package session

import (
	"bufio"
	"encoding/json"
	"os"
	"path/filepath"
	"sync"

	"chat-agent-system/internal/agentx/llm"
)

// Store is an append-only JSONL transcript. Each line is one llm.Message.
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 }

func (s *Store) Append(msg llm.Message) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	raw, err := json.Marshal(msg)
	if err != nil {
		return err
	}
	f, err := os.OpenFile(s.path, os.O_APPEND|os.O_WRONLY, 0o644)
	if err != nil {
		return err
	}
	defer f.Close()
	raw = append(raw, '\n')
	_, err = f.Write(raw)
	return err
}

func (s *Store) Load() ([]llm.Message, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	f, err := os.Open(s.path)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	var out []llm.Message
	sc := bufio.NewScanner(f)
	sc.Buffer(make([]byte, 0, 64*1024), 8*1024*1024)
	for sc.Scan() {
		line := sc.Bytes()
		if len(line) == 0 {
			continue
		}
		var msg llm.Message
		if err := json.Unmarshal(line, &msg); err != nil {
			return nil, err
		}
		out = append(out, msg)
	}
	return out, sc.Err()
}