v3 candidate

internal/leviathan/document/session.go

@@ -0,0 +1,62 @@
+package document
+
+import (
+	"errors"
+	"sync"
+)
+
+// Slot identifies one of the documents in a session.
+type Slot string
+
+const (
+	SlotOriginal Slot = "original"
+	SlotCompare  Slot = "compare"
+)
+
+// Session tracks loaded documents and addresses them by slot.
+// The original slot is the active working document; compare is
+// used by the diff tooling.
+type Session struct {
+	mu        sync.RWMutex
+	documents map[Slot]*Document
+}
+
+// NewSession returns an empty session.
+func NewSession() *Session {
+	return &Session{documents: make(map[Slot]*Document)}
+}
+
+// Load replaces the document in the given slot.
+func (s *Session) Load(slot Slot, name string, src []byte) *Document {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	d := New(name, src)
+	s.documents[slot] = d
+	return d
+}
+
+// Get returns the document for a slot, or an error if not loaded.
+func (s *Session) Get(slot Slot) (*Document, error) {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	d, ok := s.documents[slot]
+	if !ok {
+		return nil, errors.New("slot not loaded: " + string(slot))
+	}
+	return d, nil
+}
+
+// Has reports whether a slot has a document loaded.
+func (s *Session) Has(slot Slot) bool {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+	_, ok := s.documents[slot]
+	return ok
+}
+
+// Drop removes a slot.
+func (s *Session) Drop(slot Slot) {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	delete(s.documents, slot)
+}