1 files changed, 104 insertions, 0 deletions
diff --git a/object/signed/commit/parse.go b/object/signed/commit/parse.go
new file mode 100644
index 00000000..1714327f
--- /dev/null
+++ b/object/signed/commit/parse.go
@@ -0,0 +1,104 @@
+package signedcommit
+
+import (
+	"bytes"
+
+	objectid "codeberg.org/lindenii/furgit/object/id"
+)
+
+// Parse parses one raw commit object body for signature extraction.
+//
+// The returned Commit remains valid only while body remains unchanged.
+//
+// Labels: Deps-Borrowed, Life-Parent.
+func Parse(body []byte) (*Commit, error) {
+	commit := &Commit{
+		body:       body,
+		signatures: make(map[objectid.Algorithm][]byteRange),
+	}
+
+	payloadStart := 0
+	i := 0
+
+	for i < len(body) {
+		lineStart := i
+
+		rel := bytes.IndexByte(body[i:], '\n')
+		next := len(body)
+		lineEnd := len(body)
+		if rel >= 0 {
+			lineEnd = i + rel
+			next = lineEnd + 1
+		}
+
+		line := body[lineStart:lineEnd]
+		i = next
+
+		if len(line) == 0 {
+			commit.appendPayloadRange(payloadStart, len(body))
+
+			return commit, nil
+		}
+
+		if line[0] == ' ' {
+			continue
+		}
+
+		if !bytes.HasPrefix(line, []byte("gpgsig")) {
+			continue
+		}
+
+		commit.appendPayloadRange(payloadStart, lineStart)
+
+		key, valueStart, found := bytes.Cut(line, []byte{' '})
+		if found {
+			if algo, ok := objectid.ParseSignatureHeaderName(string(key)); ok {
+				commit.signatures[algo] = append(commit.signatures[algo], byteRange{
+					start: lineEnd - len(valueStart),
+					end:   next,
+				})
+			}
+		}
+
+		for i < len(body) {
+			rel := bytes.IndexByte(body[i:], '\n')
+			next = len(body)
+			lineEnd = len(body)
+			if rel >= 0 {
+				lineEnd = i + rel
+				next = lineEnd + 1
+			}
+
+			contStart := i
+			cont := body[contStart:lineEnd]
+			if len(cont) == 0 || cont[0] != ' ' {
+				break
+			}
+
+			if found {
+				if algo, ok := objectid.ParseSignatureHeaderName(string(key)); ok {
+					commit.signatures[algo] = append(commit.signatures[algo], byteRange{
+						start: contStart + 1,
+						end:   next,
+					})
+				}
+			}
+
+			i = next
+		}
+
+		payloadStart = i
+	}
+
+	commit.appendPayloadRange(payloadStart, len(body))
+
+	return commit, nil
+}
+
+func (commit *Commit) appendPayloadRange(start, end int) {
+	if start >= end {
+		return
+	}
+
+	commit.payload = append(commit.payload, byteRange{start: start, end: end})
+}