix(line, []byte("gpgsig-sha256 ")):
+			// TODO: handle this
+			for i < len(body) {
+				nextRel := bytes.IndexByte(body[i:], '\n')
+				if nextRel < 0 {
+					return nil, errors.New("furgit: commit: unterminated gpgsig")
+				}
+				if body[i] != ' ' {
+					break
+				}
+				i += nextRel + 1
+			}
+		default:
+			key, value, found := bytes.Cut(line, []byte{' '})
+			if !found {
+				return nil, errors.New("furgit: commit: malformed header")
+			}
+			c.ExtraHeaders = append(c.ExtraHeaders, ExtraHeader{Key: string(key), Value: value})
+		}
+	}
+
+	if i > len(body) {
+		return nil, ErrInvalidObject
+	}
+
+	c.Message = append([]byte(nil), body[i:]...)
+	return c, nil
+}
+
+func commitBody(c *Commit) []byte {
+	var buf bytes.Buffer
+	fmt.Fprintf(&buf, "tree %s\n", c.Tree.String())
+	for _, p := range c.Parents {
+		fmt.Fprintf(&buf, "parent %s\n", p.String())
+	}
+	buf.WriteString("author ")
+	buf.Write(c.Author.Serialize())
+	buf.WriteByte('\n')
+	buf.WriteString("committer ")
+	buf.Write(c.Committer.Serialize())
+	buf.WriteByte('\n')
+	buf.WriteByte('\n')
+	buf.Write(c.Message)
+
+	return buf.Bytes()
+}
+
+// Serialize renders a Commit into canonical Git format.
+func (c *Commit) Serialize() ([]byte, error) {
+	body := commitBody(c)
+	header, err := headerForType(ObjCommit, body)
+	if err != nil {
+		return nil, err
+	}
+	raw := make([]byte, len(header)+len(body))
+	copy(raw, header)
+	copy(raw[len(header):], body)
+	return raw, nil
+}