package session

import (
	"os"
	"path/filepath"
	"sync"

	"agent-native/runtime/llm"
)

// Store is an append-only JSONL transcript. New sessions are a tree of
// entries (id / parentId). Load still returns the model-visible message
// path, and files written as one llm.Message per line remain readable.
type Store struct {
	path string
	mu   sync.Mutex
}

func Open(path string) (*Store, error) {
	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
		return nil, err
	}
	f, err := os.OpenFile(path, os.O_CREATE, 0o644)
	if err != nil {
		return nil, err
	}
	_ = f.Close()
	return &Store{path: path}, nil
}

func (s *Store) Path() string { return s.path }

// Append records one message on the active branch.
func (s *Store) Append(msg llm.Message) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	_, err := s.appendEntryLocked(Entry{Type: TypeMessage, Message: &msg})
	return err
}

// Load returns the model-visible messages on the active branch.
// A compaction entry replaces earlier turns with its summary plus the
// retained tail; the file itself is never rewritten.
// Crash residue: a trailing line without a newline that is not valid JSON
// is dropped. A bad line in the middle is still an error.
func (s *Store) Load() ([]llm.Message, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	entries, err := s.readEntriesLocked()
	if err != nil {
		return nil, err
	}
	return visibleMessages(entries, s.leafLocked(entries)), nil
}