object: Add basic object code

1 files changed, 122 insertions, 0 deletions

diff --git a/object/ident.go b/object/ident.go
new file mode 100644
index 00000000..e601802a
--- /dev/null
+++ b/object/ident.go
@@ -0,0 +1,122 @@
+package object
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Ident represents a Git identity (author/committer/tagger).
+type Ident struct {
+	Name          []byte
+	Email         []byte
+	WhenUnix      int64
+	OffsetMinutes int32
+}
+
+// ParseIdent parses a canonical Git identity line:
+// "Name <email> 123456789 +0000".
+func ParseIdent(line []byte) (*Ident, error) {
+	lt := bytes.IndexByte(line, '<')
+	if lt < 0 {
+		return nil, errors.New("object: ident: missing opening <")
+	}
+	gtRel := bytes.IndexByte(line[lt+1:], '>')
+	if gtRel < 0 {
+		return nil, errors.New("object: ident: missing closing >")
+	}
+	gt := lt + 1 + gtRel
+
+	nameBytes := append([]byte(nil), bytes.TrimRight(line[:lt], " ")...)
+	emailBytes := append([]byte(nil), line[lt+1:gt]...)
+
+	rest := line[gt+1:]
+	if len(rest) == 0 || rest[0] != ' ' {
+		return nil, errors.New("object: ident: missing timestamp separator")
+	}
+	rest = rest[1:]
+	sp := bytes.IndexByte(rest, ' ')
+	if sp < 0 {
+		return nil, errors.New("object: ident: missing timezone separator")
+	}
+	when, err := strconv.ParseInt(string(rest[:sp]), 10, 64)
+	if err != nil {
+		return nil, fmt.Errorf("object: ident: invalid timestamp: %w", err)
+	}
+
+	tz := rest[sp+1:]
+	if len(tz) < 5 {
+		return nil, errors.New("object: ident: invalid timezone encoding")
+	}
+	sign := 1
+	switch tz[0] {
+	case '-':
+		sign = -1
+	case '+':
+	default:
+		return nil, errors.New("object: ident: invalid timezone sign")
+	}
+
+	hh, err := strconv.Atoi(string(tz[1:3]))
+	if err != nil {
+		return nil, fmt.Errorf("object: ident: invalid timezone hours: %w", err)
+	}
+	mm, err := strconv.Atoi(string(tz[3:5]))
+	if err != nil {
+		return nil, fmt.Errorf("object: ident: invalid timezone minutes: %w", err)
+	}
+	if hh < 0 || hh > 23 {
+		return nil, errors.New("object: ident: invalid timezone hours range")
+	}
+	if mm < 0 || mm > 59 {
+		return nil, errors.New("object: ident: invalid timezone minutes range")
+	}
+	total := int64(hh)*60 + int64(mm)
+	if total > math.MaxInt32 {
+		return nil, errors.New("object: ident: timezone overflow")
+	}
+
+	offset := int32(total)
+	if sign < 0 {
+		offset = -offset
+	}
+	return &Ident{
+		Name:          nameBytes,
+		Email:         emailBytes,
+		WhenUnix:      when,
+		OffsetMinutes: offset,
+	}, nil
+}
+
+// Serialize renders the identity in canonical Git format.
+func (ident Ident) Serialize() ([]byte, error) {
+	var b strings.Builder
+	b.Grow(len(ident.Name) + len(ident.Email) + 32)
+	b.Write(ident.Name)
+	b.WriteString(" <")
+	b.Write(ident.Email)
+	b.WriteString("> ")
+	b.WriteString(strconv.FormatInt(ident.WhenUnix, 10))
+	b.WriteByte(' ')
+
+	offset := ident.OffsetMinutes
+	sign := '+'
+	if offset < 0 {
+		sign = '-'
+		offset = -offset
+	}
+	hh := offset / 60
+	mm := offset % 60
+	fmt.Fprintf(&b, "%c%02d%02d", sign, hh, mm)
+	return []byte(b.String()), nil
+}
+
+// When returns a time.Time with the identity's timezone offset.
+func (ident Ident) When() time.Time {
+	loc := time.FixedZone("git", int(ident.OffsetMinutes)*60)
+	return time.Unix(ident.WhenUnix, 0).In(loc)
+}