ident: implement full representation

This can be used with both system and member identifiers.

Signed-off-by: Yonah <contrib@gensokyo.uk>

ident/ident.go

@@ -7,10 +7,16 @@ import (
 	"errors"
 	"fmt"
 	"strconv"
+	"unsafe"
 )
 
-// ErrNewline is returned for identifiers found to contain newline characters.
-var ErrNewline = errors.New("identifier contains newline characters")
+var (
+	// ErrNewline is returned for identifiers found to contain newline characters.
+	ErrNewline = errors.New("identifier contains newline characters")
+	// ErrSeparator is returned for representations of [F] missing its separator
+	// byte in its expected index.
+	ErrSeparator = errors.New("identifier has incorrect separator byte")
+)
 
 // UnexpectedSizeError describes a malformed string representation of an
 // identifier, with unexpected length.
@@ -41,3 +47,53 @@ type MS interface {
 	// behaviour: a type is an identifier part if it has an ident method.
 	ident()
 }
+
+// F represents a full system or member identifier.
+type F[V any, T interface {
+	MS
+	*V
+}] struct {
+	// Underlying system or member.
+	I T
+	// Split from instance suffix after [Separator] byte.
+	Remote Remote
+}
+
+// Separator is the byte separating representation of [MS] from [Remote].
+const Separator = ':'
+
+// Encode appends the canonical string representation of full to dst and returns
+// the extended buffer.
+func (full *F[V, T]) Encode(dst []byte) []byte {
+	dst = full.I.Encode(dst)
+	dst = append(dst, Separator)
+	dst = full.Remote.Encode(dst)
+	return dst
+}
+
+// String returns the canonical string representation of full.
+func (full *F[V, T]) String() string {
+	s := full.Encode(nil)
+	return unsafe.String(unsafe.SliceData(s), len(s))
+}
+
+// MarshalText returns the result of Encode.
+func (full *F[V, T]) MarshalText() (data []byte, err error) {
+	return full.Encode(nil), nil
+}
+
+// UnmarshalText strictly decodes data into full.
+func (full *F[V, T]) UnmarshalText(data []byte) (err error) {
+	sz := full.I.EncodedSize()
+	if len(data) < sz+1 || data[sz] != Separator {
+		return ErrSeparator
+	}
+
+	if full.I == nil {
+		full.I = new(V)
+	}
+	if err = full.I.UnmarshalText(data[:sz]); err != nil {
+		return
+	}
+	return full.Remote.UnmarshalText(data[sz+1:])
+}